Thermal Aging Effects on High Temperature Tensile Strength of Mod.9Cr-1Mo Steel With Stress Release Treatment

Abstract This paper evaluates the effect of thermal aging on the normalizing and tempering (NT)+ stress relief heat treatment (SR) of Mod. 9Cr-1Mo steel in more detail than previous studies. The evaluation in this paper used tensile test results of material that had been actually thermal aged at 550°C for approximately 200,000 hours. The tensile specimen used in this study was a micro specimen taken from the threaded portion of a creep specimen for which testing had been completed. Therefore, in this paper, we first confirmed that it is possible to obtain tensile test data using micro specimens. Tensile test results of materials aged with temperature acceleration were also used in this study. Aging times for temperature-accelerated materials were calculated using Hollomon-Jaffe parameter type equations. The results of post aging tensile tests showed that there was a difference in strength loss after aging between the NT materials and NT+SR materials. In addition to tensile test results, hardness test results were used to evaluate strength reduction after aging. This paper discusses the differences between NT materials and NT+SR materials from the tensile test results and the hardness test results obtained and identifies issues that need to be resolved for further analysis.