ばね鋼の結晶粒度と低温焼鈍と疲労強度に関する共同研究報告

結晶粒径を微細化すると鋼の強度が向上することはよく知られているが、ばねの疲労強度やばねのへたり量への影響は明らかではない。本研究では、SWOSC-Vオイルテンパー線を用いて通常の製造条件範囲で製造できるばねについて、結晶粒径と焼鈍温度が疲労特性と耐へたり性に及ぼす影響を調査した。その結果、結晶粒径の微細化により疲労寿命は向上したが、低温焼鈍温度の低下により疲労寿命は向上しなかった。いずれの場合も降伏強度の増加が期待されたが、今回は結晶粒径の微細化による降伏強度の増加量が低温焼鈍温度の低下による降伏強度の増加量よりも大きかったためと考えられた。また一定応力セッチングの影響を考慮すると、結晶粒径の微細化と低温焼鈍温度の低下の両方でばねの常温へたり量は減少した。いずれの場合も、降伏強度の増加と硬さの増加が影響したと考えられた。

Refining the grain size improves the strength of steel. This fact is well known, but the effect on the spring fatigue strength and the amount of spring relaxation is unclear. This study investigated the effect of grain size and annealing temperature on fatigue properties and resistance on relaxation of spring that can be manufactured within the normal manufacturing conditions using SWOSC-V oil-tempered wire. As a result, the fatigue life was improved by the refinement of the grain size, but not improved by lowing the low-temperature annealing temperature. Although an increase in yield strength was expected in both cases, this was thought to be because the increase in yield strength due to the refinement of the grains was greater than the increase in yield strength at the low-temperature annealing temperature. On the other hand, refining grain size and lowing the low-temperature annealing temperature reduced the amount of spring relaxation in room temperature when the effect of constant stress setting was taken into account. In both cases, this was thought to be caused by an increase of yield strength and hardness.

Refining the grain size, fatugue strength of spring, amout of spring relaxation, SWOSC-V oil temperd wire