Microstructure and Mechanical Properties of New Type Bainitic Carburized Steel for Gear

This paper presents the microstructure, mechanical properties and carburized behavior of new type bainitic carburized steel. The results show that after new carburized steel is normalized at 920 inverted perpendicular C and tempered at 300 degrees C, its microstructure consists of bainitic ferrite and residual austenite, and belongs to the carbide-free bainite or atypical bainite. Large or small cross-section size new carburized steel bar all have reached the performance requirements of Cr-Ni carbonized steel. The microstructure of new carburized steel surface consists of high carbon martensite and residual austenite after carburized and air-cooled, It retains austenite fraction of the new carburized steel and 18Cr2Ni4WA steel are about 18% and 38%, respectively. Carbon concentration gradient of new carburized steel changes smoothly and have ideal carbon concentration distribution. Effective carburizing surface depth of new carburized steel is about 0.6mm and is smaller than 18Cr2Ni4WA steel. The gear entities made of new carburized steel meet the technical requirements of heavy duty carburized gear.