Abstract: This invention provides a ferritic heat-resistant steel suitable for a pressure-resistant member to be used at a temperature of 400 to 550.degree. C. The ferritic heat-resistant steel having an excellent high temperature strength contains, in terms of wt %, 0.05 to 0.15% of C, 0.10 to 0.08% of Si, 0.20 to 1.5% of Mn, 0.5 to 1.5% of Cr, 0.10 to 1.15% of Mo, 0.005 to 0.30% of V, 0.005 to 0.05% of Nb, 0.0002 to 0.0050% of B, and if necessary, 0.005 to 0.05% of Ti and 0.4 to 1.0% of W, either alone or in combination, and having a structure comprising not greater than 15% of pro-eutectoid ferrite, in terms of a metallic structural area ratio, and the balance of bainite. The present invention provides also a process for producing a ferritic heat-resistant steel having an excellent high temperature strength, comprising tempering the steel having the composition at a temperature within the range 950 to 1,010.degree. C., and conducting tempering while keeping a T.P. value within the range of 18.50.times.10.sup.

Abstract: This invention provides a ferritic heat-resistant steel having excellent HAZ softening resistance characteristics and exhibiting a high creep strength up to a high temperature of not lower than 500.degree. C., and a method of producing such a steel, the steel comprising in terms of mass %, 0.01 to 0.30% of C, 0.02 to 0.80% of Si, 0.20 to 1.50% of Mn, 0.50 to 5.00% of Cr, 0.01 to 1.50% of Mo, 0.01 to 3.50% of W, 0.02 to 1.00% of V, 0.01 to 0.50% of Nb, 0.001 to 0.06% of N, one or both of 0.001 to 0.8% of Ti and 0.001 to 0.8% of Zr, wherein a value (Ti+Zr) in (Cr, Fe, Ti, Zr) of a M.sub.23 C.sub.6 type carbide in the steel is 5 to 65%, and the present invention provides a method of producing the same.

Abstract: A martensitic heat-resisting steel comprises, in terms of % by mass, 0.01 to 0.30% of C, 0.02 of 0.80% of Si, 0.20 to 1.00% of Mn, 5.00 to 18.00% of Cr, 0.005 to 1.00% of Mo, 0.20 to 3.50% of W, 0.02 to 1.00% of V, 0.01 to 0.50% of Nb, 0.01 to 0.25% of N, and at least one element selected from the group consisting of Ti, Zr, Ta and Hf in an amount of 0.005 to 2.0% for each of the elements, the volume of (Ti %+Zr %+Ta %+Hf %) in the metal component M of M.sub.23 C.sub.6 type carbides therein being from 5 to 65%. The heat-resisting steel is produced by a process comprising the steps ofadding Ti, Zr, Ta and Hf to a molten steel having chemical components as mentioned above, during the period from 10 minutes before completion of refining to completion of refining, casting said molten steel, working the resulting casting, solution treating said worked product, subjecting said worked product to temporary cooling stop at a temperature from 950.degree. to 1,000.degree. C.