The purpose of the present invention is to provide a steel plate for a pressure vessel having excellent resistance to high-temperature post-welding heat treatment, in which deterioration of strength and toughness is minimized even when a long-term post welding heat treatment (PWHT) is applied at high temperature, and a method for manufacturing same.

Provided herein are methods of transforming a first carbon material into a second carbon material, and uses thereof.

A steel material according to the present disclosure has a chemical composition consisting of, in mass %: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr 0.55 to 1.10%, Mo: 0.70 to 1.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, and the balance being Fe and impurities, and satisfying Formula (1) described in the specification. A grain diameter of a prior-austenite grain is 15.0 m or less, and an average area of precipitate which is precipitated in a prior-austenite grain boundary is 12.510.sup.3 m.sup.2 or less. A yield strength is 758 to 862 MPa.

The invention relates to a microstructure of an alloy for a tube for reformers, having an austenitic matrix structure, characterised in that: i) primary micrometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr, and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the solidification of the alloy; ii) secondary nanometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the activation of the tube; and iii) between 0.1 and 0.3% of Ni.sub.16Si7Nb.sub.6-type intermetallic precipitates is formed during the use of the tube.

The invention relates to a microstructure of an alloy for a tube for reformers, having an austenitic matrix structure, characterised in that: i) primary micrometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr, and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the solidification of the alloy; ii) secondary nanometric precipitates in the form of M.sub.23C.sub.6-type carbides, where M=Fe, Ni or Cr and/or M(C,N)-type carbides, where M==Nb or Ti, are formed during the activation of the tube; and iii) between 0.1 and 0.3% of Ni.sub.16Si7Nb.sub.6-type intermetallic precipitates is formed during the use of the tube.

A martensitic stainless steel containing, by mass %, C: 0.20% to 0.40%, N: 0.1% or less, Mo: 3% or less, and Cr: 12.0% to 16.0%, such that 0.3%C+N0.4% and a PI value (=Cr+3.3Mo+16N) is 18 or more, with the remainder being substantially Fe and unavoidable impurities is quenched from a temperature of 1,030 C. to 1,140 C. and subjected to a subzero treatment and tempering so as to obtain a prior austenite crystal grain size of a surface layer of 30 m to 100 m and a surface hardness of 58 HRc to 62 HRc.

A martensitic stainless steel containing, by mass %, C: 0.20% to 0.40%, N: 0.1% or less, Mo: 3% or less, and Cr: 12.0% to 16.0%, such that 0.3%C+N0.4% and a PI value (=Cr+3.3Mo+16N) is 18 or more, with the remainder being substantially Fe and unavoidable impurities is quenched from a temperature of 1,030 C. to 1,140 C. and subjected to a subzero treatment and tempering so as to obtain a prior austenite crystal grain size of a surface layer of 30 m to 100 m and a surface hardness of 58 HRc to 62 HRc.

Disclosed herein is high-strength special steel containing about 0.1 to 0.5 wt % of carbon (C), about 0.1 to 2.3 wt % of silicon (Si), about 0.3 to 1.5 wt % of manganese (Mn), about 1.1 to 4.0 wt % of chromium (Cr), about 0.3 to 1.5 wt % of molybdenum (Mo), about 0.1 to 4.0 wt % of nickel (Ni), about 0.01 to 0.50 wt % of vanadium (V), about 0.05 to 0.50 wt % of titanium (Ti), and the remainder of iron (Fe) and other inevitable impurities.

Disclosed herein is a high strength special steel including, by weight %: carbon (C): from about 0.1 to 0.5%; silicon (Si): from about 0.1 to 2.3%; manganese (Mn): from about 0.3 to 1.5%; chromium (Cr): from about 1.1 to 4.0%; molybdenum (Mo): from about 0.3 to 1.5%; nickel (Ni): from about 0.1 to 4.0%; vanadium (V): from about 0.01 to 0.50%; boron (B): from about 0.001 to 0.010%; niobium (Nb): from about 0.05 to 0.50%; and the balance of iron (Fe) and inevitable impurities.

A method of joining a first work piece and a second workpiece. The first and second workpieces may be rotor wheels of a rotor for a turbomachine. At least one of the workpieces includes an oxide dispersion strengthened alloy material and the first and second work pieces may be joined by welding a cladding on at least one of the workpieces to the other of the workpieces, without welding a substrate of the at least one workpiece which includes an oxide dispersion strengthened alloy material.