Effects of Specimen Surface Condition and Atmosphere on Small Punch Creep Property of Low Alloy Steel

The effects of various factors such as the surface finish condition of specimens, lubricant and argon gas flow rate on both the creep deformation behavior and time to rupture for 2.25Cr-1Mo low alloy steel used for boilers by small punch testing were studied. There was little difference in both the small punch creep deformation behavior and time to rupture due to the difference in surface roughness between #1200 polished specimens and those in mirror polished condition. The application of BN lubricant to the specimen surface resulted in the decrease in time to rupture, due to the lowering of friction coefficient. Furthermore, the time to rupture increased according to the increase of argon gas flow rate. The depth analysis by μ-ESCA for surface oxide film formed in an argon gas atmosphere demonstrated that the formation of Fe-rich oxide film with a low friction coefficient produced a decrease in time to rupture under a low argon gas flow rate condition. The formation of Cr-rich oxide film with high friction coefficient produced the increase in time to rupture under high argon gas flow rate condition. This suggests that the reliable control of argon gas flow rate is very important in order to evaluate the life of material by small punch creep testing.