High-strength high-toughness non-quenched and tempered front axle steel and production method thereof

Abstract

The invention discloses high-strength high-toughness non-quenched and tempered front axle steel and a production method thereof. The high-strength high-toughness non-quenched and tempered front axle steel comprises the chemical components of, by mass, 0.21%-0.25% of C, 0.15%-0.35% of Si, 1.40%-1.60% of Mn, 0.20%-0.40% of Cr, 0.009%-0.020% of N, 0.020%-0.050% of Al, 0.040%-0.070% of S, less than orequal to 0.030% of P, less than or equal to 0.15% of Ni, 0.11%-0.16% of V, less than or equal to 0.06% of Mo, and the balance Fe and inevitable impurities, wherein Fn1 is equal to 0.79-0.85%, and Fn2is less than or equal to 1.80%. The steel has an excellent strength and low-temperature toughness, is low in production cost, and is suitable for being used on heavy-duty automobiles. Molten steel obtained through the method is good in liquidity, and a single tundish continuous drawing molten steel amount reaches 600 tons; a liquid level fluctuation of a crystallizer is within + / -3 mm, and the surface of a continuous casting billet is good; a yield strength of a front axle of an obtained product is 590-650 Mpa, a tensile strength is 850-916 Mpa, a percentage elongation after fracture is 19%-23%, a percentage reduction of area is 55%-58%, the normal-temperature impact toughness is 70-90 J / cm < 2 >, and the low-temperature (minus 50 DEG C) impact toughness is 27-45 J / cm < 2 >; and an average value of fatigue life tests of a front axle assembly reaches 1,300,000 times.

Description

technical field [0001] The invention relates to a non-quenched and tempered steel, in particular to a high-strength, high-toughness non-quenched and tempered steel for front axles and a production method thereof. Background technique [0002] The front axle of the car is one of the important safety parts of the front axle of the car. The front axle bears alternating stresses such as bending load and impact load in the front axle assembly at the same time, and the working environment is extremely poor. Therefore, the front axle is required to have a high resistance to bending fatigue Strength, while strength and toughness need to have a good match. Traditional materials such as 45#, 50#, 40Cr, and 42CrMo are usually used for the production of front axles. The front axles made of these materials need to be quenched and tempered after hot forging, which cannot meet the requirements of strength and toughness of parts and cost reduction at the same time. [0003] Chinese Inventi...

AI Technical Summary

Problems solved by technology

Peritectic steel, high Mn and high sulfur content cause metallurgical difficulties such as steel surface cracks, internal cracks and poor fluidity of molten steel in the metallurgical production of the steel. At the same time, due to the coarse grains, the strength and toughness of the front axle are insufficient.

[0005] The document "Research on the Application of New Non-Quenched and Tempered Steel in the Front Axle of Heavy Trucks" ("Automobile Technology and Materials" 2015 Issue 08) proposed that the content of C is 0.22-0.28%, and the content of Mn is 1.8-2.1%, which belongs to low carbon and high Manganese content steel type, the phase transition shrinkage of the primary shell in the mold is large, and the high Mn reduces the thermal conductivity of the green shell in the mold, and the growth of the shell is slower than that of ordinary steel. When the liquid steel level fluctuates, it is easy to make the billet shell grow unevenly and form transverse defects. High Mn will easily reduce the viscosity of the mold slag at the interface of the steel slag in the crystallizer, and easily cause slag inclusion defects. Therefore, the metallurgical production of this steel is more difficult. Sensitive to cracks, requires grinding, high production cost

At the same time, the tensile strength of the steel front axle is 975Mpa, the yield strength is 700-725Mpa, the elongation is 7%, the area shrinkage is 6.5%, and the impact toughness at room temperature is 50J / cm 2 , has the disadvantages of excess strength and insufficient toughness, and it is prone to fracture during the operation of the vehicle, causing accidents

Images