Effect of ferrite formation on abnormal austenite grain coarsening in low-alloy steels during hot rolling process

Journal Article · Fri May 01 04:00:00 EDT 1998 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-998-0352-2· OSTI ID:616262

Asahi, Hitoshi; Ueno, Masakatsu ^[1]; Yagi, Akira ^[2]

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1. Nippon Steel Corp., Chiba (Japan). Pipe and Tube Lab.
2. Nippon Steel Corp., Fukuoka (Japan). Yawata R and D Lab.

Abnormal coarsening of austenite ({gamma}) grains occurred in low-alloy steels during a seamless pipe hot-rolling process. Often, the grains became several hundred micrometer in diameter. This made it difficult to apply direct quenching to produce high-performance pipes. The phenomenon of grain coarsening was successfully reproduced using a thermomechanical simulator, and the factors which affected grain coarsening were clarified. The mechanism was found to be basically strain-induced grain growth which occurred during reheating at around 930 C. Furthermore, once a pipe temperature decreased to the dual-phase region after the minimal hot working and prior to the reheating process, the grain coarsening was more pronounced. It was understood that the formation of ferrite along grain boundaries had the role of reducing the migration of grain boundaries into neighboring grains, leaving a strain-free, recrystallized region behind. This abnormal grain coarsening was found to be effectively prevented by an addition of Nb, the content of which varied depending on the C content. The effect of the Nb addition was confirmed by an in-line test.

• Sponsoring Organization: USDOE
• OSTI ID: 616262
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 5 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
GRAIN SIZE
HOT WORKING
LOW ALLOY STEELS
METALLURGICAL EFFECTS
MICROSTRUCTURE
NIOBIUM ADDITIONS
PIPES
ROLLING