CN113652612B - Manganese steel in heterogeneous lamellar structure and preparation method thereof - Google Patents
Manganese steel in heterogeneous lamellar structure and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a manganese steel in a heterogeneous lamellar structure and a preparation method thereof, wherein the manganese steel has a heterogeneous lamellar structure formed by mutually overlapping Mn-rich retained austenite and Mn-poor martensite nanosheets, and the preparation method comprises the following steps: carrying out two-stage heat treatment on medium manganese steel with pearlite as an initial structure, wherein the first-stage heat treatment is carried out until the temperature is raised to a preheating temperature lower than the austenite forming temperature at a temperature rise rate of less than 30 ℃/s, and carrying out heat preservation and preheating treatment; the second stage heat treatment is carried out, wherein the temperature rise rate is less than 30 ℃/s, the temperature is raised from the preheating temperature to the austenite reverse transformation temperature, and the heat is preserved for carrying out the austenite reverse transformation treatment; and finally carrying out tempering treatment. The invention can prepare the medium manganese steel with the same microstructure and mechanical property as the rapid heating process by two-stage heating treatment at a lower heating rate, obviously reduces the industrial production conditions and provides a new technical route for preparing the large and thick steel plate with the heterogeneous structure in the traditional industrial production.
Description
Technical Field
The invention relates to the technical field of medium manganese steel materials.
Background
Advanced high strength steels are widely used as structural materials in the automotive industry, with medium manganese steels being one of the most promising third generation high strength steels. Typical microstructures of medium manganese steels are ferrite/martensite and retained austenite, which achieve matching between strength and elongation by inducing plasticity through transformation of the retained austenite, whereas the austenite reverse transformation process can partition austenite stabilizing elements (such as carbon (C) and manganese (Mn)) into austenite through annealing in a two-phase region, thereby improving the stability of austenite so that it can be retained at room temperature, but in order to obtain sufficiently stable austenite, a higher annealing temperature or a longer annealing time is often required to ensure the partitioning of elements. This not only reduces the production efficiency and cost, but also high-temperature or long-time annealing inevitably causes ferrite/martensite grain coarsening, thereby deteriorating the mechanical properties of the medium manganese steel.
Recently, the rapid heating process (more than or equal to 100 ℃/s) can effectively reduce the energy consumption in the production process of the strip steel, improve the processing efficiency, effectively inhibit the recrystallization of a deformed structure to promote the formation of non-equilibrium austenite, and further remarkably improve the mechanical property. For example, chinese patent document CN112063931A discloses a low-carbon medium-manganese high-residual-austenite high-toughness steel and a heat treatment thereof, which is prepared by performing rapid heating and very short austenitizing treatment on an initial structure of a deformed martensite and a fine cementite to prepare an isomeric structure consisting of a high-content residual austenite and an incomplete recrystallized ferrite with excellent mechanical properties, wherein the heating rate of the steel heated to a two-phase region is not lower than 100 ℃/s, and the heat preservation time of the two-phase region is very short to limit recrystallization of the deformed structure; or as disclosed in chinese patent documents CN112251679A and CN110468263A, a rapid heating process based on lamellar pearlite composed of Mn-rich cementite and Mn-poor ferrite, which can avoid the diffusion of Mn element inside austenite, thereby preparing a nano-lamellar structure composed of Mn-rich metastable retained austenite and Mn-poor martensite lamellar alternately.
Although the above-described rapid heating technique has shown great potential in the production of advanced high strength steels, its practical limitations are very significant, including: (1) because the heating rate of the rapid heating technology is too fast (more than or equal to 100 ℃/s), while the heating rate of the traditional heating equipment is generally lower than 20 ℃/s, the heat treatment technology has higher difficulty and very strict requirement on the heating equipment, and the rapid heating treatment mode is difficult to expand to a large industrial scale equivalent to that of the current continuous annealing production line; (2) the rapid heating technology needs to complete austenite reverse transformation in a very short time, so the thickness of the steel plate is generally not more than 1.5mm, and the industrial production of large and thick steel plates is greatly limited; (3) the rapid heating technique is very likely to cause bending deformation of steel and the like.
How to obtain the medium manganese steel with the microstructure and the mechanical property which are the same as those of the medium manganese steel which is rapidly heated in the current large-scale industrial production is a problem which needs to be solved urgently.
Disclosure of Invention
The invention aims to provide a method for preparing medium manganese steel by two-stage heating for heat treatment, in the heat treatment mode, the medium manganese steel with a heterogeneous lamellar structure consisting of ultrafine residual austenite and martensite lamellar layers alternately can be obtained at a lower heating rate, the industrial production condition can be obviously reduced, and the technical problem that the product is easy to bend and deform in the prior art is solved.
The invention firstly provides the following technical scheme:
the preparation method of the manganese steel in the heterogeneous lamellar structure comprises the following steps:
(1) heating the hot rolled steel plate to the temperature for forming an austenite single-phase region, preserving heat for austenitizing treatment, cooling to the temperature of a ferrite and cementite two-phase region, preserving heat for pearlite transformation, and finally cooling to room temperature;
(2) heating the hot rolled plate subjected to pearlite transformation to a preheating temperature at a first heating rate, and carrying out heat preservation and preheating treatment until the temperature of the material is uniformly distributed to obtain a preheated material; heating the preheated material to austenite reverse transformation temperature at a second heating rate, preserving heat for austenite reverse transformation, and then cooling to room temperature to obtain an austenite reverse transformed material;
(3) tempering the austenite reverse transformed material to obtain the manganese steel in the heterogeneous lamellar structure;
wherein the preheating temperature is lower than the austenite start forming temperature (A)c1) And both the first temperature rise rate and the second temperature rise rate are less than 30 ℃/s.
According to some preferred embodiments of the present invention, the austenite single-phase region forming temperature in step (1) is 800 to 900 ℃ and/or the holding time thereof is 10 to 60 min.
According to some preferred embodiments of the present invention, the ferrite and the cementite have a two-phase region formation temperature of 500 to 650 ℃, and/or a holding time of 2 to 24 hours.
This preferred embodiment can further ensure that the obtained material contains pearlite in an amount of 95% or more, and can control the degree of distribution of Mn element in cementite by adjusting the holding time.
According to some preferred embodiments of the present invention, the first temperature increase rate is 0.1 to 25 ℃/s.
According to some preferred embodiments of the present invention, the second temperature increase rate is 1 to 25 ℃/s.
More preferably, the first temperature rise rate is 0.5-1.5 ℃/s, and the second temperature rise rate is 5-10 ℃/s.
According to some preferred embodiments of the present invention, in the preheating treatment, the preheating temperature is 500 to 680 ℃, and/or the holding time is 0 to 300 s.
According to some preferred embodiments of the present invention, in the austenite reverse transformation, the temperature of the austenite reverse transformation is 730 to 800 ℃, and/or the holding time thereof is 0 to 120 s.
According to some preferred embodiments of the present invention, the conditions of the tempering treatment in the step (3) are: heating the mixture from room temperature to 150-300 ℃, preserving the heat for 10 s-120 min, and then cooling the mixture to room temperature.
According to some preferred embodiments of the present invention, the cooling rate is 20-200 ℃/s.
According to some preferred embodiments of the present invention, the steel material of the hot rolled steel plate comprises the following elements by mass percent:
C：0.20～0.45％，
Mn：2.0～8.0％，
Si：0～3.0％，
Cr：0～1％，
V：0～0.8％，
Nb：0～0.8％，
Ti：0～0.8％，
Mo：0～0.6％，
the balance being Fe and unavoidable impurities.
More preferably, the steel has an Si content of more than 0.
The invention further provides manganese steel in a heterogeneous lamellar structure, which is prepared by any one of the preparation methods.
In the structure, the heterogeneous lamellar structure is formed by overlapping Mn-rich retained austenite and Mn-poor martensite nanosheets, and the microstructure morphology and chemical heterogeneity of the heterogeneous lamellar structure are inherited in a lamellar pearlite structure.
The preparation method of the invention comprises the following steps:
the transformation from austenite to pearlite is obvious diffusive phase transformation and depends on the long-range diffusion of elements, so the formation process of pearlite is accompanied by the gradual enrichment of C and Mn elements in cementite, while ferrite is poor in C and Mn, and thus the pearlite with obvious heterogeneous Mn concentration and gradient distribution is obtained; in the heat treatment process of the preparation method, the preheating temperature is lower than the austenite starting transformation temperature, so that the element distribution hardly changes in the preheating stage; then the element is heated to the austenite reverse transformation temperature at a higher speed, so that the heterogeneous distribution of the element can be effectively retained in the austenite; during the subsequent cooling process, the austenite transformed from the cementite of the original layer can be retained to room temperature due to the manganese enrichment, while the austenite transformed from the ferrite of the original layer is transformed to martensite due to the Mn-poor instability. Finally, a Mn-rich lamellar residual austenite and Mn-poor lamellar martensite overlapped heterogeneous nano lamellar structure can be obtained.
The preparation method of the invention has the following beneficial effects:
traditionally, medium manganese steel with a heterogeneous lamellar structure is prepared by relying on rapid heating to maintain the uneven distribution of Mn in austenite, thereby stabilizing the austenite to room temperature; however, the rapid heating technology still has the problems that the rapid heating technology is difficult to be applied to a production line in a large scale, the thickness of a heated steel plate is small, the steel plate is easy to bend and deform and the like, the preparation method can prepare the superfine residual austenite and the martensite structure with the heterogeneous distribution of Mn elements through two-stage heating treatment at a lower heating rate, and the defects of the rapid heating technology are overcome;
the preparation method of the invention can be realized by two-stage heating: (1) the temperature rise rate before preheating is effectively reduced; (2) through specific preheating treatment, uniform temperature distribution can be obtained, the heating difficulty of the later stage can be reduced, the problem that the steel plate is easy to bend and deform due to a rapid heating process can be solved, and meanwhile, the uneven distribution of manganese in the initial pearlite can be kept by controlling the preheating temperature to be lower than the austenite transformation temperature and not generating austenite phase transformation after the preheating stage; (3) on the premise of having the same microstructure and mechanical property with the rapid heating, the method can be suitable for the current industrial mass production application by adjusting the heating rate after preheating, and provides a new idea for the subsequent preparation of large and thick steel plates with heterogeneous structures.
Drawings
FIG. 1 is a flow chart of a specific manufacturing process of the present invention;
FIG. 2 is an SEM photograph of a sample obtained after step (2) in example 1;
FIG. 3 is a tensile curve of the product obtained in example 1;
FIG. 4 is a TEM comparison of the product obtained in example 1 with that obtained from the prior art;
FIG. 5 is an SEM photograph of a sample obtained after step (2) in example 2;
FIG. 6 is an SEM photograph of a sample obtained after step (2) in example 4.
Detailed Description
The present invention is described in detail below with reference to the following embodiments and the attached drawings, but it should be understood that the embodiments and the attached drawings are only used for the illustrative description of the present invention and do not limit the protection scope of the present invention in any way. All reasonable variations and combinations that fall within the spirit of the invention are intended to be within the scope of the invention.
According to the technical scheme of the invention, the preparation method of some specific manganese steel in the heterogeneous lamellar structure comprises the following steps:
(1) forging an ingot containing iron, carbon and manganese components, then preserving heat at 1100-1300 ℃ for 24-36 h for homogenization treatment, and carrying out hot rolling on a forged piece obtained after homogenization treatment to obtain a hot rolled steel plate;
(2) heating the obtained hot rolled steel plate to an austenite single-phase region at 800-900 ℃ for austenitizing treatment, preserving heat for 10-60 min, cooling to a two-phase region of ferrite and cementite for heat preservation to obtain a pearlite structure, and continuously cooling to room temperature;
(3) rapidly austenitizing the hot-rolled steel sheet after pearlite transformation by two-stage heating treatment, wherein the two-stage heating treatment comprises the following steps: firstly, slowly heating the hot rolled steel plate transformed by pearlite to a preheating temperature, and preserving heat for a certain time to ensure that the temperature distribution of the steel plate is uniform, wherein the preheating temperature is lower than the austenite transformation starting temperature; then, rapidly heating to raise the temperature to austenite reverse transformation temperature, preserving heat to perform austenite reverse transformation treatment, and finally rapidly cooling to room temperature;
(4) tempering the steel plate after the step (3);
wherein the content of the first and second substances,
the temperature of the ferrite and cementite in the two-phase region in the step (2) is preferably 500-650 ℃; the heat preservation time at the temperature is preferably 2-24 h, so that more than 95% of pearlite can be obtained, and the Mn distribution degree of cementite in the pearlite can be regulated and controlled;
the preheating temperature in the step (3) is preferably 500-680 ℃ and is lower than the austenite transformation starting temperature, so that austenite transformation does not occur in preheating, and the uneven distribution of Mn in pearlite is not changed; the preheating time at the preheating temperature is preferably 0-300 s, so that the uniform temperature distribution of the steel plate during preheating can be ensured;
in the step (3), the reverse transformation temperature of austenite is preferably 730-800 ℃, and the heat preservation time of the reverse transformation treatment of austenite at the temperature is preferably 0-120 s;
the heating rate in the process of heating to the preheating temperature in the step (3) is preferably 0.1-25 ℃/s; the heating rate in the rapid heating process above the preheating temperature is preferably 1-25 ℃/s, so that the condition that the austenite cannot be stabilized due to serious Mn diffusion can be prevented, and a heterogeneous structure of more than 40% can be obtained; then, the cooling rate in the process of rapidly cooling to room temperature is preferably 20-200 ℃/s;
the condition of the tempering treatment in the step (4) is preferably that the temperature is kept at 150-300 ℃ for 10 s-120 min.
Example 1
Vacuum melting and forging a steel material with specific components of Fe-0.39C-3.69Mn (wt.%) to form 250 x 40mm3Forging; taking 100X 40X 26mm from the center of the forging3The square forging is heated to 1250 ℃ in argon atmosphere, and is subjected to homogenization treatment after being kept for 24 hours; and (3) carrying out 5-8 rolling passes on the homogenized forge piece to obtain a hot rolled plate with the thickness of 6mm, wherein the final rolling temperature is higher than 850 ℃, and after rolling, air cooling to room temperature to form a martensite matrix structure.
The two-stage heating treatment shown in fig. 1 is carried out on the hot rolled steel plate, and the specific treatment steps are as follows:
(1) the hot rolled steel plate is kept warm in a muffle furnace at 800 ℃ for 10min for austenitizing, then is moved to a salt bath furnace at 570 ℃ and is kept warm for 6h for complete pearlite transformation, and then is water-quenched to room temperature;
(2) heating the sample after completing the pearlite transformation from room temperature to 650 ℃ at a heating rate of 1 ℃/s (austenite transformation does not occur), directly heating the sample to 750 ℃ at a heating rate of 5 ℃/s, and finally cooling the sample from 750 ℃ to room temperature at a cooling rate of 80 ℃/s;
(3) heating the sample to 200 ℃ at the heating rate of 5 ℃/s, tempering for 30min, and then cooling to room temperature at the cooling rate of 80 ℃/s;
the microstructure after the treatment of the step (2) of this example is shown in FIG. 2, and it can be seen that a pearlite-like lamellar structure in which gray-colored lamellar retained austenite and black lamellar quenched martensite are overlapped with each other and a normal martensite structure in which the percentage of lamellar structure is about 70% are included. After the tempering treatment, the quenched martensite is transformed into tempered martensite.
Compared with the two-stage heating process of the embodiment, the rapid heating process (heating to 750 ℃ at 100 ℃/s, quenching after keeping the temperature for 10s, and tempering at 200 ℃ for 30min) in the chinese patent document CN110468263A is used, and the microstructures of the two products have similar content of lamellar structures (about 70%); the results of comparative tests on mechanical properties of the product are shown in fig. 3-4, in which the yield strength and tensile strength of the product obtained by the two-stage heating process are 1678MPa and 2010MPa, respectively, the uniform elongation and elongation after fracture are 6.7% and 13.5%, respectively, and the sample obtained by the rapid heating process has similar strength and relatively lower elongation (4.7%) and elongation after fracture (12%). Microstructure representation shows that the concentration difference of Mn element in austenite in the product obtained by rapid heating is large, as shown in figure 4(a), the residual austenite is too stable and can not play the TRIP effect in the stretching process, and compared with the prior art, the Mn element is sufficiently diffused in the slow two-stage heating process, so that the stability of the austenite presents step distribution, as shown in figure 4(b), the strain hardening capacity of the sample is improved by being beneficial to gradual transformation of the residual austenite under different strains.
That is, by the two-stage heating process of this embodiment, a higher content of lamellar structure can be obtained at the fastest heating rate of only 5 ℃/s, and the product has a similar microstructure and better mechanical properties (the uniform elongation is improved by 30%) than the product obtained by the rapid heating process.
Example 2
Vacuum melting and forging a steel material with specific components of Fe-0.39C-3.69Mn (wt.%) to form 250 x 40mm3Forging piece(ii) a Taking 100X 40X 26mm from the center of the forging3Heating the square forging to 1200 ℃ in an argon atmosphere, and preserving heat for 36 hours for homogenization treatment; and (3) carrying out 9 rolling passes on the homogenized forge piece to obtain a hot rolled plate with the thickness of 6mm, wherein the final rolling temperature is more than 900 ℃, and air cooling to room temperature after rolling to form a martensite matrix structure.
The hot rolled steel sheet was subjected to a heat treatment as shown in FIG. 1, and the specific treatment steps were as follows:
(1) the hot rolled steel plate is kept warm for 6min in a muffle furnace at 850 ℃ for austenitizing, then is moved to a salt bath furnace at 550 ℃ and is kept warm for 12h, and then is water-quenched to room temperature to obtain pearlite with higher Mn distribution degree;
(2) heating the sample after completing the pearlite transformation from room temperature to 600 ℃ at the heating rate of 5 ℃/s, preheating for 10s, then heating from 600 ℃ to 760 ℃ at the heating rate of 5 ℃/s, and finally cooling the sample from 760 ℃ to room temperature at the cooling rate of 80 ℃/s;
(3) heating the sample to 200 ℃ at the heating rate of 5 ℃/s, tempering for 30min, and then cooling to room temperature at the cooling rate of 80 ℃/s;
the microstructure after the treatment of step (2) of this example is shown in FIG. 5, and the percentage of lamellar structure is about 60%; the yield strength and tensile strength of the sample were 1640MPa and 1978MPa, respectively, and the uniform elongation and elongation after fracture were 5.7% and 12%, respectively. It can be seen that the Mn partition degree in pearlite can be adjusted by changing the holding time in step (1), thereby adjusting the final microstructure and mechanical properties.
Example 3
Vacuum melting and forging a steel material with specific components of Fe-0.39C-3.69Mn (wt.%) to form 250 x 40mm3Forging; taking 100X 40X 26mm from the center of the forging3Heating the square forging to 1200 ℃ in an argon atmosphere, and preserving heat for 36 hours for homogenization treatment; and (3) carrying out 9 rolling passes on the homogenized forge piece to obtain a hot rolled plate with the thickness of 6mm, wherein the final rolling temperature is more than 900 ℃, and air cooling to room temperature after rolling to form a martensite matrix structure.
The hot rolled steel sheet was subjected to a heat treatment as shown in FIG. 1, and the specific treatment steps were as follows:
(1) the hot rolled steel plate is subjected to heat preservation in a muffle furnace at 840 ℃ for 8min for austenitizing, then is moved to a salt bath furnace at 575 ℃ and is subjected to heat preservation for 6h for complete pearlite transformation, and then is subjected to water quenching to room temperature;
(2) heating the sample after completing the pearlite transformation from room temperature to 650 ℃ at a heating rate of 1 ℃/s, then immediately heating the sample from 650 ℃ to 750 ℃ at a heating rate of 1 ℃/s, and finally cooling the sample from 750 ℃ to room temperature at a cooling rate of 80 ℃/s;
(3) heating the sample to 200 ℃ at the heating rate of 5 ℃/s, tempering for 30min, and then cooling to room temperature at the cooling rate of 80 ℃/s;
the microstructure treated in step (2) of this example contained 45% lamellar structure; the yield strength and tensile strength of the test specimen were 1560MPa and 1971MPa, respectively, and the uniform elongation and elongation after fracture were 5.9% and 12%, respectively.
Example 4
Vacuum melting and forging a steel material with specific components of Fe-0.39C-3.69Mn (wt.%) to form 250 x 40mm3Forging; taking 100X 40X 26mm from the center of the forging3The square forging is heated to 1200 ℃ in the argon atmosphere, and the heat is preserved for 36 hours for homogenization treatment. And (3) carrying out 9 rolling passes on the homogenized forge piece to obtain a hot rolled plate with the thickness of 6mm, wherein the final rolling temperature is more than 900 ℃, and air cooling to room temperature after rolling to form a martensite matrix structure.
The hot rolled steel sheet was subjected to a heat treatment as shown in FIG. 1, and the specific treatment steps were as follows:
(1) the hot rolled steel plate is subjected to heat preservation in a muffle furnace at 850 ℃ for 6min for austenitizing, then is moved to a salt bath furnace at 550 ℃ and is subjected to heat preservation for 12h for complete pearlite transformation, and then is subjected to water quenching to room temperature;
(2) heating the sample after completing the pearlite transformation from room temperature to 650 ℃ at the heating rate of 1 ℃/s, directly heating to 750 ℃ at the heating rate of 20 ℃/s, preserving heat at 750 ℃ for 5s, and finally cooling the sample from 750 ℃ to room temperature at the cooling rate of 80 ℃/s;
(3) heating the sample to 200 ℃ at the heating rate of 5 ℃/s, tempering for 30min, and then cooling to room temperature at the cooling rate of 80 ℃/s;
the microstructure treated in step (2) of this example is shown in FIG. 6, with a percentage of lamellar structure exceeding 90%; the yield strength and the tensile strength of the sample are 1701MPa and 2018MPa respectively, the uniform elongation and the elongation after fracture are 4.9% and 11% respectively, compared with examples 1, 2 and 3, example 4 obtains an almost complete heterogeneous lamellar structure, the yield strength is obviously increased, but the elongation is reduced to 4.9%, the enrichment degree of Mn in the retained austenite has influence on the stability of the retained austenite, and on the premise of obtaining as many heterogeneous microstructures as possible to ensure higher yield strength, the stability (gradient distribution) of the retained austenite needs to be further adjusted to achieve the mechanical property of strong plastic matching.
As can be seen from the comparison of the above examples, in the case where each heating rate is low in step (2), example 1 obtains a high content of heterogeneous structure (70%) after reverse austenitizing treatment using a slower heating rate (5 ℃/s) after preheating, compared to example 3 where heating is slower, thus ensuring a higher yield strength (1678MPa), whereas it obtains a stability gradient distribution of lamellar retained austenite (fig. 4b), compared to example 4 where heating is faster (20 ℃/s), thus having a higher uniform elongation (6.7%).
Example 5
Vacuum melting and forging steel with specific components of Fe-0.4C-3.7Mn-1.5Si (wt.%) to form 250 x 40mm3 forgings; taking a square forging piece of 3 mm in size of 100 multiplied by 40 multiplied by 26 from the center of the forging piece, heating to 1200 ℃ in an argon atmosphere, and preserving heat for 36h for homogenization treatment; and (3) carrying out 9 rolling passes on the homogenized forge piece to obtain a hot rolled plate with the thickness of 6mm, wherein the final rolling temperature is more than 900 ℃, and air cooling to room temperature after rolling to form a martensite matrix structure.
The hot rolled steel sheet was subjected to a heat treatment as shown in FIG. 1, and the specific treatment steps were as follows:
(1) the hot rolled steel plate is subjected to heat preservation in a muffle furnace at 800 ℃ for 10min for austenitizing, then is moved to a salt bath furnace at 590 ℃ and is subjected to heat preservation for 6h for complete pearlite transformation, and then is subjected to water quenching to room temperature;
(2) heating the sample after completing the pearlite transformation from room temperature to 620 ℃ at the heating rate of 10 ℃/s for preheating for 30s, immediately heating from 620 ℃ to 770 ℃ at the heating rate of 5 ℃/s for heat preservation for 10s, and finally cooling the sample from 770 ℃ to room temperature at the cooling rate of 80 ℃/s;
(3) heating the sample to 200 ℃ at the heating rate of 5 ℃/s, tempering for 30min, and then cooling to room temperature at the cooling rate of 80 ℃/s;
the microstructure treated in step (2) of this example contained about 52% lamellar structure; the yield strength and tensile strength of the sample were 1737MPa and 2086MPa, respectively, and the uniform elongation and elongation after fracture were 5.7% and 11.2%, respectively. The percentage of heterogeneous structure obtained in example 5 was substantially the same as that obtained in example 3 (about 50%), the elongation was substantially the same (uniform elongation: 5.9%, elongation after fracture: 12%), and the strength of example 5 was significantly higher than that of example 3 (yield strength: 1560MPa, tensile strength: 1971MPa), and particularly the yield strength was higher than that of nearly 200 MPa.
Based on the technical scheme of the present invention, the inventor indicates that a person skilled in the art can also extend the way of the two-stage heat treatment of the present invention to a way of heating by multi-stage heating or non-linear heating to reduce the heating rate and obtain a uniform temperature distribution, thereby providing new technical routes for the subsequent preparation of large and thick steel plates with a non-homogeneous structure. Meanwhile, the two-section heating method is also suitable for preparing medium manganese steel with a heterogeneous distribution microstructure by using a rapid heating process, and the heating mode can be adjusted by considering the phase change temperature, so that the heating rate is reduced to be suitable for the traditional industrial production.
The above examples are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the above examples. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.
Claims (9)
1. The preparation method of the manganese steel in the heterogeneous lamellar structure is characterized by comprising the following steps of:
(1) heating a hot-rolled steel plate obtained by using a base steel to an austenite single-phase region forming temperature, preserving heat for austenitizing treatment, cooling to a ferrite and cementite two-phase region temperature, preserving heat for pearlite transformation, and finally cooling to room temperature;
(2) heating the hot rolled plate subjected to pearlite transformation to a preheating temperature at a first heating rate, and carrying out heat preservation and preheating treatment until the temperature of the material is uniformly distributed to obtain a preheated material; heating the preheated material to austenite reverse transformation temperature at a second heating rate, preserving heat for austenite reverse transformation, and then cooling to room temperature to obtain an austenite reverse transformed material;
(3) tempering the austenite reverse transformed material to obtain the manganese steel in the heterogeneous lamellar structure;
wherein the preheating temperature is lower than the temperature at which austenite begins to form, and the first temperature rise rate and the second temperature rise rate are both less than 30 ℃/s;
the base steel comprises the following elements in percentage by mass:
C：0.20～0.45％，
Mn：2.0～8.0％，
Si：0～3.0％，
Cr：0～1％，
V：0～0.8％，
Nb：0～0.8％，
Ti：0～0.8％，
Mo：0～0.6％，
the balance being Fe and unavoidable impurities.
2. The preparation method according to claim 1, wherein in the austenitizing treatment in the step (1), the temperature for forming the austenite single-phase region is 800-900 ℃ and/or the holding time is 10-60 min; and/or in the pearlite transformation in the step (1), the formation temperature of a two-phase region of the ferrite and the cementite is 500-650 ℃, and/or the heat preservation time is 2-24 hours.
3. The method according to claim 1, wherein the first temperature rise rate is 0.1 to 25 ℃/s, and/or the second temperature rise rate is 1 to 25 ℃/s.
4. The method according to claim 3, wherein the first temperature rise rate is 0.5 to 1.5 ℃/s, and/or the second temperature rise rate is 5 to 10 ℃/s.
5. The method according to claim 1, wherein in the step (2), the preheating temperature is 500 to 680 ℃, and/or the holding time is 0 to 300 s.
6. The method according to claim 1, wherein in the step (2), the austenite reverse transformation temperature is 730-800 ℃, and/or the holding time is 0-120 s.
7. The production method according to claim 1, wherein in the step (3), the tempering treatment conditions are: heating the mixture from room temperature to 150-300 ℃, preserving the heat for 10 s-120 min, and then cooling the mixture to room temperature.
8. The preparation method according to claim 7, wherein in the steps (2) and (3), the temperature reduction rate is 20-200 ℃/s.
9. Manganese steel in a heterogeneous lamellar structure, produced according to the method of production described in any one of claims 1 to 8.
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