Characteristics and uses of C350 stainless steel 18Ni maraging steel:
Representative steel grades for 18Ni steel include 022Ni18Co8Mo3TiA [18Ni (200)], 022Ni18Co8Mo5TiA [18Ni (250)], 022Ni18Co9Mo5TiA [18Ni (300)], and 00Ni18Co13Mo4TiA [18Ni (350)] steel.
18Ni steel is a typical maraging steel with low carbon content. The alloy elements that play a role in age hardening are Ti, Al, Co and Mo. Impurities have a great impact on the properties of martensite age hardening steel, and the effect on steel with higher yield strength is more obvious. This requires this type of steel to undergo vacuum smelting to reduce impurities, segregation, and gas content in the ingot, so that the steel has good toughness and performance.
In 18Ni steel, carbon has a great influence on the strength of the steel. Even if the carbon content is very small, the strength of martensite will be significant. However, the yield strength of steel will be reduced after the carbon mass fraction is increased by 0.03 percent , so the carbon mass fraction in 18Ni maraging steel should not exceed 0.03 percent .
The S in C350 maraging steel is harmful. S exists in steel as sulfides and is distributed along the hot rolling direction, resulting in anisotropy of the steel. Therefore, it is required to minimize the sulfur content of the steel as much as possible.
A large amount of Ni is added to 18Ni steel to obtain a single martensite after solid solution quenching, and the second effect of Ni on Mo is to form an aging strengthening phase Ni3Mo. When the mass fraction of Ni exceeds 10 percent , the fracture toughness of maraging steel can be improved.
18Ni steel forms ultra-low carbon martensite after solid solution, with hardness of 28~30HRC; After aging treatment, due to the precipitation of various types of intermetallic compounds, aging hardening can be achieved, and the hardness can increase to 50HRC. This type of steel still has good toughness and high fracture toughness under high strength and toughness conditions. At the same time, this type of steel has no cold work hardening, small deformation during aging heat treatment, good weldability, and the surface can also be nitrided.
18Ni low-carbon maraging steel is mainly used to manufacture mechanical parts and plastic molds with high precision, ultra mirror surface, complex cavity, large cross section and mass production, but its use is limited due to its high price.
