High-strength steel material having excellent fatigue characteristics

Abstract

Provided is a steel material such as a high-strength spring having excellent fatigue characteristics. Particularly provided is a steel material such as a high-strength spring, which has been easily improved in terms of the fatigue characteristics in a high-strength region without increasing the alloy cost. The steel material is characterized by containing, in mass%, 0.5-1.0% of C, 1.5-2.50% of Si, 0.5-1.50% of Mn, more than 0% but 0.020% or less of P, more than 0% but 0.020% or less of S, more than 0% but 0.2% or less of Cr, more than 0% but 0.010% or less of Al, more than 0% but 0.0070% or less of N and more than 0% but 0.0040% or less of O, with the balance made up of iron and unavoidable impurities. The steel material is also characterized in that: the Cr content and the Si content satisfy Cr * Si <= 0.20; the ratio of tempered martensite in the steel structure is 80% by area or more; and the number density of Cr-containing carbonitrides having a circle-equivalent diameter of 50 nm or more in the steel structure is 0.10 carbonitride / [mu]m2 or less.

Description

technical field [0001] The present invention relates to a high-strength steel material excellent in fatigue properties, particularly spring fatigue properties. The high-strength steel material includes a spring steel wire obtained by quenching and tempering a drawing material; a spring obtained by performing a coil spring on the spring steel wire; the spring. Background technique [0002] Along with weight reduction and high stress of automobiles, valve springs and clutch springs used in engines, clutches, etc. are also directed to high stress. This leads to an increase in the applied stress to the spring. Therefore, the spring is required to have excellent fatigue properties and permanent residual strain resistance. In particular, it is required to be less prone to fatigue fracture due to internal defects and to have excellent fatigue properties. [0003] In recent years, most valve springs, clutch springs, etc. are produced by subjecting wire drawing materials to quenchi...

AI Technical Summary

Problems solved by technology

However, the above-mentioned steel wire has the problem of high alloy cost because Co is essential and the amount of Cr added is large.

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