Mechanical Properties and Microstructure of F82H Steel Doped with Boron or Boron and Nitrogen as a Function of Heat Treatment

Abstract

Effect of heat treatment on mechanical properties and microstructures of Fe-8Cr-2W-0.1C-0.2V-0.04Ta martensitic steel F82H doped with about 60 mass ppm B or both of 60 mass ppm B and 200 mass ppm N has been examined. The normalization was heated at temperatures from 950 to 1250°C for 1.8 ks, followed by air cooling or water quenching. After tempering treatment at 780°C or 750°C, the distributions of boron, boron nitride and oxygen were measured by a secondary ion mass spectrometry (SIMS). Optical microstructural observation and tensile and Charpy impact tests were performed also. In the boron doped F82H the tensile properties were similar to the non-doped F82H, but the ductile-brittle transition temperature (DBTT) shifted from -43°C to 15°C. SIMS images with high intensity of boron were observed in localized regions of the boron doped F82H. Water quenching reduced the DBTT shift, about 30°C, and the localized boron intensity was slightly decreased. In the boron and nitrogen doped tempered-F82H heat-treated by the water quenching from the normalizing temperature, the properties of tensile and Charpy impact were similar to the non doped F82H, and no pronounced localized boron image was observed in the SIMS image and no intensities of oxides and boron nitride were observed either.