Abstract
High elastic limit and high fatigue strength are necessary for valve springs, but small settling is also necessary. We have made an observation on this phenomena and an investigation on the effect of bluing conditions. The results obtained were as follows. (1) The settling curves (settling value—testing time curves) are the same as the primary and secondary creep curves. (2) In the case of a large compression, the settling value is largely affected by the bluing temperature. (3) The minimum of settling value is obtained by bluing at 300°C when the testing time is one hour. (4) Under the bluing temperature below 200°C, the longer the bluing time the smaller is the settling. If the bluing temperature is over 350∼400°C, the settling value reaches the maximum and gradually grows smaller. (5) By microscopic examination, structual changes were observed over 350°C. (6) These results are the same as the strain-aging of low carbon steel.
