Microstructure and mechanical properties of laser solid formed 300M steel

Microstructure and mechanical properties of laser solid formed 300M steel were investigated. The as-deposited microstructure presented the tempered martensite, the martensite with a small amount of bainite, and the mixture of martensite and bainite from the bottom to the top of the deposits. After heat treatment, the microstructure was refined and uniform, and consisted of the mixture of tempered martensite, bainite and retained austenite. The hardness only showed a little increase from the bottom to the middle-upper of the as-deposited 300M steel, there was a significant increase in the hardness at the top of as-deposited 300M steel. The hardness in the heat treated deposits tended to be uniform and higher than that in the as-deposited 300M steel. Tensile strength and yield strength of the as-deposited 300M steel were much lower than the wrought standard. Through heat treatment, the tensile properties of laser solid formed 300M steel were improved significantly and reached the forgings standard.