Effect of austenite grain size on acicular ferrite transformation in a HSLA steel

Journal Article · Thu Nov 15 04:00:00 EST 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.09.013· OSTI ID:22805880

Zhao, Haitao ^[1]; Palmiere, Eric J. ^[1]

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1. The University of Sheffield, Department of Materials Science and Engineering, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD (United Kingdom)

Highlights: • The fraction of acicular ferrite increases with reduced austenite grain sizes. • The reduction of austenite grain size refines and homogenises the microstructure. • There is a limit to increase the acicular ferrite fraction by reducing austenite size. • An equation relating effective grain sizes with processing parameters was proposed. - Abstract: Austenite grain size is well known to have a significant influence on various phase transformations in steels. Although the effects of many thermomechanical processing parameters on acicular ferrite (AF) transformation in HSLA steels have been investigated, little attention has been paid to the influence of austenite grain size. Therefore, in this research, different parameters of solid-solution heat treatment and rough deformation were adopted to generate austenite with different grain sizes and the effects of austenite grain size before deformation on the AF transformation and grain refinement were investigated. It was found that the reduction of prior-austenite grain size (PAGS) from 62.8 μm to 37.0 μm before austenite deformation promotes the AF transformation and simultaneously refines and homogenises the transformed microstructures. A reciprocally increased density of deformation induced dislocations with the reduction of PAGS was proposed to account for these results, which not only increase the nucleation sites of AF but also suppress the lengthening of BF laths. Further reducing PAGS from 37.0 μm to 22.3 μm, the fraction of AF is not increased and the transformed microstructure is not refined. Possible differences in the type, distribution, and density of austenite deformation substructures between austenite with PAGSs of 37.0 μm and 22.3 μm were argued to be responsible for the cease of grain refinement. The relationship between effective grain sizes and the S{sub v} parameter was investigated and an equation relating effective grain sizes with processing parameters was also proposed.

• OSTI ID: 22805880
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 145; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITE
DEFORMATION
DISLOCATIONS
DISTRIBUTION
GRAIN REFINEMENT
HEAT TREATMENTS
NUCLEATION
PHASE TRANSFORMATIONS
SOLID SOLUTIONS
STEELS