Short-Time Tensile and Long-Time Creep-Rupture Properties of the HK-40 Alloy and Type 310 Stainless Steel at Temperatures to 2000 F

The short-time tensile properties of the A CI Type HK-40 cast heat-resistant alloy and AISI Type 310 wrought stainless steel were investigated from room temperature to 2000 F. The creep-rupture properties of the HK-40 alloy were studied in the range of 1400 to 2000 F for times long enough to permit extrapolation to 100,000 hr. In addition, the creep-rupture properties of Type 310 were investigated at 1800 to 2000 F, and observations were made of the microstructural changes that occurred in the two materials during creep exposure. The Type 310 material tended to have a higher yield strength and ultimate tensile strength at moderate temperatures than the HK-40; however, from 1200 to 2000 F, the HK-40 was the stronger. The Type 310 was more ductile at all temperatures. The HK-40 displayed about twice the rupture strength of the Type 310 at each test temperature. On the basis of comparable minimum creep rates, the HK-40 showed five to six times the strength of the Type 310 at the same temperature. During exposure at the lower temperatures, chromium carbides precipitated in finely dispersed form in the matrix of the HK-40; isolated islands of sigma phase also tended to form. At high temperatures, the primary eutectic carbides in the HK-40 alloy tended to spheroidize; and both materials absorbed nitrogen from the atmosphere, needles of chromium nitride forming in the matrix.