Study On Dual-layer Temper Technique For Laser Cladding Repair Of P20Mold Steel

Mold is important process equipment for manufacturing industries.Due to the complex machining process and harsh service condition, manykinds of failures will occur during mold’s production or service process,which result in the need for welding repair. Mold repair using conventionalwelding methods is likely to cause a large heat input, resulting in thedeterioration of performance of the heat affected zone and the need fortime-consuming and costly subsequent high-temperature heat treatment.By drawing lessons from temper bead welding method used in weldingrepair field of pressure vessel, this work developed a dual-layer temperlaser cladding repair technique, which can avoid subsequenthigh-temperature heat treatment by taking full advantage of the tempereffect of the2ndlayer against the1stlayer, thus achieve a rapid and savingrepair of failure mold.First, by studying the position and size relationships between adjacentbeads of both the inner and inter layers regarding dual-layer temper lasercladding repair technique, theoretical formula to determine the optimalinner-layer beads overlap ratio was deduced. Based on the characteristicsof laser cladding, the Higuchi process parameters optimization model wasmodified. With this modified model, only a simple set of single-beadcladding tests and a few data derivation were required to rapidly determinethe optimal process parameters (the beads overlap ratio of inner-layer andpower density combination of inter-layer) for any given failure moldmaterials.Then, a set of single-bead cladding tests were carried out on P20moldsteel plates using a3.5kW diode laser. Based on this obtained experimental data, the theoretical optimal process parameters weredetermined using the modified Higuchi model: the beads overlap ratio ofinner-layer=70%and the power density combination of inter-layer is5&10kJ/cm~2.To verify the effectiveness of modified Higuchi parametersoptimization model, a set of laser cladding tests for P20steel weredesigned. The result showed that the optimal process parameters ofdual-layer temper laser cladding repair technique for P20steel are: thebeads overlap ratio of inner-layer=70%and the power densitycombination of inter-layer is5&10kJ/cm~2, which means that thetheoretical result derived from modified Higuchi model is in goodagreement with the actual laser cladding test result.Finally, in order to evaluate the feasibility of rapid repair of failuremold using the dual-layer temper laser cladding repair technique,comparison was made between the results of two tests that applieddual-layer temper repair technique (using above-mentioned optimalparameters) and traditional mono-layer repair technique respectively. Theresults reveal that dual-layer temper laser cladding repair technique usingappropriate process parameters determined by modified Higuchi model canobtain a better repair effect than the traditional single-layer repairtechnique which need subsequent heat treatment. That is, themicrostructure of its repair heat affected zone is tempered sorbite andhardness of it is approximately400HV, which are closer to the P20basematerial.