Engineering machinery steel with excellent plate shape and yield strength larger than or equal to 1200 MPa and production method

Abstract

The invention discloses engineering machinery steel with excellent plate shape and yield strength larger than or equal to 1200 MPa. The engineering machinery steel comprises, by weight, 0.03%-0.12% of C, 0.35%-0.45% of Si, 1.40%-1.80% of Mn, 0.01%-0.02% of Nb, 0.25%-0.35% of Mo, 0.03%-0.04% of V, 0.001%-0.01% of Ti, 0.3%-0.4% of Cr, smaller than or equal to 0.015% of P, smaller than or equal to 0.002% of S, 0.0025%-0.0030% of B, 0.02%-0.10% of Als and the balance Fe. The production method comprises the following steps: continuously casting into a blank after converter smelting and LF + RH refining; heating the casting blank; after descaling, hot rolling is conducted, traditional two-section rolling is adopted, and the finish rolling temperature of finish rolling is 850-900 DEG C; carrying out laminar cooling; performing coiling; uncoiling and quenching; tempering after sizing; and straightening. The yield strength is larger than or equal to 1200 MPa, the tensile strength is larger than or equal to 1300 MPa, the elongation is larger than or equal to 9%, and the unevenness is smaller than or equal to 2 mm / m, that is, the plate type quality is excellent, and the market requirement can be completely met.

Description

Technical Field

[0001] The present invention relates to a steel for engineering machinery and a production method thereof, and in particular to a steel for engineering machinery with excellent plate shape and a yield strength of ≥1200MPa and a production method thereof. Background Art

[0002] With the lightweight development of the construction machinery industry, the requirements for high-strength structural steel are increasing. Compared with 960MPa grade steel plates, high-strength steel above 1200MPa can reduce the weight of key structural parts of concrete pump trucks by about 10-20%. At the same weight, the boom length is extended by more than 3 meters, which greatly reduces driving and operating fuel consumption, so the demand has increased significantly. This type of product needs to ensure ultra-high strength while achieving excellent plate shape and bending performance to meet the needs of boom bending and extension.

[0003] After searching:

[0004] The patent document with Chinese patent application number 202310984640.X discloses "High-strength steel for welding structure of engineering machinery with yield strength of 900-1100MPa and production method", and its chemical composition by weight percentage is: C: 0.08-0.13%, Si: 0-0.1%, Mn: 0.1-1%, P≤0.020%, S≤0.010%, Als: 0.02-0.03%, Mo: 0-0.22%, Ti: 0-0.02%, B: 0-0.003%, and the rest is Fe and impurities. The process route of smelting, continuous casting, heating, rolling, cooling, coiling, uncoiling, quenching, cross-cutting and tempering is adopted, but the yield strength is less than 1200MPa. Summary of the invention

[0005] The present invention aims to address the shortcomings of the prior art, such as low yield strength and high cost, and to provide a steel for engineering machinery with excellent plate shape, which has a yield strength ≥1200MPa, a tensile strength ≥1300MPa, an elongation ≥9%, and an unevenness ≤2mm / m, and a production method thereof.

[0006] Measures to achieve the above objectives:

[0007] A steel for engineering machinery with excellent plate shape and yield strength ≥1200MPa, wherein the components and weight percentage contents are as follows: C: 0.03-0.12%, Si: 0.35-0.45%, Mn: 1.40-1.80%, Nb: 0.01-0.02%, Mo: 0.25-0.35%, V: 0.03-0.04%, Ti: 0.001-0.01%, Cr: 0.3-0.4%, P≤0.015%, S≤0.002%, B: 0.0025-0.0030%, Als: 0.02-0.10%, and the rest is Fe and unavoidable impurities.

[0008] Preferably, the weight percentage of Mo is 0.25-0.32%.

[0009] A method for producing a steel for engineering machinery with excellent plate shape and yield strength ≥1200MPa, comprising the following steps:

[0010] 1) After converter smelting and LF+RH refining, continuous casting into billets;

[0011] 2) heating the ingot at a temperature of 1230-1280°C;

[0012] 3) After descaling, hot rolling is carried out, using traditional two-stage rolling, and the final rolling temperature is 850-900℃;

[0014] 4) laminar cooling is performed at a cooling rate of 20 to 30°C / s to the coiling temperature;

[0015] 5) Coil the steel sheet and control the coiling temperature at 650-700°C;

[0016] 6) Uncoil and quench, the quenching temperature is 900-930°C, and the quenching holding time is 5-10 minutes; then take out of the furnace and quickly cool to 100-200°C;

[0017] 7) Tempering after sizing: The tempering temperature is 550-600℃, and it is kept at this temperature for 15-30 minutes;

[0018] 8) Perform straightening.

[0019] Preferably, the heating temperature of the casting is between 1238°C and 1275°C.

[0020] Preferably, the quenching temperature is 905-918°C, the quenching holding time is 5-8 minutes, and then the steel is taken out of the furnace and rapidly cooled to 130-175°C.

[0021] Preferably, the tempering and holding temperature is between 555° C. and 595° C., and the tempering and holding time is between 15 and 25 minutes.

[0022] Functions and mechanisms of the components and main processes in the present invention

[0023] Carbon (C) of the present invention: Carbon is one of the indispensable cheap elements in steel for improving the strength of steel. Too high carbon content will reduce the toughness and welding performance of the steel, while too low carbon content cannot meet the strength requirements. Therefore, the present invention limits the carbon content to 0.03% to 0.12%.

[0024] Silicon (Si) of the present invention: Si has a good deoxidizing effect in steel, and its solid solution strengthening coefficient in ferrite is higher than that of Mn. It is an effective and inexpensive strengthening element and can effectively improve hardenability. However, adding too much is detrimental to the plasticity and surface quality of the steel. Therefore, the present invention selects the Si content to be 0.35% to 0.45%.

[0025] Manganese (Mn) in the present invention: Mn can improve hardenability, while making the quenched and tempered structure uniform and refined, and improving the yield strength and tensile strength of steel. However, excessive addition of Mn is prone to segregation, which is unfavorable to toughness and welding performance. Therefore, the present invention controls the Mn content to 1.4% to 1.8%.

[0026] Niobium (Nb) of the present invention: A certain amount of Nb can significantly refine the grains and improve the tensile strength. During the controlled rolling process, Nb can increase the recrystallization temperature of the steel and reduce the mill load. At the same time, by inhibiting recrystallization and preventing grain growth, it can refine the austenite grain size, providing a basis for obtaining a refined quenching structure. The Nb content of the present invention is 0.01% to 0.02%.

[0027] Molybdenum (Mo) of the present invention: Molybdenum exists in the solid solution and carbide of steel and has a solid solution strengthening effect. When Mo and Nb are added simultaneously, Mo can increase the inhibition of austenite recrystallization during the controlled rolling process, thereby promoting the refinement of austenite microstructure. At the same time, Mo is conducive to the stability of tempering performance and is conducive to obtaining excellent plate shape by high temperature tempering. Therefore, the content of Mo in the present invention is 0.25% to 0.35%.

[0028] Chromium (Cr) of the present invention: Cr slows down the decomposition rate of austenite, significantly improves the hardenability of steel, improves the strength of steel plate, and has low price. Therefore, the Cr content is controlled to 0.3% to 0.4% in the present invention.

[0029] Vanadium (V) in the present invention: when V is less than 0.03%, most of V exists in a solid solution state, which can significantly increase the hardenability in heat-treated steel and has a good strengthening effect. Cr can promote the solid solution of V, so the present invention controls the V content to 0.03-0.04%.

[0030] Titanium (Ti) in the present invention: In the present invention, micro-Ti treatment is adopted, and 0.001-0.01% of Ti element is added to the steel to improve welding performance.

[0031] Boron (B) in the present invention: The main function of B is to improve the hardenability of steel. Boron, as a surface active element, is adsorbed on the austenite grain boundary, delaying the transformation of austenite to ferrite. Its segregation at the austenite grain boundary hinders the nucleation of ferrite and is conducive to the formation of martensite, thereby improving the structure strengthening effect. However, if the B content is higher than the specified value, the hardenability decreases, and a low melting point eutectic will be formed, which is concentrated at the boundary of the grains, thereby causing hot brittleness. Therefore, the boron content of the present invention is limited to 0.0025% to 0.0030%.

[0032] The phosphorus (P) content of the present invention is ≤0.015%, and the sulfur (S) content is ≤0.002%. Phosphorus is easy to cause segregation in steel, and sulfur is easy to combine with manganese to form MnS inclusions, both of which are unfavorable to strength. Therefore, the present invention should minimize the adverse effects of phosphorus and sulfur elements on strength, and control the P and S contents of steel to P: ≤0.015%, S: ≤0.002%.

[0033] The reason why the present invention controls the heating temperature of the casting billet at 1230-1280°C is that it ensures complete solid solution and sufficient austenitization of alloy elements, while improving the uniformity of the slab temperature, reducing deformation resistance and rolling load, and laying the foundation for controlling the rolled plate shape.

[0034] The reason why the final rolling temperature is controlled at 850-900° C. in the present invention is to facilitate obtaining lower original internal stress and excellent rolled plate shape.

[0035] The reason why the coiling temperature is controlled at 650-700° C. in the present invention is to make the steel coil cool evenly through a higher coiling temperature, so as to avoid large internal stress and plate shape defects caused by uneven temperature when the steel plate is cooled to room temperature.

[0036] The quenching heating temperature of the present invention is 900-930° C., mainly to make the temperature of the steel plate uniform and reduce the internal stress of the steel plate, so as to facilitate the control of the quenched plate shape.

[0037] The reason why the quenching cooling termination temperature is controlled to be 100-200° C. in the present invention is mainly to avoid the adverse effect of residual water on the surface of the steel plate after quenching on the surface quality.

[0038] The reason why the tempering and holding temperature is controlled at 550-600°C and the tempering and holding time is controlled at 15-30 minutes in the present invention is mainly to eliminate the internal stress of the steel plate through high temperature tempering to obtain the final excellent plate shape.

[0039] Compared with the prior art, the yield strength of the present invention is ≥1200MPa, the tensile strength is ≥1300MPa, the elongation is ≥9%, and the unevenness is ≤2mm / m, that is, the plate quality is excellent and can fully meet the needs of the market. DETAILED DESCRIPTION

[0040] The present invention is described in detail below:

[0041] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0042] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0043] Table 3 is a table of performance test results of various embodiments and comparative examples of the present invention.

[0044] Each embodiment of the present invention is produced according to the following steps

[0045] 1) After converter smelting and LF+RH refining, continuous casting into billets;

[0046] 2) heating the ingot at a temperature of 1230-1280°C;

[0047] 3) After descaling, hot rolling is carried out, using traditional two-stage rolling, and the final rolling temperature is 850-900℃;

[0049] 4) laminar cooling is performed at a cooling rate of 20 to 30°C / s to the coiling temperature;

[0050] 5) Coil the steel sheet and control the coiling temperature at 650-700°C;

[0051] 6) Uncoil and quench, the quenching temperature is 900-930°C, and the quenching holding time is 5-10 minutes; then take out of the furnace and quickly cool to 100-200°C;

[0052] 7) Tempering after sizing: The tempering temperature is 550-600℃, and it is kept at this temperature for 15-30 minutes;

[0053] 8) Perform straightening.

[0054] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0055]

[0056] Table 2 List of main process parameters of various embodiments and comparative examples of the present invention

[0057]

[0058]

[0059] Table 3 Performance test results of various embodiments and comparative examples of the present invention

[0060]

[0061] It can be seen from the results in Table 3 above that the steel of the present invention has a yield strength of ≥1200 MPa, a tensile strength of ≥1300 MPa, an elongation of ≥9%, and a roughness of ≤2 mm / m, which can meet the demand for ultra-high-strength engineering machinery steel with excellent plate shape.

[0062] The above embodiments are only the best examples and are not all of the technical solutions of the present invention.

Claims

1. A steel for engineering machinery with excellent plate shape and yield strength ≥1200MPa, the components and weight percentage of which are: C: 0.03~0.12%, Si: 0.35~0.45%, Mn: 1.40~1.80%, Nb: 0.01~0.02%, Mo: 0.25~0.35%, V: 0.03-0.04%, Ti: 0.001~0.01%, Cr: 0.3~0.4%, P≤0.015%, S≤0.002%, B: 0.0025~0.0030%, Als: 0.02~0.10%, the rest are Fe and unavoidable impurities.

2. The engineering machinery steel with excellent plate shape and yield strength ≥1200MPa as claimed in claim 1, characterized in that: The weight percentage content of Mo is 0.25-0.32%.

3. A method for producing a steel for engineering machinery with excellent plate shape and yield strength ≥1200 MPa as claimed in claim 1, comprising the following steps: 1) After converter smelting and LF+RH refining, continuous casting into billets; 2) heating the ingot at a temperature of 1230-1280°C; 3) After descaling, hot rolling is carried out, using traditional two-stage rolling, and the final rolling temperature is 850-900℃; 4) laminar cooling is performed at a cooling rate of 20 to 30°C / s to the coiling temperature; 5) Coil the steel sheet and control the coiling temperature at 650-700°C; 6) Uncoil and quench, the quenching temperature is 900-930°C, and the quenching holding time is 5-10 minutes; then take out of the furnace and quickly cool to 100-200°C; 7) Tempering after sizing: The tempering temperature is 550-600℃, and it is kept at this temperature for 15-30 minutes; 8) Perform straightening.

4. The method for producing a steel for engineering machinery with excellent plate shape and yield strength ≥1200 MPa as claimed in claim 3, characterized in that: The heating temperature of the casting is between 1238 and 1275°C.

5. The method for producing a steel for engineering machinery with excellent plate shape and yield strength ≥1200 MPa as claimed in claim 3, characterized in that: The quenching temperature is between 905 and 918°C, and the quenching holding time is between 5 and 8 minutes; then the steel is taken out of the furnace and rapidly cooled to 130 to 175°C.

6. The method for producing a steel for engineering machinery with excellent plate shape and yield strength ≥1200 MPa as claimed in claim 3, characterized in that: The tempering temperature is between 555 and 595°C, and the tempering holding time is between 15 and 25 minutes.

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