Free-machining pinion steel and production technique thereof

Abstract

The invention discloses a free-machining pinion steel and a production technique thereof. The pinion steel comprises the following components in percentage by weight: 0.14-0.22% of C, 0.20-0.35% of Si, 0.95-1.15% of Mn, 0.95-1.15% of Cr, 0.020-0.060% of Al, at most 0.035% of P, 0.012-0.030% of S, and the balance of Fe and inevitable impurities. The technique comprises the following steps: smelting, continuous casting and rolling. In the invention, the Cr-Mn-Al-S pinion steel is used instead of the original Cr-Mn-Ti pinion steel, Al and S elements are added, and the intracrystalline ferrite is sufficiently utilized to refine the crystalline grains. The invention can stabilize the Jominy hardenability, reduce the pinion deformation after heat treatment, enhance the brittle fracture resistance and crack propagation resistance, and improve the free machining capacity of the pinion in the machining process. The invention is applicable to pinion steel as a substitute of 20CrMnTi.

Description

technical field [0001] The invention belongs to the field of metallurgy and relates to a gear steel, in particular to a free-cutting gear steel and a production process thereof. Background technique [0002] my country's gear steel, since the first batch of automobile production in the 1950s, quoted the grade and performance indicators in the former Soviet Union's I'OCT standard. The largest amount was 18CrMnTi steel, which was changed to 20CrMnTi in the 1980s. The steel number is still in use today. It is currently the most widely used gear steel grade in the production of various construction machinery, automobiles, agricultural vehicles and other transmission gears and gear materials. This material is in line with my country's resources and has low cost, good process performance and low price. advantages and can meet the requirements of most gear materials in China. Therefore, this material still accounts for about 50% of China's automotive gear steel manufacturing. Becau...

AI Technical Summary

Problems solved by technology

The matrix structure of 20CrMnTi steel is ferrite + pearlite structure, but 20CrMnTi steel has added Ti in the composition design, which inevitably produces large or small TiN inclusions inside the steel. Ti is an important element in gear steel. However, Ti is easy to form TiN with large particles and sharp edges in steel, which is the source of fatigue cracks, and its damage is more serious than oxide inclusions.

As for the development prospect of 20CrMnTi, there have been discussions as early as the "Sixth Five-Year Plan" period. The main reason is that the TiN non-deformable inclusions are harder than the matrix, which affects the machining accuracy, and will become a source of fatigue during use and affect the fatigue life of the gear.

Images