National Institute for Materials Science

Mitsubishi Heavy Industries Limited

Japan as Represented by Director General of National Research Institute for Metals

Kazuhiro Kimura

Kota Sawada

Takashi Watanabe

Nobuyoshi Komai

Yuichi Hirakawa

Hiroaki Fukushima

Nobuhiko Saito

Kaoru Sekido

Junichi Kinugawa

Hideaki Kushima

Hiromichi Hongo

Yasushi Taniuchi

Masayoshi Yamazaki

Toshio Ohba

A faulted condition determination method is designed to detect a chromium content and a nickel content in a predetermined boundary region proximate to a boundary between a high-strength ferrite steel and a weld material in a welded joint in which the high-strength ferrite steel and another steel are welded together using the weld material containing nickel and to thereby determine the faulted condition of the predetermined boundary region based on the chromium content and the nickel content. Accordingly, it is possible to appropriately determine the faulted condition of welding of a replacement part in which a high-strength ferrite steel and another steel are welded together using a nickel-based weld material.

Faulted condition determination device and faulted condition determination method

The invention provides a ferritic heat-resistant steel whose creep rupture ductility in a long-term region is improved without detrimental to creep strengths. The ferritic heat-resistant steel has a chemical composition comprising, in % by mass, C: 0.03 to 0.15, Si: 0 to 0.8, Mn: 0.1 to 0.8, Cr: 8.0 to 11.5, Mo: 0.2 to 1.5, (W: 0.4 to 3.0), V: 0.1 to 0.4, Nb: 0.02 to 0.12 N: 0.02 to 0.10 with the balance of iron and inevitable impurities. This steel has a tempered martensite microstructure, and has an improved creep rupture ductility even when there is a load within the elastic limits at temperatures at which the ferritic heat-resistant steel is used, because internal strain or internal stress induced by martensitic transformation is relaxed or released by an intermediate tempering heat treatment in a two-phase state temperature in which a portion of an austenitic phase undergoes martensitic transformation.

Ferritic heat-resistant steel and method for producing the same

A high-Cr containing ferrite heat resistant steel having not only an excellent long-term creep strength at a high temperature exceeding 650&deg; C., but also an improved oxidation resistance, which is based on ferritic phase and contains 13% by weight or more of chromium, and containing precipitates of intermetallic compounds.

High-chromium containing ferrite based heat resistant steel

The creep strength of a welded joint portion is improved, and damage of the welded joint portion based on the generation or development of cracks is suppressed. A postweld heat treatment process, wherein a welded joint made of carbon steel and low alloy steel is held within austenite single-phase temperature range for a given time and subsequently the joint is cooled by air-cooling or by slow cooling at a cooling rate lower than that of the air-cooling.

Postweld heat treatment process of carbon steel and low alloy steel

Growing community of inventors

Ibaraki, Japan

Kazuhiro Kimura