The Effect of Cold Working on Creep Rupture Strength and Microstructure of Ni-23Cr-7W Alloy

摘要

In order to clarify the reason why the creep rupture time of pre-strained Ni-23Cr-7W Alloy (HR6W) is longer than that of the non-pre-strained HR6W, microstructures of HR6W after a series of creep tests were investigated. The creep tests were conducted at 750 style="white-space:nowrap;">°C, 90 and 100 MPa. In the pre-strained samples, the grain boundary shielding ratio by precipitates was larger than that of the non-pre-strained sample. In addition, in the pre-strained samples the size of the M₂₃C₆ carbide in the grains was finer than in the non-pre-strained sample. The W content in the M₂₃C₆ carbide in the pre-strained samples tended to be larger than in the non-pre-strained sample. Therefore, the Ostwald ripening of the carbide was delayed and the size of M₂₃C₆ carbide was thought to be fine for a long time. These observations show that creep strength in the pre-strained samples is higher than that of the non-pre-strained sample because of both precipitation strengthening inside of the grains and grain boundaries.