Enhancing Hardness of Medium Carbon Steel by Boriding Process for Punching Tool Applications

A punch is a tool used to make holes or shapes in materials by compressive loading. During service, it is repeatedly subjected to impact, friction, and heavy surface contact, making surface hardness an important factor in maintaining cutting performance, edge retention, and tool life. Tool steels are widely used in punching applications because of their high hardness and wear resistance. However, they are relatively expensive, less readily available, and more difficult to machine. In contrast, C45 medium carbon steel is common, inexpensive, and easy to manufacture, but its hardness in the untreated condition is generally insufficient for demanding punching operations.

This study investigated boriding as a thermochemical surface treatment to improve the surface hardness of C45 steel. Unlike conventional pack boriding, only one side of the specimen was buried in amorphous boron powder to selectively harden the working surface. Preliminary experiments were conducted on rectangular C45 steel specimens in the temperature range of 800 to 950 °C for a treatment duration of 2 to 4 hours, with the treatment conditions selected based on commonly reported boriding conditions for C45 steel. Based on the hardness results, 800 °C for 2 hours was selected for application to a punching blade.

The surface hardness of the punching blade increased significantly from 240 HV0.1 in the untreated condition to 970 HV0.1 after boriding, representing an increase of more than four times. These findings demonstrate that the proposed partial boriding approach effectively improves the surface hardness of C45 steel and shows potential for localized surface hardening of punching blades. Further investigation of the borided layer characteristics, wear resistance, and tool-life performance is recommended to validate its practical applicability.