A method for producing high-strength and low-surface-hardness steel plates

Abstract

The invention discloses a method for producing a high-strength and low-surface-hardness steel plate, comprising rolling, normalizing and two tempering processes; wherein the normalizing process comprises a normalizing temperature of 910 to 930°C, a steel plate holding time of 1.2 min / mm to 1.5 min / mm, water cooling after exiting the furnace, a water cooling water pressure of ≤0.25 MPa, and a steel plate red-returning temperature of 250-300°C. The steel plate produced by the method of the invention has a yield strength of ≥450 MPa, a tensile strength of 570 to 650 MPa, an elongation of ≥20%, an average impact energy of 1 / 4 at 20°C of more than 100 J, a steel plate surface hardness HBW ≤192, a steel plate with matching strength and toughness and a low hardness, which is conducive to subsequent chip processing.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a production method of a high-strength and low-surface-hardness steel plate. Background Art

[0002] When steel is cooled quickly from high temperature, the carbon and nitrogen in ferrite are supersaturated, and it can slowly form iron carbonitride at room temperature, so the strength and hardness of the steel are improved, while the plasticity and toughness are reduced, especially the increase in the surface hardness of the steel plate is particularly obvious. Some key equipment materials require high strength, good plasticity and toughness, improved cutting processability, elimination of residual stress, and reduction of crack tendency caused by processing deformation. These high technologies have relatively strict requirements on the surface hardness of the steel plate. It is necessary to reduce the surface hardness of the steel plate while ensuring high strength and high plasticity and toughness to solve the problems existing in the subsequent processing of the steel plate. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for producing a high-strength and low-surface-hardness steel plate, wherein the steel plate produced by the method has matched strength and toughness and has relatively low hardness.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0005] A method for producing a high-strength and low-surface-hardness steel plate comprises rolling, normalizing and two tempering processes; wherein in the normalizing process, the normalizing temperature is 910-930°C, the steel plate is kept warm for 1.2 min / mm-1.5 min / mm, the steel plate is water-cooled after leaving the furnace, the water-cooling pressure is ≤0.25 MPa, and the steel plate is returned to red temperature at 250-300°C.

[0006] The production method of the present invention, wherein, in the rolling process, the steel thickness is ≥2H~2.5H, the starting rolling temperature of the II stage is 830℃-850℃, the final rolling temperature is 800℃-820℃, and the steel is put into water after rolling, and the red return temperature is controlled at 600℃-650℃.

[0007] The production method of the present invention, wherein the two tempering processes, the first stage tempering 640 ~ 660 ° C, heat preservation 2 ~ 2.5min / mm; the second stage tempering 610 ~ 630 ° C, heat preservation 2.5 ~ 3min / mm.

[0008] The present invention adopts two tempering treatments. The first tempering deepens the recovery degree of the non-uniform structure, reduces the dislocation density in the matrix, enhances the softening effect, and achieves a balanced state of properties such as strength, hardness, and plastic toughness; the second tempering further softens the equilibrium structure after the first tempering, avoiding the steel plate softening at high temperature for a long time, which causes the strength of the steel plate to drop sharply and fail to meet the order requirements.

[0009] The chemical composition of the steel plate of the present invention and their mass percentages are: C 0.14%-0.16%, Si 0.25%-0.35%, Mn 1.55%-1.65%, Cr 0.20%-0.25%, Nb 0.025%-0.035%, V 0.075%-0.085%, Alt 0.20%-0.40%, and the balance is Fe and unavoidable impurities.

[0010] The thickness of the steel plate of the present invention is 45 to 50 mm.

[0011] The steel plate produced by the method of the present invention has a yield strength of ≥450MPa, a tensile strength of 570-650MPa, an elongation of ≥20%, an average impact energy of more than 100J at -20°C at 1 / 4, and a surface hardness of HBW≤192; the steel plate has matched strength and toughness and a low hardness, which is conducive to subsequent chip processing.

[0012] The method of the invention is easy to operate, only the production process is innovated, the equipment investment is not increased, and the production cost is low. DETAILED DESCRIPTION

[0013] The present invention is described in detail below by way of examples.

[0014] The invention provides a production method of a high-strength and low-surface-hardness steel plate, comprising rolling, normalizing and two tempering processes.

[0015] In the rolling process, the steel thickness is ≥2H~2.5H, the starting rolling temperature of stage II is 830℃-850℃, the final rolling temperature is 800℃-820℃, and the steel is put into water after rolling, and the temperature returning to red is controlled at 600℃-650℃.

[0016] In the normalizing process, the normalizing temperature is 910-930°C, the steel plate insulation time is 1.2min / mm-1.5min / mm, the steel plate is water-cooled after leaving the furnace, the water cooling pressure is ≤0.25MPa, and the steel plate red-returning temperature is 250-300°C.

[0017] The two tempering processes include tempering at 640-660°C in the first stage and keeping warm for 2-2.5 min / mm; and tempering at 610-630°C in the second stage and keeping warm for 2.5-3 min / mm.

[0018] The chemical composition of the steel plate and its mass percentage are: C 0.14%-0.16%, Si 0.25%-0.35%, Mn 1.55%-1.65%, Cr 0.20%-0.25%, Nb 0.025%-0.035%, V 0.075%-0.085%, Alt 0.20%-0.40%, and the balance is Fe and unavoidable impurities.

[0019] The thickness of the steel plate is 45 to 50 mm.

[0020] The present invention will be further described in detail below in conjunction with specific embodiments.

[0021] Examples 1-8

[0022] The thickness and composition of the finished steel plates of each embodiment are shown in Table 1.

[0023] Table 1 Thickness and composition of steel plates in various examples (wt %)

[0024]

[0025] The rolling process parameters of the steel plates in each embodiment are shown in Table 2, and the normalizing and tempering process parameters are shown in Table 3.

[0026] Table 2 Steel plate rolling process parameters of each embodiment

[0027]

[0028] Table 3 Normalizing and tempering process parameters of steel plates in various examples

[0029]

[0030] The properties of the steel plates of various embodiments are shown in Table 4.

[0031] Table 4 Properties of steel plates in various examples

[0032]

[0033] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing a high-strength and low-surface-hardness steel plate, characterized in that: It includes rolling, normalizing and two tempering processes; wherein the normalizing process, the normalizing temperature is 910-930°C, the steel plate insulation time is 1.2min / mm-1.5min / mm, the furnace is water-cooled, the water cooling pressure is ≤0.25MPa, and the steel plate red-returning temperature is 250-300°C; The two tempering processes include tempering at 640-660°C in the first stage and keeping warm for 2-2.5 min / mm; tempering at 610-630°C in the second stage and keeping warm for 2.5-3 min / mm; The chemical composition of the steel plate and its mass percentage are: C 0.14% to 0.16%, Si 0.25% to 0.35%, Mn 1.55% to 1.65%, Cr 0.20% to 0.25%, Nb 0.025% to 0.035%, V 0.075% to 0.085%, Alt 0.20% to 0.40%, and the balance is Fe and unavoidable impurities; In the rolling process, the starting rolling temperature in stage II is 830°C-850°C, the final rolling temperature is 800°C-820°C, and the steel is put into water after rolling, and the temperature of the steel returning to red is controlled at 600°C-650°C; The steel plate produced by the method has a yield strength of ≥450MPa, a tensile strength of 570-650MPa, an elongation of ≥20%, an average impact energy of more than 100J at -20°C at 1 / 4, and a surface hardness of the steel plate HBW≤192.

2. The method for producing a high-strength and low-surface-hardness steel plate according to claim 1, characterized in that: The thickness of the steel plate is 45 to 50 mm.

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