Method for improving yield strength and impact toughness of 22Cr12NiWMoV steel

Abstract

The invention relates to a method for improving yield strength and impact toughness of 22Cr12NiWMoV steel, which comprises the following steps: step S1, smelting raw materials to obtain a steel billet; step S2, forging deformation, which comprises the following steps: step 1, putting a steel billet into a furnace, heating to 1160-1190 DEG C along with the furnace, and preserving heat; 2, the steel billet is subjected to upsetting, and the upsetting ratio ranges from 2.85 to 3.70; thirdly, the steel billet is drawn out, and the drawing-out ratio ranges from 2.13 to 2.85; fourthly, after the steel billet is vertically reversed, upsetting and drawing-out are repeatedly conducted once, and a forge piece is obtained; s3, ring rolling: upsetting the forge piece, then punching the forge piece, leveling and discharging, and finally rolling a ring; s4, treatment after forging is conducted, specifically, a forge piece is cooled to 300 DEG C in a furnace, high-temperature tempering is conducted, and the high-temperature tempering temperature is 700 DEG C; s5, machining before heat treatment; s6, quenching is conducted, the quenching temperature ranges from 1031 DEG C to 1044 DEG C, heat preservation is conducted, and cooling is conducted to 300 DEG C or below; and S7, tempering is conducted, the tempering temperature ranges from 652 DEG C to 682 DEG C, heat preservation is conducted, and discharging and air cooling are conducted. The method has the advantage that the yield strength and impact toughness of the material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel manufacturing, in particular to a method for improving yield strength and impact toughness of 22Cr12NiWMoV steel. BACKGROUND

[0002] Martensitic stainless steel is a kind of steel material with main alloying elements of iron, chromium and carbon, which has excellent structural strength mainly depending on martensite phase and carbide strengthening. Due to the excellent performance of martensitic stainless steel, martensitic stainless steel is widely used in the manufacturing of aviation equipment.

[0003] At present, parts such as turbine discs, blades and fasteners in an aero-engine are generally made of martensitic stainless steel. The parts of this type not only need to bear huge centrifugal force and thermal mechanical fatigue load during service, but also need to work in high temperature oxidation and corrosion medium for a long time, so extremely strict requirements are put forward for the yield strength (Rp0.02) and impact toughness of the material to ensure the anti-deformation ability of the parts under extreme load. However, because the martensite phase of the traditional martensitic stainless steel is brittle, and the metal elements such as Cr, W and Mo form coarse carbides in the manufacturing process, the coarse carbides are hard and brittle, so the coarse carbides are easy to become crack sources, which is reflected in the insufficient yield strength and impact toughness of the material in macroscopic aspect.

[0004] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present disclosure, and therefore can include information which does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application discloses a method for improving yield strength and impact toughness of 22Cr12NiWMoV steel.

[0006] A method for improving yield strength and impact toughness of 22Cr12NiWMoV steel, comprising the following steps: Step S1, raw material smelting to obtain a billet; Step S2, forging deformation, comprising the following working steps: First working step, heating the billet, and heating the billet to 1160-1190℃ in the furnace and keeping the temperature; Second working step, upsetting the billet, and the upsetting ratio range is 2.85-3.70; Third working step, elongating the billet, and the elongation ratio range is 2.13-2.85; Fourth working step, after the vertical reversal of the billet, repeating the upsetting and elongation with the same upsetting ratio and elongation ratio once to obtain a forged piece; Step S3, ring rolling, the forging is upset, then the forging is punched, flattened and the blank is finally rolled into a ring; Step S4, post-forging treatment, the forging is cooled in a furnace to 300℃, then high-temperature tempering is performed at a temperature of 700℃; Step S5, machining before heat treatment; Step S6, quenching, the quenching temperature ranges from 1031 to 1044℃, and then the forging is cooled to below 300℃; Step S7, tempering, the tempering temperature ranges from 652 to 682℃, and then the forging is discharged and air-cooled.

[0007] Further, in step S1, the steel billet comprises the following elements in percentage by mass: C, 0.20-0.25%; Si, 0.20-0.50%; Mn, 0.50-1.00%; P≤0.025%; S≤0.015%; Cr, 11.00-12.50%; W, 0.90-1.25%; Mo, 0.90-1.25%; Ni, 0.50-1.00%; V, 0.20-0.30%; Nb≤0.05%; Sn≤0.02%; Ti≤0.025%; Al≤0.025%; Co≤0.20%; Cu≤0.15%; and the balance is Fe.

[0008] Further, in the first working step of step S2, the holding time is determined according to the height of the steel billet, T=h*1.5min / mm.

[0009] Further, in the second working step of step S2, the final forging temperature of the forging ranges from 1010℃±30℃ in the second working step of step S2.

[0010] Further, in the third working step of step S2, the final forging temperature of the forging ranges from 960℃±30℃ in the third working step of step S2.

[0011] Further, in step S3, the upsetting ratio ranges from 3.74 to 4.22.

[0012] Further, in step S3, the ring rolling ratio ranges from 4.00 to 4.50.

[0013] Further, in step S4, the high-temperature tempering holding time is 5.5h, and the forging is discharged and air-cooled after the holding time ends.

[0014] Further, in step S6, the holding time comprises a thermal penetration time of 1h and a structure transformation time calculated according to the thickness of the forging, T=δ*1.5min / mm, and the cooling mode is oil cooling.

[0015] Further, in step S7, the holding time includes a thermal penetration time, a structure transformation time and a residual heat time, the thermal penetration time is 1h, the structure transformation time is calculated according to the thickness of the forged piece, T=δ×1.5min / mm, and the residual heat time is 1h.

[0016] The present application has the following beneficial effects: 1. The forged piece adopts multi-directional alternating forging and ring rolling, the single deformation and total deformation are strictly controlled, the dynamic recrystallization is realized, the coarse-grained structure of the cast state is crushed, the grain refinement is realized, the toughness and yield strength of the structure are improved, after the deformation of the forged piece, the tempering treatment is carried out to promote the spheroidization transformation of the cementite in the lamellar pearlite, the dispersed distribution of the spherical carbide structure is formed, the hardness is reduced, the plasticity and toughness are improved, the original grain state of the forged structure is significantly improved, a good structure foundation is laid for the subsequent heat treatment, then quenching is carried out, the forged piece is completely austenitized, finally high-temperature tempering is carried out, the structure is spheroidized and the alpha-Fe matrix is recrystallized, the martensite is transformed into tempered sorbite, the strength is reduced and the plasticity and toughness are improved, the toughness and yield strength of the material are balanced, and both meet the strict use requirements.

[0017] 2. The formula of the 22Cr12NiWMoV steel is optimized, the Cr content is strictly controlled, the appropriate Cr atoms are ensured to be dissolved in the austenite to increase the lattice distortion of the austenite, the austenite grain growth is hindered, the Cr also affects the oxidation film, and the oxidation resistance, corrosion resistance, hardenability and high-temperature strength of the structure are comprehensively improved; the Mo content is controlled, there is sufficient Mo in the form of supersaturated solid solution in the martensite, the high-temperature strength and creep resistance are enhanced, the Mo also improves the corrosion resistance, especially the acid resistance; the W content is controlled, the W also exists in the form of supersaturated solid solution in the martensite to play a strengthening role, improve the thermal strength and high-temperature hardness of the structure, and enhance the anti-creep ability; the Ni atom content is controlled, after the Ni is dissolved in the austenite, the migration resistance of the austenite is increased, which is beneficial to the structure refinement, the Ni atom content is prevented from being too high, the brittle sigma phase is prevented from being precipitated, and the toughness and strength of the steel are improved; the Ni atom content is controlled, the V raw material forms carbides, refines the grains, improves the strength and wear resistance, and enhances the tempering stability.

[0018] 3. The quenching temperature is set to be 50-100℃ higher than the A3 point of the steel to ensure complete austenitization, according to the size of the forged piece, the quenching holding time is determined, the forged piece core is quenched, and the overburning of the outer part of the forged piece is avoided, after the quenching is completed, the surface cooling rate is about 8.5℃ / s by using the oil cooling process, the cooling process is more gentle and uniform, the thermal stress and structure stress in the cooling process are reduced, and the risk of structure cracking is reduced.

[0019] 4、quenching is completed, high temperature tempering is carried out, carburizing body in the organization spheroidization and α-Fe matrix recrystallization is promoted, martensite is converted into tempered sorbite, compared with lath martensite obtained after quenching, the yield strength of the tempered sorbite is slightly lower, but the toughness is greatly improved, the product with yield strength and toughness is obtained, and the anti-deformation ability of the product under extreme load is ensured.

[0020] 5、Cr-Ni-Mo-V base alloy system is used, no Co and Nb and other strengthening alloy elements are used, the performance gap of the product is compensated by forging deformation process, the cost is lower compared with the same performance material, the initial organization state is optimized by fine forging control, and the subsequent heat treatment process is not needed, so that the heat treatment can be simplified into one quenching and one tempering, and the process difficulty is greatly simplified.

[0021] 6、In the repeated upsetting and elongation process of forging deformation, the upsetting and elongation ratio and other deformation process windows are strictly controlled, in order to maximize the crushing of coarse grain organization within the deformation degree that can be tolerated by the alloy organization, avoid the fracture of the crystal organization caused by the exceeding of internal stress, and strictly control the deformation temperature window of the forging in the upsetting and elongation, avoid the situation that the organization is too cold, the organization brittleness is too large, and cracks are caused. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A schematic diagram of steps of a method for improving yield strength and impact toughness of 22Cr12NiWMoV steel.

[0023] Figure 2 A metallographic detection diagram of Example 1.

[0024] Figure 3 A metallographic detection diagram of Example 2.

[0025] Figure 4 A metallographic detection diagram of Example 3.

[0026] Figure 5 A metallographic detection diagram of Example 4. DETAILED DESCRIPTION

[0027] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object, the specific embodiments, structures, features and effects of the present application will be described in detail below in combination with the drawings and preferred embodiments.

[0028] Example 1: A method for improving yield strength and impact toughness of 22Cr12NiWMoV steel, as shown in Figure 1 , includes the following steps: Step S1, raw material smelting, to get billet, the billet includes elements in mass percentage: C, 0.25%; Si, 0.32%; Mn, 0.84%; P, 0.014%; S, 0.005%; Cr, 11.42%; W, 0.91%; Mo, 0.90%; Ni, 0.94%; V, 0.22%; Nb, 0.04%; Sn, 0.005%; Ti, 0.003%; Al, 0.011%; Co, 0.04%; Cu, 0.07%; the balance is Fe.

[0029] Step S2, forging deformation, including the following steps: The first step, billet heating, the initial size of the billet is φ450mm*1330mm (volume 0.21m 3 ), the billet is heated to 1180℃ in the furnace, and the holding time is determined according to the height of the billet, T=h*1.5min / mm=1330*1.5=1995min.

[0030] The second step, the billet is upset to the size of φ810mm*405mm (volume 0.21m 3 ), the forging ratio is 1330 / 450=3.28, and the final forging temperature of the billet is 1040℃.

[0031] The third step, the billet is drawn to the size of φ510mm*1025mm (volume 0.21m 3 ), the forging ratio is 1025 / 450=2.27, and the final forging temperature of the billet is 950℃.

[0032] The fourth step, after the billet is vertically reversed, the same upsetting ratio and drawing ratio are repeated once to get the forged piece.

[0033] Step S3, ring rolling, first, the forged piece is upset to the size of φ1085mm*265mm (volume 0.21m 3 ), the forging ratio is 1025 / 266=3.85. Then punch, the inner hole diameter of the forged piece is φ410mm, then flatten the surface, output the blank, and roll the ring to the size of Φ2070mm*Φ1665mm*160mm (volume 0.19m 3 ), the ring rolling ratio is 1665 / 410=4.06.

[0034] Step S5, machining before heat treatment, cutting the surface to the size of Φ2060mm*Φ1675mm*150mm.

[0035] Step S6, quenching, the forged piece is heated to a quenching temperature according to the power of the furnace, the quenching temperature is 1040℃, the holding time includes a hot penetration time and a microstructure transformation time, the first holding time is 1h, the hot penetration time is ensured, the microstructure transformation time is calculated according to the thickness of the forged piece, T = δ * 1.5min / mm = (2070-1665) * 1.5 = 607.5min, and the forged piece is cooled to below 300℃ in an oil cooling mode.

[0036] Step S6, tempering, the forged piece is heated to a tempering temperature according to the power of the furnace, the tempering temperature is 660℃, the holding time includes a hot penetration time, a microstructure transformation time and a residual heat time. The hot penetration time is 1h, the microstructure transformation time is calculated according to the thickness of the forged piece, T = δ * 1.5min / mm = (2070-1665) * 1.5 = 607.5min, and the residual heat time is 1h. After the holding time ends, the forged piece is air-cooled to room temperature.

[0037] Example 2: The difference from Example 1 is that: Step S1, raw material smelting, to obtain a billet, the billet includes elements in percentage by mass: C, 0.23%; Si, 0.35%; Mn, 0.83%; P, 0.017%; S, 0.003%; Cr, 11.44%; W, 0.95%; Mo, 0.97%; Ni, 0.88%; V, 0.23%; Nb, 0.04%; Sn, 0.003%; Ti, 0.002%; Al, 0.007%; Co, 0.04%; Cu, 0.05%; and the balance is Fe.

[0038] Step S2, forging deformation, including the following working steps: The first working step, billet heating, the initial size of the billet is φ450mm*1330mm (volume 0.21m3), the billet is heated to 1190℃ according to the power of the furnace, and the holding time is determined according to the height of the billet, T = h * 1.5min / mm = 1330 * 1.5 = 1995min.

[0039] Example 3: The difference from Example 1 is that: Step S1, raw material smelting, to obtain a billet, the billet includes elements in percentage by mass: C, 0.23%; Si, 0.35%; Mn, 0.83%; P, 0.017%; S, 0.003%; Cr, 11.44%; W, 0.95%; Mo, 0.97%; Ni, 0.88%; V, 0.23%; Nb, 0.04%; Sn, 0.003%; Ti, 0.002%; Al, 0.007%; Co, 0.04%; Cu, 0.05%; and the balance is Fe.

[0040] Step S6, quenching, the forged piece is heated to quenching temperature according to power, the quenching temperature is 1035℃, the holding time includes heat penetration time and microstructure transformation time, the first holding time is 1h, to ensure heat penetration of the forged piece, the microstructure transformation time is calculated according to the thickness of the forged piece, T=δ*1.5min / mm=(2070-1665)*1.5=607.5min, and the forged piece is cooled to below 300℃ by oil cooling.

[0041] Step S6, tempering, the forged piece is heated to tempering temperature according to power, the tempering temperature is 673℃, the holding time includes heat penetration time, microstructure transformation time and afterheat time. The heat penetration time is 1h, the microstructure transformation time is calculated according to the thickness of the forged piece, T=δ*1.5min / mm=(2070-1665)*1.5=607.5min, the afterheat time is 1h, and the forged piece is air cooled to room temperature after the holding time ends.

[0042] Example 4: Step S1, raw material smelting, to obtain a billet, the billet includes elements in percentage by mass: C, 0.21%; Si, 0.35%; Mn, 0.82%; P, 0.015%; S, 0.002%; Cr, 11.38%; W, 0.95%; Mo, 0.96%; Ni, 0.88%; V, 0.23%; Nb, 0.04%; Sn, 0.003%; Ti, 0.002%; Al, 0.005%; Co, 0.04%; Cu, 0.05%; and the balance is Fe.

[0043] Step S6, quenching, the forged piece is heated to quenching temperature according to power, the quenching temperature is 1042℃, the holding time includes heat penetration time and microstructure transformation time, the first holding time is 1h, to ensure heat penetration of the forged piece, the microstructure transformation time is calculated according to the thickness of the forged piece, T=δ*1.5min / mm=(2070-1665)*1.5=607.5min, and the forged piece is cooled to below 300℃ by oil cooling.

[0044] Step S6, tempering, the forged piece is heated to tempering temperature according to power, the tempering temperature is 681℃, the holding time includes heat penetration time, microstructure transformation time and afterheat time. The heat penetration time is 1h, the microstructure transformation time is calculated according to the thickness of the forged piece, T=δ*1.5min / mm=(2070-1665)*1.5=607.5min, the afterheat time is 1h, and the forged piece is air cooled to room temperature after the holding time ends.

[0045] Product performance verification: The comprehensive detection result details are shown in Table 1.

[0046] Table 1 Conclusion: 1. The average yield strength of the samples in Examples 1-4 was 1054.25 MPa, which is nearly 9.25% higher than that of the standard.

[0047] 2. The average tensile strength of samples in Examples 1-4 was 631.85 MPa, an increase of nearly 1.91% compared to the standard. 3. The average elongation of the samples in Examples 1-4 was 17.38%, which is more than 3% higher than the standard.

[0048] 4. The average elongation of the samples in Examples 1 to 4 was 46.52%, which exceeded the standard by more than 10%.

[0049] 5. The triaxial impact energy of samples in Examples 1-4 is about 25J, which is nearly twice the standard.

[0050] 6. Samples from Examples 1 to 4 were tested in a high-temperature environment, and no breakage occurred within 25 hours.

[0051] Metallographic test results of the sample: 1. Grain size 4.5, such as Figure 2 As shown, the microstructure is uniform tempered martensite with no ferrite observed.

[0052] 2. Grain size 4.0, such as Figure 3 As shown, the microstructure is uniform tempered martensite with no ferrite observed.

[0053] 3. Grain size 4.5, such as Figure 4 As shown, the microstructure is uniform tempered martensite with no ferrite observed.

[0054] 4. Grain size 4.5, such as Figure 5 As shown, the microstructure is uniform tempered martensite with no ferrite observed.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel, characterized in that, Includes the following steps: Step S1: The raw materials are smelted to obtain steel billets; Step S2, forging deformation, includes the following steps: The first step is to heat the steel billet. The steel billet is put into the furnace and heated to 1160~1190℃ and held at that temperature. The second step is to upset the steel billet, with an upsetting ratio ranging from 2.85 to 3.

70. The third step is to draw the steel billet, with a drawing ratio ranging from 2.13 to 2.

85. The fourth step is to reverse the vertical direction of the billet, and then repeat the upsetting and drawing process once more with the same upsetting ratio and drawing ratio to obtain the forging. Step S3, ring rolling: The forging is upset, then punched, leveled and rolled into a ring; Step S4, post-forging treatment: the forging is cooled to 300°C in the furnace, followed by high-temperature tempering at 700°C. Step S5: Machining before heat treatment; Step S6, quenching, holding at a quenching temperature range of 1031~1044℃, and then cooling to below 300℃; Step S7: Tempering, holding at a tempering temperature of 652~682℃, then air cooling after removal from the furnace.

2. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In step S1, the steel billet comprises the following elements by mass percentage: C, 0.20~0.25%; Si, 0.20~0.50%; Mn, 0.50~1.00%; P≤0.025%; S≤0.015%; Cr, 11.00~12.50%; W, 0.90~1.25%; Mo, 0.90~1.25%; Ni, 0.50~1.00%; V, 0.20~0.30%; Nb≤0.05%; Sn≤0.02%; Ti≤0.025%; Al≤0.025%; Co≤0.20%; Cu≤0.15%; with the balance being Fe.

3. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In the first step of step S2, the heat preservation time is determined according to the height of the billet, T=h*1.5min / mm.

4. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 2, characterized in that: In the second step of step S2, the final forging temperature range of the forging is 1010℃±30℃.

5. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 3, characterized in that: In the third step of step S2, the final forging temperature range of the forging is 960℃±30℃.

6. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In step S3, the upsetting ratio ranges from 3.74 to 4.

22.

7. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 4, characterized in that: In step S3, the ring ratio is 4.00~4.

50.

8. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In step S4, the high-temperature tempering holding time is 5.5 hours, and after the holding time is completed, the furnace is removed and air-cooled.

9. The method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In step S6, the heat preservation time includes the heat penetration time and the microstructure transformation time. The heat penetration time is 1 hour, and the microstructure transformation time is calculated based on the thickness of the forging, T=δ*1.5min / mm. The cooling method is oil cooling.

10. A method for improving the yield strength and impact toughness of 22Cr12NiWMoV steel according to claim 1, characterized in that: In step S7, the heat preservation time includes heat penetration time, microstructure transformation time, and residual heat time. The heat penetration time is 1 hour, the microstructure transformation time is calculated based on the thickness of the forging, T=δ×1.5min / mm, and the residual heat time is 1 hour.

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