Roller shaft is an important part of high speed wire mill, and the shaft journal is easy to wear. In order to extend the service life of the roller shaft, the worn shaft journal can be remanufactured by laser cladding. However, the hardness of the roller shaft is high. And there will be large number of cracks when laser cladding high hardness powder. But gradient cladding can be used to solve this problem. Previous researches of gradient cladding mainly focus on theory and technology, but few works touch the practical repairing. In this paper, Fe1 alloy powder and Fe5 alloy powder were coated on the surface of 45# steel by 4 kW fiber laser. The former was transition la-yer, and the latter was strengthened layer. The defects on the surface of the coating were detected by penetrant inspection. Furthermore, the microstructure and element content of the coating were analyzed by means of OM, SEM and EDS. And the phase composition of each layer was investigated by XRD. Meanwhile, the microhardness of the coating was measured by microhardness tester. The results showed that the sample presented good surface morphologies. No macroscopic cracks formed on its surface. And the coating was compact and free of defects. Moreover, metallurgical combinations were achieved between the layers. And the grains at the junction of the transition layer and the strengthened layer were refined. In general, the upper grains are smaller than the lower ones. XRD analysis showed that the transition layer was mainly composed of austenite and the reinforcement layer was made up of austenite and martensite. The hardness of the cladding layer presented a typical gradient distribution. And the average hardness of the strengthened layer was 566.12HV0.2, which met the hardness requirement of the mill roll shaft. Furthermore, the average hardness of the transition layer was 385.98HV0.2, which played a good role in buffering. The relationship between the speed of mechanical arm and the rotating speed of journal during laser cladding were deduced. Meanwhile, a good repair effect has been achieved. © 2019, Materials Review Magazine. All right reserved.
