Effect of boron on G115 martensitic heat resistant steel during aging at 650°C

Microstructure and strength evolution of the G115 steels with different B content aging at 650 degrees C for 5000 h were investigated in this research. The results showed that properly increasing B content in steels would reduce the coarsening rate of M23C6 carbides and martensitic laths, slow down the reduction rate of dislocation density, and decelerate the evolution of microstructure. Phase analysis and electron probe micro-analyzer (EPMA) studies showed that when B was added to the steel, B atoms would enter M23C6 carbides to replace part of the C atoms, leading to the reduction in the coarsening rate of M23C6 carbides during aging. In terms of mechanical properties of G115 steels during aging, properly increasing B content in steels would slow down the reduction of yield strength, and the dislocation strengthening was the main factor affecting the yield strength evolution during aging.