STEEL FOR CHISELS AND CHISEL

The present invention provides a steel for chisels and a chisel, which have improved durability. The steel that constitutes the chisel (10) according to the present invention is characterized by comprising 0.40-0.45 mass% carbon, 0.50-0.80 mass% silicon, 1.00-1.30 mass% manganese, 0.001-0.005 mass% sulfur, 2.90-3.80 mass% chromium, and 0.20-0.40 mass% molybdenum, with the remainder being composedof iron and unavoidable impurities; and by the ideal critical diameter DI, as defined in formula (1), being 600 or greater. DI = 7 .(%C)1/2 .(1+0.64.%Si) .(1+4.1.%Mn) .(1+2.83.%P). (1-0.62.%S) .(1+2.33.%Cr).(1+3.14.%Mo). 本发明提供种提高了耐久性的钻头用钢及钻头。构成本发明的钻头(10)的钢的特征在于，含有：0.40质量％以上且0.45质量％以下的碳、0.50质量％以上且0.80质量％以下的硅、1.00质量％以上且1.30质量％以下的锰、0.001质量％以上且0.005质量％以下的硫、2.90质量％以上且3.80质量％以下的铬、以及0.20质量％以上且0.40质量％以下的钼，余量为铁及不可避免的杂质，式(1)中定义的理想临界直径DI的值为600以上。DI＝7·(％C)·(1+0.64·％Si)·(1+4.1·％Mn)·(1+2.83·％P)·(1-0.62·％S)·(1+2.33·％Cr)·(1+3.14·％Mo)···(1)。