12Cr steel alloy preparation method based on vacuum sintering and ion implantation technology

Abstract

The invention mainly provides a 12Cr steel alloy preparation method based on a vacuum sintering and ion implantation technology. The 12Cr steel alloy preparation method comprises the following steps that 1, Fe, Cr and a plurality of alloying element raw materials are pretreated; 2, the pretreated raw materials are prepared into mother alloy, then vacuum melting and pouring forming are conducted, and a steel ingot is obtained; 3, the steel ingot is subjected to hot working treatment; 4, thermal refining is conducted on the hot-rolled plate blank; 5, the quenched and tempered workpiece is subjected to surface modification through a Cr target in an ion implantation mode; and 6, post-processing the injected workpiece. According to the technical scheme, the problem that a common high-Cr steel alloy is prone to failure due to large quenching / normalizing stress in the using process can be solved, meanwhile, the problem that F / M steel is poor in comprehensive mechanical property can be solved, the ductility of the prepared 12Cr steel is improved by about 30%-50% compared with an existing material, and meanwhile the strength still meets the using requirement. The application possibility of the high CrF / M alloy steel under engineering conditions is enhanced, and the service stability is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy preparation surface treatment, and in particular relates to a method for preparing a 12Cr steel alloy based on vacuum sintering and ion implantation technology. Background Art

[0002] 9%-12%Cr ferrite / martensitic steel (F / M steel) is listed as a priority candidate system for the cladding material of the fourth-generation nuclear reactor, the lead-cooled fast reactor, due to its excellent resistance to lead-bismuth corrosion and neutron irradiation swelling. In traditional technology, by adding solid solution strengthening elements such as Mo and W and optimizing the normalizing-tempering process, F / M steel can maintain a yield strength of ≥500MPa at a high temperature of 600℃. However, the existing technology has the following bottlenecks: Element distribution defects: Conventional vacuum melting process still leads to dendritic segregation of key elements such as Cr and C (segregation coefficient ≥ 1.5), especially the formation of Cr-rich carbide bands (width > 50 μm) in the core of the ingot, which become the priority initiation zone of stress corrosion cracking; Insufficient stress regulation: After traditional quenching and tempering (quenching + high temperature tempering), the residual tensile stress inside the material is as high as 200-300 MPa, which induces stress corrosion cracking along the original austenite grain boundaries under long-term thermal cycle loads; Limitations of surface modification: Although existing surface strengthening technologies (such as carburizing and nitriding) can improve hardness, they will aggravate the brittleness of the surface (when the nanoindentation hardness is greater than 8GPa, the fracture toughness decreases by 40%), and cannot simultaneously improve the resistance to radiation embrittlement. Summary of the invention

[0003] In order to solve the above problems, the present invention proposes a method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology, comprising the following steps: Step 1: Raw material pretreatment, Fe, Cr and multiple alloying element raw materials are subjected to ultrasonic pickling, ultrasonic alcohol cleaning, ultrasonic deionized water rinsing and dehydration and drying in sequence; Step 2: vacuum melting, the pretreated raw materials are mixed into a master alloy according to the Fe-12Cr matrix ratio, and melted and cast in a vacuum electromagnetic induction suspension melting furnace to obtain a steel ingot; Step 3: hot working treatment, hot forging and hot rolling the steel ingot; Step 4: quenching and tempering treatment, quenching, normalizing and tempering the hot-rolled slab in sequence; Step 5: ion implantation, placing the tempered workpiece in an ion implantation device and using a Cr target for surface modification; Step 6: Post-processing: cleaning, drying and packaging the injected workpiece.

[0004] Furthermore, in step 1, the ultrasonic pickling adopts acetic acid solution, and the ultrasonic pickling time is ≥15min; the ultrasonic alcohol cleaning time is ≥25min; and the ultrasonic deionized water rinsing time is ≥25min.

[0005] Furthermore, in step 2, the master alloy composition includes 83%-85% Fe and 12% Cr.

[0006] Furthermore, the master alloy composition is as follows by mass percentage: Cr 12%, C 0.22%, Ni 0.8%, Mo 0.5%, Mn 1.0%, V 0.2%, Si 0-1.6%, W 0.5%, Ta 0.1%, Ti 0.03%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, in step 2, the smelting times are 2 to 4 times, and the smelting temperature is 1600 to 1800°C.

[0008] Furthermore, in step 3, the temperature is kept at 1100-1200° C. for 30-60 min before hot forging; the hot rolling speed is 100-200 m / s, and the total deformation is greater than 60%; and the thickness of the slab after rolling is 5-20 mm.

[0009] Furthermore, in step 4, the quenching medium is water / oil, and the cooling rate is 50~100℃ / s; normalizing is performed by room temperature cooling, and the time is ≥1h; the tempering temperature is 600~720℃, the insulation is 2~4h, and the furnace cooling rate is 5~10℃ / min.

[0010] Furthermore, in step 5, the background vacuum is 1.0~1.5Pa; the injection energy is 1~3MeV, the beam intensity is 1~100mA; the injection dose is 1×10¹ 6 ~1×10¹ 8 atoms / cm²; Cr target power supply DC 40~60A, anode power supply DC 20~30A.

[0011] Therefore, the beneficial effects of the present invention are: Firstly, the problem that common high-Cr steel alloys are prone to failure due to high quenching / normalizing stress during use is solved. By injecting Cr ions into the material surface, the stress environment is greatly improved and the service life of the high-Cr steel alloy is enhanced.

[0012] Secondly, to solve the problem of poor comprehensive mechanical properties of F / M steel, through quenching and tempering treatment and changing the content of various trace elements inside the workpiece, F / M high Cr steel alloy with excellent comprehensive mechanical properties was successfully prepared, and its elongation was increased by about 30%-50% compared with existing materials, while the strength still met the use requirements. It has enhanced the application possibility of high Cr F / M alloy steel under engineering conditions and improved service stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of the steps of the present invention.

[0014] Figure 2 This is a local optical corrosion photograph of the 12Cr steel alloy prepared by the present invention.

[0015] Figure 3 This is an optical corrosion photograph of the 12Cr steel alloy prepared by the present invention after the modulation treatment.

[0016] Figure 4a-4d The present invention shows scanning electron microscope (SEM) images of different proportions of the 12Cr steel alloy prepared by the present invention after the modulation treatment.

[0017] Figure 5 It is an X-ray diffraction (XRD) diagram of the 12Cr steel alloy prepared by the present invention.

[0018] Figure 6 This is a diagram of ion implantation SRIM simulation results of the 12Cr steel alloy prepared by the present invention. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, reference may be made to the accompanying drawings and embodiments to further illustrate the technical solutions of the present invention. It should be understood that the embodiments described herein are only used to explain the technical solutions or principles of the present invention and are not intended to limit the scope of protection of the present invention. Example

[0020] The following combination Figures 1 to 6 This embodiment 1 is described in detail, wherein Figure 4a-4d The scanning electron microscope (SEM) images of 12Cr steel alloy at different scales after modulation treatment are shown in Figure 2. Figure 4c and Figure 4d The red frame in the middle indicates the location of the precipitated phase.

[0021] This embodiment provides a method for preparing a 12Cr steel alloy based on vacuum sintering and ion implantation technology, comprising the following steps: Step 1: using block high-purity Fe (99.999%), granular high-purity Cr (99.999%), granular high-purity C (99.999%), granular high-purity Ni (99.999%), granular high-purity Mo (99.999%), granular high-purity Mn (99.999%), granular high-purity V (99.999%), granular high-purity Si (99.999%), granular high-purity W (99.999%), granular high-purity Ta (99.999%), and granular high-purity Ti (99.999%) as raw materials, ultrasonic pickling, ultrasonic alcohol cleaning, ultrasonic deionized water rinsing, and dehydration and drying are carried out in sequence, wherein the washing time of ultrasonic pickling, ultrasonic alcohol cleaning, and ultrasonic deionized water rinsing is not less than 15 minutes, 25 minutes, and 25 minutes, respectively.

[0022] Step 2: The pretreated raw materials are formulated into a master alloy according to the Fe-12Cr matrix, wherein the master alloy comprises Cr12%, C 0.22%, Ni 0.8%, Mo 0.5%, Mn 1.0%, V 0.2%, Si 0-1.6%, W 0.5%, Ta 0.1%, Ti 0.03% by mass percentage, and the remainder is Fe and unavoidable impurities, and the master alloy is melted and cast in a vacuum electromagnetic induction suspension melting furnace to obtain a steel ingot; in this embodiment, a 12Cr steel ingot with a height of 20 mm and a width of 80 mm is cast.

[0023] Step 3: Heat treatment: place the cast ingot into a high-temperature box furnace for homogenization and heat preservation at a temperature of 1100°C to 1200°C for 30min-60min. Then take the sample out of the heat treatment furnace for hot rolling at a rolling speed of 100m / s~200m / s, and the total deformation is >60%.

[0024] Step 4: Tempering treatment, quenching, normalizing and tempering treatment of hot-rolled slabs in sequence; cut 12Cr steel block alloy into five pieces of uniform size, put them into a box-type heating furnace for heating respectively, the heating termination temperatures are 950℃, 1000℃, 1100℃, 1200℃, the heating rate is 5℃ / min, keep warm for 1h after reaching the specified temperature, then take the samples out of the high-temperature furnace, and put the quenched samples into a water / oil cooling quenching box for cooling, the cooling rate is 50℃-100℃ / s; for the normalized samples, place the samples in the air for room temperature cooling, the cooling time is more than 60min, and then temper the samples, and reduce the temperature of the box-type heating furnace from 950℃-1200℃ to 600℃-720℃ at a cooling rate of 5℃ / min, and the cooling time should be no less than 60min. Then open the furnace door, and put the samples into the heating furnace for insulation and tempering treatment in sequence, and the insulation time is 180min. After completion, leave the sample in the box-type heating furnace to cool down naturally with the furnace body. The cooling time should not be less than 12 hours, and then take out the sample.

[0025] Step 5: Ion implantation. Place the tempered workpiece in the ion implantation equipment and use a Cr target for surface modification. After the 12Cr steel has been tempered in step 4, the surface is cleaned. The sample is immersed in a 98% alcohol solution and ultrasonically treated in an ultrasonic machine for 1 hour to remove impurities attached to the surface. After the ultrasonic treatment, it is washed in deionized water and dried. Then the sample is placed in the vacuum chamber of the ion implantation equipment, and the Cr target is installed. The background vacuum of the vacuum chamber of the ion implantation equipment is adjusted and heated. The ion implantation source is turned on, and the ion implantation energy is adjusted to 1~3MeV, the ion beam current intensity is adjusted to 1~100mA, and the ion implantation metering is 1.0×10 16 ~1.0×10 18 atoms / cm 2 , the Cr arc target power supply uses DC 40-60A, the anode power supply uses DC 20~30A, the working gas pressure is 1.0~1.5Pa, the power-on time is not less than 30min, open the baffle, when the ion injection metering reaches the preset value, close the baffle, turn off the ion source, wait for the workpiece temperature to drop below 100℃, and turn off the vacuum system.

[0026] Step 6: Post-processing: ultrasonic alcohol cleaning is performed on the injected workpiece, and then drying and packaging is performed in a vacuum bag.

[0027] The technical solution of the present invention has the following beneficial effects: Element distribution optimization and stress coordinated regulation Through the synergistic effect of vacuum induction suspension melting (2-4 remelting) and gradient hot rolling process (1100-1200℃ / >60% deformation), the Cr element segregation coefficient is reduced from more than 1.5 in the traditional process to less than 1.1, and the carbide aggregation zone of more than 50μm is eliminated. Combined with multi-stage quenching and tempering treatment (950-1200℃ homogenization + graded tempering), the residual tensile stress inside the material is reduced from 200-300 MPa in the conventional process to less than 80 MPa, significantly inhibiting the tendency of stress corrosion cracking.

[0028] Innovation of surface composite strengthening mechanism Using high energy Cr ion implantation technology (1-3 MeV / 1×10¹ 6 -1×10¹ 8 atoms / cm², forming a 10-50μm gradient Cr-enriched layer on the surface (Cr content in the surface layer ≥ 18wt.%). This structure has a surface compressive stress layer to offset the tensile stress of the substrate; a dense oxide film (Cr 2 O 3 The layer thickness is 200-500nm) which reduces the lead-bismuth corrosion rate to less than 0.1 mm / year; high-dose Cr injection induces nanoscale precipitation phase (5-20nm Cr 3 C 2 ), improve the anti-irradiation swelling performance (swelling rate after 3 MeV Au⁺ ion irradiation <0.5%).

[0029] Strong and tough synergistic improvement Through the "high temperature homogenization + oil quenching + two-stage tempering" process (600-720℃ / 2-4h), a fine-grained tempered martensitic matrix (grain size 5-8μm) and uniformly distributed M 23 C 6 Carbides (average size 0.8μm). Elongation increased by 30-50% (room temperature elongation ≥20% vs. 14-15% for traditional materials); excellent strength retention (600℃ high temperature tensile strength ≥550MPa, drop rate <10%); improved cyclic creep resistance (steady-state creep rate ≤1×10⁻ at 550℃ / 200 MPa) 8 s⁻¹).

[0030] Breakthrough in engineering applicability The size of the 12Cr steel product is controllable (100-150mm×50-100mm×5-20mm), which meets the processing requirements of fast reactor cladding tubes. 7 n / cm² irradiation), the service life is increased from 3000 hours of traditional materials to more than 8000 hours, and the cladding damage rate is reduced to <5×10⁻ 6 / Cycle times.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology, characterized in that: The following steps are involved: Step 1: Raw material pretreatment, Fe, Cr and multiple alloying element raw materials are subjected to ultrasonic pickling, ultrasonic alcohol cleaning, ultrasonic deionized water rinsing and dehydration and drying in sequence; Step 2: vacuum melting, the pretreated raw materials are mixed into a master alloy according to the Fe-12Cr matrix ratio, and melted and cast in a vacuum electromagnetic induction suspension melting furnace to obtain a steel ingot; Step 3: hot working treatment, hot forging and hot rolling the steel ingot; Step 4: quenching and tempering treatment, quenching, normalizing and tempering the hot-rolled slab in sequence; Step 5: ion implantation, placing the tempered workpiece in an ion implantation device and using a Cr target for surface modification; Step 6: Post-processing: cleaning, drying and packaging the injected workpiece.

2. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In step 1: ultrasonic pickling uses acetic acid solution, and the ultrasonic pickling time is ≥15min; the ultrasonic alcohol cleaning time is ≥25min; the ultrasonic deionized water rinsing time is ≥25min.

3. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In step 2, the master alloy composition includes 83%-85% Fe and 12% Cr.

4. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 3, characterized in that: The master alloy components are as follows by mass percentage: Cr 12%, C 0.22%, Ni 0.8%, Mo 0.5%, Mn 1.0%, V 0.2%, Si 0-1.6%, W 0.5%, Ta 0.1%, Ti 0.03%, and the balance is Fe and unavoidable impurities.

5. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In the step 2, the smelting times are 2 to 4 times, and the smelting temperature is 1600 to 1800°C.

6. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In the step 3, the temperature is kept at 1100-1200° C. for 30-60 min before hot forging; the hot rolling speed is 100-200 m / s, and the total deformation is greater than 60%; and the thickness of the slab after rolling is 5-20 mm.

7. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In step 4, the quenching medium is water / oil, and the cooling rate is 50-100°C / s; normalizing is performed by cooling at room temperature for a time of ≥1h; the tempering temperature is 600-720°C, the temperature is kept for 2-4h, and the furnace cooling rate is 5-10°C / min.

8. The method for preparing 12Cr steel alloy based on vacuum sintering and ion implantation technology according to claim 1, characterized in that: In step 5, the background vacuum is 1.0~1.5Pa; the injection energy is 1~3MeV, the beam intensity is 1~100mA; the injection dose is 1×10¹ 6 ~1×10¹ 8 atoms / cm²; Cr target power supply DC 40~60A, anode power supply DC 20~30A.

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