750MPa-grade high-strength and high-toughness automobile transmission shaft steel and production method thereof

Abstract

The invention discloses 750MPa-grade high-strength and high-toughness steel for an automobile transmission shaft. The 750MPa-grade high-strength and high-toughness steel comprises the following chemical components in percentage by mass: 0.06 to 0.09 percent of C, less than or equal to 0.15 percent of Si, 1.70 to 2.0 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.010 percent of S, 0.040 to 0.070 percent of Nb, 0.10 to 0.14 percent of Ti, 0.020 to 0.060 percent of Als, less than or equal to 0.005 percent of N and the balance of iron and inevitable impurities. The production method comprises the steps of molten iron pretreatment, converter smelting, LF furnace refining, slab continuous casting, slab heating, high-pressure water descaling, controlled rolling, cooling, curling and slow cooling in a slow cooling pit. Production of the 750MPa-grade high-strength and high-toughness steel for the automobile transmission shaft is achieved, the strength of the steel for the transmission shaft can be improved, the service life of the steel for the transmission shaft can be prolonged, automobile light weight is promoted, and energy conservation and emission reduction are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and specifically relates to a 750MPa-grade high-strength and toughness steel for automobile transmission shafts and a production method thereof. Background Art

[0002] In recent years, with the attention paid to environmental protection issues at home and abroad, the state has put forward strict environmental protection policy requirements for various industries. With the rapid development of the domestic automobile industry and the promotion of environmental protection policies, the development of high-strength and lightweight automobiles is imperative. As one of the important parts of automobiles, the demand for high-strength automobile transmission shaft steel is also increasing under the trend of lightweight development. At present, the market demand is still large for automobile transmission shaft steel with a tensile strength of 500MPa, and the demand for 700MPa and above is relatively small, but it is still steadily increasing.

[0003] Patent publication number CN 116904880 A discloses a steel for automobile transmission shaft with a tensile strength of 800MPa and a manufacturing method thereof, the performance of which meets the requirements of yield strength ≥750MPa, tensile strength ≥800MPa, and elongation after fracture ≥17%. However, the expensive alloys ferromolybdenum and ferrovanadium are used in its preparation for Mo and V microalloying to improve the strength of the product, resulting in a high production cost. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a 750MPa grade high-strength and toughness steel for automobile transmission shaft and a production method, and to achieve the production of 750MPa grade high-strength and toughness steel for automobile transmission shaft by composite microalloying of niobium and titanium and utilizing their solid solution, precipitation and fine grain strengthening effects.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A 750MPa grade high-strength and toughness steel for automobile transmission shafts, the chemical composition of which is calculated by mass percentage: C: 0.06-0.09%, Si: ≤0.15%, Mn: 1.70-2.0%, P: ≤0.025%, S: ≤0.010%, Nb: 0.040-0.070%, Ti: 0.10-0.14%, Als: 0.020-0.060%, N: ≤0.005%, and the balance is iron and unavoidable impurities.

[0006] Furthermore, the performance indicators of the 750MPa grade high-strength and toughness automobile transmission shaft steel are as follows: yield strength ≥750MPa, tensile strength ≥825MPa, elongation after fracture ≥28%, and -20°C Charpy V-type impact ≥25J.

[0007] Furthermore, the 750MPa grade high-strength and toughness steel for automobile transmission shaft has a thickness of 2.0-8.0mm and a width of 1000-1650mm.

[0008] The present invention also provides a method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel, which comprises: molten iron pretreatment, converter smelting, LF furnace refining, slab continuous casting, slab heating, high-pressure water descaling, controlled rolling, cooling, curling and slow cooling in a slow cooling pit; The controlled rolling includes: rough rolling, hot coil box and finishing rolling.

[0009] Furthermore, the converter smelting process smelts molten steel according to the set chemical composition, and the molten steel is refined in an LF furnace and cast into a slab protection casting to obtain a qualified continuous casting billet.

[0010] Furthermore, in the slab heating process, the slab is in the furnace for 140-240 minutes and the heating temperature is 1200-1260°C.

[0011] Furthermore, the rough rolling is performed in five passes, and the outlet temperature is 1040-1100°C.

[0012] Furthermore, the final rolling temperature after the finish rolling is 850-890°C.

[0013] Furthermore, the curling temperature in the curling process is 580-640°C.

[0014] The beneficial effects of adopting the above technical solution are: The present invention fully exerts the solid solution, precipitation and fine grain strengthening effects of niobium and titanium through niobium and titanium composite microalloying and rolling process control, so that the yield strength of the steel is ≥750MPa, the tensile strength is ≥825MPa, the elongation after fracture is ≥28%, and the -20°C Charpy V-type impact is ≥25J, thereby realizing the production of 750MPa-level high-strength and toughness automobile transmission shaft steel, improving the strength and life of the transmission shaft steel, promoting automobile lightweighting, and achieving energy conservation and emission reduction. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below in conjunction with specific embodiments.

[0016] Table 1 shows the chemical composition (wt, %) of each embodiment of the present invention; Table 2 shows the rolling process control parameters of various embodiments of the present invention; Table 3 shows the mechanical properties of various embodiments of the present invention.

[0017] The production process of each embodiment of the present invention is controlled as follows: The chemical composition of the production process of the present invention is controlled as follows: C: 0.06-0.09%, Si: ≤0.15%, Mn: 1.70-2.0%, P: ≤0.025%, S: ≤0.010%, Nb: 0.040-0.070%, Ti: 0.10-0.14%, Als: 0.020-0.060%, N: ≤0.005%, and the remainder is iron and inevitable impurities.

[0018] The production process of the present invention is to smelt molten steel according to the set chemical composition, and the molten steel is refined by LF furnace and cast by slab protection to obtain qualified continuous casting billets; the qualified continuous casting billets are placed in a heating furnace for heating, the heating temperature is 1200-1260℃, and the heating time is 140-240min; the rough rolling outlet temperature is 1040-1100℃, and the rough rolling adopts 5 passes of rolling; the final rolling temperature after finishing rolling is 850-890℃; the curling temperature of the curling process after rolling is 580-640℃, and the steel coil is placed in a slow cooling pit for slow cooling after curling, and slowly cooled to room temperature. The steel plate embodiment with a thickness of 5mm and a width of 1480mm is selected for research and analysis.

[0019] Table 1 Chemical composition of various embodiments of the present invention (wt, %)

[0020] Table 2 Rolling process control parameters of various embodiments of the present invention

[0021] Table 3 Mechanical properties of various embodiments of the present invention

[0022] It can be seen from the above data that the mechanical properties of the seven embodiments of the present invention have met the technical requirements for 750MPa grade high-strength and toughness steel for automobile transmission shafts.

[0023] 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 750MPa grade high strength and toughness steel for automobile transmission shaft, characterized in that: The chemical composition thereof is calculated by mass percentage as follows: C: 0.06-0.09%, Si: ≤0.15%, Mn: 1.70-2.0%, P: ≤0.025%, S: ≤0.010%, Nb: 0.040-0.070%, Ti: 0.10-0.14%, Als: 0.020-0.060%, N: ≤0.005%, and the remainder is iron and unavoidable impurities.

2. The 750MPa grade high-strength and toughness steel for automobile transmission shaft according to claim 1, characterized in that: The performance indicators thereof are yield strength ≥750MPa, tensile strength ≥825MPa, elongation after fracture ≥28%, and -20℃ Charpy V-type impact ≥25J.

3. The 750MPa grade high-strength and toughness steel for automobile transmission shaft according to claim 1, characterized in that: The thickness is 2.0-8.0 mm and the width is 1000-1650 mm.

4. A method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claims 1-3, characterized in that: The following steps are involved: Hot metal pretreatment, converter smelting, LF furnace refining, slab continuous casting, slab heating, high-pressure water descaling, controlled rolling, cooling, curling and slow cooling in slow cooling pit; The controlled rolling includes: rough rolling, hot coil box and finishing rolling.

5. The method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claim 4, characterized in that: The converter smelting process smelts molten steel according to the set chemical composition, and the molten steel is refined in the LF furnace and cast through slab protection to obtain qualified continuous casting billets.

6. The method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claim 4, characterized in that: In the slab heating process, the slab is kept in the furnace for 140-240 minutes and the heating temperature is 1200-1260°C.

7. The method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claim 4, characterized in that: The rough rolling is performed in five passes, and the outlet temperature is 1040-1100°C.

8. The method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claim 4, characterized in that: The final rolling temperature after finishing rolling is 850-890℃.

9. The method for producing 750MPa grade high-strength and toughness automobile transmission shaft steel according to claim 4, characterized in that: The curling temperature of the curling process is 580-640°C.

Images