Staged cooling heat treatment method for microalloyed high manganese steel

Abstract

The invention provides a staged cooling heat treatment method for microalloyed high manganese steel, and relates to the technical field of metal material heat treatment. The method comprises the steps of solution treatment, salt bath treatment and quenching treatment of a high manganese steel sample as cast. And the as-cast high manganese steel sample comprises the following chemical components in percentage by mass: 1.1-1.3% of C, 12-15% of Mn, 0.2-0.6% of Si, 1.5-2.9% of Cr, 0.1-0.2% of V, 0.02-0.06% of Ti, 0.02-0.08% of N, less than or equal to 0.03% of P, less than or equal to 0.02% of S and the balance of Fe and other inevitable impurities. By innovatively exploring the cooling process, the precipitation behavior and distribution condition of carbides in the microstructure of the high-manganese steel are regulated and controlled, so that the wear resistance and impact toughness of the high-manganese steel are synergistically improved, and the traditional water toughening treatment process of the high-manganese steel is reformed; the method is simple and easy to operate, green and environment-friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of metal materials, and particularly to a staged cooling heat treatment method for microalloyed high manganese steel. Background Art

[0002] As an austenitic steel, high manganese steel has good impact toughness. Under strong impact or extrusion conditions, work hardening will occur on the surface layer, showing the characteristics of hard surface and tough core. It is often used as wear-resistant parts in the liners of mine wet ball mills, the hammers of hammer crushers, the moving and stationary cone liners of cone crushers, and the jaw plates of jaw crushers. Under low stress conditions, due to its low initial yield strength and insufficient work hardening, high manganese steel shows poor wear resistance. With the gradual development of mining equipment towards large-scale and high-efficiency, wear-resistant materials are facing more severe challenges. On the basis of ensuring a certain impact toughness, improving its initial hardness and wear resistance is one of the important development directions of high manganese steel.

[0003] To improve the wear resistance of high manganese steel, many scholars have conducted extensive research in aspects such as alloying and modification treatment, heat treatment process improvement, and surface strengthening. For example, Chinese Patent CN113941430A discloses a preparation method of wear-resistant high manganese steel based on the TWIP effect and nano-precipitation strengthening. By adding appropriate amounts of alloying elements such as Mo, V, and Nb, the stacking fault energy of high manganese steel is controlled within the range of 20 - 40 mJ / m 2 to cause the TWIP effect to occur during the production and use of the liner, generating twins, and combining with the nano-precipitation strengthening effect to improve the wear resistance of the steel.

[0004] At present, the improvement of the heat treatment process of high manganese steel mainly focuses on the segmented heating and holding of solution treatment and the method of combining water toughening treatment with aging treatment. For example, Chinese Patent CN109487047A alloyizes high manganese steel with Ti - V - Nb, and then obtains high manganese steel with high yield strength and surface hardness through segmented heating and holding and quenching; however, the total holding time is relatively long, the impact toughness is relatively low, and the hardness is relatively high, and the coordinated improvement of impact toughness and hardness cannot be achieved. Chinese Patent CN115572800A discloses a treatment method for improving the performance of high manganese steel with composite precipitates. The alloyed high manganese steel is subjected to high-temperature solution treatment and air-cooled after ultra-long aging treatment, and a relatively large number of composite sub-micron-sized precipitates are precipitated in the austenite matrix; although it can play a role in composite precipitation strengthening for high manganese steel, it only improves the hardness, and the improvement of impact toughness is not ideal.

[0005] With the upgrading of industrial heat treatment equipment, some new heat treatment processes have been developed. For example, Chinese Patent CN110923429A discloses that after solution treating high manganese steel by water toughening and then subjecting it to ultra-high pressure heat treatment, followed by normal pressure heat treatment; although it can improve the hardness and wear resistance of the steel, it will simultaneously reduce the impact toughness. Chinese Patent CN116083813A discloses an N microalloyed high manganese steel and its heat treatment method, which adopts composition regulation and water toughening treatment. Although the impact toughness of the prepared high manganese steel has been greatly improved, the hardness has decreased instead. Summary of the Invention

[0006] In order to solve the technical problems in the prior art that high manganese steel cannot synergistically improve impact toughness and hardness through alloy regulation and / or existing heat treatment; the present invention proposes a staged cooling heat treatment method for microalloyed high manganese steel that can solve the aforementioned technical problems. The technical solution is as follows:

[0007] A staged cooling heat treatment method for microalloyed high manganese steel, the specific steps of the staged cooling heat treatment method for microalloyed high manganese steel are as follows:

[0008] S1. Subject the as-cast high manganese steel specimen to solution treatment in a heating furnace to dissolve the large blocky network carbide in the as-cast state and obtain a fully austenitic structure;

[0009] S2. Quickly take out the high manganese steel specimen after heat preservation in the solution treatment and put it into a salt bath furnace for heat preservation, so that partial dispersed granular carbonitrides precipitate in the austenite matrix of the high manganese steel specimen;

[0010] S3. Put the high manganese steel specimen after salt bath heat preservation treatment into water for rapid cooling, so that the heated structure is retained to room temperature, and finally obtain microalloyed high manganese steel.

[0011] Optionally, the chemical composition of the as-cast high manganese steel specimen in S1 is calculated by mass percentage as follows: C 1.1 - 1.3%, Mn 12 - 15%, Si 0.2 - 0.6%, Cr 1.5 - 2.9%, V 0.1 - 0.2%, Ti 0.02 - 0.06%, N 0.02 - 0.08%, P ≤ 0.03%, S ≤ 0.02%, and the rest is Fe and other inevitable impurities.

[0012] Optionally, the heating rate of the solution treatment is not greater than 5 °C / min, the temperature is 1070 - 1130 °C, and the solution treatment is carried out for 1 - 3 h.

[0013] Optionally, the temperature of the salt bath furnace is 750 - 850 °C, and the heat preservation time is 20 - 60 min.

[0014] Optionally, the cooling water temperature after the specimen enters the water is not greater than 50 °C.

[0015] Optionally, the microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbonitrides with a volume fraction not greater than 5%; the average grain size of equiaxed austenite is 420±50 μm, the carbonitrides are uniformly distributed inside the austenite grains, and the size is less than 5 μm; the impact toughness is 50 - 80 / J•cm -2 , and the hardness is 245 - 260 HBW.

[0016] Optionally, the stepwise cooling heat treatment method of the microalloyed high manganese steel further includes S4, cutting standard U-notch impact specimens from the microalloyed high manganese steel in S3 according to national standards for room temperature impact tests; cutting metallographic specimens, and observing the microstructure after grinding, polishing, and etching; measuring the hardness of the specimens using a Brinell hardness tester.

[0017] Technical principle of the present invention: The microalloyed high manganese steel obtains a single-phase austenite structure after solution treatment, and then is rapidly cooled to the salt bath holding temperature, which inhibits the appearance of large-sized brittle M7C3-type carbides. Furthermore, granular carbonitrides precipitate during the salt bath holding process, and microalloying helps the precipitation of granular carbonitrides. Finally, a microalloyed high manganese steel with a microstructure of an austenite matrix and granular carbides is obtained, improving the hardness and wear resistance.

[0018] The above technical solution has at least the following beneficial effects compared with the prior art:

[0019] The above solution, the present invention proposes a stepwise cooling heat treatment method for microalloyed high manganese steel, which can solve the technical problems that existing high manganese steels cannot synergistically improve impact toughness and hardness through alloy regulation and / or existing heat treatments.

[0020] The present invention controls the cooling stage of the solution treatment, so that the microstructure of the microalloyed high manganese steel consists of austenite and partial carbonitrides. Combining with the existing water toughening treatment plus aging treatment method, while ensuring sufficient toughness of the high manganese steel, it has good wear resistance.

[0021] Through solution treatment, the present invention dissolves the large blocky network carbides in the as-cast high manganese steel specimen to obtain a fully austenite structure; through salt bath treatment, partial dispersed granular carbonitrides precipitate in the austenite matrix; through quenching treatment, the heated structure is retained to room temperature.

[0022] The microstructure of the microalloyed high manganese steel prepared by the present invention consists of an austenite matrix and carbonitrides with a volume fraction not greater than 5%; the average grain size of equiaxed austenite is 420±50 μm, the carbonitrides are uniformly distributed inside the austenite grains, and the size is less than 5 μm; the impact toughness is 50 - 80 / J•cm -2 , and the hardness is 245 - 260 HBW.

[0023] In summary, compared with the traditional technology, through the innovative exploration of the cooling process, the present invention regulates the precipitation behavior and distribution of carbides in the microstructure of high manganese steel, thereby synergistically improving the wear resistance and impact toughness of high manganese steel, and revolutionizing the traditional water toughening treatment process of high manganese steel; this method is simple and easy to operate, environmentally friendly, with low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 is the process route diagram of the step-by-step cooling heat treatment method for a microalloyed high manganese steel of the present invention;

[0026] Figure 2 is the mass fraction distribution diagram of each phase at different temperatures simulated and calculated by the JmatPro software for the microalloyed high manganese steel in the step-by-step cooling heat treatment method for a microalloyed high manganese steel of the present invention;

[0027] Figure 3 is the optical micrograph of the microalloyed high manganese steel obtained by the step-by-step cooling heat treatment method for a microalloyed high manganese steel in Embodiment 2 of the present invention;

[0028] Figure 4 is the scanning electron microscope micrograph and the EDS energy spectrum element surface distribution diagram of the microalloyed high manganese steel obtained by the step-by-step cooling heat treatment method for a microalloyed high manganese steel in Embodiment 2 of the present invention; among them, label (a) is the scanning electron microscope micrograph; label (b) is the Cr element surface distribution diagram; label (c) is the Ti element surface distribution diagram; label (d) is the V element surface distribution diagram. Detailed Embodiments

[0029] The following will describe the technical solutions in the present invention with reference to the drawings.

[0030] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "example" in the present invention should not be construed as more preferred or more advantageous than other embodiments or design solutions. Exactly speaking, the use of the word "example" is intended to present concepts in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one of the two.

[0031] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, their intended meanings are the same.

[0032] In the embodiments of the present invention, sometimes subscripts such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, their intended meanings are the same.

[0033] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] A method for staged cooling heat treatment of microalloyed high manganese steel, and the method for staged cooling heat treatment of microalloyed high manganese steel is specifically as follows:

[0035] S1. Perform solution treatment on the as-cast high manganese steel sample in a heating furnace to dissolve the large block network carbide in the as-cast state and obtain a fully austenitic structure;

[0036] S2. Quickly take out the high manganese steel sample after heat preservation in the solution treatment and put it into a salt bath furnace for heat preservation, so that part of the dispersed granular carbonitrides precipitate in the austenite matrix of the high manganese steel sample;

[0037] S3. Put the high manganese steel sample after salt bath heat preservation treatment into water for rapid cooling, so that the heated structure is retained to room temperature, and finally obtain microalloyed high manganese steel.

[0038] Particularly, the chemical composition of the as-cast high manganese steel sample in S1 is calculated by mass percentage as follows: C 1.1-1.3%, Mn 12-15%, Si 0.2-0.6%, Cr 1.5-2.9%, V 0.1-0.2%, Ti 0.02-0.06%, N 0.02-0.08%, P≤0.03%, S≤0.02%, and the rest is Fe and other inevitable impurities.

[0039] Particularly, the heating rate of the solution treatment is not greater than 5°C / min, the temperature is 1070-1130°C, and the solution treatment is carried out for 1-3 h.

[0040] Particularly, the temperature of the salt bath furnace is 750-850°C, and the heat preservation time is 20-60 min.

[0041] Particularly, the cooling water temperature is not greater than 50°C after the sample enters the water.

[0042] Specifically, the microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbides and nitrides with a volume fraction not greater than 5%; the average grain size of equiaxed austenite is 420±50μm, the carbides and nitrides are evenly distributed inside the austenite grains, and the size is less than 5μm; the impact toughness is 50 - 80 / J•cm -2 , and the hardness is 245 - 260HBW.

[0043] Specifically, the stepwise cooling heat treatment method of the microalloyed high manganese steel further includes S4, cutting standard U-notch impact specimens from the microalloyed high manganese steel in S3 according to the national standard, and conducting room temperature impact tests; cutting metallographic specimens, observing the microstructure after grinding, polishing, and etching; and measuring the hardness of the specimens using a Brinell hardness tester.

[0044] According to Figure 2 As shown, compared with the traditional Mn13Cr2 high manganese steel, the microalloyed high manganese steel of the present invention has increased the precipitation temperature of M7C3-type carbides. The solubility product of Ti(C,N) in austenite is small, and it is easy to precipitate directly from the liquid phase during the casting process and hardly dissolves during the solution treatment process. The solubility product of V(C,N) in austenite is high, and it will dissolve during the solution treatment process and re-precipitate during the stepwise cooling process after solution. During the salt bath heat preservation process at 750 - 850°C, V(C,N) particles precipitate dispersedly in the austenite matrix, and at the same time, a certain volume fraction of granular M7C3-type carbides precipitate, producing a second-phase strengthening effect and improving the hardness and wear resistance of the microalloyed high manganese steel.

[0045] Example 1

[0046] The stepwise cooling heat treatment method of a microalloyed high manganese steel in this example is specifically as follows:

[0047] S1. The chemical composition of the as-cast high manganese steel is by mass percentage: C 1.26%, Mn 12.92%, Si 0.38%, Cr 2.45%, V 0.15%, Ti 0.06%, N 0.04%, P 0.008%, S 0.006%, and the rest are Fe and other inevitable impurities; cut a 12mm×12mm×70mm block specimen from the as-cast high manganese steel with the aforementioned component contents, place the specimen in a box-type resistance furnace, and heat it to 1130°C at a heating rate of 5°C / min and hold for 1.5h to dissolve the large blocky network carbides in the as-cast state and obtain a complete austenite structure;

[0048] S2. Quickly take out the high manganese steel sample after solution treatment heating and holding, and put it into a salt bath furnace heated to 820 °C at a heating rate of 5 °C / min for holding, so that the high-temperature salt is in a molten state. Measure the temperature of the molten salt with a thermocouple and adjust the heating furnace to make its temperature stable at 800 °C. Quickly take out the sample after solution heat treatment from the box-type heating furnace and put it into the salt bath furnace. Hold it in the 800 °C salt bath furnace for 30 min to precipitate some dispersed granular carbonitrides in the austenite matrix of the high manganese steel sample;

[0049] S3. Quickly cool the high manganese steel sample after salt bath heat treatment in water to retain the heated structure to room temperature, and finally obtain microalloyed high manganese steel.

[0050] The step-by-step cooling heat treatment method of the microalloyed high manganese steel further includes S4. Cut standard U-notch impact specimens from the microalloyed high manganese steel in S3 according to the national standard for room temperature impact tests; cut metallographic specimens, and observe the microstructure after grinding, polishing, and etching; measure the hardness of the specimens with a Brinell hardness tester.

[0051] The microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbonitrides; the average grain size of equiaxed austenite is 420 ± 50 μm, and the carbonitrides are evenly distributed inside the austenite grains; the impact toughness is 69.8 / J•cm -2 and the hardness is 247.9 HBW.

[0052] Example 2

[0053] A step-by-step cooling heat treatment method of a microalloyed high manganese steel in this example. The step-by-step cooling heat treatment method of the microalloyed high manganese steel is specifically as follows:

[0054] S1. The chemical composition of the as-cast high manganese steel is by mass percentage: C 1.26%, Mn 12.92%, Si 0.38%, Cr 2.45%, V 0.15%, Ti 0.06%, N 0.04%, P 0.008%, S 0.006%, and the rest are Fe and other inevitable impurities; cut a 12 mm × 12 mm × 70 mm block sample from the as-cast ingot of the high manganese steel with the above composition content, put the sample into a box-type resistance furnace, and heat it to 1130 °C at a heating rate of 5 °C / min for holding for 1.5 h, so as to dissolve the large block network carbide in the as-cast state and obtain a complete austenite structure;

[0055] S2. Quickly take out the high manganese steel sample after solution heat treatment and heat preservation, and put it into a salt bath furnace heated to 820 °C at a heating rate of 5 °C / min for heat preservation, so that the high-temperature salt is in a molten state. Measure the temperature of the molten salt with a thermocouple and adjust the heating furnace to make its temperature stable at 800 °C. Quickly take out the sample after solution heat preservation from the box-type heating furnace and put it into the salt bath furnace. Keep it in the 800 °C salt bath furnace for 60 min to precipitate some dispersed granular carbonitrides in the austenite matrix of the high manganese steel sample;

[0056] S3. Quickly cool the high manganese steel sample after salt bath heat preservation treatment in water to retain the heating structure to room temperature, and finally obtain microalloyed high manganese steel.

[0057] The step-by-step cooling heat treatment method of the microalloyed high manganese steel also includes S4. Cut standard U-notch impact specimens from the microalloyed high manganese steel in S3 according to the national standard for room temperature impact tests; cut metallographic specimens, and observe the microstructure after grinding, polishing, and etching; measure the hardness of the specimens with a Brinell hardness tester.

[0058] As Figure 3 and Figure 4 shown, the microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbonitrides; the average grain size of equiaxed austenite is 420 ± 50 μm, and the carbonitrides are evenly distributed inside the austenite grains; the impact toughness is 58.6 / J•cm -2 , and the hardness is 253.8 HBW. Figure 3 The conclusion and beneficial effect that can be brought is that the microstructure shows that the microalloyed high manganese steel obtains a microstructure of austenite matrix + granular carbides after step-by-step cooling heat treatment. Figure 4 The conclusion and beneficial effect that can be brought is that the existence form of the dispersed precipitation of microalloy carbides is determined by energy spectrum analysis.

[0059] Example 3

[0060] A step-by-step cooling heat treatment method of a microalloyed high manganese steel in this embodiment. The step-by-step cooling heat treatment method of the microalloyed high manganese steel is specifically as follows:

[0061] S1. The chemical composition of as-cast high manganese steel by mass percentage is as follows: C 1.12%, Mn 12.92%, Si 0.38%, Cr 1.85%, V 0.15%, Ti 0.06%, N 0.04%, P 0.008%, S 0.006%, and the rest is Fe and other inevitable impurities; for the as-cast high manganese steel with the aforementioned component contents, a block-shaped sample of 12 mm×12 mm×70 mm is cut from the ingot. The sample is placed in a box-type resistance furnace and heated at a heating rate of 5°C / min to 1130°C and held for 1.5 h, so that the large block-shaped network carbide in the as-cast state is dissolved to obtain a fully austenitic structure;

[0062] S2. The high manganese steel sample after solution treatment heating and holding is quickly taken out and placed in a salt bath furnace heated at a heating rate of 5°C / min to 800°C for holding, so that the high-temperature salt is in a molten state. The temperature of the molten salt is measured with a thermocouple and the heating furnace is adjusted to make its temperature stable at 780°C. The sample after solution treatment and holding is quickly taken out from the box-type heating furnace and placed in the salt bath furnace, and held in the 780°C salt bath furnace for 60 min, so that partial dispersed granular carbonitrides are precipitated in the austenite matrix of the high manganese steel sample;

[0063] S3. The high manganese steel sample after salt bath holding treatment is quickly cooled in water, so that the heated structure is retained to room temperature, and finally a microalloyed high manganese steel is obtained.

[0064] The step-by-step cooling heat treatment method of the microalloyed high manganese steel further includes S4. Standard U-notch impact specimens are cut from the microalloyed high manganese steel in S3 according to national standards for room temperature impact tests; metallographic specimens are cut, and after grinding, polishing, and etching, microstructure observation is carried out; the hardness of the specimens is measured with a Brinell hardness tester.

[0065] The microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbonitrides; the average grain size of equiaxed austenite is 420±50 μm, and the carbonitrides are evenly distributed inside the austenite grains; the impact toughness is 79.4 / J•cm -2 , and the hardness is 245.5 HBW.

[0066] Example 4

[0067] A step-by-step cooling heat treatment method of a microalloyed high manganese steel in this example, the step-by-step cooling heat treatment method of the microalloyed high manganese steel is specifically as follows:

[0068] S1. The chemical composition of as-cast high manganese steel is by mass percentage: C 1.26%, Mn 12.92%, Si 0.38%, Cr 2.45%, V 0.15%, Ti 0.06%, N 0.04%, P 0.008%, S 0.006%, and the rest is Fe and other inevitable impurities; for the as-cast high manganese steel with the above component contents, a block sample of 12 mm × 12 mm × 70 mm is cut from the ingot. The sample is placed in a box-type resistance furnace and heated at a heating rate of 5 °C / min to 1130 °C and held for 2 h, so that the large block network carbide in the as-cast state is dissolved to obtain a fully austenitic structure;

[0069] S2. The high manganese steel sample after solution treatment heating and holding is quickly taken out and placed in a salt bath furnace heated at a heating rate of 5 °C / min to 840 °C and held, so that the high-temperature salt is in a molten state. The temperature of the molten salt is measured with a thermocouple and the heating furnace is adjusted to make its temperature stable at 820 °C. The sample after solution holding is quickly taken out from the box-type heating furnace and placed in the salt bath furnace, and held in the 820 °C salt bath furnace for 60 min, so that partial dispersed granular carbonitrides are precipitated in the austenite matrix of the high manganese steel sample;

[0070] S3. The high manganese steel sample after salt bath holding treatment is cooled in water for quenching, so that the heated structure is retained to room temperature, and finally a microalloyed high manganese steel is obtained.

[0071] The step-by-step cooling heat treatment method of the microalloyed high manganese steel further includes S4. Standard U-notch impact specimens are cut from the microalloyed high manganese steel in S3 according to the national standard for room temperature impact tests; metallographic specimens are cut, and after grinding, polishing, and etching, the microstructures are observed; the hardness of the specimens is measured using a Brinell hardness tester.

[0072] The microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbonitrides; the average grain size of equiaxed austenite is 420 ± 50 μm, and the carbonitrides are evenly distributed inside the austenite grains; the impact toughness is 54.3 / J•cm -2 and the hardness is 258.5 HBW.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Examples 1 - 4 is that this comparative example selects traditional high manganese steel Mn13Cr2, and its chemical composition and mass percentage are as follows, C: 1.13%; Si: 0.56%; Mn: 13.12%; Cr: 1.59%; P: 0.008%; S: 0.003%; and the rest is Fe and other inevitable impurities.

[0075] The Mn13Cr2 high manganese steel of this comparative example was produced using the same casting process as the above-mentioned embodiment. Block specimens with dimensions of 12 mm × 12 mm × 70 mm were cut from the as-cast steel ingot. The specimens were placed in a box-type resistance furnace and heated to 1100 °C at a heating rate of 5 °C / min and held for 2 h for solution treatment. After the solution heat treatment was completed, the specimens were taken out of the box-type heating furnace and quickly immersed in cooling water for quenching to cool the specimens to room temperature, thus obtaining the traditional high manganese steel Mn13Cr2 in the water toughened state.

[0076] The traditional high manganese steel Mn13Cr2 also includes S4. Standard U-notch impact specimens were cut from the traditional high manganese steel Mn13Cr2 according to national standards for room temperature impact tests; metallographic specimens were cut, ground, polished, and etched for microstructural observation; the hardness of the specimens was measured using a Brinell hardness tester.

[0077] The impact toughness of the traditional high manganese steel Mn13Cr2 is 156.2 / J•cm -2 and the hardness is 218.6 HBW.

[0078] Through the comparison of mechanical properties, it was found that by adding V and Ti microalloying elements and appropriately increasing the content of Cr element, after the microalloyed high manganese steel was successively subjected to solution heat treatment and staged cooling heat treatment methods, its hardness increased by 12 - 18% compared with the traditional water toughened Mn13Cr2, and the impact toughness still remained at a relatively high level.

[0079] For the above-mentioned scheme, the present invention proposes a staged cooling heat treatment method for microalloyed high manganese steel, which can solve the technical problems in the prior art that high manganese steel cannot synergistically improve impact toughness and hardness through alloy regulation and / or existing heat treatment.

[0080] By controlling the cooling stage of the solution treatment, the present invention makes the microstructure of the microalloyed high manganese steel consist of austenite and some carbonitrides. Combining with the method of water toughening treatment plus aging treatment in the prior art, while ensuring sufficient toughness of the high manganese steel, it has good wear resistance.

[0081] Through solution treatment, the large block network carbide in the as-cast high manganese steel specimen is dissolved to obtain a fully austenite structure; through salt bath treatment, some dispersed granular carbonitrides are precipitated in the austenite matrix; through quenching treatment, the heated structure is retained to room temperature.

[0082] The microstructure of the microalloyed high manganese steel prepared by the present invention consists of an austenite matrix and carbonitrides with a volume fraction not greater than 5%; the average grain size of equiaxed austenite is 420 ± 50 μm, and the carbonitrides are evenly distributed inside the austenite grains with a size less than 5 μm; the impact toughness is 50 - 80 / J•cm -2, with a hardness of 245 - 260 HBW.

[0083] In summary, compared with the traditional technology, through the innovative exploration of the cooling process, the present invention regulates the precipitation behavior and distribution of carbides in the microstructure of high manganese steel, thereby synergistically improving the wear resistance and impact toughness of high manganese steel, and revolutionizing the traditional water toughening treatment process of high manganese steel; this method is simple and easy to operate, environmentally friendly, low-cost, short-process, and high-efficiency, facilitating large-scale industrial production and promotion.

[0084] It should be understood that the term "and / or" in this article is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: the individual existence of A, the simultaneous existence of A and B, and the individual existence of B. Here, A and B can be singular or plural. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after, but it may also represent an "and / or" relationship, which can be specifically understood with reference to the context before and after.

[0085] In the present invention, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or similar expressions refer to any combination of these items, including any combination of single (item) or plural (items). For example, at least one (item) of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0086] It should be understood that in various embodiments of the present invention, the magnitude of the sequence numbers of the above processes does not mean the sequence of execution. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0087] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A staged cooling heat treatment method for microalloyed high manganese steel, characterized in that, The step-by-step cooling heat treatment method for the microalloyed high manganese steel is specifically as follows: S1. Solution treatment is carried out on the as-cast high manganese steel sample in a heating furnace to dissolve the large blocky network carbide in the as-cast state and obtain a fully austenitic structure; S2. The high manganese steel sample after heat preservation in the solution treatment is quickly taken out and put into a salt bath furnace for heat preservation, so that some dispersed granular carbonitrides are precipitated in the austenite matrix of the high manganese steel sample; S3. The high manganese steel sample after salt bath heat preservation treatment is quickly cooled in water to retain the heated structure to room temperature, and finally the microalloyed high manganese steel is obtained.

2. The stepwise cooling heat treatment method of the microalloyed high manganese steel according to claim 1, characterized in that, The chemical composition of the as-cast high manganese steel sample in S1 is calculated by mass percentage as follows: C 1.1-1.3%, Mn 12-15%, Si 0.2-0.6%, Cr 1.5-2.9%, V 0.1-0.2%, Ti 0.02-0.06%, N 0.02-0.08%, P≤0.03%, S≤0.02%, and the rest are Fe and other inevitable impurities.

3. The stepwise cooling heat treatment method for the microalloyed high manganese steel according to claim 1, wherein The heating rate of the solution treatment is not greater than 5 °C / min, the temperature is 1070-1130 °C, and the solution treatment is carried out for 1-3 h.

4. The stepwise cooling heat treatment method for microalloyed high manganese steel according to claim 1, characterized in that, The temperature of the salt bath furnace is 750-850 °C, and the heat preservation time is 20-60 min.

5. The stepwise cooling heat treatment method for the microalloyed high manganese steel according to claim 1, wherein, The temperature of the cooling water after the sample enters the water is not greater than 50 °C.

6. The stepwise cooling heat treatment method for the microalloyed high manganese steel according to claim 1, wherein The microstructure of the microalloyed high manganese steel consists of an austenite matrix and carbides and nitrides with a volume fraction of not more than 5%; the average grain size of equiaxed austenite is 420±50μm, the carbides and nitrides are evenly distributed inside the austenite grains, and the size is less than 5μm; the impact toughness is 50-80 / J•cm -2 , and the hardness is 245-260HBW.

7. The stepwise cooling heat treatment method for the microalloyed high manganese steel according to claim 1, wherein, The step-by-step cooling heat treatment method for the microalloyed high manganese steel further includes S4. The microalloyed high manganese steel in S3 is cut into standard U-notch impact specimens according to the national standard for room temperature impact tests; metallographic specimens are cut, and after grinding, polishing and etching, the microstructure is observed; the hardness of the specimen is measured by a Brinell hardness tester.

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