An economic high-toughness engineering machinery steel with yield strength greater than or equal to 960 MPa and a production method

Abstract

A high-toughness, economical engineering machinery steel with a yield strength ≥960MPa, comprising the following components (wt%): C: 0.10–0.16%, Si ≤0.1%, Mn: 0.7–1.2%, P ≤0.015%, S ≤0.010%, Als: 0.03–0.05%, Ti: 0.05–0.08%, B: 0.001–0.003%. The production method involves conventional smelting and continuous casting into billets; heating the billets; rough rolling; finish rolling; rapid cooling; coiling; quenching after uncoiling; tempering after cross-cutting to length; and then storing. This invention ensures a yield strength ≥960MPa, tensile strength ≥990MPa, elongation ≥13%, and Kv2 ≥70J at -40℃. Furthermore, by modifying the composition, replacing the previously added expensive elements Cr and Mo with Ti and B, the production cost can be reduced by at least 5% compared to existing technologies.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of engineering machinery steel and production method, specifically belongs to a kind of yield strength ≥960MPa economic type high toughness engineering machinery steel and production method. BACKGROUND

[0002] Engineering machinery industry 960MPa grade high-strength steel is used in large quantities, such as excavator bucket liner and side plate, mine car compartment liner, etc. The steel of this level generally adds valuable alloy elements Cr, Mo, Ni, etc. in composition design, and is produced by quenching and tempering process. This design idea causes high alloy design cost. For example, the search of:

[0003] The document of Chinese patent application No. CN201110098008.2 discloses "a yield strength 960MPa grade ultra-high strength steel and its production method", the chemical composition is as follows in percentage by weight: C: 0.07-0.09%; Si: 0.15-0.25%; Mn: 1.00-1.20%; Cr: 1.05-1.15%; Mo: 0.15-0.20%; Al: 0.01-0.06%; P: ≤0.02%; S: ≤0.01%; N: ≤0.008%; the rest is Fe and inevitable impurities; the production method is: smelting, casting into billet; heating to 1150-1250℃; final rolling temperature is 840-900℃; final cooling temperature is 640-700℃; quenching and tempering treatment is carried out, quenching heating temperature is 880-920℃, holding time is 20-60min, tempering heating temperature is 150-450℃, holding time is 90-180min. The steel plate reaches the performance requirements of 960MPa ultra-high strength steel, and has good elongation and impact toughness, but due to the presence of Cr: 1.05-1.15%; Mo: 0.15-0.20%, the production cost is high. SUMMARY

[0004] The present application overcomes the high production cost of the prior art, and provides a yield strength ≥960MPa economic type high toughness engineering machinery steel and production method, which guarantees yield strength ≥960MPa, tensile strength ≥990MPa, elongation ≥13%, and makes -40℃Kv2≥70J, and the production cost is reduced by at least 5% compared with the prior art.

[0005] The measures to achieve the above-mentioned purposes are:

[0006] An economic high-toughness engineering machinery steel with yield strength ≥960MPa, its components and weight percentage contents are: C: 0.10-0.16%, Si ≤0.1%, Mn: 0.7-1.2%, P ≤0.015%, S ≤0.010%, Als: 0.03-0.05%, Ti: 0.05-0.08%, B: 0.001-0.003%, the rest is Fe and impurities.

[0007] Preferably: the weight percentage content of Mn is 0.92-1.20%.

[0008] Preferably: the weight percentage content of Ti is 0.06-0.072%.

[0009] Preferably: the weight percentage content of B is 0.0017-0.0022%.

[0010] A method for producing an economic high-toughness engineering machinery steel with yield strength ≥960MPa, the steps are:

[0011] 1) conventional smelting and continuous casting into billets;

[0012] 2) heating the billet: control the billet heating temperature at 1220-1260℃;

[0013] 3) rough rolling, and control the rough rolling end temperature at 1020-1100℃;

[0014] 4) finish rolling, control the opening rolling temperature not more than 1060℃, and the finish rolling temperature at 820-920℃;

[0015] 5) rapid cooling, cool to coiling temperature at a cooling speed of 60-120℃ / S;

[0016] 6) coiling: control the coiling temperature at 520-660℃;

[0017] 7) quenching after uncoiling: control the quenching temperature at 810-920℃, and keep at this temperature for 4-18min;

[0018] 8) tempering after cross-cutting according to the size: control the tempering temperature at 460-620℃, and the tempering time at 8-20min;

[0019] 9) standby.

[0020] Preferably: the opening rolling temperature is 960-1030℃, and the finish rolling temperature is 840-900℃.

[0021] Preferably: the cooling speed is 75-110℃ / S.

[0022] Preferably: the coiling temperature is 555-635℃.

[0023] Preferably, the quenching temperature is 850-910℃, and the quenching holding time is 6-12 minutes.

[0024] Preferably, the tempering temperature is 515-620℃.

[0025] Effects and mechanisms of components and main processes in the application

[0026] C: C is the cheapest element for improving material strength. With the increase of carbon content, the hardness and strength are improved, but the plasticity, toughness and welding performance are reduced. If the content of C is less than 0.10%, the requirement of material strength cannot be met; if the content of C is greater than 0.16%, the welding performance and forming performance are affected. Therefore, the content of C is limited to the range of 0.10-0.16%.

[0027] Mn: Mn significantly reduces the Ar1 temperature and the austenite decomposition rate, improves the stability of supercooled austenite, promotes the stress release of austenite, increases the residual austenite content in the final structure, and improves the cold bending performance. However, if the content of Mn is too high, the temper brittleness is increased, and serious center segregation is caused. Therefore, the content of Mn is preferably 0.7-1.2% by weight.

[0028] Si: Si can reduce the diffusion rate of carbon in ferrite, promote the formation of ferrite, and also deteriorate the surface quality. Therefore, the content of Si is preferably 0-0.1% by weight.

[0029] Als: Als can be deoxidized in steel, reduce the inclusion content, and also play a role in refining grains. Therefore, the content of Als is preferably 0.03-0.05%.

[0030] Ti: Ti can combine with N to form stable TiN in the solidification process of steel, strongly hinder the migration of austenite grain boundary, refine the austenite grains, provide a microstructure basis for the refined microstructure after heat treatment, improve the strength-toughness match of the steel, and control the precipitation of nanoscale TiC precipitates in the process of controlled rolling and controlled cooling to improve the strength of the steel. Therefore, the content of Ti is preferably 0.05-0.08% by weight.

[0031] P and S: P and S are harmful impurity elements in steel. P in steel is easy to form segregation in steel, reduce the toughness and welding performance of the steel, and S is easy to form plastic sulfide, which causes the steel plate to be layered and deteriorates the performance of the steel plate. Therefore, the lower the content of P and S, the better. Therefore, the content of P and S in the steel is preferably P≤0.015% and S≤0.010%.

[0032] B: B can greatly improve the hardenability, but when B is too much, it is easy to enrich at the grain boundary, which can reduce the grain boundary binding energy, so that the steel plate is more prone to intergranular fracture under impact load, and the low temperature impact energy of the steel plate is reduced. Therefore, the addition amount of B in the present application is 0.001-0.003%.

[0033] The reason why the present application controls the casting blank heating temperature to be 1220-1260℃ is that the austenite homogenization and the sufficient diffusion of C, B and other elements are controlled.

[0034] The reason why the present application controls the rough rolling end temperature to be 1020-1100℃ is that the austenite growth after rough rolling is inhibited, and the effect of refining the grain is achieved.

[0035] The reason why the present application controls the rough rolling end temperature to be 1020-1100℃ is that the austenite growth after rough rolling is inhibited, and the effect of refining the grain is achieved.

[0036] The reason why the present application controls the cooling speed to be 60-120℃ / S is that the microstructure transformation is carried out quickly after the finishing rolling, and the microstructure is refined.

[0037] The reason why the present application controls the coiling temperature to be 520-660℃ is that the microstructure transformation and TiC precipitation are carried out quickly.

[0038] The reason why the present application controls the quenching temperature to be 810-920℃ and the holding time at this temperature to be 4-18min is that the austenitization is completed.

[0039] The reason why the present application controls the tempering temperature to be 460-620℃ and the tempering time to be 8-20min is that the tempering transformation of the quenched martensite is carried out.

[0040] Compared with the prior art, the present application can ensure that the yield strength is ≥960MPa, the tensile strength is ≥990MPa, the elongation is ≥13%, the Kv2 at-40℃ is ≥70J, and the production cost is reduced by at least 5% compared with the prior art by replacing the expensive elements Cr and Mo with Ti and B. DETAILED DESCRIPTION

[0041] The present application will be described in detail as follows:

[0042] Table 1 is a list of chemical compositions of each embodiment and the comparative example of the present application;

[0043] Table 2 is a list of main process parameters of each embodiment and the comparative example of the present application;

[0044] Table 3 is a list of performance test conditions of each embodiment and the comparative example of the present application.

[0045] Each embodiment of the present application is produced according to the following steps

[0046] 1) Conventional smelting and continuous casting into billets;

[0047] 2) Heating the billet: Control the billet heating temperature between 1220 and 1260℃;

[0048] 3) Perform rough rolling and control the rough rolling end temperature at 1020-1100℃;

[0049] 4) Perform finishing rolling, controlling the initial rolling temperature to not exceed 1060℃ and the final rolling temperature to be between 820℃ and 920℃;

[0050] 5) Perform rapid cooling at a cooling rate of 60–120 °C / s to the winding temperature;

[0051] 6) Perform winding: Control the winding temperature between 520 and 660℃;

[0052] 7) After uncoiling, quenching treatment is performed: the quenching temperature is controlled at 810~920℃, and the temperature is held at this temperature for 4~18min;

[0053] 8) After being cut to length, tempering is performed, with the tempering temperature controlled at 460-620℃ and the tempering time at 8-20 minutes;

[0054] 9) Reserved.

[0055] Table 1. List of chemical components (wt%) of various embodiments and comparative examples of the present invention.

[0056]

[0057]

[0058] Table 2. List of main process parameters for each embodiment and comparative example of the present invention.

[0059]

[0060] Table 3. List of mechanical property test results for each embodiment and comparative example of the present invention.

[0061]

[0062]

[0063] As can be seen from Table 3, the yield strength and tensile strength of the 960MPa grade low-cost, high-toughness high-strength steel for engineering machinery prepared in Examples 1-7 of the present invention are similar to those of Comparative Examples 1-2, but the elongation and Kv2 at -40℃ are significantly better than those of the comparative examples. In particular, the Kv2 at -40℃ is greater than 70J, which is much higher than that of the comparative examples. This indicates that the products of Examples 1-7 have good low-temperature toughness. Moreover, by replacing the expensive elements originally added with Ti and B, the production cost can be reduced by at least 5% compared with the prior art.

[0064] This specific embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.

Claims

1. An economical high-toughness engineering machinery steel with a yield strength ≥960MPa, comprising the following components and weight percentages: C: 0.138~0.16%, Si≤0.1%, Mn: 1.05~1.2%, P≤0.015%, S≤0.010%, Als: 0.032~0.05%, Ti: 0.05~0.08%, B: 0.001~0.003%, with the remainder being Fe and impurities; Production method: 1) Conventional smelting and continuous casting into billets; 2) Heating the billet: Control the billet heating temperature between 1220 and 1260℃; 3) Perform rough rolling, and control the rough rolling end temperature at 1020-1100℃; 4) Perform finishing rolling, controlling the initial rolling temperature to not exceed 1060℃ and the final rolling temperature to be between 820℃ and 920℃; 5) Perform rapid cooling at a rate of 75~120℃ / s to the winding temperature; 6) Perform winding: Control the winding temperature at 520~660℃; 7) After uncoiling, quenching treatment is performed: the quenching temperature is controlled at 810~920℃, and the temperature is held at this temperature for 4~18 minutes; 8) After being cut to length, tempering is performed, with the tempering temperature controlled at 460~620℃ and the tempering time at 16~20min; 9) Reserved.

2. The economical high-toughness engineering machinery steel with a yield strength ≥960MPa as described in claim 1, characterized in that: The weight percentage content of Ti is 0.06~0.072%.

3. A method for producing an economical, high-toughness engineering machinery steel with a yield strength ≥960MPa as described in claim 1, comprising the following steps: 1) Conventional smelting and continuous casting into billets; 2) Heating the billet: Control the billet heating temperature between 1220 and 1260℃; 3) Perform rough rolling, and control the rough rolling end temperature at 1020-1100℃; 4) Perform finishing rolling, controlling the initial rolling temperature to not exceed 1060℃ and the final rolling temperature to be between 820℃ and 920℃; 5) Perform rapid cooling at a rate of 75~120℃ / s to the winding temperature; 6) Perform winding: Control the winding temperature at 520~660℃; 7) After uncoiling, quenching treatment is performed: the quenching temperature is controlled at 810~920℃, and the temperature is held at this temperature for 4~18 minutes; 8) After being cut to length, tempering is performed, with the tempering temperature controlled at 460~620℃ and the tempering time at 16~20min; 9) Reserved.

4. The production method of an economical high-toughness engineering machinery steel with a yield strength ≥960MPa as described in claim 3, characterized in that: The cooling rate is 75~110℃ / s.

5. The production method of an economical high-toughness engineering machinery steel with a yield strength ≥960MPa as described in claim 3 is characterized in that: The winding temperature is 555~635℃.

6. The production method of an economical high-toughness engineering machinery steel with a yield strength ≥960MPa as described in claim 3 is characterized in that: The tempering temperature is 515~620℃.

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