Wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting and preparation method thereof

Abstract

The application discloses a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting and a preparation method thereof. A double-phase wear-resistant and corrosion-resistant layer is formed in situ on the surface of the ball valve casting. The layer comprises, from inside to outside, an oxide ceramic transition layer, a Ti-O-N interface anchoring area, a nitride ceramic-metal composite dense layer and a passivation auxiliary area. The oxide ceramic transition layer comprises a Cr2O3 enrichment area and a FeCr2O4 spinel area. The Ti-O-N interface anchoring area connects the oxide phase and the nitride phase. In the composite dense layer, TiN hard phases are dispersedly distributed in an austenitic metal binder phase. The passivation auxiliary area comprises a Cr, Mo or Nb enrichment structure. The preparation comprises surface pretreatment, low-oxygen partial pressure in-situ oxidation, Ti source plasma surface alloying, sectional nitrogen potential nitriding and stable film polishing treatment. The application can improve the surface bonding stability, wear resistance and corrosion resistance of the ball valve casting, and is suitable for strengthening the sealing surface, the valve seat contact surface and the flow passage scouring surface.

Description

Technical Field

[0001] This application relates to the field of surface modification technology of metallic materials, specifically to a wear-resistant and corrosion-resistant composite layer on the surface of austenitic stainless steel ball valve castings and its preparation method. In particular, it relates to a surface strengthening technology that constructs an oxide ceramic transition layer, a Ti-ON interface anchoring zone, and a nitride ceramic-metal composite dense layer on the surface of austenitic stainless steel ball valve castings through in-situ oxidation, plasma surface alloying, and segmented nitrogen potential treatment. Background Technology

[0002] Austenitic stainless steel ball valve castings, due to their excellent corrosion resistance, formability, and comprehensive mechanical properties, are suitable for applications in chemical, marine, oil and gas, pharmaceutical, and chlorine-containing media transportation. During use, if the ball valve's sealing surfaces, seat contact surfaces, and flow path erosion surfaces are subjected to prolonged opening and closing friction, particle erosion, media corrosion, and localized stress concentration, surface problems such as wear, pitting, erosion pits, scratches on the sealing surfaces, and localized peeling can easily occur, affecting the valve's sealing reliability and service life.

[0003] In the prior art, Chinese patent application CN103953772A discloses an ultra-hard wear-resistant valve with a tungsten carbide-chromium nitride composite coating and its preparation method. This type of valve has a WC undercoat and a CrN topcoat formed from the inside out on the valve substrate surface. The WC undercoat is formed by supersonic flame spraying, and the CrN topcoat is formed by magnetron sputtering. Although this can improve the hardness and wear resistance of the valve surface, the technical effect relies heavily on the layered protection of the external hard coatings. Under long-term opening and closing friction, erosion, and corrosive media, the coating and substrate may still gradually detach from each other. Its improvement in corrosion resistance mainly relies on the outer CrN top coating, lacking a continuous transition from the substrate side to the outer surface side for the anti-corrosion barrier and interface buffering effect; Chinese patent application with publication number CN111118443A discloses a method for preparing a metal-ceramic coating on the surface of austenitic stainless steel. The ceramic layer is formed by surface carbonitriding and chromium infiltration, and then a metal-ceramic hybrid structure is formed by laser irradiation. This makes the surface coating have both the corrosion resistance of austenitic stainless steel and the high mechanical strength of the ceramic layer. Therefore, the corrosion resistance mainly depends on chromium infiltration and the metal-ceramic hybrid layer.

[0004] It is evident that current technologies for improving the materials of ball valve castings are still focused on single wear-resistant reinforcement or corrosion protection technologies, making it difficult to simultaneously achieve high surface hardness load-bearing capacity, stable interface bonding, pitting corrosion inhibition, and long-term integrity under coupled wear and corrosion conditions. Summary of the Invention

[0005] To address the aforementioned deficiencies, this invention provides a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting and its preparation method. This application achieves a synergistic design from matrix bonding, interface anchoring, hard phase dispersion strengthening to outer layer corrosion protection through the continuous construction of an oxide ceramic transition layer, a Ti-ON interface anchoring zone, a nitride ceramic-metal composite dense layer, and a passivation auxiliary zone. This simultaneously improves the interface bonding strength, wear resistance, and corrosion resistance of the austenitic stainless steel ball valve casting, making it suitable for surface strengthening treatment of ball valve sealing surfaces, valve seat contact surfaces, and flow channel scouring surfaces.

[0006] The present invention provides the following technical solution: a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting, comprising a ball valve casting substrate and a duplex wear-resistant and corrosion-resistant layer formed in situ on the surface of the ball valve casting substrate, wherein the ball valve casting substrate is formed of austenitic stainless steel at least at the sealing surface, the valve seat contact surface or the flow channel scouring surface. The dual-phase wear-resistant and corrosion-resistant layer comprises, in sequence, an oxide ceramic transition layer, a Ti-ON interface anchoring zone, and a nitride ceramic-metal composite dense layer, from the side closest to the ball valve casting substrate to the side furthest from the ball valve casting substrate. The oxide ceramic transition layer is a gradient oxide layer formed by the in-situ reaction of at least two metal elements of Fe, Cr and Ni in the austenitic stainless steel with oxygen. The Ti-ON interface anchoring region connects the oxide ceramic transition layer and the nitride ceramic-metal composite dense layer. The nitride ceramic-metal composite dense layer includes an austenitic metal binder phase and a TiN hard phase dispersed in the austenitic metal binder phase.

[0007] Furthermore, the thickness of the oxide ceramic transition layer is 0.8 μm to 4.5 μm, and the oxide ceramic transition layer includes a Cr2O3 enriched region near the ball valve casting substrate and a FeCr2O4 spinel region near the Ti-ON interface anchoring region. Along the direction from the ball valve casting matrix to the Ti-ON interface anchoring zone, the oxygen content in the oxide ceramic transition layer shows an increasing trend, and the Cr / Fe atomic ratio shows a decreasing trend from the Cr2O3 enriched region to the FeCr2O4 spinel region.

[0008] Furthermore, the thickness of the Ti-ON interface anchoring region is 0.1 μm to 1.5 μm, and both Ti-O and Ti-N bonding structures exist in the Ti-ON interface anchoring region. Moreover, the Ti content in the Ti-ON interface anchoring region increases from the oxide ceramic transition layer side to the nitride ceramic-metal composite dense layer side.

[0009] Furthermore, the thickness of the nitride ceramic-metal composite dense layer is 15μm to 65μm, and the TiN hard phase is distributed in the austenitic metal binder phase in at least one of the following forms: nanoparticles, short rods, or discontinuous dispersed phases. The equivalent particle size of the TiN hard phase is 20nm to 300nm, and the area ratio of the TiN hard phase in the cross section of the nitride ceramic-metal composite dense layer is 8% to 45%. The area ratio of the TiN hard phase decreases from the outer surface of the nitride ceramic-metal composite dense layer to the ball valve casting substrate.

[0010] Furthermore, the outer side of the nitride ceramic-metal composite dense layer has a passivation auxiliary region, which is enriched with at least one element selected from Cr, Mo, or Nb. In the passivation auxiliary region, TiN forms a multi-component nitride synergistic region with at least one of CrN, MoN, and NbN, and the CrN, MoN, or NbN are distributed in the passivation auxiliary region in a discontinuous particulate or island-like manner.

[0011] This application also provides a method for preparing the wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting as described above, comprising the following steps: S1: Surface pretreatment is performed on the austenitic stainless steel ball valve casting substrate to obtain the pretreated ball valve casting substrate; S2: Under low oxygen partial pressure conditions, the pretreated ball valve casting substrate is subjected to in-situ oxidation treatment, so that at least two of the metal elements Fe, Cr and Ni in the austenitic stainless steel react with oxygen to form an oxide ceramic transition layer on the surface of the ball valve casting substrate. S3: The ball valve casting substrate with the oxide ceramic transition layer is placed in a dual glow plasma surface alloying device, with a Ti-containing target as the source electrode and the ball valve casting substrate as the cathode, and Ti source plasma surface alloying treatment is performed in an argon atmosphere, so that Ti enters the outer side of the oxide ceramic transition layer and forms the precursor region of the Ti-ON interface anchoring region. S4: Introduce a nitrogen-containing atmosphere into the dual glow plasma surface alloying equipment and use segmented nitrogen potential treatment to allow Ti and active nitrogen to react in situ outside the anchoring zone of the Ti-ON interface to generate a TiN hard phase, while retaining a continuous austenitic metal bonding phase to form a nitride ceramic-metal composite dense layer. S5: The ball valve casting substrate after S4 is subjected to cooling and film stabilization treatment or precision polishing treatment to obtain the wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting.

[0012] Furthermore, in steps S1 and S2, the surface pretreatment includes at least three of the following: mechanical polishing, degreasing cleaning, vacuum desorption, and Ar plasma pre-cleaning; The working gas pressure for the Ar plasma pre-cleaning is 10 Pa to 50 Pa, and the processing time is 5 min to 30 min. The in-situ oxidation treatment is carried out at a temperature of 420℃~560℃, an oxygen partial pressure of 5Pa~80Pa, and a holding time of 0.5h~2.5h. The in-situ oxidation treatment is carried out using a continuous oxygen supply or pulsed oxygen supply method.

[0013] Further, in step S3, the Ti-containing target material is one of Ti target material, Ti-Cr alloy target material, Ti-Mo alloy target material, or Ti-Nb alloy target material; The distance between the Ti-containing target and the ball valve casting substrate is 12mm to 40mm, the working air pressure is 20Pa to 70Pa, the source voltage is 650V to 1000V, the cathode voltage is 300V to 650V, the processing temperature is 620℃ to 850℃, and the processing time is 0.5h to 3h. The volume fraction of N2 in the argon-containing atmosphere is not higher than 10%.

[0014] Furthermore, in step S4, the segmented nitrogen potential treatment includes a low nitrogen potential introduction stage, a medium nitrogen potential precipitation stage, and a low nitrogen potential integration stage. During the low nitrogen potential introduction stage, nitrogen gas is introduced for 20 min to 90 min, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 5% to 18%. During the nitrogen potential precipitation stage, nitrogen gas is introduced for 1 to 5 hours, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 20% to 45%. During the low nitrogen potential integration stage, nitrogen gas is introduced for 20 to 90 minutes, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 5% to 15%. The temperature of the segmented nitrogen potential treatment in step S4 is 560℃~780℃, and the cathode voltage or pulse bias is adjusted to prevent CrN, MoN or NbN from forming a continuous network precipitate.

[0015] Furthermore, the austenitic stainless steel is one of 304 stainless steel, 316L stainless steel, CF8 austenitic stainless steel casting, CF8M austenitic stainless steel casting or CF3M austenitic stainless steel casting. The cooling and film stabilization treatment involves holding the material at 280℃~420℃ and an oxygen partial pressure of 1Pa~30Pa for 10min~60min. After precision polishing, the surface roughness Ra of the sealing surface of the ball valve casting is 0.05μm~0.25μm.

[0016] The beneficial effects of this invention are as follows: 1. This application employs low-oxygen partial pressure in-situ oxidation treatment, causing controlled oxidation reactions of elements such as Fe, Cr, and Ni in the austenitic stainless steel ball valve casting matrix on the surface, forming an oxide ceramic transition layer containing Cr2O3 enrichment regions and FeCr2O4 spinel regions. This transition layer is not an independent film obtained by external coating, but is generated in situ by the matrix elements. It enables a gradient transition of elemental concentration and phase composition between the ball valve casting matrix and the outer functional layer, thereby improving the interlayer bonding stability and providing an inner foundation for the corrosion-resistant barrier.

[0017] 2. This application further forms a Ti-ON interface anchoring region between the oxide ceramic transition layer and the nitride ceramic-metal composite dense layer. This interface anchoring region contains both Ti-O and Ti-N bond structures. One side of the Ti-ON interface anchoring region can connect with the oxide in the oxide ceramic transition layer, and the other side can connect with the composite dense layer containing the TiN hard phase. The Ti-ON interface anchoring region in the bidirectional wear-resistant and corrosion-resistant layer prepared by the method of this application can prevent and reduce the interface abrupt change between the oxide layer and the nitride layer, minimizing the risk of delamination of the hard layer under frictional loads or thermal cycling.

[0018] 3. This application utilizes Ti-source plasma surface alloying and segmented nitrogen potential treatment to induce an in-situ reaction between Ti and active nitrogen on the surface, generating a TiN hard phase. This TiN hard phase is distributed within the austenitic metal binder phase as nanoparticles, short rods, or discontinuous dispersed phases. The resulting nitride ceramic-metal composite dense layer possesses both the wear-resistant and load-bearing capacity provided by the TiN hard phase and retains the toughness and buffering effect of the austenitic metal binder phase, avoiding the problems of excessive brittleness and rapid crack propagation in a single ceramic layer.

[0019] 4. This application forms a passivation auxiliary region containing Cr, Mo, or Nb enrichment structures on the outer side of the nitride ceramic-metal composite dense layer, and can further form a multi-component synergistic nitride region where TiN coexists with at least one of CrN, MoN, and NbN. This structure can improve the passivation stability and pitting resistance of the outer surface, enabling the ball valve casting to maintain good surface integrity under the combined effects of chlorine-containing media, particle erosion, and opening and closing friction. Attached Figure Description

[0020] The invention will now be described in more detail with reference to embodiments and the accompanying drawings. Figure 1 A schematic diagram of the microstructure of the cross-section of the wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting provided in this application; Figure 2The image shows the cross-section of the ball valve casting material prepared in Example 1 and Comparative Example 1 of this application. Figure 3 This is a comparative diagram showing the results of EDS energy dispersive spectroscopy detection of the ball valve casting materials prepared in Example 1 and Comparative Example 1 in this application; Figure 4 This is a representative XPS depth profile of the Ti-ON interface anchoring zone of the ball valve casting substrate prepared in Example 2 of this application at three sputtering depths of 0 nm, 50 nm and 100 nm. Figure 5 This is a transmission electron microscope image of the ball valve casting material prepared in Example 3 of this application; Figure 6 This is the X-ray diffraction analysis diagram of the ball valve casting material prepared in Example 3 of this application; Figure 7 The figures provided are curves showing the change in microhardness along depth and a bar chart comparing the reciprocating friction and wear rates of the ball valve castings prepared in various embodiments and comparative examples in Test Example 4 of this application. Figure 8 This is a comparison chart of the electrodynamic polarization curve detection results for Examples 1-3 and Comparative Examples 1-6 in Test Example 5 of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1 As shown, the wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting provided in this application includes a ball valve casting substrate 1 and a duplex wear-resistant and corrosion-resistant layer 2 formed in situ on the surface of the ball valve casting substrate 1. The ball valve casting substrate 1 can be one of 304 stainless steel, 316L stainless steel, CF8 austenitic stainless steel casting, CF8M austenitic stainless steel casting, or CF3M austenitic stainless steel casting. The duplex wear-resistant and corrosion-resistant layer 2 can be formed on the sealing surface, valve seat contact surface, or flow channel scouring surface of the ball valve casting substrate 1 to improve the service stability of the ball valve casting under opening and closing friction, media scouring, and chloride-containing corrosion environments.

[0023] Specifically, the dual-phase wear-resistant and corrosion-resistant layer 2 comprises, sequentially from the side closest to the ball valve casting substrate 1 to the side furthest from the ball valve casting substrate 1, an oxide ceramic transition layer 21, a Ti-ON interface anchoring region 22, a nitride ceramic-metal composite dense layer 23, and a passivation auxiliary region 24. The oxide ceramic transition layer 21 is not an externally coated independent film, but rather is generated by the in-situ reaction of at least two of the metal elements Fe, Cr, and Ni in austenitic stainless steel with oxygen under low oxygen partial pressure conditions. Therefore, there is no obvious mechanical interface between it and the ball valve casting substrate 1; instead, it forms a continuously transitioning elemental bond structure.

[0024] Furthermore, the oxide ceramic transition layer 21 includes a Cr2O3 enriched region 211 near the ball valve casting substrate 1 and a FeCr2O4 spinel region 212 near the Ti-ON interface anchoring region 22. The Cr2O3 enriched region 211 is mainly formed by the diffusion of Cr elements from the ball valve casting substrate 1 to the surface and their reaction with oxygen. It has good chemical continuity with the ball valve casting substrate 1 and can serve as the inner base layer of the corrosion-resistant barrier. The FeCr2O4 spinel region 212 is located outside the Cr2O3 enriched region 211. It is formed by the further reaction of Fe, Cr and oxygen and can provide a transition in composition and thermal expansion behavior between the Cr2O3 enriched region 211 and the subsequent Ti-ON interface anchoring region 22. Along the direction from the ball valve casting matrix 1 to the Ti-ON interface anchoring region 22, the oxygen content in the oxide ceramic transition layer 21 generally increases, and the Cr / Fe atomic ratio decreases from the Cr2O3 enriched region 211 to the FeCr2O4 spinel region 212, thus forming a gradient structure that gradually transitions from the matrix metal phase to the oxide ceramic phase.

[0025] The Ti-ON interface anchoring region 22 is disposed between the oxide ceramic transition layer 21 and the nitride ceramic-metal composite dense layer 23. The Ti-ON interface anchoring region 22 contains both Ti-O and Ti-N bonding structures. One side can interfacially bond with the oxide phase in the oxide ceramic transition layer 21, while the other side can structurally connect with the TiN hard phase 231 in the nitride ceramic-metal composite dense layer 23. Therefore, the Ti-ON interface anchoring region 22 is not merely a separating layer, but rather an interface anchoring region used to connect the oxide ceramic transition layer 21 and the nitride ceramic-metal composite dense layer 23 into a continuous composite structure, reducing the risk of delamination of the hard nitride layer under frictional loads or thermal cycling.

[0026] The nitride ceramic-metal composite dense layer 23 is located outside the Ti-ON interface anchoring region 22, and includes a TiN hard phase 231 and an austenitic metal binder phase 232. The TiN hard phase 231 can be distributed in the austenitic metal binder phase 232 in at least one of the following forms: nanoparticles, short rods, or discontinuous dispersed phases. The austenitic metal binder phase 232 acts as a continuous phase to coat and connect the TiN hard phase 231, so that the nitride ceramic-metal composite dense layer 23 has both the wear resistance of the hard ceramic phase and the toughness buffering capacity of the austenitic metal phase. Compared with a single ceramic coating, this composite dense layer is not entirely composed of a brittle ceramic phase, but rather the TiN hard phase 231 is dispersed and embedded in the continuous austenitic metal binder phase 232, which is beneficial for dispersing contact loads when subjected to valve opening and closing friction and fluid scouring, and inhibiting the rapid propagation of cracks along a single brittle interface.

[0027] The passivation auxiliary region 24 is located on the outer side of the nitride ceramic-metal composite dense layer 23. The passivation auxiliary region 24 is enriched with at least one element selected from Cr, Mo, or Nb, and forms a multi-component nitride synergistic region 241 on or near the outer surface. The multi-component nitride synergistic region 241 can be a region where TiN coexists with at least one of CrN, MoN, or NbN, where Cr, Mo, or Nb helps improve the passivation stability of the outer surface, while the TiN hard phase 231 continues to provide wear-resistant support. Thus, the passivation auxiliary region 24 and the nitride ceramic-metal composite dense layer 23 together constitute the outer wear-resistant and corrosion-resistant functional region, enabling the dual-phase wear-resistant and corrosion-resistant layer 2 to maintain good surface integrity under the combined action of friction, wear, and corrosive media.

[0028] Through the above structure, the ball valve casting matrix 1, Cr2O3 enriched region 211, FeCr2O4 spinel region 212, Ti-ON interface anchoring region 22, nitride ceramic-metal composite dense layer 23, and passivation auxiliary region 24 form a continuous compositional and functional transition from the inside to the outside. Specifically, the oxide ceramic transition layer 21 mainly improves interfacial bonding stability and provides an internal corrosion barrier; the Ti-ON interface anchoring region 22 mainly enhances the connection between the oxide ceramic transition layer 21 and the nitride ceramic-metal composite dense layer 23; the nitride ceramic-metal composite dense layer 23 mainly provides wear-resistant load-bearing capacity; and the passivation auxiliary region 24 improves the corrosion resistance stability of the outer surface. The layers are not simply physically superimposed, but rather form an interconnected gradient composite structure through in-situ oxidation, Ti-source plasma surface alloying, and segmented nitrogen potential treatment, thereby enabling the ball valve casting to possess high interfacial bonding strength, wear resistance, and corrosion resistance.

[0029] Example 1 This embodiment provides a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting, the preparation method of which includes the following steps S1-S5: S1: Select the sealing surface of the 316L stainless steel ball valve casting as the area to be treated, and perform mechanical grinding, degreasing and cleaning, vacuum desorption and Ar plasma pre-cleaning on the sealing surface in sequence; wherein, the working gas pressure of Ar plasma pre-cleaning is 10Pa and the treatment time is 30min, to obtain the pre-treated ball valve casting substrate. S2: The pretreated ball valve casting substrate is placed in a vacuum heat treatment furnace and subjected to in-situ oxidation treatment at 560℃. The oxygen partial pressure is 40Pa, the holding time is 1.5h, and the oxygen supply method is continuous oxygen supply. This allows the Fe, Cr, and Ni elements in the 316L stainless steel to react with oxygen in situ, forming an oxide ceramic transition layer on the surface of the ball valve casting substrate. S3: The ball valve casting substrate with the oxide ceramic transition layer is placed in a dual glow discharge plasma surface alloying device. A Ti-Mo alloy target is used as the source electrode and the ball valve casting substrate is used as the cathode. The distance between the Ti-Mo alloy target and the ball valve casting substrate is 40 mm. The working gas pressure is 45 Pa, the source electrode voltage is 1000 V, the cathode voltage is 475 V, the processing temperature is 735 ℃, the processing time is 0.5 h, and the volume fraction of N2 in the working atmosphere is 5%, with the remainder being Ar. This allows Ti to enter the outer side of the oxide ceramic transition layer and form the precursor region of the Ti-ON interface anchoring zone. S4: A nitrogen-containing atmosphere is introduced into the dual-glow plasma surface alloying equipment, and segmented nitrogen potential treatment is performed; the N2 volume fraction in the low nitrogen potential introduction stage is 18%, and the treatment time is 55 min; the N2 volume fraction in the medium nitrogen potential precipitation stage is 32%, and the treatment time is 1 h; the N2 volume fraction in the low nitrogen potential integration stage is 10%, and the treatment time is 90 min; the segmented nitrogen potential treatment temperature is 780℃, so that Ti and active nitrogen react in situ on the outside of the Ti-ON interface anchoring zone to generate TiN hard phase, and Mo forms a passivation auxiliary zone on the outside; S5: The ball valve casting substrate after S4 treatment is subjected to cooling and film stabilization treatment at a temperature of 350℃, an oxygen partial pressure of 1Pa, and a holding time of 35min. Subsequently, precision polishing is performed to make the surface roughness Ra of the sealing surface 0.25μm, thus obtaining a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting.

[0030] In the dual-phase wear-resistant and corrosion-resistant layer obtained in this embodiment, the oxide ceramic transition layer has a thickness of 0.8 μm, of which the Cr2O3 enriched region has a thickness of 0.35 μm and the FeCr2O4 spinel region has a thickness of 0.45 μm; the Ti-ON interface anchoring region has a thickness of 1.5 μm; the nitride ceramic-metal composite dense layer has a thickness of 36 μm, and the TiN hard phase is dispersed in the austenitic metal binder phase in the form of nanoparticles and short rods. The equivalent particle size of the TiN hard phase is 300 nm, and the area ratio of the TiN hard phase in the cross section of the nitride ceramic-metal composite dense layer is 28%; a passivation auxiliary region enriched with Mo is formed on the outside of the nitride ceramic-metal composite dense layer, and a TiN and MoN synergistic region is formed on the outer surface.

[0031] Example 2 This embodiment provides a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting, the preparation method of which includes the following steps S1-S5: S1: Select the valve seat contact surface of the CF8M austenitic stainless steel ball valve casting as the area to be treated, and perform mechanical grinding, degreasing cleaning, vacuum desorption and Ar plasma pre-cleaning on the valve seat contact surface in sequence; wherein, the working gas pressure of Ar plasma pre-cleaning is 50Pa and the treatment time is 15min, to obtain the pre-treated ball valve casting matrix. S2: The pretreated ball valve casting substrate is placed in a vacuum heat treatment furnace and subjected to in-situ oxidation treatment at 420℃. The oxygen partial pressure is 5Pa, the holding time is 2.5h, and the oxygen supply method is pulse oxygen supply. This allows the Fe, Cr, and Ni elements in CF8M austenitic stainless steel to react with oxygen in situ, forming an oxide ceramic transition layer on the surface of the ball valve casting substrate. S3: The ball valve casting substrate with the oxide ceramic transition layer is placed in a dual glow discharge plasma surface alloying device. A Ti-Cr alloy target is used as the source electrode and the ball valve casting substrate is used as the cathode. The distance between the Ti-Cr alloy target and the ball valve casting substrate is 12mm. The working gas pressure is 70Pa, the source electrode voltage is 650V, the cathode voltage is 300V, the processing temperature is 850℃, the processing time is 1.8h, and the working atmosphere is Ar atmosphere. This allows Ti to enter the outer side of the oxide ceramic transition layer and form the precursor region of the Ti-ON interface anchoring zone. S4: A nitrogen-containing atmosphere is introduced into the dual-glow plasma surface alloying equipment, and a segmented nitrogen potential treatment is performed. The N2 volume fraction in the low nitrogen potential introduction stage is 10%, and the treatment time is 20 min. The N2 volume fraction in the medium nitrogen potential precipitation stage is 45%, and the treatment time is 5 h. The N2 volume fraction in the low nitrogen potential integration stage is 15%, and the treatment time is 55 min. The segmented nitrogen potential treatment temperature is 670℃, which allows Ti and active nitrogen to react in situ on the outside of the Ti-ON interface anchoring zone to generate a TiN hard phase, and allows Cr to form a passivation auxiliary zone on the outside. S5: The ball valve casting substrate treated by S4 is subjected to a cooling and film stabilization treatment at a temperature of 280℃, an oxygen partial pressure of 30Pa, and a holding time of 60min. Subsequently, a precision polishing treatment is performed to make the surface roughness Ra of the valve seat contact surface 0.12μm, thus obtaining a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting.

[0032] In the dual-phase wear-resistant and corrosion-resistant layer obtained in this embodiment, the oxide ceramic transition layer has a thickness of 4.5 μm, of which the Cr2O3 enriched region has a thickness of 2.10 μm and the FeCr2O4 spinel region has a thickness of 2.40 μm; the Ti-ON interface anchoring region has a thickness of 0.1 μm; the nitride ceramic-metal composite dense layer has a thickness of 65 μm, and the TiN hard phase is distributed in the austenitic metal binder phase as nanoparticles and discontinuous dispersed phases. The equivalent particle size of the TiN hard phase is 150 nm, and the area ratio of the TiN hard phase in the cross section of the nitride ceramic-metal composite dense layer is 8%; a Cr-enriched passivation auxiliary region is formed on the outside of the nitride ceramic-metal composite dense layer, and a TiN and CrN synergistic region is formed on the outer surface.

[0033] Example 3 This embodiment provides a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting, the preparation method of which includes the following steps S1-S5: S1: Select the flow channel scouring surface of the 304 stainless steel ball valve casting as the area to be treated, and perform mechanical grinding, degreasing cleaning, vacuum desorption and Ar plasma pre-cleaning on the flow channel scouring surface in sequence; wherein, the working gas pressure of Ar plasma pre-cleaning is 30Pa and the treatment time is 5min, to obtain the pre-treated ball valve casting substrate. S2: The pretreated ball valve casting substrate is placed in a vacuum heat treatment furnace and subjected to in-situ oxidation treatment at 490℃. The oxygen partial pressure is 80Pa, the holding time is 0.5h, and the oxygen supply method is pulse oxygen supply. This allows the Fe, Cr, and Ni elements in the 304 stainless steel to react with oxygen in situ, forming an oxide ceramic transition layer on the surface of the ball valve casting substrate. S3: The ball valve casting substrate with the oxide ceramic transition layer is placed in a dual glow discharge plasma surface alloying device. A Ti-Nb alloy target is used as the source electrode and the ball valve casting substrate is used as the cathode. The distance between the Ti-Nb alloy target and the ball valve casting substrate is 26 mm. The working gas pressure is 20 Pa, the source electrode voltage is 820 V, the cathode voltage is 650 V, the processing temperature is 620 °C, the processing time is 3 h, and the volume fraction of N2 in the working atmosphere is 10%, with the remainder being Ar. This allows Ti to enter the outer side of the oxide ceramic transition layer and form the precursor region of the Ti-ON interface anchoring zone. S4: A nitrogen-containing atmosphere is introduced into the dual-glow plasma surface alloying equipment, and a segmented nitrogen potential treatment is performed. The N2 volume fraction in the low nitrogen potential introduction stage is 5%, and the treatment time is 90 min. The N2 volume fraction in the medium nitrogen potential precipitation stage is 20%, and the treatment time is 3 h. The N2 volume fraction in the low nitrogen potential integration stage is 5%, and the treatment time is 20 min. The segmented nitrogen potential treatment temperature is 560℃, which allows Ti and active nitrogen to react in situ on the outside of the Ti-ON interface anchoring zone to generate a TiN hard phase, and allows Nb to form a passivation auxiliary zone on the outside. S5: The ball valve casting substrate after S4 treatment is subjected to cooling and film stabilization treatment at a temperature of 420℃, an oxygen partial pressure of 15Pa, and a holding time of 10min. Subsequently, precision polishing is performed to make the surface roughness Ra of the flow channel scouring surface 0.05μm, thus obtaining a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting.

[0034] In the dual-phase wear-resistant and corrosion-resistant layer obtained in this embodiment, the oxide ceramic transition layer has a thickness of 2.6 μm, of which the Cr2O3 enriched region has a thickness of 1.20 μm and the FeCr2O4 spinel region has a thickness of 1.40 μm; the Ti-ON interface anchoring region has a thickness of 0.8 μm; the nitride ceramic-metal composite dense layer has a thickness of 15 μm, and the TiN hard phase is dispersed in the austenitic metal binder phase in the form of nanoparticles and short rods. The equivalent particle size of the TiN hard phase is 20 nm, and the area ratio of the TiN hard phase in the cross section of the nitride ceramic-metal composite dense layer is 45%. A passivation auxiliary region containing Nb enrichment is formed on the outer side of the nitride ceramic-metal composite dense layer, and a TiN and NbN synergistic region is formed on the outer surface.

[0035] Comparative Example 1 Compared with Example 1, this comparative example differs in that the in-situ oxidation treatment step in Example 1 is omitted, and the oxide ceramic transition layer is not formed. The remaining substrate materials, Ti source plasma alloying treatment, segmented nitrogen potential treatment, cooling film stabilization treatment and precision polishing treatment are the same as in Example 1.

[0036] This comparative example illustrates that, without the presence of an oxide ceramic transition layer generated in situ from the matrix elements, the subsequent nitride ceramic-metal composite dense layer lacks the gradient transition foundation provided by the Cr2O3 enrichment region and the FeCr2O4 spinel region between it and the ball valve casting matrix, thus weakening the interfacial bonding stability and the continuity of the corrosion resistance barrier.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that the low oxygen partial pressure in-situ oxidation treatment in Example 1 is replaced with air atmosphere oxidation treatment. The air atmosphere oxidation treatment temperature is 560°C, the holding time is 1.5h, and the treatment pressure is atmospheric pressure; the remaining steps are the same as in Example 1.

[0038] This comparative example is used to illustrate that when using atmospheric pressure air oxidation treatment, the oxide layer is prone to form a thick and uneven oxide scale, making it difficult to form an oxide ceramic transition layer with Cr2O3 enrichment zone, FeCr2O4 spinel zone, and oxygen content gradient.

[0039] Comparative Example 3 Compared with Example 1, this comparative example differs in that the Ti source plasma alloying treatment step in Example 1 is omitted, and the ball valve casting substrate with the oxide ceramic transition layer is directly subjected to segmented nitrogen potential treatment; the remaining in-situ oxidation treatment, segmented nitrogen potential treatment, cooling film stabilization treatment and precision polishing treatment are the same as in Example 1.

[0040] This comparative example illustrates that, without the introduction of a Ti source, it is difficult to form a dense nitride ceramic-metal composite layer with TiN hard phase as the main reinforcing phase in the treated layer. The resulting surface layer mainly relies on the elemental nitriding reinforcement of the stainless steel matrix itself, and its wear resistance and load-bearing capacity are insufficient.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is that the segmented nitrogen potential treatment in Example 1 is replaced with a single nitrogen potential treatment; the N2 volume fraction of the single nitrogen potential treatment is 32%, the treatment time is 145 min, and the treatment temperature is 780℃; the remaining steps are the same as in Example 1.

[0042] This comparative example is used to illustrate that when a single nitrogen potential is used for treatment, the reaction and diffusion process between Ti and active nitrogen is not easy to control in stages, which can easily lead to uneven distribution or local coarsening of the TiN hard phase, and is not conducive to the formation of a gradient composite structure jointly regulated by low nitrogen potential introduction, medium nitrogen potential precipitation and low nitrogen potential integration.

[0043] Comparative Example 5 The difference between this comparative example and Example 2 is that the Ti-Cr alloy target in Example 2 is replaced with a pure Ti target, and the cooling and film stabilization treatment is cancelled. Only the precision polishing treatment is performed after the segmented nitrogen potential treatment. The remaining steps are the same as in Example 2.

[0044] This comparative example illustrates that, in the absence of a Cr auxiliary source and without cooling and film stabilization treatment, it is difficult to form a stable Cr-enriched passivation auxiliary region on the outer side of the nitride ceramic-metal composite dense layer, and the synergistic effect between TiN and CrN on the outer surface is weakened.

[0045] Comparative Example 6 The difference between this comparative example and Example 3 is that the Ti-Nb alloy target in Example 3 is replaced with a pure Ti target, and the N2 volume fraction in the nitrogen potential precipitation stage is increased from 20% to 45%, while the treatment time in the nitrogen potential precipitation stage remains 3 hours; the remaining steps are the same as in Example 3.

[0046] This comparative example is used to illustrate that when the Nb auxiliary element is not introduced and the volume fraction of N2 in the medium nitrogen potential precipitation stage is increased, it is not easy to form a Nb-rich passivation auxiliary area on the outside. At the same time, a higher nitrogen potential is likely to cause the nitride phase to precipitate concentratedly in local areas, weakening the uniform dispersion of the TiN hard phase in the austenite metal bonding phase.

[0047] Test Example 1: Cross-sectional morphology and EDS energy spectrum test In order to verify the cross-sectional structure and elemental gradient distribution of the surface modification layer of the ball valve castings obtained in each group of examples and comparative examples, SEM observation of the sample cross-section and EDS energy spectrum analysis should be carried out first. Specifically, 2 specimens of 10mm×10mm×5mm are cut from each specimen in the treatment area, and the cutting direction is perpendicular to the surface treatment layer. After cold embedding with epoxy resin, it is polished with 800-mesh, 1200-mesh, 2000-mesh and 5000-mesh SiC sandpaper, then polished with 1μm diamond polishing fluid, and finally ultrasonically cleaned with absolute ethanol for 3 min and dried. A SEM5000P type field emission scanning electron microscope produced by Guoyi Quantum Technology Co., Ltd. is used for cross-sectional observation; an EDS energy spectrum module supporting the equipment is used for elemental analysis. Before testing, a SXSC-1000C type vacuum carbon coating instrument produced by Shanghai Shouxiang Vacuum Technology Co., Ltd. is used to deposit a conductive carbon film on the sample cross-section, and the carbon coating time is 60 s. The acceleration voltage of the scanning electron microscope is 15 kV, the working distance is 8 mm, and the beam current is 1.0 nA. The overall cross-sectional morphology is observed in the backscattered electron mode with a magnification of 2000 times; the local morphology of the interface area is observed in the secondary electron mode with a magnification of 10000 times.

[0048] During EDS line scanning, 3 line scanning paths perpendicular to the outer surface are selected on each sample cross-section. Each line scanning path starts from the outer surface of the passivation auxiliary area and successively passes through the nitride ceramic-metal composite dense layer, the Ti-O-N interface anchoring area, the oxide ceramic transition layer and enters the matrix of the ball valve casting. The line scanning step size is 0.10 μm, the acquisition time for each point is 80 ms, and the detected elements are Fe, Cr, Ni, O, Ti and N. For those containing Mo or Nb, Mo or Nb elements are also detected; according to the SEM cross-sectional diagram and the EDS line scanning results, the thickness of each layer is statistically analyzed, and the average value is measured at 5 positions for each sample. The oxide ceramic transition layer is determined by the area where O and Cr are co-enriched, the Ti-O-N interface anchoring area is determined by the area where Ti, O and N signal overlap, and the nitride ceramic-metal composite dense layer is determined by the area where Ti and N are co-enriched and contains the contrast of dispersion particles, and the cross-sectional morphology and EDS line scanning results of the samples of each example and comparative example are obtained, as shown in Table Figure 2 . Figure 2The test results of Example 1 and Comparative Example 1 were selected as representative illustrations to compare and illustrate the continuity of the hierarchical structure and the change of the elemental gradient distribution of the surface modification layer after setting the oxide ceramic transition layer.

[0049] Table 1 Note: The thickness and particle size data in the table are the average values ​​of measurements taken at 5 different locations for each sample; the cross-sectional area ratio of the TiN hard phase was obtained from 5 SEM fields of view. "No continuous layer or no continuous region detected" refers to the inability to confirm a continuous layered structure or stable overlapping area of ​​elements in the cross-sectional SEM image and EDS line scan results, but does not exclude the possibility of a small number of corresponding elements existing locally.

[0050] Depend on Figure 2 (a) It can be seen that the surface modified layer of Example 1 exhibits a relatively clear and continuous layered structure. From the ball valve casting substrate outwards, an oxide ceramic transition layer, a Ti-ON interface anchoring zone, and a nitride ceramic-metal composite dense layer can be identified sequentially. The interlayer interfaces are continuous, and no obvious through-pores or local debonding are observed. According to Table 1, the oxide ceramic transition layer of Example 1 has a thickness of 0.8 μm, the Ti-ON interface anchoring zone has a thickness of 1.5 μm, the nitride ceramic-metal composite dense layer has a thickness of 36.0 μm, the equivalent particle size of the TiN hard phase is 300 nm, the cross-sectional area accounts for 28%, and the Cr / Fe atomic ratio continuously decreases from 2.36 to 1.18 along the thickness direction. The Ti, O, and N overlapping areas are obvious and continuous. In comparison, Figure 2 (b) Comparative Example 1 did not form a continuous oxide ceramic transition layer and Ti-ON interface anchoring region. Pores, microcracks and local debonding were present at the interface. Table 1 further shows that the equivalent particle size of its TiN hard phase increased to 520 nm and was unevenly distributed. There was no continuous gradient in the Cr / Fe atomic ratio and the Ti, O and N overlapping regions were not obvious. This indicates that it is difficult to obtain a stable gradient transition structure by relying solely on subsequent nitriding treatment.

[0051] Figure 3 In Example 1 (a), the characteristic peaks of O and Cr are more obvious, and the Ti, N, and Fe peaks appear together, indicating that not only was a continuous oxide ceramic transition layer formed in Example 1, but also a composite dense layer containing a TiN hard phase was formed on the outer side; while Figure 3 (b) The O and Cr peaks in Comparative Example 1 are significantly weakened, indicating the lack of a continuous oxide ceramic transition layer, which is consistent with... Figure 2The weak interfacial bonding observed in (b) corroborates this. Further, referring to Table 1, Examples 2 and 3 also formed continuous hierarchical structures. In Example 2, the oxide ceramic transition layer thickness reached 4.5 μm and the composite dense layer thickness reached 65.0 μm. In Example 3, the equivalent particle size of the TiN hard phase was refined to 20 nm and the area ratio increased to 45%, both exhibiting good interlayer transition integrity. In contrast, Comparative Examples 2 to 6 exhibited problems such as excessively thick and loose oxide layers, failure to form a dispersed TiN strengthening structure, localized coarsening of TiN, indistinct outer passivation auxiliary regions, or nitride phase agglomeration. Therefore, this application, through in-situ oxidation to construct an oxide ceramic transition layer, combined with Ti source alloying and segmented nitrogen potential treatment to form a Ti-ON interface anchoring region and a nitride ceramic-metal composite dense layer, can effectively achieve a continuous gradient transition from the substrate to the surface, taking into account interfacial bonding stability, dispersed distribution of the TiN hard phase, and surface wear and corrosion resistance.

[0052] Test Example 2: X-ray photoelectron spectroscopy depth profiling test To further verify the chemical bonding state of Ti, O, and N elements in the Ti-ON interface anchoring region, X-ray photoelectron spectroscopy (XPS) depth profiling was performed on the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 6. Two 8mm × 8mm × 3mm samples were cut from the surface-treated area of ​​each group of samples, ultrasonically cleaned with anhydrous ethanol for 3 min, dried with nitrogen, and vacuum-dried at 60℃ for 20 min. If the nitride ceramic-metal composite dense layer was thick, its surface was first precisely polished and thinned with low-energy Ar ions according to the cross-sectional thickness obtained in Example 1, so that the area to be tested was close to the Ti-ON interface anchoring region, before XPS depth profiling was performed. XPS was performed using an XPS-X5 fully automatic multifunctional X-ray photoelectron spectrometer manufactured by Suzhou Huacui Instruments Co., Ltd., with a monochromatic Al Kα X-ray source, photon energy of 1486.6 eV, and a vacuum level in the analysis chamber not exceeding 5.0 × 10⁻⁶ eV. -7 Pa; full-spectrum scanning pass energy 100 eV, step size 1.0 eV; high-resolution narrow-spectrum scanning pass energy 30 eV, step size 0.05 EV. Selected test elements include Ti 2p, N 1s, O 1s, Cr 2p, and Fe 2p; for samples using Ti-Mo alloy targets and Ti-Nb alloy targets, Mo 3d or Nb 3d spectra were obtained simultaneously.

[0053] It is carried out using the Ar ion gun provided with the equipment. The Ar ion energy is 1.0 keV. The etching area is specified as 2 mm × 2 mm. The etching rate is set at 5 nm / min with a SiO2 standard sample for depth profiling. High-resolution spectra are obtained for each sample at etching depths of 0 nm, 20 nm, 50 nm, 80 nm, and 100 nm respectively according to the above procedure; for the comparative example without a continuous Ti-O-N interface anchoring region, spectra of the area near the corresponding interface are taken according to the same etching procedure. The spectra are charge-corrected using the C 1s peak at 284.8 eV, and the Shirley background and Gaussian-Lorentzian mixed peak shape are used to fit the sub-peaks. To judge whether the Ti-O-N interface anchoring region is formed and its continuity, the changes in the peak areas of the Ti-O, Ti-N, and Ti-O-N components in Ti 2p, the change in the peak area of the Ti-N component in N 1s, and the changes in the lattice oxygen and defect oxygen components in O 1s are used as the basis. The test results are shown in Table 2 and the sub-peak fitting of the three sputtering depths of 0 nm, 50 nm, and 100 nm of Example 2 is selected as the representative illustration of the XPS depth profiling results Figure 4 .

[0054] Table 2 Note: The changes in the proportion of the peak area of the Ti-N component, the change in the proportion of the peak area of the Ti-O component, and the change in the O 1s lattice oxygen peak are all statistically counted in the direction from the nitride ceramic-metal composite dense layer side to the oxide ceramic transition layer side; for Example 2, corresponding to the three representative sputtering depths of 0 nm, 50 nm, and 100 nm, it is consistent with the Figure 4 XPS depth profiling results. Not detected means that there is no component peak that can be stably fitted and has a continuous depth change law in the corresponding high-resolution spectrum

[0055] As can be seen from Figure 4 , the O 1s, N 1s, and Ti 2p spectra of Example 2 at different sputtering depths show continuous chemical state changes. When approaching the nitride ceramic-metal composite dense layer side, the Ti-N component is stronger; as the sputtering depth increases, the Ti-N component gradually weakens, and the Ti-O component and the O 1s lattice oxygen peak gradually strengthen; at the intermediate depth, the Ti-O-N component peak is more obvious, indicating that the oxide ceramic transition layer and the nitride ceramic-metal composite dense layer in Example 2 are not simply physically overlapped, but a recognizable Ti-O-N interface anchoring region is formed

[0056] In Table 2, the "→" in columns 5, 6, and 7 indicates the change in the peak area ratio of the corresponding components as the XPS sputtering depth increases, i.e., as the sputtering progresses from the nitride ceramic-metal composite dense layer to the oxide ceramic transition layer. For example, in Example 2, the peak area ratio of the Ti-N component is 62.0%→34.2%→7.8%, indicating that the Ti-N bonding gradually decreases from the outside to the inside; correspondingly, the peak area ratio of the Ti-O component is 8.4%→24.1%→64.0%, indicating that the test area gradually transitions from a composite dense layer containing the TiN hard phase to an oxygen-rich oxide ceramic transition layer. This change is consistent with... Figure 4 The results show that the Ti-ON peak at 50 nm is quite obvious.

[0057] As shown in Table 2, Examples 1 to 3 all exhibit a pattern of gradually decreasing Ti-N composition, gradually increasing Ti-O composition, and a peak Ti-ON composition at an intermediate depth. This indicates that the present application can stably form a Ti-ON interface anchoring region with chemical bonding. In contrast, the maximum area ratio of the Ti-ON composition peak in Comparative Example 1 is only 5.6%, no stable Ti-ON composition was detected in Comparative Example 3, and Comparative Examples 4 and 6 show a persistently high Ti-N composition and a lack of concentration of Ti-ON composition, indicating poor interfacial transition continuity. Therefore, the present application, through in-situ oxidation, Ti-source plasma surface alloying, and segmented nitrogen potential treatment, enables a continuous chemical transition between the oxide ceramic transition layer and the nitride ceramic-metal composite dense layer, which is beneficial for improving interlayer bonding stability and provides a structural basis for the synergistic improvement of wear and corrosion resistance.

[0058] Test Example 3: TEM Microstructure and X-ray Diffraction Phase Analysis To verify the dispersed distribution of the TiN hard phase in the nitride ceramic-metal composite dense layer and the phase composition within the surface modification layer of each sample, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses were performed on the samples obtained in Examples 1-3 and Comparative Examples 1-6. TEM samples were taken from the surface-treated area of ​​each sample, and cross-sectional thin sections were prepared using a DB550 focused ion beam electron beam dual-beam microscope manufactured by QuantumCTek Co., Ltd. The thin sections were taken from the middle part of the nitride ceramic-metal composite dense layer, with a final thinning voltage of 5 kV and a final polishing current of 48 pA. The thickness of the thin sections ranged from 70 nm to 100 nm. TEM observation was performed using a TH-F120 field emission transmission electron microscope manufactured by QuantumCTek Co., Ltd., with an accelerating voltage of 120 kV. Bright-field images were obtained under both low and high magnification conditions. Five different fields of view were selected for each sample, and at least 500 TiN hard phase particles were counted. The equivalent particle size was calculated based on the particle projection area, and the particle size distribution of the TiN hard phase was statistically analyzed. Figure 5The TEM results of Example 3 were selected as a representative illustration.

[0059] XRD analysis was performed using a TD-3500 X-ray diffractometer manufactured by Dandong Tongda Technology Co., Ltd. The radiation source for XRD was Cu Kα rays. A tube voltage of 40 kV and a tube current of 40 mA were used, with a scanning step size of 0.02° within the 2θ = 20°–80° range and a scanning rate of 4° / min. The measured spectra were compared with the standard diffraction peak positions of TiN, Cr2O3, FeCr2O4, CrN, MoN, and NbN to obtain the formation of the oxide ceramic transition layer, nitride ceramic-metal composite dense layer, and passivation auxiliary region in each sample. The results are as follows: Figure 6 As shown.

[0060] Depend on Figure 5 (a) and Figure 5 (b) It can be seen that the nitride ceramic-metal composite dense layer of Example 3 contains a large number of fine TiN nanoparticles and a small amount of TiN short rod phase. At the same time, the above-mentioned TiN hard phase is uniformly distributed in the austenitic continuous phase, and no obvious continuous brittle ceramic network structure is found. Figure 5 (c) is a histogram of TiN nanoparticle size in Example 3. The horizontal axis is the equivalent particle size of TiN nanoparticles, and the vertical axis is the number of particles in the corresponding particle size range. Figure 5 (c) It further shows that the particle size of TiN nanoparticles in Example 3 is mainly concentrated between 18nm and 24nm, with an average particle size of about 20nm, which is consistent with the equivalent particle size of TiN hard phase in Example 3 above, which is 20nm and the cross-sectional area accounts for 45%. This result shows that through Ti source plasma surface alloying and segmented nitrogen potential treatment in Example 3, TiN hard phase can be precipitated in situ in a finer dispersed state instead of forming a coarse agglomerate phase, which is conducive to its formation of a dispersed strengthening structure in the austenite continuous phase.

[0061] Depend on Figure 6It can be seen that TiN characteristic peaks can be detected in Examples 1-3, and Cr2O3 and FeCr2O4 related diffraction peaks are also present, indicating that this application retains the basic oxide ceramic transition layer while forming the TiN hard phase. Among them, Example 1 contains a small amount of MoN related peaks, Example 2 contains a small amount of CrN related peaks, and Example 3 contains a small amount of NbN related peaks, indicating that the auxiliary elements corresponding to different Ti-containing targets can form multiple nitride synergistic regions on the outside. Comparative Example 1 did not undergo in-situ oxidation treatment, so the Cr2O3 and FeCr2O4 related peaks were missing or weakened; Comparative Example 3 did not have a Ti source, so TiN did not occur; although Comparative Examples 4 and 6 have TiN peaks, the peak shapes of these two comparative examples are broader than other parts, or locally enhanced, indicating that their nitride phase distribution is not uniform. Therefore, it can be seen that this application does not only produce a simple TiN hard layer, but also constructs it through an oxide ceramic transition layer, a Ti-ON interface anchoring zone and a TiN dispersion strengthening phase, so that the surface modification layer has phase continuity, dispersion strengthening effect and outer layer corrosion resistance auxiliary effect, which reflects the joint determining role of wear resistance and corrosion resistance.

[0062] Test Example 4: Cross-sectional microhardness test and reciprocating friction and wear test To evaluate the wear resistance and load-bearing capacity of the surface modification layers of the ball valve castings obtained in Examples 1 to 3 and Comparative Examples 1 to 6, cross-sectional microhardness tests and reciprocating friction and wear tests were performed on each sample. Microhardness test samples were cut from the treated area, cold-mounted, progressively ground, and polished, and then tested using an HVS-1000ZL digital display micro Vickers hardness tester manufactured by Laizhou Huayin Testing Instruments Co., Ltd. The test force was 0.98 N, and the holding time was 15 s. Test locations were sequentially taken from the outer surface of the surface treatment layer towards the ball valve casting substrate at depths of 0 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 60 μm, and 70 μm. Three indentations were measured at each depth, and the average value was taken. Figure 7 (a) shows the hardness variation curve along depth.

[0063] Friction and wear tests were conducted using an MMW-1A vertical universal friction and wear testing machine manufactured by Jinan Yihua Tribology Testing Technology Co., Ltd. The friction pair consisted of 6mm diameter GCr15 steel balls. The test method was ball-disc reciprocating friction, with a normal load of 10N, a reciprocating frequency of 5Hz, a reciprocating stroke of 5mm, and a test time of 30min. The test environment was room temperature 25℃ and relative humidity 50%. After the test, the three-dimensional morphology of the wear tracks was measured using a SuperView W1 optical 3D surface profilometer manufactured by Shenzhen Zhongtu Instrument Co., Ltd. Three wear track sections were selected for each sample to calculate the wear volume, and the wear rate was calculated based on the ratio of wear volume to load and sliding distance. The results are shown below. Figure 7 As shown in (b).

[0064] Depend on Figure 7 (a) It can be seen that the microhardness of the surface layer of Examples 1 to 3 is significantly higher than that of the key comparative examples, and shows a gradual decreasing trend with increasing depth, without any abrupt change in hardness. Among them, the surface hardness of Example 3 is 1285 HV0.1, while the surface hardness of Examples 1 and 2 is 1210 HV0.1 and 1170 HV0.1, respectively; at a depth of 40 μm, Examples 1 to 3 still maintain 690 HV0.1, 755 HV0.1 and 760 HV0.1, respectively. This result shows that the nitride ceramic-metal composite dense layer formed in this application is not a simple brittle hard layer, but has a hardness gradient structure that gradually transitions from the surface to the matrix, which is beneficial for buffering stress concentration under friction load.

[0065] Comparative Example 1, lacking a continuous oxide ceramic transition layer, had a surface hardness of only 780 HV0.1, and its overall hardness level was significantly lower than that of the Example. Comparative Example 3, lacking a Ti source, could not form a TiN hard phase, resulting in a surface hardness of only 555 HV0.1. Data from Comparative Example 4 showed that although its prepared dual-phase wear-resistant and corrosion-resistant layer could form a certain number of nitride-reinforced layers, the surface hardness was 935 HV0.1 due to the use of a single nitrogen potential treatment, and the hardness gradient was more gradual and stable than that of the Example. In conclusion, in-situ oxidation, Ti-source plasma surface alloying, and segmented nitrogen potential treatment are the key factors in obtaining a surface layer with high hardness and a continuous gradient.

[0066] Depend on Figure 7 (b) It can be seen that the wear rates of Examples 1 to 3 are 1.8 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 2.1×10 -5 mm 3 ·N -1 ·m -1 and 1.4×10-5 mm 3 ·N -1 ·m -1 All were significantly lower than those of Comparative Examples 1 to 6. Among them, the wear rates of Comparative Examples 1, 3, and 4 increased to 5.6 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 6.4×10 -5 mm 3 ·N -1 ·m -1 and 3.9×10 -5 mm 3 ·N -1 ·m -1 This indicates that the lack of an oxide ceramic transition layer, the absence of a TiN dispersed reinforcing phase, or the lack of segmented nitrogen potential control will all reduce the wear resistance and load-bearing capacity of the surface layer. Figure 7 (a) and Figure 7 (b) It can be seen that this application constructs a dual-phase wear-resistant and corrosion-resistant layer with an oxide ceramic transition layer, a Ti-ON interface anchoring zone and a TiN dispersion-reinforced nitride ceramic-metal composite dense layer to achieve the advantages of high hardness, gentle hardness gradient and low wear rate on the surface of the ball valve casting, demonstrating good wear resistance and structural synergy.

[0067] Test Example 5: Corrosion Resistance Test To evaluate the corrosion resistance of the modified surface layers of the ball valve castings obtained in Examples 1-3 and Comparative Examples 1-6, potentiodynamic polarization tests were performed on each group of samples. Samples of varying sizes (10mm × 10mm × 5mm) were cut from the machined surfaces. Except for the surface to be tested, all other surfaces were sealed with epoxy resin and exposed to the external space with a test area of ​​1.0 cm². 2 Testing was conducted. Before testing, all samples were sequentially washed with anhydrous ethanol and deionized water, dried, and then pretreated with nitrogen. The testing equipment used was a CHI760F electrochemical workstation manufactured by Shanghai Chenhua Instrument Co., Ltd. A three-electrode system was used to receive the measurement signals: the working electrode of the tested sample, and a platinum sheet and a saturated calomel electrode as reference electrodes. The corrosive medium was a 3.5% (w / w) NaCl aqueous solution, and the test temperature was 25℃. The samples were immersed in the aqueous solution for 30 minutes, and the open-circuit potential was recorded. Once the open-circuit potential change was within 5 mV, potentiodynamic polarization testing was performed; the scan range was -0.55 V to 0.80 V, and the scan rate was 1 mV / s relative to the saturated calomel electrode. The self-corrosion potential, self-corrosion current density, and pitting potential were obtained from the polarization curves. The results are as follows: Figure 8 As shown.

[0068] Depend on Figure 8 It can be seen that the polarization curves of Examples 1-3 generally shift towards lower current density and higher pitting potential, indicating that the dual-phase wear-resistant and corrosion-resistant layer obtained in this application can effectively reduce the corrosion reaction rate and improve the surface's resistance to pitting corrosion. Specifically, the self-corrosion current densities of Examples 1 to 3 are 2.2 × 10⁻⁶. -7 A·cm -2 1.8×10 -7 A·cm -2 and 1.2×10 -7 A·cm -2 This is significantly lower than the 8.6 × 10⁻⁶ of Comparative Example 1. -7 A·cm -2 And Comparative Example 3, 1.3 × 10 -6 A·cm -2 Meanwhile, the pitting potentials of Examples 1 to 3 were increased to 0.38V, 0.42V and 0.46V respectively, all of which were higher than the pitting potential test results of each comparative example.

[0069] The increased corrosion current density and decreased pitting potential in Comparative Example 1 indicate that the lack of an inner oxide barrier weakens the corrosion resistance of the surface layer. This is precisely because the preparation method in Comparative Example 1 failed to form a continuous oxide ceramic transition layer during the preparation of the dual-phase wear-resistant and corrosion-resistant layer in the process of preparing the ball valve casting substrate. In Comparative Example 3, the absence of a Ti source prevented the formation of the TiN hard phase and the Ti-ON interface anchoring zone, which is reflected in… Figure 8 The data in the examples show that Comparative Example 3 has the highest self-corrosion current density, exhibiting poor corrosion inhibition ability. Although Comparative Examples 4 and 6 possess certain nitride phases, their corrosion resistance is still lower than that of the examples due to the lack of segmented nitrogen potential control or uneven distribution of the nitride phases. This demonstrates that the present application, through the construction of an oxide ceramic transition layer, a Ti-ON interface anchoring zone, a nitride ceramic-metal composite dense layer, and an outer passivation auxiliary zone, can improve surface hardness and wear resistance while reducing corrosion current and increasing pitting potential.

[0070] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. For those skilled in the art, without departing from the technical concept of this application, adaptive adjustments can be made to the in-situ oxidation treatment conditions, Ti-containing target composition, segmented nitrogen potential parameters, film stabilization treatment method, and surface polishing precision based on the material of the ball valve casting, the service medium, the load on the sealing surface, and the wear and corrosion resistance requirements. All equivalent substitutions, parameter optimizations, or conventional modifications made based on the technical solutions disclosed in this application should fall within the scope of protection of this application.

Claims

1. A wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting, wherein, It includes a ball valve casting substrate and a dual-phase wear-resistant and corrosion-resistant layer formed in situ on the surface of the ball valve casting substrate, wherein the ball valve casting substrate is formed of austenitic stainless steel at least at the sealing surface, valve seat contact surface or flow channel scouring surface; The dual-phase wear-resistant and corrosion-resistant layer comprises, in sequence, an oxide ceramic transition layer, a Ti-ON interface anchoring zone, and a nitride ceramic-metal composite dense layer, from the side closest to the ball valve casting substrate to the side furthest from the ball valve casting substrate. The oxide ceramic transition layer is a gradient oxide layer formed by the in-situ reaction of at least two metal elements of Fe, Cr and Ni in the austenitic stainless steel with oxygen. The Ti-ON interface anchoring region connects the oxide ceramic transition layer and the nitride ceramic-metal composite dense layer. The nitride ceramic-metal composite dense layer includes an austenitic metal binder phase and a TiN hard phase dispersed in the austenitic metal binder phase.

2. The wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting according to claim 1, wherein, The thickness of the oxide ceramic transition layer is 0.8 μm to 4.5 μm, and the oxide ceramic transition layer includes a Cr2O3 enrichment region near the ball valve casting substrate and a FeCr2O4 spinel region near the Ti-ON interface anchoring region. Along the direction from the ball valve casting matrix to the Ti-ON interface anchoring zone, the oxygen content in the oxide ceramic transition layer shows an increasing trend, and the Cr / Fe atomic ratio shows a decreasing trend from the Cr2O3 enriched region to the FeCr2O4 spinel region.

3. The wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting according to claim 1, wherein, The thickness of the Ti-ON interface anchoring region is 0.1μm to 1.5μm. The Ti-ON interface anchoring region contains both Ti-O and Ti-N bonding structures. Furthermore, the Ti content in the Ti-ON interface anchoring region increases from the oxide ceramic transition layer side to the nitride ceramic-metal composite dense layer side.

4. The wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting according to claim 1, wherein, The thickness of the nitride ceramic-metal composite dense layer is 15μm to 65μm, and the TiN hard phase is distributed in the austenitic metal binder phase in at least one of the following forms: nanoparticles, short rods, or discontinuous dispersed phases. The equivalent particle size of the TiN hard phase is 20nm to 300nm, and the area ratio of the TiN hard phase in the cross section of the nitride ceramic-metal composite dense layer is 8% to 45%. The area ratio of the TiN hard phase decreases from the outer surface of the nitride ceramic-metal composite dense layer to the ball valve casting substrate.

5. The wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting according to claim 1, wherein, The outer side of the nitride ceramic-metal composite dense layer has a passivation auxiliary region, which is enriched with at least one element selected from Cr, Mo or Nb. In the passivation auxiliary region, TiN forms a multi-component nitride synergistic region with at least one of CrN, MoN, and NbN, and the CrN, MoN, or NbN are distributed in the passivation auxiliary region in a discontinuous particulate or island-like manner.

6. A method for preparing a wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting as described in any one of claims 1 to 5, wherein, Includes the following steps: S1: Surface pretreatment is performed on the austenitic stainless steel ball valve casting substrate to obtain the pretreated ball valve casting substrate; S2: Under low oxygen partial pressure conditions, the pretreated ball valve casting substrate is subjected to in-situ oxidation treatment, so that at least two of the metal elements Fe, Cr and Ni in the austenitic stainless steel react with oxygen to form an oxide ceramic transition layer on the surface of the ball valve casting substrate. S3: The ball valve casting substrate with the oxide ceramic transition layer is placed in a dual glow plasma surface alloying device, with a Ti-containing target as the source electrode and the ball valve casting substrate as the cathode, and Ti source plasma surface alloying treatment is performed in an argon atmosphere, so that Ti enters the outer side of the oxide ceramic transition layer and forms the precursor region of the Ti-ON interface anchoring region. S4: Introduce a nitrogen-containing atmosphere into the dual glow plasma surface alloying equipment and use segmented nitrogen potential treatment to allow Ti and active nitrogen to react in situ outside the anchoring zone of the Ti-ON interface to generate a TiN hard phase, while retaining a continuous austenitic metal bonding phase to form a nitride ceramic-metal composite dense layer. S5: The ball valve casting substrate after S4 is subjected to cooling and film stabilization treatment or precision polishing treatment to obtain the wear-resistant and corrosion-resistant modified austenitic stainless steel ball valve casting.

7. The preparation method according to claim 6, wherein, In steps S1 and S2, the surface pretreatment includes at least three of the following: mechanical polishing, degreasing cleaning, vacuum desorption, and Ar plasma pre-cleaning. The working gas pressure for the Ar plasma pre-cleaning is 10 Pa to 50 Pa, and the processing time is 5 min to 30 min. The in-situ oxidation treatment is carried out at a temperature of 420℃~560℃, an oxygen partial pressure of 5Pa~80Pa, and a holding time of 0.5h~2.5h. The in-situ oxidation treatment is carried out using a continuous oxygen supply or pulsed oxygen supply method.

8. The preparation method according to claim 6, wherein, In step S3, the Ti-containing target material is one of Ti target material, Ti-Cr alloy target material, Ti-Mo alloy target material, or Ti-Nb alloy target material; The distance between the Ti-containing target and the ball valve casting substrate is 12mm to 40mm, the working air pressure is 20Pa to 70Pa, the source voltage is 650V to 1000V, the cathode voltage is 300V to 650V, the processing temperature is 620℃ to 850℃, and the processing time is 0.5h to 3h. The volume fraction of N2 in the argon-containing atmosphere is not higher than 10%.

9. The preparation method according to claim 6, wherein, In step S4, the segmented nitrogen potential treatment includes a low nitrogen potential introduction stage, a medium nitrogen potential precipitation stage, and a low nitrogen potential integration stage. During the low nitrogen potential introduction stage, nitrogen gas is introduced for 20 min to 90 min, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 5% to 18%. During the nitrogen potential precipitation stage, nitrogen gas is introduced for 1 to 5 hours, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 20% to 45%. During the low nitrogen potential integration stage, nitrogen gas is introduced for 20 to 90 minutes, and the volume fraction of N2 in the nitrogen-containing atmosphere after the introduction of nitrogen gas is 5% to 15%. The temperature of the segmented nitrogen potential treatment in step S4 is 560℃~780℃, and the cathode voltage or pulse bias is adjusted to prevent CrN, MoN or NbN from forming a continuous network precipitate.

10. The preparation method according to claim 6, wherein, The austenitic stainless steel is one of 304 stainless steel, 316L stainless steel, CF8 austenitic stainless steel casting, CF8M austenitic stainless steel casting or CF3M austenitic stainless steel casting. The cooling and film stabilization treatment involves holding the material at 280℃~420℃ and an oxygen partial pressure of 1Pa~30Pa for 10min~60min. After precision polishing, the surface roughness Ra of the sealing surface of the ball valve casting is 0.05μm~0.25μm.

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