Enhancing the corrosion, tribological and tribocorrosion performance of AIsI H13 steel by the pack and electrochemical based boriding methods

AISI H13 is used in poly(vinyl chloride) (PVC) extrusion and injection mold and tool manufacturing due to its excellent high temperature performance along with high hardness, toughness and hardenability properties. One drawback associated with the high temperature processing of PVC-containing materials is the non-negligible concentration of free chloride species originating from the cleavage of C–Cl bonds, which may strongly accelerate corrosion and wear rates. Nevertheless, it is necessary to improve the wear and corrosion resistance of H13 steel, which is preferred in most hot forming applications such as forging and casting, at room and high temperatures. During hot forming applications, molds and tools are generally exposed to severe static/cyclic loads at high temperatures, and this can lead to erosion, thermal fatigue, and abrasive/adhesive wear in major areas of the mold and tool, which can significantly shorten the service life of the mold and tools. Additionally, molds and tools can suffer damage due to the combined effect of corrosion, temperature, and aggressive lubricants. The weak corrosion and wear resistance of H13 steel pose challenges in terms of its tribological and tribocorrosion performance. To address this issue, pack and electrochemical-based boriding have been investigated as a potential solution. This study demonstrates that pack (using a mixture powder of 90% B4C and 10% KBF4 at 950°C for 6 hours) and electrochemical (using a mixture of 90% Na2B4O7 and 10% Na2CO3 electrolyte at 950°C for 15 min with an applied current density of 200 mA/cm2, followed by a 45-min soaking) based boriding can significantly enhance the surface hardness and self-lubrication performance of H13 steel, while maintaining impressive corrosion and tribocorrosion performance. The borided layer obtained through pack boriding is approximately 59 µm thick, and through electrochemical boriding, it is approximately 25 µm thick. The borided layer is primarily composed of FeB, Fe2B, and CrB. After pack and electrochemical boriding, the surface hardness of H13 steel reaches approximately 1573 HV0.05 and 1805 HV0.05, respectively. The untreated H13 steel exhibits a wear rate of 25.6 x 10-6 mm3 Nm-1 in a 3.5% NaCl solution, which is 95% lower than that under dry conditions. For pack and electrochemical borided H13 steel, the wear rates in a 3.5% NaCl solution are 8.38 x 10-6 mm3 Nm-1 and 1.66 x 10-6 mm3 Nm-1, respectively, representing a reduction of 36 % and 69 % compared to dry conditions. When compared to untreated H13 steel, the wear rates of pack and electrochemical borided H13 steel under 3.5% NaCl solution conditions are reduced by 67% and 94%, respectively.