Ultrafine-grain steel pipe and process for manufacturing the same

US6290789A · kind A · utility

Assignee

• Kawasaki Steel Corporation · JP

Inventors

• Takaaki Toyooka · Ebeye, US
• Akira Yorifuji · Handa, JP
• Masanori Nishimori · Handa, JP
• Motoaki Itadani · Handa, JP
• Yuji Hashimoto · Tokyo, JP
• Takatoshi Okabe · Tokyo, JP
• Taro Kanayama · Tokyo, JP
• Masahiko Morita · Chiba, JP
• Saiji Matsuoka · Chiba, JP
• Nobuki Tanaka · Ebeye, US
• Osamu Furukimi · Chiba, JP
• Takaaki Hira · Tokyo, JP

Key dates

• Filing date: Feb 26, 1999
• Grant date: Sep 18, 2001
• Expiry date: Feb 26, 2019

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C21D2201/00
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A steel pipe containing fine ferrite crystal grains, which has excellent toughness and ductility and good ductility-strength balance as well as superior collision impact resistance, and a method for producing the same are provided. A steel pipe containing super-fine crystal grains can be produced by heating a base steel pipe having ferrite grains with an average crystal diameter of di (.mu.m), in which C, Si, Mn and Al are limited within proper ranges, and if necessary, Cu, Ni, Cr and Mo, or Nb, Ti, V, B, etc. are further added, at not higher than the Ac.sub.3 transformation point, and applying reducing at an average rolling temperature of .theta.m (.degree.C.) and a total reduction ration Tred (%) within s temperature range of from 400 to Ac.sub.3 transformation point, with di, .theta.m and Tred being in a relation satisfying a prescribed equation.