Influence of nickel content on machinability of a hot-work tool steel in prehardened condition

In the present study, the influence of nickel content on the machinability of a prehardened hot-work tool steel was investigated. The machinability with varying nickel content from 1 to 5 wt.% was characterized in end milling and drilling by evaluating tool life, cutting forces, and tool/chip interface temperature.Nickel content showed to have a positive effect on the machinability of the hot-work tool steel; with increasing nickel content in the steel, the longer tool life was reached in end milling and drilling operations. Machining the higher nickel containing steels generated lower cutting forces and tool/workpiece interface temperature. In addition, less adhesive wear and built-up edge formation were observed on the tools.The difference in the steel machinability was discussed in terms of their microstructure and mechanical properties. Increasing nickel content tends to decrease the carbon in the martensite and to retain a fine distribution of small primary carbides. It resulted in a reduction in yield strength with increasing nickel content related to the cutting force reduction and machinability improvement.