A high-toughness wear-resistant medium-thick steel plate suitable for use in -40°C environment and a production method thereof

Abstract

A high-toughness wear-resistant medium-thick steel plate suitable for use in an environment of ‑40°C, wherein the components and weight percentage contents thereof are: C: 0.17-0.25%, Mn: 1.7-2.1%, P≤0.020%, S≤0.010%, Als: 0.03-0.06%, Ti: 0.010-0.02%, Si not exceeding 0.17%, Cr not exceeding 0.6%, B not exceeding 0.0003%, or a composite of two or more thereof in any proportion; production method: conventional smelting and casting into billets; hot rolling after heating the billets; continuous uncoiling and quenching after coiling; high-speed cooling; tempering after cross-cutting to a fixed length; and natural cooling to room temperature. The invention provides a steel plate with a width of 2000-2100 mm, a thickness of 15-25 mm, a product yield strength of not less than 1140 MPa, a tensile strength of not less than 1260 MPa, and an elongation of not less than 10%, an impact energy of not less than 40 J at -40°C, and simple components.

Description

Technical Field

[0001] The invention relates to wear-resistant steel for mechanical engineering and a production method thereof, in particular to a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment and a production method thereof. Background Art

[0002] Low-alloy high-strength wear-resistant steel is widely used in mechanical equipment such as metallurgy, mining, building materials, railways, electricity, coal, etc. The use environment is harsh, and the quality requirements for strength, toughness, hardness and wear resistance are increasing day by day. In particular, low-temperature toughness has a far-reaching impact on the risk of cracking during the application process. Traditional thin-gauge wear-resistant steel is optimized through rolling and cooling processes. The lower coiling temperature is conducive to refining the microstructure, thereby improving low-temperature toughness. However, with the increase in thickness, at a lower coiling temperature, the strength of thick-gauge steel coils poses a greater challenge to coiling and cross-cutting equipment. Therefore, for hot-rolled thick-gauge wear-resistant steel, in order to ensure equipment safety, its coiling temperature is usually high, the original grains are coarse, and the low-temperature toughness of -40°C can only reach 10 to 20J, which is difficult to meet the application requirements of low-temperature environments.

[0003] The document with Chinese patent publication number CN102605234A discloses "A wear-resistant steel plate and its manufacturing method", whose weight percentage is: C: 0.08-0.24%, Si: 0.10-0.30%, Mn: 0.70-1.70%, P: ≤0.050%, S: ≤0.030%, Cr: ≤1.00%, Mo: ≤0.60%, Al: 0.01-0.10%, B: 0.0005-0.0040%, Ti: 0.005-0.06%, and meets: 0.15≤Cr+Mo≤1.20%, 0.011%≤Al+Ti≤0.15%, and the balance is Fe and unavoidable impurities. It is produced by casting-controlled rolling-quenching and tempering heat treatment process. Although it has excellent performance, it can only be used to manufacture easily worn equipment in engineering machinery. Higher strength will deteriorate low-temperature toughness. At -40℃, it is generally around 20J, which cannot meet the low-temperature environment of -40℃ and is prone to cracking.

[0004] Since wear-resistant steel mainly uses organizational strengthening to ensure its organization and performance, the martensite has high strength and the original austenite grains are coarse after quenching, resulting in the strength of wear-resistant steel usually reaching 1200MPa to 1400MPa level, but the toughness after low-temperature tempering is poor, and it is difficult to meet both strength and toughness at the same time. Summary of the invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment and a production method thereof, which is produced by CSP and has simple components and is suitable for use in a -40°C environment, under the premise that the steel plate width is 2000-2100 mm, the thickness is 15-25 mm, the yield strength of the product is not less than 1140 MPa, the tensile strength is not less than 1260 MPa, the elongation is not less than 10%, the impact energy at -40°C is not less than 40 J, and the components are simple.

[0006] Measures to achieve the above objectives:

[0007] A high-toughness wear-resistant medium-thick steel plate suitable for use in an environment of -40°C, wherein the components and weight percentage contents are: C: 0.17-0.25%, Mn: 1.7-2.1%, P≤0.020%, S≤0.010%, Als: 0.03-0.06%, Ti: 0.010-0.02%, Si not exceeding 0.17%, Cr not exceeding 0.6%, B not exceeding 0.0003%, or a composite of two or more thereof in any proportion, and the remainder being Fe and unavoidable impurities.

[0008] Preferably, the weight percentage of Mn is 1.75-1.90%.

[0009] A method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment, comprising the following steps:

[0010] 1) Conventional smelting and casting into billets, during which, during the smelting process, rare earth is added at a rate of 0.05 to 0.15 kg / ton of steel to modify the inclusions;

[0011] 2) Heat the ingot, control the heating temperature of the ingot to be between 1180 and 1230°C, and control the heating time in the high temperature section to be no less than 60 minutes;

[0012] 3) Performing rough rolling: controlling the reduction rate of at least one of the first three passes to be not less than 20%, and controlling the slab thickness to be 40-80 mm at the end of rough rolling;

[0013] 4) Finish rolling, control the final rolling temperature FT7 at 780-820°C, control the total cumulative reduction rate to be no less than 60%, and the cumulative reduction rate of the last three passes to be no less than 40%;

[0014] 5) Coil the steel sheet and control the coiling temperature CT at 700-750°C;

[0015] 6) Continuously unwind and quench, control the quenching temperature at 790-830°C, and control the quenching time at 5-10 minutes;

[0016] 7) After cutting to a fixed length, tempering is performed, and the tempering temperature is controlled at 150-200°C and the tempering time is 10-30 minutes;

[0017] 8) Cool naturally to room temperature.

[0018] Preferably, the final rolling temperature FT7 is between 785 and 815°C.

[0019] Preferably, the coiling temperature CT is between 708 and 723°C.

[0020] Preferably, the quenching temperature is between 796°C and 823°C.

[0021] Preferably, the tempering temperature is between 156 and 194°C.

[0022] Functions and mechanisms of each element and main process in the present invention

[0023] C: C is the cheapest element to improve material strength. As the carbon content increases, hardness and strength increase, but plasticity, toughness and welding performance decrease. Taking all factors into consideration, the C weight percentage is 0.17-0.25%;

[0024] Mn: Mn significantly reduces Ar1 temperature and austenite decomposition rate, improves the stability of supercooled austenite, promotes stress release of austenite, increases the residual austenite content in the final structure, and improves cold bending performance. However, if the Mn content is too high, it will increase temper brittleness and cause serious center segregation. Taking all factors into consideration, the Mn weight percentage should be 0.5-2%.

[0025] Als: Als can deoxidize steel, reduce inclusion content, and also play a role in grain refinement. Taking all factors into consideration, Als is between 0.03 and 0.06%.

[0026] Ti: Ti has a strong affinity with C and N in steel, forming a stable Ti(C, N) compound, which can be induced to precipitate during controlled rolling, effectively preventing recrystallization, and has a significant effect on precipitation and grain refinement. Considering all factors, the Ti weight percentage is preferably 0.010-0.020%;

[0027] The reason why the present invention adds Si not exceeding 0.17% or Cr not exceeding 0.6% or B not exceeding 0.0003% or a composite of two or more thereof in any proportion is that Si can reduce the diffusion rate of carbon in ferrite, promote the formation of ferrite, and also deteriorate the surface quality; Cr can improve hardenability, and can also improve tempering stability, and reduce the cooling rate of obtaining martensite, but too high Cr reduces processability and weldability; B can greatly improve hardenability, but when B is too much, it is easy to enrich at the grain boundary, which will reduce the grain boundary binding energy, making the steel plate more inclined to fracture along the grain when subjected to impact load, and reducing the low-temperature impact work of the steel plate. Therefore, the addition amount of B in the present invention is ≤0.0003%.

[0028] P, S: P and S are harmful impurity elements in steel. P in steel is easy to form segregation in steel, reducing the toughness and welding performance of steel. S is easy to form plastic sulfide, causing stratification of steel plate and deteriorating the performance of steel plate. Therefore, the lower the P and S content, the better. Taking comprehensive consideration, the P and S content of steel is P≤0.020%, S≤0.010%.

[0029] The reason why the final rolling temperature FT7 is controlled at 780-820°C, preferably at 785-815°C, is that when the final rolling temperature is high, it is easy to cause coarse grains, and when the final rolling temperature is low, it is beneficial to grain refinement during the rolling process. When the final rolling temperature is lower than 780°C, it is easy to cause mixed crystals, affecting the final structure and performance.

[0030] The reason why the coiling temperature CT is controlled at 708-723°C, preferably at 708-723°C, is that the thickness of the steel coil is relatively thin. When the coiling temperature is lower than 708°C, it is difficult to resist thermal stress, which deteriorates the shape of the steel plate and the coil. When the coiling temperature is higher than 723°C, the cooling rate in the cooling stage is insufficient, the austenite grains are coarse, and the performance of the finished product is also adversely affected.

[0031] The reason why the quenching temperature is controlled at 790-830°C in the present invention, preferably at 796-823°C, is that when the quenching temperature is lower than 796°C, the steel plate cannot be completely austenitized, and a mixed crystal structure will appear in the steel plate, affecting the uniformity of the structure and performance of the finished steel plate. When the quenching temperature is higher than 823°C, the original austenite grains are coarse, and after transforming into martensite, the lath size is large and the toughness is seriously affected.

[0032] The reason why the tempering temperature is controlled at 150-200°C, preferably at 156-194°C, is that when the tempering temperature is lower than 156°C, the tempering effect is poor, and the ability to improve the plate shape and internal stress is weak. When the tempering temperature is higher than 194°C, the supersaturated carbon in the martensite is easy to precipitate, the solid solubility decreases, the strength and hardness are greatly affected, and the risk of performance mismatch is greater.

[0033] Compared with the prior art, the present invention has the advantages that the steel plate has a width of 2000-2100 mm, a thickness of 15-25 mm, and the yield strength of the product is not less than 1140 MPa, the tensile strength is not less than 1260 MPa, and the elongation is not less than 10%, and the impact energy at -40°C is not less than 40 J, so that the steel plate will not crack when used in a low temperature environment; the problem that the traditional hot rolling production line is difficult to coil and cross-cut is solved; under the condition of high-temperature coiling, the plate shape quality of the hot-rolled coil is significantly improved; and the components are simple. DETAILED DESCRIPTION

[0034] The present invention is described in detail below:

[0035] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0036] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0037] Table 3 is a table of performance test results of various embodiments and comparative examples of the present invention.

[0038] Each embodiment of the present invention is produced according to the following steps

[0039] 1) Conventional smelting and casting into billets, during which, during the smelting process, rare earth is added at a rate of 0.05 to 0.15 kg / ton of steel to modify the inclusions;

[0040] 2) Heat the ingot, control the heating temperature of the ingot to be between 1180 and 1230°C, and control the heating time in the high temperature section to be no less than 60 minutes;

[0041] 3) Performing rough rolling: controlling the reduction rate of at least one of the first three passes to be not less than 20%, and controlling the slab thickness to be 40-80 mm at the end of rough rolling;

[0042] 4) Finish rolling, control the final rolling temperature FT7 at 780-820°C, control the total cumulative reduction rate to be no less than 60%, and the cumulative reduction rate of the last three passes to be no less than 40%;

[0043] 5) Coil the steel sheet and control the coiling temperature CT at 700-750°C;

[0044] 6) Continuously unwind and quench, control the quenching temperature at 790-830°C, and control the quenching time at 5-10 minutes;

[0045] 7) After cutting to a fixed length, tempering is performed, and the tempering temperature is controlled at 150-200°C and the tempering time is 10-30 minutes;

[0046] 8) Cool naturally to room temperature.

[0047] illustrate:

[0048] During the smelting process, rare earth is added in an amount of 0.05-0.15 kg / ton of steel to modify the inclusions;

[0049] At the end of rough rolling, the slab thickness can be anywhere between 40 and 80 mm.

[0050] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0051]

[0052] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0053]

[0054] Table 3 List of mechanical properties test results of various embodiments of the present invention and comparative examples

[0055]

[0056] As can be seen from Table 3, this patent has a simpler composition design and lower alloy content. Through process innovation, without reducing the strength, the low-temperature toughness of wide and thick wear-resistant steel has been essentially improved compared with traditional wear-resistant steel, reaching a level 1.5 to 2 times that of the comparative process performance.

[0057] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment, comprising the following steps: 1) Conventional smelting and casting into billets, during which, during the smelting process, rare earth is added at a rate of 0.05-0.15 kg / ton of steel to modify inclusions; 2) Heat the ingot, control the heating temperature of the ingot to be between 1208 and 1230°C, and control the heating time in the high temperature section to be no less than 60 minutes; 3) Rough rolling: control the reduction rate of at least one of the first three passes to be no less than 20%, and control the slab thickness to be 40-80 mm at the end of rough rolling; 4) Finish rolling, control the final rolling temperature FT7 at 780~820℃, control the total cumulative reduction rate to be no less than 60%, and the cumulative reduction rate of the last three passes to be no less than 40%; 5) Coil the steel sheet and control the coiling temperature CT at 700-750°C; 6) Continuously unwind and quench, control the quenching temperature at 790~830℃, and control the quenching time at 5~10 minutes; 7) After cutting to the specified length, tempering is carried out, and the tempering temperature is controlled at 150~200℃ and the tempering time is 10~30min; 8) Cool naturally to room temperature; The high-toughness wear-resistant medium and thick steel plate suitable for use in a -40°C environment has the following components and weight percentage contents: C: 0.23-0.25%, Mn: 1.7-2.1%, P≤0.020%, S≤0.010%, Als: 0.04-0.06%, Ti: 0.010-0.012%, Si not exceeding 0.1% or Cr not exceeding 0.1% or Cr between 0.4% and 0.6% or B not exceeding 0.0003% or a composite of two or more thereof in any proportion, and the rest being Fe and unavoidable impurities.

2. The method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment as claimed in claim 1, characterized in that: The final rolling temperature FT7 is between 785 and 815°C.

3. The method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment as claimed in claim 1, characterized in that: The coiling temperature CT is between 708 and 723°C.

4. The method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment as claimed in claim 1, characterized in that: The quenching temperature is 796~823℃.

5. The method for producing a high-toughness wear-resistant medium-thick steel plate suitable for use in a -40°C environment as claimed in claim 1, characterized in that: The tempering temperature is between 156 and 194°C.

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