Low-alloy NM600-grade wear-resistant steel and preparation method thereof

Abstract

The invention discloses low-alloy NM600-grade wear-resistant steel and a preparation method thereof. The preparation method comprises the following steps: KR desulfurization and smelting treatment; refining and continuous casting treatment; heating and hot rolling treatment; slow cooling and cutting treatment; quenching and tempering treatment; the low-alloy NM600 wear-resistant steel with the hardness of 570-630 HBW is prepared through performance regulation and control treatment, a base body of the low-alloy NM600 wear-resistant steel is nanoscale martensite, and nanoscale precipitated phases and high-density dislocation clusters are distributed in martensite laths. By optimizing chemical components and strictly controlling smelting and heat treatment processes, the wear-resistant steel has excellent wear resistance. Refining of a martensite phase and uniform distribution of a precipitated phase are achieved, and the abrasion resistance and the crack resistance of the steel are further improved. By introducing trace elements such as Nb, Ti and the like, nanoscale precipitated phases such as (NbxTiy) C, NbC, TiC and the like are formed in martensite laths, so that the strength, hardness and wear resistance of the material are greatly improved, and the service life of the steel is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy materials, and in particular relates to a low-alloy NM600 grade wear-resistant steel and a preparation method thereof. Background Art

[0002] Wear is one of the main forms of material failure, and more than one million tons of steel are consumed each year due to abrasive wear. Wear-resistant steel is a type of steel material widely used in various wear conditions, such as excavators, bulldozers, mining machinery, roadbed equipment, and dump trucks. The function of wear-resistant steel is to reduce the wear and consumption of mechanical parts, improve the life of the product, and extend the time before mechanical products fail due to wear. It is required to have a higher hardness value to ensure friction and wear resistance under harsh conditions. Low-alloy wear-resistant steel is usually alloyed with elements such as Mn, Cr, Ni, and Mo, and then a martensitic structure with higher hardness is obtained through quenching and low-temperature tempering heat treatment processes. However, the prices of alloys such as Ni and Mo are relatively high, which significantly increases the production cost of wear-resistant steel.

[0003] The high-toughness wear-resistant materials currently used in China mainly include high manganese steel, low alloy cast iron, and low alloy steel. After water toughening treatment, the surface hardness of high manganese steel is greatly improved under high impact conditions; under low impact conditions, due to the insignificant work hardening effect, a good effect cannot be achieved. Low alloy cast iron mostly enhances its hardness through carbides, that is, wear resistance is enhanced through high hardness, but the large difference in hardness between carbides and the matrix will cause cracks to form and reduce the plastic toughness of the steel. Low alloy steel produces a wear-resistant hard phase by adding a small amount of alloying elements, and the resulting steel has good wear resistance, but the difference in hardness between the hard phase and the matrix will cause cracks to form and expand, reducing the plastic toughness of the steel.

[0004] With the progress of industrial development, various types of mechanical equipment are increasingly developing in the direction of complexity, large-scale and lightweight, which puts forward higher requirements on the toughness, wear resistance and weldability of engineering machinery component materials, especially in the field of mining equipment. This also promotes the development and production of steel for engineering machinery to continuously develop towards higher strength levels and better comprehensive mechanical properties. Therefore, the development of a low-alloy ultra-high strength wear-resistant steel with good comprehensive performance and low cost is of great significance to the development of engineering machinery. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above or existing problems of low alloy NM600 grade wear-resistant steel and preparation method thereof, the present invention is proposed.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The embodiment of the present invention provides a low-alloy NM600 grade wear-resistant steel, comprising: the chemical composition and mass percentage of the wear-resistant steel are: C: 0.35% to 0.45%, Si: 0.30% to 0.80%, Mn: 0.80% to 1.30%, Cr: 0.60% to 1.10%, Nb: 0.005% to 0.020%, Ti: 0.010% to 0.030%, P≤0.010%, S: ≤0.004%, N: ≤0.0060%, B: 0.0015 to 0.0060, Als: 0.03% to 0.08%, and the remainder is Fe and unavoidable residual elements, wherein Ti / N≥4.0.

[0009] As a preferred solution of the preparation method of the low alloy NM600 grade wear-resistant steel of the present invention, the process includes: KR desulfurization and smelting; refining and continuous casting; heating and hot rolling; slow cooling and cutting; quenching and tempering; and performance control.

[0010] As a preferred solution of the preparation method of the low alloy NM600 grade wear-resistant steel of the present invention, the KR desulfurization and smelting treatment includes: adding molten iron to the KR device, using a calcium-based desulfurizer for stirring desulfurization, controlling the content of P and S, controlling the temperature of the desulfurization process at 1350-1450°C, ensuring that the sulfur content in the molten iron is reduced to ≤0.004%; using a top and bottom double-blown converter for smelting. In the smelting process, adding pre-prepared alloy elements, and controlling the temperature at 1580-1650°C, adding a deoxidizer FeSi in the middle of smelting, adding aluminum in the late stage of smelting for deep deoxidation, and adding deoxidizers aluminum, calcium and silicon calcium in the final alloying and refining stage to eliminate residual oxygen.

[0011] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the refining and continuous casting treatment includes: performing refining treatment outside the furnace in an LF furnace, degassing by argon stirring, and further removing impurities, and performing microalloying according to the requirements of the steel grade to ensure the accurate addition and distribution of trace elements Nb, Ti, and B. At the same time, Al is added to increase the Al content in the steel, and the Als content is controlled at 0.03% to 0.08%; the refined molten steel is cast into a steel billet through a continuous casting process, and the cooling rate of the billet is controlled at 1.0°C / s to 3.0°C / s during the continuous casting process to prevent center segregation and grain coarsening.

[0012] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the heating and hot rolling treatment includes: heating the steel billet in a heating furnace, and controlling the temperature at 1150-1250°C to ensure that the temperature inside and outside the steel billet is consistent to prevent rolling cracks caused by uneven temperature; hot rolling the heated steel billet, controlling the rolling temperature at 800-950°C, and adopting a multi-pass rolling process during the rolling process to ensure that the thickness and width of the steel plate meet the requirements, and the final rolling temperature is not less than 700°C to ensure uniform structure and prevent secondary phase precipitation.

[0013] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the slow cooling and cutting treatment includes: after hot rolling, cooling the rolled steel plate to room temperature to prevent deformation or cracks caused by thermal stress, and using air cooling to control the cooling process. After cooling to room temperature, the steel plate is cut into the required size to prepare for the subsequent heat treatment process.

[0014] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the quenching treatment includes: preheating the heating furnace to 860-920°C and keeping the temperature in the furnace stable; placing the steel plate in the heating furnace, and determining the furnace time t (min) = 1.4 × h + 15 according to the thickness of the steel plate, where h is the thickness of the steel plate in mm; after reaching the furnace time, immediately taking the steel plate out of the heating furnace, performing rapid water quenching, controlling the water temperature at 10-50°C, and continuously cooling until the temperature of the steel plate is consistent with the water temperature, to ensure that the steel plate is completely quenched and form a nano-scale martensitic structure.

[0015] As a preferred embodiment of the method for preparing the low alloy NM600 grade wear-resistant steel of the present invention, the tempering treatment comprises: heating the tempering furnace to 150-200°C, and after the furnace temperature stabilizes, immediately placing the quenched steel plate into the tempering furnace, and keeping the steel plate in the tempering furnace for 10-40 minutes. After tempering, the steel plate is taken out of the furnace and air-cooled to room temperature, and a stable nano-scale precipitate phase is formed during the tempering process.

[0016] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the performance control includes: the hardness of the low-alloy NM600 grade wear-resistant steel after heat treatment is controlled at 570-630 HBW, and its hardness is adjusted by quenching-tempering process, and the organizational structure is nano-scale martensite, and high-density dislocation clusters and nano-scale precipitation phases are distributed in the martensite laths.

[0017] As a preferred solution of the preparation method of the low-alloy NM600 grade wear-resistant steel described in the present invention, the performance regulation also includes: the types of nano-scale precipitation phases are (NbxTiy)C, NbC, TiC, M2.5C ​​and M3C, and their equivalent diameters are less than 60nm.

[0018] The beneficial effects of the present invention are as follows: by optimizing the chemical composition and strictly controlling the smelting and heat treatment processes, excellent wear resistance is achieved. The presence of nanoscale precipitated phases and the nanoscale martensitic structure after heat treatment effectively refine the grain structure and significantly improve the toughness and impact resistance of the material. The present invention achieves the refinement of the martensitic phase and the uniform distribution of the precipitated phase, further improving the wear resistance and crack resistance of the steel. The present invention introduces trace elements such as Nb and Ti to form nanoscale precipitated phases such as (NbxTiy)C, NbC, and TiC in the martensitic laths, thereby greatly improving the strength, hardness, and wear resistance of the material and extending the service life of the steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0020] Figure 1 A process flow chart of a method for preparing low alloy NM600 grade wear-resistant steel provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0024] Example 1

[0025] Reference Figure 1 , is an embodiment of the present invention, which provides a low alloy NM600 grade wear-resistant steel and a preparation method thereof, wherein the alloy composition of the wear-resistant steel is: C: 0.35% to 0.45%, Si: 0.30% to 0.80%, Mn: 0.80% to 1.30%, Cr: 0.60% to 1.10%, Nb: 0.005% to 0.020%, Ti: 0.010% to 0.030%, P≤0.010%, S: ≤0.004%, N: ≤0.0060%, B: 0.0015 to 0.0060, Als: 0.03% to 0.08%, the remainder being Fe and unavoidable residual elements, wherein Ti / N≥4.0 (the precise composition of the steel billet shall be subject to Table 1). The preparation process of the wear-resistant steel of this embodiment is as follows:

[0026] Steel plate preparation: The above alloy components are subjected to KR desulfurization, smelting, refining, continuous casting, heating, hot rolling, quenching, tempering and performance control to obtain a 10 mm thick steel plate.

[0027] The heat treatment process of a low alloy NM600 grade wear-resistant steel is described as follows:

[0028] (1) The slowly cooled steel plate is cut into steel plates to be heat treated.

[0029] (2) Quenching treatment: The heating furnace is heated to 880±10°C. After the temperature stabilizes, the steel plate is placed in the heating furnace. The furnace time is set to 29 minutes. After the furnace time is reached, the steel plate is immediately quenched in water at a water temperature of 25±5°C. After quenching, the steel plate is transported out.

[0030] (3) Tempering treatment: Heat the tempering furnace to 180℃±5℃. After the furnace temperature stabilizes, place the quenched steel plate in the tempering furnace immediately. Tempering time in the furnace is 15 minutes. After the tempering time is reached, the steel plate is taken out of the furnace and air-cooled.

[0031] Comparative Example 1:

[0032] The alloy composition of Comparative Example 1 is different from that of Example 1, and the microalloying elements Nb and Ti are not added. However, the preparation process and conditions of the wear-resistant steel of Comparative Example 1 are the same as those of Example 1.

[0033] The chemical composition of the steel billets obtained in Example 1 and Comparative Example 1 is shown in Table 1, the heat treatment process parameters used are shown in Table 2, and the mechanical properties after heat treatment are shown in Table 2.

[0034] Example 2

[0035] The present embodiment provides a low alloy NM600 grade wear-resistant steel and a preparation method thereof, wherein the alloy composition of the wear-resistant steel is: C: 0.35% to 0.45%, Si: 0.30% to 0.80%, Mn: 0.80% to 1.30%, Cr: 0.60% to 1.10%, Nb: 0.005% to 0.020%, Ti: 0.010% to 0.030%, P≤0.010%, S: ≤0.004%, N: ≤0.0060%, B: 0.0015 to 0.0060, Als: 0.03% to 0.08%, the remainder being Fe and unavoidable residual elements, wherein Ti / N≥4.0 (the precise composition of the steel billet shall be subject to Table 1). The preparation process of the wear-resistant steel of the present embodiment is as follows:

[0036] Steel plate preparation: The above alloy components are subjected to KR desulfurization, smelting, refining, continuous casting, heating, hot rolling, quenching, tempering and performance control to obtain a 10 mm thick steel plate.

[0037] The heat treatment process of a low alloy NM600 grade wear-resistant steel is described as follows:

[0038] (1) The slowly cooled steel plate is cut into steel plates to be heat treated.

[0039] (2) Quenching treatment: The heating furnace is heated to 900±10°C. After the temperature stabilizes, the steel plate is placed in the heating furnace. The furnace time is set to 29 minutes. After the furnace time is reached, the steel plate is immediately quenched in water at a water temperature of 25±5°C. After quenching, the steel plate is transported out.

[0040] (3) Tempering treatment: Heat the tempering furnace to 190℃±5℃. After the furnace temperature stabilizes, place the quenched steel plate in the tempering furnace immediately. Tempering time in the furnace is 15 minutes. After the tempering time is reached, the steel plate is taken out of the furnace and air-cooled.

[0041] Comparative Example 2:

[0042] The alloy composition of Comparative Example 2 is similar to that of Example 2, but Ti / N is less than 4. The preparation process of the hot-rolled steel plate and the heat-treated steel plate is the same as that of Example 2.

[0043] The chemical composition of the steel billets obtained in Example 2 and Comparative Example 2 is shown in Table 1, the heat treatment process parameters used are shown in Table 2, and the mechanical properties after heat treatment are shown in Table 2.

[0044] Example 3

[0045] The present embodiment provides a low alloy NM600 grade wear-resistant steel and a preparation method thereof, wherein the alloy composition of the wear-resistant steel is: C: 0.35% to 0.45%, Si: 0.30% to 0.80%, Mn: 0.80% to 1.30%, Cr: 0.60% to 1.10%, Nb: 0.005% to 0.020%, Ti: 0.010% to 0.030%, P≤0.010%, S: ≤0.004%, N: ≤0.0060%, B: 0.0015 to 0.0060, Als: 0.03% to 0.08%, the remainder being Fe and unavoidable residual elements, wherein Ti / N≥4.0 (the precise composition of the steel billet shall be subject to Table 1). The preparation process of the wear-resistant steel of the present embodiment is as follows:

[0046] Steel plate preparation: The above alloy components are subjected to KR desulfurization, smelting, refining, continuous casting, heating, hot rolling, quenching, tempering and performance control to obtain a 16 mm thick steel plate.

[0047] The heat treatment process of a low alloy NM600 grade wear-resistant steel is described as follows:

[0048] (1) The slowly cooled steel plate is cut into steel plates to be heat treated.

[0049] (2) Quenching treatment: Heat the heating furnace to 900±10°C. After the temperature stabilizes, place the steel plate in the heating furnace. Set the furnace time to 32 minutes. After the furnace time is reached, the steel plate is immediately quenched in water at 30±5°C. When the temperature of the steel plate is the same as the water temperature, the steel plate is transported out.

[0050] (3) Tempering treatment: Heat the tempering furnace to 200℃±5℃. After the furnace temperature stabilizes, place the quenched steel plate in the tempering furnace immediately. Tempering time in the furnace is 30 minutes. After the tempering time is reached, the steel plate is taken out of the furnace.

[0051] Comparative Example 3:

[0052] The alloy composition and hot-rolled steel plate preparation process of Comparative Example 3 are the same as those of Example 3, but the quenching and tempering process of the wear-resistant steel of Comparative Example 3 is different from that of Example 3. The quenching process of Comparative Example 3 is as follows: the heating furnace is heated to 950±10°C, and after the temperature stabilizes, the steel plate is placed in the heating furnace, and the furnace time is set to 32 minutes. After the furnace time is reached, the steel plate is immediately water quenched when it is taken out of the furnace, and the water temperature is 30±5°C. When the steel plate temperature is quenched to the same as the water temperature, the steel plate is transported out. The tempering process is as follows: the tempering furnace is heated to 350±5°C, and after the furnace temperature stabilizes, the quenched steel plate is immediately placed in the tempering furnace, and the tempering furnace time is 60 minutes. After the tempering time is reached, the steel plate is air-cooled when it is taken out of the furnace.

[0053] The chemical composition of the steel billets obtained in Example 3 and Comparative Example 3 is shown in Table 1, the heat treatment process parameters used are shown in Table 2, and the mechanical properties after heat treatment are shown in Table 2.

[0054] Table 1 Chemical composition of examples and comparative examples, wt.%

[0055]

[0056]

[0057] Table 2 Heat treatment process and mechanical properties of the embodiments and comparative examples

[0058]

[0059] Note: In Table 2, Rm is tensile strength, Re is yield strength, and A% is elongation.

[0060] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A low alloy NM600 grade wear-resistant steel, characterized in that: The chemical composition and mass percentage of the wear-resistant steel are: C: 0.35%-0.45%, Si: 0.30%-0.80%, Mn: 0.80%-1.30%, Cr: 0.60%-1.10%, Nb: 0.005%-0.020%, Ti: 0.010%-0.030%, P≤0.010%, S: ≤0.004%, N: ≤0.0060%, B: 0.0015-0.0060, Als: 0.03%-0.08%, and the remainder is Fe and unavoidable residual elements, wherein Ti / N≥4.

0.

2. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 1, characterized in that: include: KR desulfurization and smelting treatment; Refining and continuous casting processing; Heating and hot rolling treatment; Slow cooling and cutting process; Quenching and tempering treatment; Performance control processing.

3. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The KR desulfurization and smelting process includes: Add molten iron to the KR device and use calcium-based desulfurizer for stirring desulfurization to control the content of P and S. The temperature of the desulfurization process is controlled at 1350-1450℃ to ensure that the sulfur content in the molten iron is reduced to ≤0.004%; The smelting is carried out in a top and bottom combined blowing converter. During the smelting process, pre-mixed alloy elements are added and the temperature is controlled at 1580-1650°C. Deoxidizer FeSi is added in the middle stage of smelting, and aluminum is added in the later stage of smelting for deep deoxidation. Deoxidizers aluminum, calcium and silicon calcium are added in the final alloying and refining stages to eliminate residual oxygen.

4. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The refining and continuous casting process comprises: In the LF furnace, the steel is refined outside the furnace, degassed by argon stirring, and further impurities are removed. According to the requirements of the steel grade, microalloying is performed to ensure the precise addition and distribution of trace elements such as Nb, Ti, and B. At the same time, Al is added to increase the Al content in the steel, and the Als content is controlled at 0.03% to 0.08%; The refined molten steel is cast into steel billets through a continuous casting process. During the continuous casting process, the cooling rate of the billet is controlled at 1.0°C / s to 3.0°C / s to prevent center segregation and grain coarsening.

5. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The heating and hot rolling treatment comprises: The billet is heated in a heating furnace and the temperature is controlled at 1150-1250℃ to ensure that the temperature inside and outside the billet is consistent to prevent rolling cracks caused by uneven temperature; The heated steel billet is hot rolled, and the rolling temperature is controlled at 800-950℃. A multi-pass rolling process is adopted during the rolling process to ensure that the thickness and width of the steel plate meet the requirements. The final rolling temperature is not lower than 700℃ to ensure uniform structure and prevent secondary phase precipitation.

6. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The slow cooling and cutting process comprises: After hot rolling, the rolled steel plate is cooled to room temperature to prevent deformation or cracks caused by thermal stress. Air cooling is used to control the cooling process. After cooling to room temperature, the steel plate is cut into the required size and prepared for the subsequent heat treatment process.

7. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The quenching treatment comprises: Preheat the heating furnace to 860-920°C and keep the temperature inside the furnace stable; Put the steel plate into the heating furnace, and determine the furnace time t (min) = 1.4 × h + 15 according to the thickness of the steel plate, where h is the thickness of the steel plate in mm; After reaching the furnace time, the steel plate is immediately taken out of the heating furnace and quickly quenched in water. The water temperature is controlled at 10-50°C and continuously cooled until the temperature of the steel plate is consistent with the water temperature to ensure complete quenching of the steel plate and form a nano-scale martensitic structure.

8. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The tempering treatment comprises: The tempering furnace is heated to 150-200°C. After the furnace temperature stabilizes, the quenched steel plate is immediately placed in the tempering furnace. The steel plate is kept in the tempering furnace for 10-40 minutes. After tempering, the steel plate is taken out of the furnace and air-cooled to room temperature. A stable nano-scale precipitate phase is formed during the tempering process.

9. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 2, characterized in that: The performance control includes: The hardness of the low alloy NM600 grade wear-resistant steel after heat treatment is controlled at 570-630 HBW, and its hardness is adjusted through quenching-tempering process. The microstructure is nano-scale martensite, and high-density dislocation clusters and nano-scale precipitation phases are distributed in the martensite laths.

10. The method for preparing low alloy NM600 grade wear-resistant steel according to claim 9, characterized in that: The performance control further includes: The types of the nanoscale precipitated phases are (NbxTiy)C, NbC, TiC, M2.5C ​​and M3C, and their equivalent diameters are less than 60nm.

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