Microstructure, properties and wear characteristics of high-speed steel cold roller repair layers via pulse cold metal transfer welding

The cold roller operates under harsh conditions, which can lead to surface damage. Repairing damaged rollers is a cost-effective solution that significantly extends their service life. The substrate developed severe thermal deformation and a wide heat-affected zone (HAZ) when repaired using traditional gas metal arc welding (GMAW). Moreover, the GMAW repair layers had coarse grains and poor mechanical properties. Compared with conventional GMAW, pulse cold metal transfer welding (CMT-P) significantly reduced substrate deformation, HAZ width, and grain size due to its lower heat input and enhanced molten pool agitation, resulting in superior wear and bending properties of the repaired layers. The microstructure of the as-welded repair layers consisted of acicular martensite and retained austenite (RA). To further optimize the microstructure and mechanical properties of the repair layers, tempering treatment was conducted. After tempering at 500 °C for 2 h, the RA transformed into fresh martensite, and the carbide precipitates appeared uniformly within the martensite matrix. In this case, the hardness of the repair layers reached 61.8 HRC, which was higher than that of the roller matrix working layer (60.1 HRC). Furthermore, the repair layers exhibited lower friction coefficients and wear volumes, achieving superior wear resistance. Additionally, the repaired layers exhibited excellent bending properties, demonstrating a bending strength of 1912.7 MPa and deflection of 2.89 mm.