In-situ hot rolling directed energy deposition-arc repair of shafts

Abstract

The shaft is a key component in mechanical systems and it needs to be repaired and replaced regularly due to long-term service in harsh conditions. However, using the directed energy deposition-arc (DED-arc) technology to repair the shaft results in columnar grains in the repair layer which affects the repair quality. In this study, the repair process of shafts by combining DED-arc and in-situ hot rolling was investigated, in which the material was rolled immediately after deposition, and plastic deformation occurred at high temperatures. A novel piece of equipment was developed, fabricated, and tested, and repair experiments were carried out on a 316 L stainless steel shaft. The effects of rolling on the tensile properties, hardness, and microstructure of the repaired parts were investigated, and electron backscatter diffraction (EBSD) characterization was performed on the deposited layers and interfaces to explore the hot deformation mechanism during the rolling process. The results showed that rolling led to dynamic recrystallization (DRX) nucleation and produced a large number of low angle grain boundaries (LAGBs) with high dislocation density, and static recrystallization occurred during subsequent deposition, thus refining the microstructure. Compared to the base metal, the hardness of the repaired layer increased by 20 %−30 %, and the yield strength and ultimate tensile strength increased from 220 MPa to 432 MPa and from 540 MPa to 595 MPa, respectively, with almost constant elongation.