MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Precipitation of Carbonitrides and Their Strengthening upon Non-quench Aging for Micro-alloyed Acicular Ferrite Pipeline Steels
Ming-Chun ZhaoToshihiro HanamuraHai QiuKe Yang
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2005 Volume 46 Issue 4 Pages 784-789

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Abstract

A non-quench aging (reheating hot-rolled plates to 600°C for isothermal aging), different from the conventional quench aging (quench followed by temper), was carried out to improve the strength level for acicular ferrite (AF) pipeline steels, while their impact energies and ductilities did not decrease obviously, and the Charpy impact fracture appearances were similar between the as-rolled and the aged samples, showing the ductile dimple rupture over the whole fracture surface. The strengthening was ascribed to the further additional precipitation of microalloyed carbonitrides, and the little degradation of ductile and toughness is believed to relate to both the tempering of martensite in martensite/austenite (M/A) islands and the improvement of microstructural uniformity upon the non-quench aging. The nucleation and strengthening of the carbonitrides in the current non-quench aging were hypothetically calculated with the present mathematical modes and hypothesis based on the thermodynamic consideration and Orowan looping mechanism, which was somewhat consistent with the present experiment, indicating that the strengthening mechanism of the present AF pipeline steels by the current non-quench aging evidently resulted from the additional precipitation of carbonitrides in ferrite region of approximately 600°C.

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© 2005 The Japan Institute of Metals and Materials
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