Abstract: This invention relates to a method of manufacturing a martensitic stainless steel. The method comprises the following steps (a) to (c): (a) preparing a steel having a chemical composition consisting of, by mass %, C:0.003 to 0.050%, Si:0.05 to 1.00%, Mn:0.10 to 1.50%, Cr:10.5 to 14.0%, Ni:1.5 to 7.0%, V:0.02 to 0.20%, N:0.003 to 0.070%, Ti: not more than 0.300% and the balance Fe and impurities, and P and S among impurities are not more than 0.035% and not more than 0.010% respectively, and that it also satisfies the following equation: ([Ti]?3.4×[N])/[C]>4.5 wherein [C], [N] and [Ti] mean the content (mass%) of C, N and Ti, respectively, (b) heating the steel at a temperature between 850 and 950° C, (c) quenching the steel, and (d) tempering the steel at a temperature between Ac1?35° C. and Ac1+35° C. and in a condition of not more than 0.5 of the value of variation ?LMP1 in the softening characteristics LMP1, which is defined by the following equation: LMP1=T×(20+1.

Abstract: A martensitic stainless steel for seamless steel pipes, excellent in descaling property and machinability, having the following chemical composition, by weight %; 0.025 to 0.22% of C, 10.5 to 14% of Cr, 0.16 to 1.0% of Si, 0.05 to 1.0% of Mn, 0.05% or less of Al, 0.100% or less of N, 0.25% or less of V, 0.020% or less of P, 0.004 to 0.015% of S, and the balance Fe and impurities, This steel may include 0.0002 to 0.0050% of B, and/or 0.0005 to 0.005% of Ca. In this case, the upper limit of S may be extended up to 0.018%. Preferably, Al is limited to less than 0.01%.

Abstract: A martensitic stainless steel for seamless steel pipes, excellent in descaling property and machinability, having the following chemical composition, by weight %; 0.025 to 0.22% of C, 10.5 to 14% of Cr, 0.16 to 1.0% of Si, 0.05 to 1.0% of Mn, 0.05% or less of Al, 0.100% or less of N, 0.25% or less of V, 0.020% or less of P, 0.004 to 0.015% of S, and the balance Fe and impurities, This steel may include 0.0002 to 0.0050% of B, and/or 0.0005 to 0.005% of Ca. In this case, the upper limit of S may be extended up to 0.018%. Preferably, Al is limited to less than 0.01%.