Investigation on Dissolving Process of Secondary Phases and Austenitic Grain Growth in a Microalloyed Steel

Abstract:

The secondary phases such as carbonitrides in the microalloyed steel play very important roles in retarding the austenitic grains growth during reheating. The dissolving process of carbonitrides containing Nb, Ti, Mo will affect the austenitic grain sizes directly. In the present work, the dissolving behaviors of secondary phases in low carbon microalloyed steel during isothermal holding at different temperatures were investigated by electrolytic experiment, carbon extraction replicas, TEM and EDX analysis. Meanwhile, the austenitic grain sizes were measured corresponding to the temperatures. The experimental results indicate that there are two types of carbonitrides in as-forged steel. One is the coarsened Ti-rich precipitates originated from solidification, and the other is the finer Nb-rich particles attributed to strain-induced process. The strain-induced precipitates disappear after being held for 1 h at 1000°C. At 1000~1220 °C, the austenitic grains grow obviously due to rapid dissolving of the carbonitrides containing Nb and Mo. However, some undissolved Nb, Ti carbidenitrides still hinder the grain boundary migration. When the reheating temperature rises to 1270°C, the grain size grows abnormally after being held for 2h. At the holding temperature, few Nb-bearing TiN precipitates can be stable while the pinning effect weakens markedly.

• Periodical: Key Engineering Materials (Volumes 609-610)
• Pages: 509-514
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.609-610.509
• Online since: April 2014
• Authors: Bin Hao, Xiao Juan Zhang, Shao Qiang Yuan*, Guo Li Liang
• Keywords: Austenitic Grain Growth, Carbonitrides, Dissolving Behavior

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