Hitachi, Ltd.

Babcock-hitachi Kabushiki Kaisha

Masayuki Sukekawa

Seishin Kirihara

Katsumi Iijima

Kenichi Usami

Hiroyuki Doi

Masao Shiga

Norio Yamada

Takatoshi Yoshioka

Choichi Asano

Kiyoshi Hiyama

Yoshimitsu Tobita

Hisashi Morimoto

Yasuhide Sakaguchi

A high-strength austenitic steel having a fully austenite structure and consisting essentially of 0.02 to 0.15 wt % of C, not greater than 1.5 wt % of Si, not greater than 2.5 wt % of Mn, 8 to 20 wt % of Ni, 13 to 25 wt % of Cr, 0.02 to 0.25 wt % of Al, not greater than 0.1 wt % of N, at least one of 0.001 to 0.01 wt % of B, 0.02 to 0.5 wt % of Nb, 0.01 to 0.2 wt % of Ti and 0.02 to 0.6 wt % of V and the balance substantialy Fe, with the weight ratio (Al/N) ranging between 1 and 4.5. This steel is suitable for use as the material of, for example, inner casing of steam turbine, valve body incorporated in the steam turbine, rotor shaft, and chemical equipment such as reaction pipe and vessel for styrene monomer producing facility.

High-strength austenitic steel

A boiler tube having a double-tube structure constituted by an inner tube and an outer tube integrated with each other. The inner tube is made of an alloy consisting essentially of, by weight, 0.02 to 0.15% of C, 0.5 to 3.5% of Si, not greater than 2% of Mn, 25 to 40% of Ni, 20.5 to 27% of Cr, 0.5 to 3% of Mo, not greater than 1% of Nb and the balance Fe and having a substantially fully austenite structure. The outer tube is made of an alloy consisting essentially of, by weight, 0.02 to 0.2% of C, not greater than 3.5% of Si, not greater than 2% of Mn, 33 to 45% of Ni, 30 to 40% of Cr and the balance Fe and having a substantially fully austenite structure. The inner tube made of the alloy having the composition specified above exhibits a high resistance to steam oxidation without any reduction in high-temperature strength even at elevated steam temperature, while the outer tube made of the alloy having the composition specified above exhibits a superior resistance to corrosion by coal combustion gas.

Boiler tube

A heat-resistant and corrosion-resistant weld metal alloy consisting essentially of, by weight, less than 0.08% of C, 0.1 to 1.0% of Si, 2 to 3% of Mn, 32 to 42% of Ni, 21 to 25% of Cr, 0.8 to 1.7% of Mo, 0.1 to 1.0% of Nb, up to 0.5% of Ti, up to 2% of Co, up to 2% of Cu, up to 1% of W, up to 0.2% of N, up to 1.0% of V, up to 1.0% of Zr, up to 1.0% of Ta and the balance Fe, wherein the following conditions are met: Ti+Zr.ltoreq.1.0%, Ni+Co.ltoreq.42%, W+V.ltoreq.1.0%, Nb+Ta.ltoreq.1.0%, and 4.ltoreq.Nb/C.ltoreq.15; and an austenitic welded structure composed of an austenitic structural alloy and of a weld metal of the above-mentioned kind are provided by the invention.

Heat-resistant and corrosion-resistant weld metal alloy and welded

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Kitaibaraki, Japan

Masayuki Sukekawa