Abstract: Martempering and austempering treatments were conducted on three types of high-hardenability high-carbon chromium bearing steels, namely GCr18MnMo steel, GCr18MnMo1 steel and GCr19SiMnMo1 steel. The differences in their microstructure, maximum hardenability size, retained austenite and impact properties were compared. The results show that the hardenability is ranked from high to low as GCr19SiMnMo1 steel > GCr18MnMo1 steel > GCr18MnMo steel. If the hardenability standard is that the core hardness is greater than or equal to 55 HRC, the maximum hardenability size of GCr18MnMo steel is approximately 70 mm, the maximum hardenability size of GCr18MnMo1 steel is approximately 100 mm, and the maximum hardenability size of GCr19SiMnMo1 steel is approximately 130 mm. When these three tested steels undergo austempering, the retained austenite content can be guaranteed to be less than 1%. During martempering, the retained austenite content of GCr18MnMo and GCr18MnMo1 steels is less than 15%, and for GCr19SiMnMo1 steel, the retained austenite content can be reduced to less than 1% by additional tempering while ensuring high hardness. The impact properties of these three specimen steels are very close, and the impact property after austempering is approximately 70% higher than that after martempering. Only GCr19SiMnMo1 steel can be used for parts with wall thickness or diameter more than ϕ100 mm to ensure that the core troostite meets the requirements.

Key words: high hardenability high-carbon chromium bearing steel, maximum hardening size, impact property, retained austenite