High-strength and high-toughness alloy steel material and heat treatment method thereof

Abstract

The invention relates to a material and a heat treatment method thereof, in particular to a high-strength and high-toughness alloy steel material and a heat treatment method thereof. The high-strength and high-toughness alloy steel material comprises the following components in percentage by mass: 0.14-0.17% of C, 0.5-0.6% of Si, less than or equal to 1.8% of Mn, less than or equal to 1.5% of Cr, less than or equal to 2.0% of Ni, less than or equal to 0.7% of Mo, less than or equal to 0.5% of Cu, less than or equal to 0.12% of V, 0.57-0.60% of Ceq and the balance of Fe and inevitable impurities. According to the high-strength and high-toughness alloy steel material and the heat treatment method thereof provided by the invention, the problems of insufficient material strength, hardness and low-temperature impact toughness of a core part in the prior art are solved.

Description

Technical Field

[0001] The invention relates to a material and a heat treatment method thereof, and more particularly to a high-strength and high-toughness alloy steel material and a heat treatment method thereof. Background Art

[0002] High-strength and high-toughness alloy steel materials are often used in harsh conditions and fields with high safety requirements. Their strength, hardness, and low-temperature impact toughness are important mechanical performance indicators. As the service conditions become harsher, the requirements for strength and hardness are getting higher and higher, and the requirements for low-temperature impact toughness are increasing instead of decreasing, which undoubtedly brings great challenges to existing materials and heat treatment processes. At present, the wall thickness of the material service castings is gradually increasing. The gap between the core impact and the surface of the thick wall castings is too large and the core impact fluctuates greatly. The material strength, hardness, and low-temperature impact toughness of the core are insufficient. Summary of the invention

[0003] The present invention provides a high-strength and high-toughness alloy steel material and a heat treatment method thereof, which solves the problems of insufficient material strength, hardness and core low-temperature impact toughness in the prior art.

[0004] The object of the present invention is achieved by: the heat treatment method of the high-strength and high-toughness alloy steel material comprises the following steps:

[0005] S1 homogenization annealing, firstly, the high-strength and high-toughness alloy steel material is heated to a high temperature, and then slowly cooled after a certain holding time, so that the alloy elements undergo solid-state diffusion;

[0006] S2 high temperature quenching, the high strength and high toughness alloy steel material is heated to a high temperature and rapidly quenched after a certain holding time, the high temperature quenching holding temperature is set at least 50°C above AC3;

[0007] S3 two-phase quenching, the high-strength and high-toughness alloy steel material is heated to a high temperature, and then rapidly quenched after a certain holding time, and the material is heated to between AC1 and AC3;

[0008] S4 high temperature tempering, heating the high strength and high toughness alloy steel material to a high temperature, and slowly cooling it after a certain holding time, wherein the high temperature tempering temperature is controlled below AC1;

[0009] S5 slowly cools the high-strength and high-toughness alloy steel material to room temperature to complete the entire heat treatment process.

[0010] In one embodiment, the holding temperature of the homogenization annealing is set between 910° C. and 980° C.

[0011] In one embodiment, the holding temperature of the high temperature quenching is set between 880°C and 930°C.

[0012] In one embodiment, the holding temperature of the two-phase region quenching is set between 740°C and 800°C.

[0013] In one embodiment, the slow cooling has a cooling rate of 40° C. / h.

[0014] In one embodiment, the holding temperature of the high temperature tempering is set between 620°C and 670°C.

[0015] In one embodiment, the insulation time is 9 hours.

[0016] In one embodiment, the quenching time ranges from 14.4s to 18min.

[0017] The high-strength and high-toughness alloy steel material composition, calculated by mass percentage, includes: C 0.14% to 0.17%, Si 0.5% to 0.6%, Mn≤1.8%, Cr≤1.5%, Ni≤2.0%, Mo≤0.7%, Cu≤0.5%, V≤0.12%, Ceq0.57% to 0.60%, and the balance is Fe and unavoidable impurities.

[0018] In one embodiment, the maximum wall thickness of the high-strength and high-toughness alloy steel material is 220 mm.

[0019] According to the performance requirements of high-strength and high-toughness alloy steel materials, the present invention stipulates the internal control of the material composition and describes the important control points of the heat treatment process in detail. The core of the high-strength and high-toughness alloy steel material has good high-strength and high-toughness mechanical properties. The heat treatment process of homogenization annealing + high-temperature quenching + two-phase zone quenching + tempering is adopted. The overall structure of the test block is uniform. Even at the core position, the low-temperature impact can reach more than 100J, which greatly improves various indicators of the material. The production method adopted by the present invention has been repeatedly verified many times and can be mass-produced, with great economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the CCT diagram. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] The high-strength and high-toughness alloy steel material composition, by mass percentage, includes: C 0.14% to 0.17%, Si 0.5% to 0.6%, Mn ≤ 1.8%, Cr ≤ 1.5%, Ni ≤ 2.0%, Mo ≤ 0.7%, Cu ≤ 0.5%, V ≤ 0.12%, Ceq 0.57% to 0.60%, and the balance is Fe and unavoidable impurities. The difference from the current conventional materials is that the Ceq content requirement is increased, and the strength of the material can be roughly fixed within a range to prevent the phenomenon of too high strength and insufficient toughness or too high toughness and insufficient strength.

[0024] The CCT spectrum of the high-strength and high-toughness alloy steel material simulated by Jmatpro software is shown in Figure 1 .from Figure 1 It can be seen that the material organization transition points are as follows: AC1: 703.9℃, AC3812.8℃, Ms390.5℃.

[0025] The heat treatment production process of a strong and tough low alloy material described in the present invention is homogenization annealing → high temperature quenching → two-phase zone quenching → high temperature tempering. The difference from the current conventional heat treatment process is that the homogenization annealing and two-phase zone quenching processes are further added. The two added heat treatment processes effectively solve the current problem of low temperature impact instability of the core of the material. The main control contents of each process are as follows:

[0026] Homogenization annealing: During the solidification process of the material, due to the uneven distribution of alloying elements, dendrite segregation and regional segregation will occur. By heating to a high temperature and keeping it warm for a long time, the alloying elements will diffuse in the solid state, thereby reducing or eliminating the uneven chemical composition and organization, thereby improving the overall organizational structure of the casting. Considering that the thick wall test material can be quickly heated through and improve the composition and organizational segregation, the annealing holding temperature is set between 910℃ and 980℃, and slowly cooled to room temperature after a sufficient holding time.

[0027] For high temperature quenching, according to the theoretical analysis of the CCT diagram of the material, it is necessary to reduce the temperature to below 390°C within 14.4s after the insulation is completed and the material is taken out of the furnace in order to generate a martensitic structure. However, for thick-walled test blocks, the cooling rate of the core cannot meet the conditions for generating martensite. Bainitic structure can be generated by reducing the temperature to below 500°C within 14.4s to 18min after the insulation is completed and the material is taken out of the furnace. In order to obtain high strength and toughness in the core of thick-walled test blocks, the cooling rate must be accelerated to increase the heat exchange efficiency between the test block surface and the quenching medium. Therefore, the high temperature quenching insulation temperature of the present invention is set at least 50°C above AC3, specifically set between 880°C and 930°C, and the quenching time range is between 14.4s and 18min.

[0028] Two-phase zone quenching, after high-temperature quenching of thick-walled castings, the core will obtain granular bainite and M+A islands with relatively high carbon content, that is, two mixed areas of martensite M and austenite A, because the cooling rate is slower than that of the surface. The M+A islands distributed along the grain boundaries will become the priority germination points of cracks, affecting the low-temperature impact performance of the core. Conventional heat treatment is to heat the material to complete austenitization and then cool it; the two-phase zone quenching added this time is to heat the material to between AC1 and AC3, at which time the matrix structure is not completely transformed, and the original structure morphology is partially retained. By adding two-phase zone quenching, ferrite is gradually generated in the original M+A island as the temperature rises. Since the insulation temperature does not exceed AC3, the ferrite film will be retained to room temperature, so as to refine the M+A island and reduce the carbon concentration difference therein. Therefore, the two-phase zone quenching temperature of the present invention is set below AC3, specifically between 740℃ and 800℃, and the quenching time range is between 14.4s and 18min.

[0029] High temperature tempering can further transform the unbalanced bainite structure in the steel after quenching, reduce its internal stress and brittleness, and thus improve the plasticity and toughness of the steel. At high temperatures, the atomic activity is enhanced, and the atoms of iron, carbon and other alloy elements can diffuse faster, realizing the rearrangement of atoms, so that the unstable unbalanced structure is gradually transformed into a stable balanced structure, achieving the purpose of balancing strength, hardness and plasticity and toughness. Therefore, the tempering temperature of the present invention needs to be controlled below AC1, specifically set between 620℃ and 670℃, and slowly cooled to room temperature.

[0030] Furthermore, the present invention adopts the above scheme to test three groups of test pieces with a maximum wall thickness of 220 mm and different components, as follows:

[0031] Example 1

[0032] Test piece 1 contains the high-strength and high-toughness alloy steel material composition, which includes, by mass percentage: C 0.14%, Si 0.54%, Mn 1.31%, Cr 0.31%, Ni 0.82%, Mo 0.41%, Cu 0.05%, V 0.05%, Ceq0.57%, and the balance is Fe and unavoidable impurities.

[0033] The heat treatment production process of test piece 1 is homogenization annealing → high temperature quenching → two-phase zone quenching → high temperature tempering. The main control contents of each process are as follows:

[0034] For homogenization annealing, the test piece 1 was slowly heated to 910°C-980°C at a heating rate of 40°C / h, kept at that temperature for 9 hours, and then slowly cooled to below 200°C at a cooling rate of 40°C / h.

[0035] High temperature quenching: slowly heat the test piece to 880℃~930℃ at a heating rate of 40℃ / h and keep it at that temperature for 9h. Then, quickly put it into the quenching liquid and cool it to below 100℃ within 1min.

[0036] Two-phase zone quenching: slowly heat the test piece to 740℃~800℃ at a heating rate of 40℃ / h and keep it at that temperature for 9h. Then, quickly put it into the quenching liquid and cool it to below 100℃ within 1min.

[0037] High temperature tempering: slowly heat the test piece 1 to 620℃~670℃ at a heating rate of 40℃ / h, keep it at that temperature for 9h, and then slowly cool it to below 200℃ at a cooling rate of 35℃ / h.

[0038] Example 2

[0039] Test piece 2 contains the high-strength and high-toughness alloy steel material composition, which includes, by mass percentage: C 0.15%, Si 0.53%, Mn 1.29%, Cr 0.28%, Ni 0.81%, Mo 0.41%, Cu 0.04%, V 0.05%, Ceq0.57%, and the balance is Fe and unavoidable impurities.

[0040] The heat treatment production process of the test piece 2 is homogenization annealing → high temperature quenching → two-phase zone quenching → high temperature tempering. The main control contents of each process are as follows:

[0041] For homogenization annealing, the test piece 2 was slowly heated to 910°C to 980°C at a heating rate of 40°C / h, kept at that temperature for 9 hours, and then slowly cooled to below 200°C at a cooling rate of 40°C / h.

[0042] High temperature quenching: slowly heat the test piece 2 to 880℃~930℃ at a heating rate of 40℃ / h and keep it at that temperature for 9h. Then, quickly put it into the quenching liquid and cool it to below 100℃ within 1min.

[0043] Two-phase zone quenching: slowly heat the test piece 2 to 740℃~800℃ at a heating rate of 40℃ / h and keep it at that temperature for 9h. Then, quickly put it into the quenching liquid and cool it to below 100℃ within 1min.

[0044] For high temperature tempering, the test piece 2 was slowly heated to 620°C~670°C at a heating rate of 40°C / h, kept at that temperature for 9 hours, and then slowly cooled to below 200°C at a cooling rate of 35°C / h.

[0045] Example 3

[0046] Test piece three contains the high-strength and high-toughness alloy steel material components, which, in terms of mass percentage, include: C 0.15%, Si 0.53%, Mn 1.29%, Cr 0.28%, Ni 0.81%, Mo 0.41%, Cu 0.04%, V 0.05%, Ceq0.57%, and the balance is Fe and unavoidable impurities.

[0047] The heat treatment production process of test piece 3 is homogenization annealing → high temperature quenching → two-phase zone quenching → high temperature tempering. The main control contents of each process are as follows:

[0048] For homogenization annealing, the test piece 3 was slowly heated to 910°C-980°C at a heating rate of 40°C / h, kept at that temperature for 9 hours, and then slowly cooled to below 200°C at a cooling rate of 40°C / h.

[0049] High temperature quenching: slowly heat the test piece 3 to 880℃~930℃ at a heating rate of 40℃ / h and keep it at that temperature for 9h. Then, quickly put it into the quenching liquid and cool it to below 100℃ within 1min.

[0050] Two-phase zone quenching: Test piece 3 was slowly heated to 740℃~800℃ at a heating rate of 40℃ / h and kept at this temperature for 9h. Then, it was quickly placed in the quenching liquid and cooled to below 100℃ within 1min.

[0051] For high temperature tempering, the test piece 3 was slowly heated to 620°C~670°C at a heating rate of 40°C / h, kept at that temperature for 9 hours, and then slowly cooled to below 200°C at a cooling rate of 35°C / h.

[0052] After heat treatment, the core mechanical properties of the three test pieces of the three embodiments were tested respectively, and the results are shown in Table 1.

[0053] Table 1 Mechanical properties test results of test pieces

[0054]

[0055] After small-scale verification, the thick-walled castings produced by the present invention have good high-toughness mechanical properties in the core. The heat treatment process of homogenization annealing + high-temperature quenching + two-phase zone quenching + tempering is adopted. The overall structure of the test block is uniform, and even at the core position, the low-temperature impact can reach more than 100J. The production method adopted by the present invention has been repeatedly verified and can be mass-produced.

[0056] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A heat treatment method for high-strength and high-toughness alloy steel material, characterized in that: The following steps are involved: S1 homogenization annealing, firstly, the high-strength and high-toughness alloy steel material is heated to a high temperature, and then slowly cooled after a certain holding time, so that the alloy elements undergo solid-state diffusion; S2 high temperature quenching, the high strength and high toughness alloy steel material is heated to a high temperature and rapidly quenched after a certain holding time, the high temperature quenching holding temperature is set at least 50°C above AC3; S3 two-phase quenching, the high-strength and high-toughness alloy steel material is heated to a high temperature, and then rapidly quenched after a certain holding time, and the material is heated to between AC1 and AC3; S4 high temperature tempering, heating the high strength and high toughness alloy steel material to a high temperature, and slowly cooling it after a certain holding time, wherein the high temperature tempering temperature is controlled below AC1; S5 slowly cools the high-strength and high-toughness alloy steel material to room temperature to complete the entire heat treatment process.

2. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The holding temperature of the homogenization annealing is set between 910°C and 980°C.

3. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The holding temperature of the high temperature quenching is set between 880°C and 930°C.

4. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The holding temperature of the two-phase region quenching is set between 740°C and 800°C.

5. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The cooling rate of the slow cooling is 40° C. / h.

6. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The holding temperature of the high temperature tempering is set between 620°C and 670°C.

7. The heat treatment method of high-strength and high-toughness alloy steel material according to claim 1, characterized in that: The insulation time is 9 hours.

8. The heat treatment method for high-strength and high-toughness alloy steel material according to claim 1, characterized in that the quenching time ranges from 14.4s to 18min.

9. A high-strength, high-toughness alloy steel material, characterized in that: The product is obtained by the heat treatment method according to any one of claims 1 to 8.

10. The high-strength and high-toughness alloy steel material according to claim 9, characterized in that: The high-strength and high-toughness alloy steel material composition, calculated by mass percentage, includes: C 0.14% to 0.17%, Si 0.5% to 0.6%, Mn≤1.8%, Cr≤1.5%, Ni≤2.0%, Mo≤0.7%, Cu≤0.5%, V≤0.12%, Ceq 0.57% to 0.60%, and the balance is Fe and unavoidable impurities.

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