为了缩短生产时间和降低塑料成型模的成本，需要提高模具钢的切削加工性能。为此，日本神户钢铁公司技术开发部、材料研究所的科技人员为S55C型碳钢开发了一种具有切削加工性能优良的新钢号KTSM21M，其成分为0.30%C,0.30%Si,0.125%Mn,以及Cr,Mo,V,S合金元素。

根据对实际尺寸试验锻造的评定，表明该新钢号的力学性能和腐蚀性能几乎与KTSM21（模具用常规钢）的相同，而其可焊性优于KTSM21。还提高了重型铣削加工和高速机加工，例如端铣等的切削加工性能。可望新的KTSM21M钢适用于从粗机加工到精加工的所有工艺。

To shorten the production time and reduce the cost of plastic molding, the need to improve machining performance of die steel. To this end, Japan's Kobe Steel Technology Development Department, Institute of Materials Science and Technology staff to develop a S55C carbon steel with excellent cutting performance of the new steel KTSM21M, the composition 0.30% C, 0.30% Si, 0.125% Mn, and Cr, Mo, V, S alloying elements. Based on the assessment of the actual size of forging test, indicating that the new steel mechanical properties and corrosion resistance almost KTSM21 (mold using conventional steel) of the same, and its superior solderability KTSM21. Also improved heavy-duty milling and high-speed machining, for example, such as end milling cutting performance. Steel is expected to apply the new KTSM21M from rough machining to finishing all the process.