Heat treatment method of ZG1Cr17Ni3 stainless steel castings, ZG1Cr17Ni3 stainless steel

Abstract

The application relates to a heat treatment method of ZG1Cr17Ni3 stainless steel castings and ZG1Cr17Ni3 stainless steel. The heat treatment method of the ZG1Cr17Ni3 stainless steel castings comprises the following steps: heating the ZG1Cr17Ni3 stainless steel castings to a set temperature, keeping the temperature for a set time, so that long rod-shaped and / or film-shaped M 23 C6 type carbides are fully dissolved; after the keeping temperature, the ZG1Cr17Ni3 stainless steel castings are subjected to cooling treatment; wherein the cooling speed of the ZG1Cr17Ni3 stainless steel castings is controlled to be 30-80 DEG C / s; the ZG1Cr17Ni3 stainless steel castings subjected to the cooling treatment are subjected to tempering heat treatment, so that M 23 C6 type carbides are uniformly reprecipitated in a short rod-shaped and / or granular form at the ferrite and martensite interface. The application can readjust the precipitation behavior and morphological distribution of the carbides at the ferrite / martensite interface in the large-size ZG1Cr17Ni3 stainless steel castings, obtain fine and semi-continuous and uniformly distributed carbides, and improve the mechanical properties of the large-size ZG1Cr17Ni3 stainless steel castings.

Description

Technical Field

[0001] This invention relates to the field of metal material manufacturing technology, and in particular to a heat treatment method for ZG1Cr17Ni3 stainless steel castings and ZG1Cr17Ni3 stainless steel. Background Technology

[0002] ZG1Cr17Ni3 is a high-Cr martensitic-ferritic duplex stainless steel. Due to its excellent corrosion resistance and retention of the high strength of martensitic steel, it is a candidate material for load-bearing components in marine machinery. With the continuous development and upgrading of load-bearing components in marine machinery, the requirements for material strength are also increasing. ZG1Cr17Ni3 stainless steel castings prepared using existing processes and methods can no longer meet the load-bearing requirements of these components.

[0003] Previous studies have found that during the slow cooling process after casting of large-size ZG1Cr17Ni3 stainless steel castings, the carbides precipitated at the ferrite / martensite interface are mainly long rod-shaped and film-shaped, and are continuously distributed along the interface. Under stress, they are prone to stress concentration, which reduces the mechanical properties of the castings. However, traditional tempering heat treatment processes cannot eliminate or improve the size, morphology and distribution of carbides.

[0004] Therefore, it is necessary to develop a new heat treatment method to readjust the precipitation behavior and morphological distribution of carbides at the ferrite / martensite interface in large-size ZG1Cr17Ni3 stainless steel castings, so as to obtain fine-sized and semi-continuously uniformly distributed carbides, thereby inhibiting crack propagation and improving the mechanical properties of ZG1Cr17Ni3 stainless steel castings. Summary of the Invention

[0005] In view of this, the present invention provides a heat treatment method for ZG1Cr17Ni3 stainless steel castings and ZG1Cr17Ni3 stainless steel. The main purpose is to readjust the precipitation behavior and morphological distribution of carbides at the ferrite / martensite interface in large-size ZG1Cr17Ni3 stainless steel castings to obtain fine-sized and semi-continuously uniformly distributed carbides, thereby improving the mechanical properties of large-size ZG1Cr17Ni3 stainless steel castings.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] On one hand, embodiments of the present invention provide a heat treatment method for ZG1Cr17Ni3 stainless steel castings, which includes the following steps:

[0008] Carbide remelting treatment: The ZG1Cr17Ni3 stainless steel casting is heated to a set temperature and held at that temperature for a set time to allow the first morphology of martensite at the ferrite-martensite interface in the ZG1Cr17Ni3 stainless steel casting to undergo remelting. 23 The C6 type carbide was fully dissolved; after the heat treatment, a ZG1Cr17Ni3 stainless steel casting with carbide re-dissolution treatment was obtained; wherein, the first type M 23 C6 type carbides are long rod-shaped M with a length greater than 2 μm. 23 C6 type carbides and / or film-like M 23 C6 type carbides;

[0009] Cooling treatment: The ZG1Cr17Ni3 stainless steel casting after the carbide remelting treatment is subjected to cooling treatment to obtain a cooled ZG1Cr17Ni3 stainless steel casting; wherein, during the cooling treatment process, the cooling rate of the ZG1Cr17Ni3 stainless steel casting is controlled at 30-80℃ / s to suppress the re-precipitation of carbides with a length greater than 2μm and to avoid the risk of quenching cracks.

[0010] Tempering heat treatment: The ZG1Cr17Ni3 stainless steel castings after cooling are subjected to tempering heat treatment to induce M 23 C6-type carbides precipitate uniformly in a second morphology at the ferrite-martensite interface, resulting in the heat-treated ZG1Cr17Ni3 stainless steel casting; among them, the second morphology M 23 C6 type carbides have an average size of less than 1 μm, and their shapes include short rods and / or granules, and they are distributed in a semi-continuous state along the interface.

[0011] Preferably, the ZG1Cr17Ni3 stainless steel casting is a ring-shaped casting with an outer diameter ≥1m, a wall thickness ≥0.1m, and a height ≥0.5m; preferably, the outer diameter of the ZG1Cr17Ni3 stainless steel casting is 1~2m, the wall thickness is 0.1~0.2m, and the height is 0.5~1m.

[0012] Preferably, the preparation process of the ZG1Cr17Ni3 stainless steel casting is as follows: it is prepared by sand casting, then cast, and cooled in air to obtain the ZG1Cr17Ni3 stainless steel casting.

[0013] Preferably, in the carbide re-dissolution treatment step:

[0014] Set the temperature to 1000±10℃ and the time to 2~4h;

[0015] Preferably, the heating rate of the ZG1Cr17Ni3 stainless steel casting to the set temperature is 5-10℃ / min.

[0016] Preferably, the carbide remelting treatment step is carried out in a resistance furnace.

[0017] Preferably, in the cooling process: the ZG1Cr17Ni3 stainless steel casting after carbide remelting treatment is placed in an oil cooling tank for oil quenching; wherein, the flow rate of the oil in the oil cooling tank is controlled to a set flow rate so that the ZG1Cr17Ni3 stainless steel casting after carbide remelting treatment is cooled at a set cooling rate under forced convection conditions; preferably, the set flow rate is 80-90 m³ / s. 3 / h; preferably, the temperature of the oil in the oil cooling tank is 40-100℃; preferably, the ZG1Cr17Ni3 stainless steel casting after carbide remelting treatment is placed into the oil cooling tank within 3-8s.

[0018] Preferably, the oil cooling tank is provided with an oil outlet and an oil inlet; wherein, the oil outlet is connected to a circulating pump via a first pipeline; the circulating pump is connected to the oil inlet via a second pipeline; preferably, the circulating pump is equipped with a flow meter to control the flow rate of the oil in the oil cooling tank; preferably, an oil inlet valve is provided on the first pipeline; an oil outlet valve is provided on the second pipeline; wherein, the flow rate of the oil in the cooling oil tank is controlled by adjusting the oil inlet valve and the oil outlet valve; preferably, the second pipeline includes a first main pipeline, a second main pipeline, a first branch pipeline, and a second branch pipeline; wherein, the oil outlet valve is installed on the first main pipeline; the inlet of the first branch pipeline and the inlet of the second branch pipeline are connected to the first main pipeline; The first branch pipe and the second branch pipe are arranged in parallel; the outlets of the first branch pipe and the second branch pipe are connected to the second main pipe; the second main pipe is connected to the oil inlet; wherein, the first branch pipe passes through a cooling system to cool the oil passing through the first branch pipe; preferably, the inlet of the second branch pipe and the inlet of the first branch pipe are connected to the first main pipe through a diversion valve; the outlet of the second branch pipe and the outlet of the first branch pipe are connected to the second main pipe through a diversion valve; preferably, the cooling system includes a water cooling tank; wherein, a portion of the first branch pipe is immersed in the water cooling tank; preferably, a temperature display is provided on the second main pipe to detect the temperature of the oil passing through the second main pipe.

[0019] Preferably, in the tempering heat treatment step: the cooled ZG1Cr17Ni3 stainless steel casting is heated to 680±10℃ and held at 680±10℃ for 5-8 hours for tempering heat treatment. After cooling, the heat-treated ZG1Cr17Ni3 stainless steel casting is obtained. Preferably, the cooling is air cooling. Preferably, the heating rate of the cooled ZG1Cr17Ni3 stainless steel casting to 680±10℃ is 8-10℃ / min.

[0020] In another aspect, embodiments of the present invention provide a ZG1Cr17Ni3 stainless steel, wherein the ZG1Cr17Ni3 stainless steel is a ring-shaped component with an outer diameter ≥1m, a wall thickness ≥0.1m, and a height ≥0.5m; wherein the M at the ferrite and martensite interface in the ZG1Cr17Ni3 stainless steel... 23 The size of C6 type carbides is less than 1 μm, and the M 23 C6 type carbides can be granular or short rod-shaped.

[0021] Preferably, the ZG1Cr17Ni3 stainless steel is a heat-treated ZG1Cr17Ni3 stainless steel casting; preferably, the heat-treated ZG1Cr17Ni3 stainless steel casting is obtained by heat-treating the ZG1Cr17Ni3 stainless steel casting using any of the above-described heat treatment methods.

[0022] Compared with the prior art, the heat treatment method for ZG1Cr17Ni3 stainless steel castings of the present invention, and the ZG1Cr17Ni3 stainless steel, have at least the following beneficial effects:

[0023] To address the problem in existing technologies where "during the slow cooling process after casting of large-size ZG1Cr17Ni3 stainless steel castings, the carbides precipitated at the ferrite / martensite interface are mainly long rod-shaped and film-shaped, continuously distributed along the interface; this easily leads to stress concentration under stress, reducing the mechanical properties of the casting," this invention proposes a heat treatment method for ZG1Cr17Ni3 stainless steel castings. This method involves first performing a carbide re-dissolution treatment, which reduces the long rod-shaped and film-shaped carbides precipitated at the ferrite / martensite interface in the ZG1Cr17Ni3 stainless steel casting. 23 The C6 type carbides were fully dissolved; then, the ZG1Cr17Ni3 stainless steel casting after carbide re-dissolution treatment was cooled to obtain a cooled ZG1Cr17Ni3 stainless steel casting; during the cooling process, the cooling rate of the ZG1Cr17Ni3 stainless steel casting was controlled at 30-80℃ / s to suppress the re-precipitation of coarse carbides and avoid the risk of quenching cracks; finally, the cooled ZG1Cr17Ni3 stainless steel casting was tempered to induce M 23 C6-type carbides are re-precipitated uniformly in short rod-shaped or granular form at the ferrite-martensite interface, resulting in heat-treated ZG1Cr17Ni3 stainless steel castings. This invention, through the above method, eliminates the harmful effects of long rod-shaped and film-shaped carbides in large-size ZG1Cr17Ni3 stainless steel castings, readjusts the carbide precipitation morphology, and promotes M... 23 C6-type carbides precipitate in a fine, uniform, and semi-continuous state at the ferrite / martensite interface, hindering crack propagation and thus improving the mechanical properties of stainless steel.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a forced convection oil quenching cooling device provided in an embodiment of the present invention;

[0026] Figure 2 These are carbide morphology images of the first type of casting sample, the second type of casting sample, and the third type of casting sample after undergoing heat treatment scheme 1 (tempering only) and scheme 2 (carbide dissolution treatment, cooling treatment, and tempering heat treatment); among them, Figure 2 Figure a in the diagram shows the carbide morphology of the first type of casting sample after heat treatment according to scheme 1. Figure 2 Figure d in the figure shows the carbide morphology of the first type of casting sample after heat treatment according to scheme 2. Figure 2 Figure b in the figure shows the carbide morphology of the second type of casting sample after heat treatment according to scheme 1. Figure 2 Figure e in the figure shows the carbide morphology of the second type of casting sample after heat treatment according to scheme 2. Figure 2 Figure c in the figure shows the carbide morphology of the third type of casting sample after heat treatment according to scheme 1. Figure 2 Figure f in the figure shows the carbide morphology of the third type of casting sample after heat treatment according to scheme 1.

[0027] Figure 3 This is a SEM microstructure image of the ZG1Cr17Ni3 stainless steel casting sample after heat treatment obtained in Example 3.

[0028] Figure 4 This is a SEM microstructure image of the heat-treated ZG1Cr17Ni3 stainless steel casting sample obtained in Comparative Example 1.

[0029] Figure 5 This is a SEM microstructure image of the heat-treated ZG1Cr17Ni3 stainless steel casting sample obtained in Comparative Example 2. Detailed Implementation

[0030] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0031] To improve the mechanical properties of large-size ZG1Cr17Ni3 stainless steel castings, the present invention aims to provide a heat treatment method for ZG1Cr17Ni3 stainless steel castings. This method first eliminates the long rod-shaped and film-shaped ferrite at the interface between ferrite and martensite in the casting. 23 C6 carbides prevent stress concentration from reducing mechanical properties, and then promote M 23 C6 carbides precipitate again at the ferrite / martensite interface in a fine and uniform morphology, hindering crack propagation and improving the interfacial strength between ferrite and martensite, thereby optimizing the mechanical properties of stainless steel castings.

[0032] The main solution of the present invention is as follows:

[0033] 1) Carbide remelting treatment: After casting and cooling, the large-sized ZG1Cr17Ni3 stainless steel casting is placed in a box-type resistance furnace and heated to the target temperature of 1000±10℃ at a heating rate of 5~10℃ / min. The temperature is held for 2~4 hours to allow the long rod-shaped (rod-shaped carbides with a length greater than 2μm are called "long rod-shaped carbides") and film-like continuous distribution of M at the ferrite / martensite interface to be resolved. 23 The C6 type carbide was fully dissolved to obtain ZG1Cr17Ni3 stainless steel castings after carbide resolution treatment.

[0034] It should be noted that due to the large size of stainless steel castings, the slow cooling rate during the continuous cooling process after casting leads to the formation of long rod-shaped and film-shaped continuously distributed martensite at the ferrite / martensite interface. 23 C6 type carbides are prone to causing stress concentration and reducing the mechanical properties of castings, and must be eliminated.

[0035] In this step, the target temperature and holding time should be selected to ensure sufficient dissolution of the long rod-shaped and film-shaped M at the ferrite / martensite interface. 23 C6 type carbides promote uniform diffusion of elements and eliminate the influence of undissolved carbides and solute concentration gradients on the morphology and distribution of carbide reprecipitation after tempering in advance; at the same time, they avoid ferrite coarsening caused by excessively high temperatures, so as to ensure the strength of the alloy.

[0036] 2) Cooling treatment: The ZG1Cr17Ni3 stainless steel casting after the carbide remelting treatment is subjected to cooling treatment to obtain the cooled ZG1Cr17Ni3 stainless steel casting; wherein, during the cooling treatment process, the cooling rate of the ZG1Cr17Ni3 stainless steel casting is controlled at 30-80℃ / s to suppress the re-precipitation of coarse carbides and avoid the risk of quenching cracks.

[0037] It should be noted that the inventors of this invention discovered that the cooling rate is crucial. Insufficient cooling (e.g., conventional oil cooling) will still result in carbide coarsening and reduced mechanical properties. Conversely, excessively rapid cooling (e.g., water cooling) poses a risk of casting cracking. After extensive research, the inventors found that controlling the cooling rate between 30 and 80°C / s can suppress the re-precipitation of coarse carbides and avoid the risk of cracking.

[0038] To control the cooling rate at 30–80°C / s, this invention involves directly placing the ZG1Cr17Ni3 stainless steel casting, after melt-back treatment, into an oil-cooling tank equipped with a circulating pump system, at a cooling rate of 80–90°C / s. 3 Oil quenching is performed under forced convection conditions at a flow rate of / h. Preferably, the oil temperature in the oil cooling tank is controlled at 40–100°C.

[0039] In order to achieve the above control, the present invention is designed as follows, as detailed below:

[0040] The oil cooling tank measures 3.5 × 3.5 × 1.5 m. 3 Specifically, this step employs a forced convection oil quenching cooling device, the structure of which can be found in [reference needed]. Figure 1 As shown. Specifically, the oil cooling tank 1 is provided with an oil outlet 11 and an oil inlet 12; wherein, the oil outlet 11 is connected to the circulation pump 3 through a first pipeline; the circulation pump 3 is connected to the oil inlet 12 through a second pipeline; preferably, an oil inlet valve 2 is provided on the first pipeline; an oil outlet valve 4 is provided on the second pipeline; wherein, the flow rate of the oil in the cooling oil tank 1 is controlled by adjusting the oil inlet valve 2 and the oil outlet valve 4.

[0041] Preferred, such as Figure 1As shown, the second pipeline includes a first main pipeline 51, a second main pipeline 52, a first branch pipeline 54, and a second branch pipeline 53; wherein, the oil outlet valve 4 is installed on the first main pipeline 51; the inlet of the first branch pipeline 54 and the inlet of the second branch pipeline 53 are connected to the first main pipeline 51; the first branch pipeline 54 and the second branch pipeline 53 are arranged side by side; the outlets of the first branch pipeline 54 and the second branch pipeline 53 are connected to the second main pipeline 52; the second main pipeline 52 is connected to the oil inlet 12. The first branch pipe 54 passes through a cooling system to cool the oil passing through it. Preferably, the inlet of the second branch pipe 54 and the inlet of the first branch pipe 53 are connected to the first main pipe 51 via a diversion valve 7; the outlet of the second branch pipe 53 and the outlet of the first branch pipe 54 are connected to the second main pipe 52 via a diversion valve 9. Preferably, the cooling system is a water-cooled tank 6. Preferably, a temperature display meter 8 is provided on the second main pipe 52 to detect the temperature of the oil passing through it.

[0042] Specifically, during oil cooling, the circulating pump 3 is turned on, and the flow meter reading is adjusted to 80-90 m³ / h using the inlet valve 2 and outlet valve 4. 3 Forced convection oil quenching is performed at / h (where the flow meter is set on the circulating pump). The flow rate of cooling oil flowing through the water-cooling tank and hot oil not flowing through the water-cooling tank is controlled by adjusting the diversion valve 7, so that the oil temperature is controlled at 40-100℃.

[0043] It should be noted that oil temperature has a certain impact on cooling capacity. At low oil temperatures, viscosity is high, resulting in low cooling capacity. Increasing oil temperature lowers viscosity, increases fluidity, and raises the surface heat transfer coefficient, thus improving cooling capacity. However, excessively high oil temperatures can easily generate large amounts of oil fumes and even cause fires, posing a significant safety hazard. Therefore, this invention controls the cooling oil temperature to 40-100℃. Under these temperature conditions, the oil viscosity is low, and the better fluidity helps the casting dissipate heat effectively while also ensuring good safety.

[0044] 3) Tempering heat treatment: The cooled ZG1Cr17Ni3 stainless steel casting is subjected to tempering heat treatment at 680±10℃ for 5-8 hours to induce M 23 C6 type carbides are re-precipitated uniformly at the ferrite / martensite interface in the form of fine particles or short rods (rod-shaped carbides with an average length of less than 1 μm are called "short rod-shaped carbides"), resulting in heat-treated stainless steel castings.

[0045] In this step, the precipitated M 23C6 type carbides, with an average length of less than 1 μm, can reduce stress concentration during alloy loading. Furthermore, the semi-continuous and uniform distribution of carbides can effectively hinder crack propagation and improve the strength of ZG1Cr17Ni3 stainless steel.

[0046] In summary, the long rod-shaped and film-shaped M-shaped structures at the ferrite and martensite interface in large-sized ZG1Cr17Ni3 stainless steel castings after casting and cooling... 23 C6 carbides are continuously distributed along the interface; they are prone to stress concentration under stress, reducing the mechanical properties of the casting. The heat treatment method for ZG1Cr17Ni3 stainless steel castings provided by this invention first involves a carbide remelting treatment, which removes the continuous distribution of long rod-shaped and film-shaped M-carbides at the ferrite / martensite interface. 23 The C6 carbides were fully dissolved; then, quenching under forced convection conditions (controlling the cooling rate of quenching) + tempering heat treatment was used to eliminate the harmful effects of long rod-shaped and film-shaped carbides in large-size ZG1Cr17Ni3 stainless steel castings, readjust the carbide precipitation morphology, and promote M 23 C6 precipitates in fine, uniform, and semi-continuous manner at the ferrite / martensite interface, hindering crack propagation and thus improving the mechanical properties of stainless steel.

[0047] The present invention will be further illustrated below with specific embodiments:

[0048] Example 1

[0049] This embodiment provides three types of ZG1Cr17Ni3 stainless steel casting samples. The first type of casting sample is cut from the center of a large casting with an outer diameter of 1m, a wall thickness of 0.1m, and a height of 0.7m (i.e., the intersection of half the wall thickness and half the height). The second type of casting sample is a cast-on sample, i.e., a test bar adhered to the large casting and cast. Both the first and second types of casting samples are affected by the large casting size. Due to the slow cooling rate after casting, the carbides precipitated at the ferrite / martensite interface are mainly long rod-shaped and film-shaped, continuously distributed along the interface. The third type of casting sample is a single-cast sample, specifically a rod-shaped sample cast separately using a quincunx shell mold. The weight of molten steel cast per heat is approximately 4kg, and the test bar size is 16mm in diameter and approximately 150mm in length, much smaller than the first type of casting sample, resulting in a faster cooling rate after casting.

[0050] The first, second, and third casting samples were subjected to tempering treatment only. Figure 2 It can be seen that: in the first and second casting samples after tempering at 680℃ for 6.5h, the carbides at the ferrite and martensite interface are large-sized long rod-shaped and film-shaped M. 23 C6 type carbides, long rod-shaped carbides can reach sizes of more than ten micrometers (see...). Figure 2 (See Figure a in the text), the film-like carbides are continuously distributed along the interface between ferrite and martensite (see Figure a in the text). Figure 2 (See Figure b in the text). The third type of casting specimen (single-cast test bar) experienced a faster cooling rate after casting, resulting in insufficient time for carbides to grow and a smaller initial size. Therefore, even after tempering, it retained its smaller size (see Figure b). Figure 2 (Figure c in the text).

[0051] The first, second, and third casting samples were subjected to a carbide remelting treatment at 1000℃ for 3 hours, a cooling treatment at a cooling rate of 60-80℃ / s, and a tempering heat treatment at 680℃ for 6.5 hours, according to the scheme of this invention. In the first and second casting samples, after the carbide remelting treatment, cooling treatment, and tempering heat treatment, the carbides dissolved and precipitated again as small-sized particles in a semi-continuous distribution. (See [reference needed]). Figure 2 Figures d and e are shown in the diagram. After the third type of casting sample underwent carbide remelting, cooling, and tempering heat treatment, the carbide size did not show significant growth, as shown in Figure d. Figure 2 Figure f in the diagram.

[0052] Table 1 shows the room temperature tensile properties of the first type of casting sample, the second type of casting sample, and the third type of casting sample after undergoing scheme 1 (tempering treatment only as described above) and scheme 2 (carbide remelting treatment, cooling treatment, and tempering heat treatment according to the scheme of this invention).

[0053] Table 1

[0054]

[0055] As shown in Table 1, for the first and second casting samples, compared to Scheme 1 (tempering treatment only), Scheme 2 increased the room temperature yield strength of the castings by 160 MPa and 195 MPa, respectively, and the tensile strength by 62.5 MPa and 113.5 MPa, respectively. For the third casting sample, the room temperature tensile properties after Scheme 1 and Scheme 2 were comparable.

[0056] In summary, the solution of the present invention can significantly improve the mechanical properties of large-size ZG1Cr17Ni3 stainless steel, but has no significant effect on improving the mechanical properties of small-size ZG1Cr17Ni3 stainless steel.

[0057] Example 2

[0058] ZG1Cr17Ni3 stainless steel castings were prepared using induction melting and sand casting processes. The castings had an outer diameter of 1 m, a wall thickness of 0.1 m, and a height of 0.5 m. They were formed by atmospheric casting and then air-cooled. The castings exhibited long rod-shaped and film-like ferrite particles at the ferrite-martensite interface. 23 C6 type carbides are larger than 3 μm in size and are continuously distributed along the interface.

[0059] This embodiment describes the heat treatment of the ZG1Cr17Ni3 stainless steel casting, which mainly includes the following steps:

[0060] The cooled ZG1Cr17Ni3 stainless steel casting was placed in a box-type resistance furnace and heated to 1000℃ at a heating rate of 10℃ / min. After holding at this temperature for 2 hours, a carbide re-dissolution treatment was performed. After the holding period, the ZG1Cr17Ni3 stainless steel casting with the carbide re-dissolution treatment was placed in a [further context needed - likely a specific location or process]. Figure 1 In the oil cooling tank shown, the oil circulation flow rate is controlled at 80 m³ / s. 3 The ZG1Cr17Ni3 stainless steel casting was subjected to forced convection oil quenching at an oil temperature of 50℃ / h, cooling at a rate of 60℃ / s. The cooled ZG1Cr17Ni3 stainless steel casting was then placed in a box-type resistance furnace and heated to 680℃ (heating rate 10℃ / min), tempered for 5 hours, and air-cooled to obtain the heat-treated ZG1Cr17Ni3 stainless steel casting.

[0061] Example 3

[0062] ZG1Cr17Ni3 stainless steel castings were prepared using induction melting and sand casting processes. The castings had an outer diameter of 1.5 m, a wall thickness of 0.1 m, and a height of 1 m. They were formed by atmospheric casting and then air-cooled. The castings exhibited long rod-shaped and film-like ferrite particles at the ferrite-martensite interface. 23 C6 carbides are larger than 3 μm in size and are continuously distributed along the interface.

[0063] This embodiment describes the heat treatment of the ZG1Cr17Ni3 stainless steel casting, which mainly includes the following steps:

[0064] The cooled ZG1Cr17Ni3 stainless steel casting was placed in a box-type resistance furnace and heated to 1000℃ at a heating rate of 10℃ / min. After holding at this temperature for 2 hours, a carbide re-dissolution treatment was performed. After the holding period, the ZG1Cr17Ni3 stainless steel casting with the carbide re-dissolution treatment was placed in a [further context needed - likely a specific location or process]. Figure 1In the oil cooling tank shown, the oil circulation flow rate is controlled at 85 m³ / s. 3 The ZG1Cr17Ni3 stainless steel casting was subjected to forced convection oil quenching at a temperature of 60℃ / h, allowing it to cool at a rate of 70℃ / s. The cooled ZG1Cr17Ni3 stainless steel casting was then placed in a box-type resistance furnace and heated to 680℃ (heating rate 10℃ / min), tempered for 6.5 hours, and air-cooled to obtain the heat-treated ZG1Cr17Ni3 stainless steel casting.

[0065] The SEM microstructure of the heat-treated ZG1Cr17Ni3 stainless steel casting obtained in this embodiment is shown in the figure. Figure 3 As shown, the carbides at the ferrite-martensite interface are small in size, with an average size of about 0.8 μm. They are semi-continuously distributed along the interface, which can effectively hinder crack propagation and improve the mechanical properties of stainless steel.

[0066] Example 4

[0067] ZG1Cr17Ni3 stainless steel castings were prepared using induction melting and sand casting processes. The castings had an outer diameter of 2 m, a wall thickness of 0.2 m, and a height of 0.5 m. They were formed by atmospheric casting and then air-cooled. The castings exhibited long rod-shaped and film-like ferrite particles at the ferrite-martensite interface. 23 C6 carbides are larger than 4 μm in size and are continuously distributed along the interface.

[0068] This embodiment describes the heat treatment of the ZG1Cr17Ni3 stainless steel casting, which mainly includes the following steps:

[0069] The cooled ZG1Cr17Ni3 stainless steel casting was placed in a box-type resistance furnace and heated to 1000℃ at a heating rate of 10℃ / min. After holding at this temperature for 2 hours, a carbide re-dissolution treatment was performed. After the holding period, the ZG1Cr17Ni3 stainless steel casting with the carbide re-dissolution treatment was placed in a [further context needed - likely a specific location or process]. Figure 1 In the oil cooling tank shown, the oil circulation flow rate is controlled at 90 m³ / s. 3 Forced convection oil quenching was performed on the ZG1Cr17Ni3 stainless steel casting at an oil temperature of 80℃ / h, allowing the casting to cool at a rate of 80℃ / s. The cooled ZG1Cr17Ni3 stainless steel casting was then placed in a box-type resistance furnace and heated to 680℃ (heating rate 10℃ / min), tempered for 8 hours, and air-cooled to obtain the heat-treated ZG1Cr17Ni3 stainless steel casting.

[0070] Comparative Example 1

[0071] ZG1Cr17Ni3 stainless steel castings were prepared using induction melting and sand casting processes. The castings had an outer diameter of 1.5 m, a wall thickness of 0.1 m, and a height of 1 m. They were formed by atmospheric casting and then air-cooled. The castings exhibited long rod-shaped and film-like ferrite particles at the ferrite-martensite interface. 23 C6 carbides are larger than 3 μm in size and are continuously distributed along the interface.

[0072] This embodiment describes the heat treatment of the ZG1Cr17Ni3 stainless steel casting, which mainly includes the following steps:

[0073] The cooled ZG1Cr17Ni3 stainless steel casting was placed in a box-type resistance furnace and heated to 1000℃ at a heating rate of 10℃ / min. After holding at this temperature for 2 hours, a carbide re-dissolution treatment was performed. Following the holding period, the ZG1Cr17Ni3 stainless steel casting with the carbide re-dissolution treatment was placed in an oil cooling bath for static cooling (oil not circulating) at a cooling rate of 0.8℃ / s. The cooled ZG1Cr17Ni3 stainless steel casting was then placed in a box-type resistance furnace and heated to 680℃ for tempering treatment for 6.5 hours. After air cooling, the heat-treated ZG1Cr17Ni3 stainless steel casting was obtained.

[0074] The SEM microstructure of the heat-treated ZG1Cr17Ni3 stainless steel casting obtained in this embodiment is shown in the figure. Figure 4 As shown, the carbides at the ferrite-martensite interface are rod-shaped and film-shaped M. 23 C6 type carbides have an average length of about 4.3 μm. Under stress, larger carbides are prone to stress concentration and interfacial cracking.

[0075] Comparative Example 2

[0076] ZG1Cr17Ni3 stainless steel castings were prepared using induction melting and sand casting processes. The castings had an outer diameter of 1.5 m, a wall thickness of 0.1 m, and a height of 1 m. They were formed by atmospheric casting and then air-cooled. The castings exhibited long rod-shaped and film-like ferrite particles at the ferrite-martensite interface. 23 C6 carbides are larger than 3 μm in size and are continuously distributed along the interface.

[0077] This embodiment describes the heat treatment of the ZG1Cr17Ni3 stainless steel casting, which mainly includes the following steps:

[0078] The cooled ZG1Cr17Ni3 stainless steel casting was heat-treated according to the method in the China Aviation Materials Handbook. Specifically, it was solution heat-treated by heating to 1050℃ in a box-type resistance furnace at a rate of 10℃ / min and holding for 2 hours, followed by traditional static oil quenching at a cooling rate of 0.8℃ / s. After quenching, the casting was tempered at 500℃ for 2 hours in a box-type resistance furnace and then air-cooled. Subsequently, it was tempered at 680℃ for 6.5 hours and then air-cooled.

[0079] The SEM microstructure of the heat-treated ZG1Cr17Ni3 stainless steel casting obtained in this embodiment is shown in the figure. Figure 5 As shown, the carbides at the ferrite-martensite interface are mainly long rod-shaped with an average length of about 3.4 μm, which can easily cause stress concentration and reduce the mechanical properties of stainless steel.

[0080] Table 2 shows the comparison data of the tensile properties of ZG1Cr17Ni3 stainless steel castings after heat treatment obtained in Examples 2-4 and Comparative Examples 1-2 at 500℃.

[0081] Table 2

[0082]

[0083] As can be seen from Table 2, the heat treatment method of the present invention can significantly improve the tensile properties of ZG1Cr17Ni3 stainless steel castings.

[0084] In summary, the method of this invention can eliminate the harmful effects of long rod-shaped and film-shaped carbides in large-size ZG1Cr17Ni3 stainless steel castings, readjust the precipitation morphology of carbides, and promote M 23 C6-type carbides precipitate in a fine, uniform, and semi-continuous state at the ferrite / martensite interface, hindering crack propagation and thus improving the mechanical properties of stainless steel.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A heat treatment method for ZG1Cr17Ni3 stainless steel castings, characterized in that, It includes the following steps: Carbide remelting treatment: The ZG1Cr17Ni3 stainless steel casting is heated to a set temperature and held at that temperature for a set time to allow the first morphology of martensite at the ferrite-martensite interface in the ZG1Cr17Ni3 stainless steel casting to undergo remelting. 23 The C6 type carbide was fully dissolved; after the heat treatment, a ZG1Cr17Ni3 stainless steel casting with carbide re-dissolution treatment was obtained; wherein, the first type M 23 C6 type carbides are long rod-shaped M with a length greater than 2 μm. 23 C6 type carbides and / or film-like M 23 C6 type carbide; wherein, the set temperature is 1000±10℃, the set time is 2~4h; the heating rate of ZG1Cr17Ni3 stainless steel casting to the set temperature is 5~10℃ / min; Cooling treatment: The ZG1Cr17Ni3 stainless steel casting after carbide re-dissolution treatment is subjected to cooling treatment to obtain a cooled ZG1Cr17Ni3 stainless steel casting. During the cooling treatment, the cooling rate of the ZG1Cr17Ni3 stainless steel casting is controlled at 30~80℃ / s to suppress the re-precipitation of carbides longer than 2μm and to avoid the risk of quenching cracks. The ZG1Cr17Ni3 stainless steel casting after carbide re-dissolution treatment is then placed in an oil cooling tank for oil quenching. The flow rate of the oil in the oil cooling tank is controlled to a set flow rate to allow the ZG1Cr17Ni3 stainless steel casting after carbide re-dissolution treatment to cool at a set cooling rate under forced convection conditions. The ZG1Cr17Ni3 stainless steel casting after carbide re-dissolution treatment is placed in the oil cooling tank within 3~8s. Tempering heat treatment: The ZG1Cr17Ni3 stainless steel castings after cooling are subjected to tempering heat treatment to induce M 23 C6-type carbides precipitate uniformly in a second morphology at the ferrite-martensite interface, resulting in the heat-treated ZG1Cr17Ni3 stainless steel casting; among them, the second morphology M 23 The C6 type carbides have an average size of less than 1 μm and a shape including short rods and / or granules, and are distributed in a semi-continuous state along the interface. The ZG1Cr17Ni3 stainless steel casting after cooling is heated to 680±10℃ at a heating rate of 8~10℃ / min and held at 680±10℃ for 5-8 hours for tempering heat treatment. After cooling, the heat-treated ZG1Cr17Ni3 stainless steel casting is obtained.

2. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, The ZG1Cr17Ni3 stainless steel casting is a ring-shaped casting with an outer diameter ≥1m, a wall thickness ≥0.1m, and a height ≥0.5m.

3. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 2, characterized in that, The ZG1Cr17Ni3 stainless steel casting has an outer diameter of 1~2m, a wall thickness of 0.1~0.2m, and a height of 0.5~1m.

4. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, The preparation process of the ZG1Cr17Ni3 stainless steel casting is as follows: it is prepared by sand casting, then cast and cooled in air to obtain the ZG1Cr17Ni3 stainless steel casting.

5. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, The carbide remelting process is carried out in a resistance furnace.

6. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, In the cooling process step: Set the flow rate to 80~90m³ 3 / h; and / or The temperature of the oil in the oil cooling tank is 40~100℃.

7. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, The oil cooling tank is provided with an oil outlet and an oil inlet; wherein, the oil outlet is connected to the circulation pump through a first pipeline; and the circulation pump is connected to the oil inlet through a second pipeline.

8. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 7, characterized in that, An oil inlet valve is provided on the first pipeline; an oil outlet valve is provided on the second pipeline; wherein, the flow rate of the oil in the oil cooling tank is controlled by adjusting the oil inlet valve and the oil outlet valve.

9. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 8, characterized in that, The second pipeline includes a first main pipeline, a second main pipeline, a first branch pipeline, and a second branch pipeline; wherein, the oil outlet valve is installed on the first main pipeline; the inlet of the first branch pipeline and the inlet of the second branch pipeline are connected to the first main pipeline; the first branch pipeline and the second branch pipeline are arranged in parallel; the outlets of the first branch pipeline and the second branch pipeline are connected to the second main pipeline; the second main pipeline is connected to the oil inlet; wherein, the first branch pipeline passes through a cooling system to cool the oil passing through the first branch pipeline.

10. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 9, characterized in that, The inlet of the second branch pipeline and the inlet of the first branch pipeline are connected to the first main pipeline through a diversion valve; the outlet of the second branch pipeline and the outlet of the first branch pipeline are connected to the second main pipeline through a diversion valve.

11. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 9, characterized in that, The cooling system includes a water-cooled tank; wherein a portion of the first branch pipe is immersed in the water-cooled tank.

12. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 9, characterized in that, A temperature display is installed on the second main pipeline to detect the temperature of the oil passing through it.

13. The heat treatment method for ZG1Cr17Ni3 stainless steel castings according to claim 1, characterized in that, In the tempering heat treatment step: the cooling is air cooling.

14. A ZG1Cr17Ni3 stainless steel, characterized in that, The ZG1Cr17Ni3 stainless steel is a heat-treated ZG1Cr17Ni3 stainless steel casting. The ZG1Cr17Ni3 stainless steel casting is heat-treated by the heat treatment method of any one of claims 1-13 to obtain the heat-treated ZG1Cr17Ni3 stainless steel casting.

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