A Comparative Study on the Microstructures and Mechanical Properties of Two Kinds of Iron-Based Alloys by WAAM

Abstract

In order to adapt to the high temperature and heavy load process environment of large forgings, a novel die with “fist-like” structure is designed. The “fist-like” die mainly consists of “skin” layer, “bone” layer and matrix. To obtain the material with good supportability and good bonding strength with the “skin” layer, iron-based alloys RMD248 and CN72 were selected to make the “bone” layer, and the properties were compared. In this paper, the “bone” layer and the “skin” layer (CHN327) were surfaced on 5CrNiMo matrix by wire arc additive manufacture (WAAM). Then, cyclic heating to 500 °C and thermal compression with a maximum deformation of 30% were adapted to test the high temperature mechanical properties. The microstructure changes before and after thermal cycles and compressions were observed by optical microscopy (OM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and scanning electron microscopy (SEM). The results show that CN72 has more carbides than RMD248 at the joint surface, which makes it easy to form brittle fracture at the joint. Mechanical properties were tested by using microhardness machine. Meanwhile, hot tensile tests were performed to study bonding strength between the “skin” layer and the “bone” layer. The results show that the RMD248 has stable microhardness distribution while the microhardness of CN72 decreases with the distance from the interface. And the ultimate tensile strength between CN72 and CHN327 is higher than RMD248 in the temperature range of 400–450 °C. It can be inferred that CN72 has higher inter-layer wear resistance and RMD248 has more stable high temperature performance.

Keywords

iron-based alloy / wire arc additive manufacture / die / microstructure / mechanical properties