Research on the Microstructure and Microhardness of 9Cr18 Semi-Solid Billet

Abstract

Formed in the semi-solid state, materials can obtain unconventional microstructures and properties compared with traditional method. In this paper, semi-solid billet of 9Cr18 steel was obtained through a wavelike sloping plate. Microstructure analysis of the semi-solid billet was conducted through scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) test and microhardness test were also used to analyze the properties. The results showed that the structure of 9Cr18 semi-solid billet contained globular primary austenite and secondary austenite-Cr7C3 eutectic. Globular primary austenite grains were first formed during partial solidification in the sloping plate, and then the rest liquid metal formed secondary austenite and Cr7C3 eutectic structure surrounding the primary grains. Cr atoms had a concentration in the rest liquid side, which along with C atoms contributed to the formation of the Cr7C3 carbide. Hardness in the primary solid grain area and the eutectic area was about 330 HV and 650 HV, respectively. These specific properties were important for subsequent thixoforming of the functional graded materials.

Flow mechanism of 9Cr18 steel during thixoforging and its properties for functionally graded material

“…However, hardness in the inner austenite and edge dendrite area of the thixoforged specimen is quite different: hardness in the inner is about 376 HV level, while hardness in the edge is about 726 HV level. The difference is mainly due to the formation of hard (Fe, Cr) 7 C 3 carbide in the surface, which has been confirmed in the previous study [24]. Fig.…”