Studies on the Torsional Creep Strength of 5% Cr Hot Work Die Steel and Mo-High Speed Steel

Abstract

High speed steel SKH 9 and 5%Cr hot work die steel SKD 61 are used now for elevated temperature springs. An important problem in the elevated temperature spring is creep in torsion, and there has hitherto been little published information on the creep of hardened and tempered elevated temperature spring steel. The present work was made to study the torsion creep behavior and creep strength at the temperature 300 to 550°C for quenched and tempered SKD 61 and SKH 9 steel, and the effect of nitriding treatment on the creep strength was also tested for SKD 61. The dimensions of the specimen of creep test were 5mm in diameter and 30mm in length. The machine employed in the torsion creep test was made in our laboratory.
No remarkable creep was observed at 300°C of SKD 61 under 60kg/mm² of twisting stress, nor at 400°C of SKH 9 under 65kg/mm² of stress. At 400°C of SKD 61 and 500°C of SKH 9 torsion creep increased gradually with increased stress, and at higher test temperature the creep rate rose enormously. Nitriding treatment was very effective for increasing the creep strength at 500°C of SKD 61.