Process for making fine-grain weldable steel sheet for large-diameter pipes

US4494999A · kind A · utility

Assignee

• Mannesmann AG · DE

Inventor

• Michael Graf · Leutenbach, DE

Key dates

• Filing date: Jul 11, 1983
• Grant date: Jan 22, 1985
• Expiry date: Jul 11, 2003

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C21D8/0231
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

Microalloyed steel containing, among other ingredients, at least 0.02% niobium, between 0.005 and 0.01% nitrogen, and titanium in a proportion equaling about 3.5 to 4 times that of nitrogen is continuously cast into a slab which is heated to a temperature between about 1120.degree. and 1160.degree. C. whereby titanium nitride precipitates in particles ranging between about 0.06 and 0.2.mu.. The slab is thermomechanically treated at this temperature and after intermediate cooling in several hot-rolling stages, with an initial deformation of at least 55%; after final rolling, the slab is cooled in water at a rate of at least 10.degree. C. per second to a temperature of about 500.degree. to 550.degree. C. Niobium, which goes into solution at the elevated initial temperature, forms NbC precipitates during the subsequent treatment; this has a hardening and grain-refining effect.