INVESTIGATION OF CORROSION AND ADHESION BEHAVIORS OF BORONIZED ASP® 2012 STEEL

Abstract

Tool steels are extensively used in sheet metal forming dies in order to prolong the life of dies and reduce the cost of production. Powder metallurgy tool steels are also alternatively preferred because of their low-risk metallurgical behavior owing to their compositions by which bulk steel would be difficult to produce, such as high amount of carbides or high alloying elements. Such advantage is desired if the steel has a narrow range of fine grain sizes and is less metallurgically affected by the heat treatment process due to having large surface area of fine grains. In this study, ASP® 2012 powder metallurgy steel containing high amounts of Si, Cr, Mo and W was selected for boronizing by the boron-giving thermochemical process. The boride layers on the surface of ASP® 2012 tool steel were metallographically characterized by various characterization techniques including adhesion strength test, SEM and XRD. The effects of corrosion kinetics and chemical composition of steel on the amount and types of boride layers formed on P/M steel of ASP® 2012 after powder-pack boriding were investigated. The results indicate that, according to the Rockwell-C indentation test, the best adhesion in the boride layer was obtained in samples borided at 850°C for 4 h, while the worst adhesion was obtained in ASP® 2012 steel boronized at 950°C for 4 h. Corrosion rates of boronized ASP® 2012 steel were decreased compared to nonboronized ASP® 2012 steel.