焼入れ中炭素鋼の圧縮強さと硬さの関係に及ぼす加工硬化の影響

抄録

Since it is known that tensile strength and hardness are roughly proportional, a hardness test is often used as a simple and substitute test. However, it has been reported that the proportional relationship between tensile strength and hardness is broken above 595 HV (≈55 HRC). Besides, there are few examples of mechanical properties determined by compression tests despite the fact that high-hardness and high-strength materials subjected to significant compressive stress are used in machine element parts, e.g. bearings. Tensile strength is used instead of compressive strength for the design. Thus, the relationship between hardness and compressive strength in hard materials, quenched medium carbon steel, was revealed. The compressive strength at 8% plastic strain (compressive strength) was almost the same as the maximum compressive strength. The compressive strength and hardness were at their maximum in the as-quenched specimen and decreased with the increase in tempering temperature. The compressive strength and hardness had a linear relationship up to 2000 MPa similar to the relationship of tensile tests. However, the compressive strength increased slightly in relation to the hardness above 2000 MPa in contrast to tensile tests. Thus, the work-hardening index was introduced as a variation parameter to the function that expresses the relationship between compressive strength and hardness to obtain better estimation. The estimated compressive strengths using the work-hardening index are agreed well to the experimental results.