As far as the amount of precipitation hardening martensite heat resistant stainless steel pipe is concerned, the amount of martensite precipitation hardening stainless steel pipe is higher than that of other types. Due to their high hardness in the solution annealed state, they are mainly used in the form of bars, rounds, wires, and large forgings, with only a very small amount of sheets used as thin sheets. Austenite and ferrite in these alloys are in equilibrium, so they are in martensite state after solution heat treatment and cooling to room temperature. Since the 1940s, martensite precipitation hardening heat resistant stainless steel tubes have developed into a complete series. In order to ensure good corrosion resistance and weldability, the carbon content of martensite precipitation hardening stainless steel pipe is low, generally less than 0.1%.