Temperature and Strain Rate Dependence of Low-Cycle Fatigue Properties of Heat Resisting Steel SUH 660

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  • 耐熱鋼ＳＵＨ６６０鋼の低サイクル疲労特性の温度，ひずみ速度依存性
  • タイネツ コウ SUH660 コウ ノ テイ サイクル ヒロウ トクセイ ノ

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Abstract

Low-cycle fatigue tests were carried out on precipitation hardening, heat resisting steel, JIS SUH 660, at room temperature, 450, 600 and 700°C under a triangular strain waveform for which the strain rate was 40, 4 or 0.4%/min.<br>The results obtained are summarized as follows:<br>(1) The stress range decreased or increased first and then decreased with increasing strain cycles depending on the test condition. The strain rate dependence of the cyclic stress-strain relation was scarcely observed at temperatures up to 600°C. At 700°C stress was smaller for the strain rate of 0.4%/min than that for 40%/min.<br>(2) For the relation between the plastic strain range and the number of cycles to failure, the strain rate dependence was scarcely observed at room temperature and 450°C, but the number of cycles to failure decreased with decreasing strain rate at 600 and 700°C. The temperature dependence of the relation was clearly found at temperatures from room temperature to 600°C, but there was no difference between the relations at 600 and 700°C.<br>(3) Transgranular fracture surface covered with striations and small dimples were observed for the specimens tested at room temperature and 450°C. Intergranular fracture occurred at 600 and 700°C.<br>(4) For the temperature range at which transgranular fracture occurs, the temperature dependence of the Δεp-Nf relation could be explained by the mechanical parameter Δεp(Δσ/σu)2 which was introduced by Tomkins.<br>(5) For the temperature range at which intergranular fracture occurs, the relation α=1/(1+an) was obtained, where a is a constant value of 4∼6 and α and n are exponents of Δεp-Nf and Δεp-Δσ relations, respectively.

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