Influence of pre-heating on the surface modification of powder-metallurgy processed cold-work tool steel during laser surface melting

• Published in: Applied surface science 2015, Vol.325, p.203-210
• Main Authors: Sturm, Roman, Stefanikova, Maria, Steiner Petrovic, Darja
• Format: Article
• Language: English
• Subjects: Assessments; Coarsening; Cold-work tool steel; Cracking; Dissolution; Heat treatment; Laser surface melting; Lasers; Liquidus; Melting; Powder metallurgy; Pre-heating; Steels; Tool steels
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2014.11.050

•Heat-treatment protocol for laser surface melting of cold-work tool steel is proposed.•The laser melted steel surface is hardened, and morphologically modified.•The pre-heating of substrate creates a crack-and pore-free steel surface.•The optimum pre-heating temperature is determined to be 350°C.•Using pre-heating the quantity of retained austenite is reduced. In this study we determine the optimal parameters for surface modification using the laser surface melting of powder-metallurgy processed, vanadium-rich, cold-work tool steel. A combination of steel pre-heating, laser surface melting and a subsequent heat treatment creates a hardened and morphologically modified surface of the selected high-alloy tool steel. The pre-heating of the steel prior to the laser surface melting ensures a crack- and pore-free modified surface. Using a pre-heating temperature of 350°C, the extremely fine microstructure, which typically evolves during the laser-melting, became slightly coarser and the volume fraction of retained austenite was reduced. In the laser-melted layer the highest values of microhardness were achieved in the specimens where a subsequent heat treatment at 550°C was applied. The performed thermodynamic calculations were able to provide a very valuable assessment of the liquidus temperature and, especially, a prediction of the chemical composition as well as the precipitation and dissolution sequence for the carbides.