2000MPa-grade high-strength tool and die steel

Abstract

The invention discloses 2000MPa-grade high-strength tool and die steel, and belongs to the technical field of tool and die steel. The 2000MPa-grade high-strength tool and die steel is prepared from the following elements in percentage by weight: 0.77 to 0.90 percent of C (carbon), 0.02 to 0.05 percent of Nb (niobium), 0.2 to 0.5 percent of Si (silicon), 0.4 to 0.8 percent of Mn (manganese) and the balance of Fe (iron) and inevitable impurities. The 2000MPa-grade high-strength tool and die steel is obtained by smelting, casting, homogenizing, rolling, cooling, quenching and tempering raw materials of the 2000MPa-grade high-strength tool and die steel. According to the high-strength tool and die steel and the preparation method thereof, a synergistic effect is achieved by optimizing the preparation process of the microalloyed high-strength tool and die steel and regulating and controlling chemical elements of the high-strength tool and die steel, a trace amount of Nb is added to replace part of alloy elements, the cost is reduced, meanwhile, the plasticity and toughness are guaranteed, the strength and hardness are improved, and the hardness of the prepared high-strength tool and die steel is larger than or equal to 640 HV; the tensile strength is not less than 2100MPa, and the ductility is not less than 10%.

Description

Technical Field

[0001] The present invention belongs to the technical field of tool steel, and in particular relates to a 2000MPa grade high-strength tool steel. Background Art

[0002] Tool and die steel (tool and die steel) is a specialized steel used to manufacture tools, molds, and mechanical components. It is the foundation of the moldmaking industry, and its selection plays a crucial role in mold design and manufacturing within the moldmaking industry. Its properties include high hardness, high wear resistance, high strength, and good toughness. Tool steel is widely used in industries such as automotive, aerospace, and radio instrumentation. With advancements in the moldmaking industry and the widespread application of tool steel, research on how to improve its performance has become increasingly important. Appropriate heat treatment processes and the appropriate addition of alloying elements can improve the performance of tool steel.

[0003] Chinese patent application CN112322868A discloses a method for preparing high-alloy tool steel. This method uses a secondary tempering heat treatment to eliminate retained austenite and newly formed martensite in the steel structure, generating tempered bainite with improved mechanical properties. This method effectively improves the mechanical properties of the tool steel. However, due to its low carbon content, the steel can only be enhanced in strength and hardness by combining multiple alloying elements, such as Mo, Cr, Ni, V, and Cu, significantly increasing production costs.

[0004] Chinese patent CN103938091B discloses a high-toughness, high-wear-resistant cold-work die steel. By controlling the C / Cr ratio, it achieves both high toughness and wear resistance. However, the addition of various alloying elements, such as Cr, V, and Nb, increases production costs. Furthermore, the high carbon content and the presence of multiple alloying elements result in less than ideal interactions between the alloying elements, resulting in a low hardness value after quenching and tempering, ≤760 HV.

[0005] Chinese patent application CN116970868A discloses a high-strength and high-wear-resistant alloy tool steel. Through composition design, process flow and control of key parameters, it can ensure stable steel composition, uniform macrostructure and high cleanliness. The processed product meets the requirements of high strength and high wear resistance. However, it contains multiple alloying elements such as Cr, Ni, V, Al, etc., which greatly increases production costs.

[0006] In summary, existing tool steels generally use a multi-alloying approach to improve steel properties, but this also results in higher costs and less than ideal performance gains. Therefore, exploring micro-alloying technology and heat treatment processes to improve tool steel properties is crucial. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention provides a 2000MPa-grade high-strength tool steel. By utilizing the synergistic effects of the composition and preparation method of the 2000MPa-grade high-strength tool steel, the present invention adds only the trace element Nb. This combined preparation method reduces costs while significantly improving hardness, tensile strength, and elongation.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A 2000 MPa grade high-strength tool steel comprising the following elements in weight percentage: C: 0.77-0.90 wt.%, Nb: 0.02-0.05 wt.%, Si: 0.2-0.5 wt.%, Mn: 0.4-0.8 wt.%, and the remainder being Fe and unavoidable impurities;

[0010] The preparation method of the 2000MPa grade high-strength tool steel comprises the following steps:

[0011] (1) smelting and casting 2000MPa grade high strength tool steel raw materials to obtain continuous casting billets;

[0012] (2) homogenizing the continuous casting billet;

[0013] (3) then rolling and cooling to room temperature to obtain the tool steel plate;

[0014] (4) heating the tool steel plate to the quenching temperature and keeping it warm, then quenching and cooling it to room temperature;

[0015] (5) The quenched tool steel plate is heated to the tempering temperature and kept warm, and then cooled to room temperature to obtain a 2000 MPa grade high-strength tool steel material.

[0016] More preferably, the 2000 MPa-grade high-strength tool steel comprises the following elements in percentage by weight: C: 0.77-0.86 wt.%, Nb: 0.045 wt.%, Si: 0.2-0.4 wt.%, Mn: 0.4-0.6 wt.%, with the remainder being Fe and unavoidable impurities. The elements in the 2000 MPa-grade high-strength tool steel are within the aforementioned defined ranges. The high-strength tool steel produced using the method of the present invention has a hardness ≥ 645 HV, a tensile strength ≥ 2100 MPa, and an elongation ≥ 10.5%.

[0017] As a preferred embodiment of the present invention, the temperature of the homogenization treatment is 1200° C. and the time is 0.5-2 hours, so that the composition of the steel is more uniform.

[0018] As a preferred embodiment of the present invention, the starting rolling temperature is 1000-1050° C., the finishing rolling temperature is 700-760° C., the rolling is performed in multiple passes, and the deformation is 70-90%.

[0019] As a preferred embodiment of the present invention, in the step (4), the quenching temperature is 1000-1150°C, the holding time is 0.5-2h, and the quenching cooling rate is above 50°C / s.

[0020] As a preferred embodiment of the present invention, in step (5), the tempering temperature is 270-320° C., and the holding time is 0.5-2 h.

[0021] As a preferred embodiment of the present invention, the microstructure of the 2000 MPa grade high strength tool steel includes tempered martensite, massive retained austenite and carbide particles.

[0022] As a preferred embodiment of the present invention, the 2000 MPa grade high strength tool steel has a hardness of ≥640 HV, a tensile strength of ≥2100 MPa, and an elongation of ≥10%.

[0023] Compared with the prior art, the present invention has the following beneficial effects: the present invention synergistically optimizes the preparation process of micro-alloyed high-strength tool steel and regulates the chemical elements of high-strength tool steel, and adds a trace amount of Nb to replace part of the alloying elements, which can reduce costs, ensure hardness and strength while improving plasticity and toughness, and achieve the prepared high-strength tool steel with a hardness of ≥640HV, a tensile strength of ≥2100MPa, and an elongation of ≥10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the 2000MPa grade high-strength tool steel prepared in Example 1.

[0025] Figure 2 This is the SEM image of the high-strength tool steel prepared in Comparative Example 1. DETAILED DESCRIPTION

[0026] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0027] Example 1

[0028] The chemical elements of a 2000 MPa grade high-strength tool steel are as follows by mass percentage: C: 0.86 wt.%, Nb: 0.045 wt.%, Si: 0.4 wt.%, Mn: 0.6 wt.%, and the remainder is Fe and unavoidable impurities.

[0029] A method for preparing 2000MPa grade high-strength tool steel comprises the following steps:

[0030] S1. Smelting and casting process

[0031] The raw materials are weighed, mixed, and smelted according to the chemical composition mass percentage of the 2000 MPa grade high-strength tool steel. After smelting, the steel is cast and forged into a steel billet having a size of 50 mm×100 mm×170 mm.

[0032] S2. Homogenization process

[0033] The continuous casting billet in step S1 is subjected to a heating homogenization treatment, with a heating temperature of 1200° C. and a holding time of 1 hour, and the microstructure is austenite.

[0034] S3. Rolling process

[0035] The continuous casting billet after the heating and homogenization treatment in step S2 is air-cooled to the start rolling temperature, and then subjected to multiple rolling passes with the start rolling temperature being 1050° C. and the final rolling temperature being 760° C. to obtain 2000 MPa grade high strength tool steel plate.

[0036] S4. Cooling process

[0037] The 2000 MPa grade high strength tool steel plate in step S3 is air-cooled to room temperature.

[0038] S5. Quenching process

[0039] The 2000 MPa grade high strength tool steel plate after air cooling in step S4 is heated to a quenching temperature of 1100° C. and kept at this temperature for 0.5 h, and then quenched, with the cooling rate controlled at above 50° C. / s, and cooled to room temperature.

[0040] S6, tempering process

[0041] The 2000 MPa grade high strength tool steel plate after quenching in step S5 is heated to a tempering temperature of 300° C. and kept at this temperature for 0.5 h, and then air-cooled to room temperature, thereby finally obtaining a 2000 MPa grade high strength tool steel material.

[0042] The microstructure of the 2000MPa grade high strength tool steel prepared in this example is as follows: Figure 1 As shown, the structure is tempered martensite, a small amount of massive retained austenite and carbide particles. Figure 1 The transformation degree of martensite in the steel is greater than that in comparative example 1, and the amount of retained austenite is small and finer. Example 1 shows higher strength and hardness levels than comparative example 1.

[0043] The 2000MPa grade high strength tool steel has a hardness of ≥760HV, a tensile strength of ≥2470MPa, and an elongation of ≥10.73%.

[0044] Example 2

[0045] The chemical elements of a 2000 MPa grade high-strength tool steel are as follows by mass percentage: C: 0.77 wt.%, Nb: 0.045 wt.%, Si: 0.2 wt.%, Mn: 0.4 wt.%, and the remainder is Fe and unavoidable impurities.

[0046] A method for preparing 2000MPa grade high-strength tool steel comprises the following steps:

[0047] S1. Smelting and casting process

[0048] The raw materials are weighed, mixed, and smelted according to the chemical composition mass percentage of the 2000 MPa grade high-strength tool steel. After smelting, the steel is cast and forged into a steel billet having a size of 50 mm×100 mm×170 mm.

[0049] S2. Homogenization process

[0050] The continuous casting billet in step S1 is subjected to a heating homogenization treatment, with a heating temperature of 1200° C. and a holding time of 1 hour, and the microstructure is austenite.

[0051] S3. Rolling process

[0052] The continuous casting billet after the heating and homogenization treatment in step S2 is air-cooled to the start rolling temperature, and then subjected to multiple rolling passes with the start rolling temperature being 1050° C. and the final rolling temperature being 760° C. to obtain 2000 MPa grade high strength tool steel plate.

[0053] S4. Cooling process

[0054] The 2000 MPa grade high strength tool steel plate in step S3 is air-cooled to room temperature.

[0055] S5. Quenching process

[0056] The 2000 MPa grade high strength tool steel plate after air cooling in step S4 is heated to a quenching temperature of 1100° C. and kept at this temperature for 0.5 h, and then quenched, with the cooling rate controlled at above 50° C. / s, and cooled to room temperature.

[0057] S6, tempering process

[0058] The 2000 MPa grade high strength tool steel plate after quenching in step S5 is heated to a tempering temperature of 300° C. and kept at this temperature for 0.5 h, and then air-cooled to room temperature, thereby finally obtaining a 2000 MPa grade high strength tool steel material.

[0059] The microstructure of the 2000 MPa grade high strength tool steel prepared in this example is tempered martensite, a small amount of massive retained austenite and carbide particles.

[0060] The 2000MPa grade high strength tool steel has a hardness of ≥647HV, a tensile strength of ≥2100MPa, and an elongation of ≥11%.

[0061] Comparative Example 1

[0062] The chemical elements of a high-strength tool steel are as follows by mass percentage: C: 0.86 wt.%, Si: 0.4 wt.%, Mn: 0.6 wt.%, and the remainder is Fe and unavoidable impurities.

[0063] A method for preparing 2000MPa grade high-strength tool steel comprises the following steps:

[0064] S1. Smelting and casting process

[0065] The raw materials are weighed, mixed, and smelted according to the mass percentage of the chemical composition of the high-strength tool steel. After smelting, the steel billets are cast and forged into 50 mm×100 mm×170 mm billets.

[0066] S2. Homogenization process

[0067] The continuous casting billet in step S1 is subjected to a heating homogenization treatment, with a heating temperature of 1200° C. and a holding time of 1 hour, and the microstructure is austenite.

[0068] S3. Rolling process

[0069] The continuous casting billet after the heating and homogenization treatment in step S2 is air-cooled to the start rolling temperature, and then subjected to multiple rolling passes with the start rolling temperature being 1050° C. and the final rolling temperature being 760° C. to obtain a high-strength tool steel plate.

[0070] S4. Cooling process

[0071] The high-strength tool steel plate in step S3 is air-cooled to room temperature.

[0072] S5. Quenching process

[0073] The high-strength tool steel plate after air cooling in step S4 is heated to a quenching temperature of 1100° C. and kept at this temperature for 0.5 h, and then quenched, with the cooling rate controlled at above 50° C. / s, and cooled to room temperature.

[0074] S6, tempering process

[0075] The high-strength tool steel plate after quenching in step S5 is heated to a tempering temperature of 300° C. and kept at this temperature for 0.5 h, and then air-cooled to room temperature, thereby finally obtaining a high-strength tool steel material.

[0076] The microstructure of the high strength tool steel prepared in this comparative example is as follows: Figure 2 As shown, the structure is tempered martensite and a small amount of massive retained austenite.

[0077] The 2000MPa grade high strength tool steel has a hardness of ≥589HV, a tensile strength of ≥1982MPa, and an elongation of ≥3.74%.

[0078] Finally, 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 scope of protection of the present invention. Although the present invention has been described in detail with reference to 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 essence and scope of the technical solutions of the present invention.

Claims

1. A 2000MPa grade high strength tool steel, characterized in that: The composition comprises the following elements in percentage by weight: C: 0.77-0.90 wt.%, Nb: 0.02-0.05 wt.%, Si: 0.2-0.5 wt.%, Mn: 0.4-0.8 wt.%, and the remainder is Fe and unavoidable impurities; The preparation method of the 2000MPa grade high-strength tool steel comprises the following steps: (1) smelting and casting 2000MPa grade high strength tool steel raw materials to obtain continuous casting billets; (2) homogenizing the continuous casting billet; (3) then rolling and cooling to room temperature to obtain the tool steel plate; (4) heating the tool steel plate to the quenching temperature and keeping it warm, then quenching and cooling it to room temperature; (5) The quenched tool steel plate is heated to the tempering temperature and kept warm, and then cooled to room temperature to obtain a 2000 MPa grade high-strength tool steel material.

2. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: The temperature of the homogenization treatment is 1200° C. and the time is 0.5-2 hours.

3. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: The starting rolling temperature of the rolling is 1000-1050° C., the finishing rolling temperature is 700-760° C., the rolling is performed in multiple passes, and the deformation amount is 70-90%.

4. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: In the step (4), the quenching temperature is 1000-1150° C., the holding time is 0.5-2 h, and the quenching cooling rate is above 50° C. / s.

5. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: In the step (5), the quenching temperature is 270-320° C., and the holding time is 0.5-2 h.

6. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: The microstructure of the 2000 MPa grade high strength tool steel includes tempered martensite, retained austenite and carbide particles.

7. The 2000MPa grade high strength tool steel according to claim 1, characterized in that: The 2000MPa grade high strength tool steel has a hardness of ≥640HV, a tensile strength of ≥2100MPa, and an elongation of ≥10%.

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