Change in Dislocation Characteristics with Cold Working in Ultralow-carbon Martensitic Steel

• Akama Daichi

  Department of Materials Science and Engineering, Kyushu University International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University

• Tsuchiyama Toshihiro

  Department of Materials Science and Engineering, Kyushu University International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University

• Takaki Setsuo

  Department of Materials Science and Engineering, Kyushu University International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University

Abstract

In a previous study, the authors used X-ray analysis with the classical Williamson–Hall (CWH) method to suggest that charging a small amount of cold working markedly decreases the dislocation density of ultralow-carbon martensitic steel, although this heightens the 0.2% proof stress. However, this method does not consider the dislocation arrangement. In the present study, a modified Williamson–Hall/Warren–Averbach (MWH/WA) method was applied to ultralow-carbon martensitic steel (Fe–18%Ni alloy) in order to evaluate not only the dislocation density but also the dislocation arrangement. Their effects on the yielding behavior were examined. With the MWH/WA method, the dislocation density did not change up to 40% cold rolling. On the other hand, the dislocation arrangement parameter M was high (M > 1) in the as-quenched state and became smaller (M < 1) when a small plastic strain was charged. This means that the dislocation distribution is random in as-quenched martensite but changes the cell structure with cold working. Owing to such a dislocation arrangement, the CWH method tends to overestimate the dislocation density of as-quenched martensite compared to the MWH/WA method. Tensile testing revealed that the elastic limit was very low in as-quenched martensite and high in cold-rolled martensite. In the case of a tangled dislocation structure, a higher stress should be required because of the stable dislocation structure. On the other hand, the random dislocations introduced by martensitic transformation can easily move at a low stress level owing to their unstable distribution, which leads to the low elastic limit in as-quenched martensite.

Journal

• ISIJ International

  ISIJ International 56 (9), 1675-1680, 2016

  The Iron and Steel Institute of Japan

Keywords

• ultralow-carbon martensitic steel
• dislocation density
• dislocation arrangement
• Williamson-Hall method
• modified Williamson-Hall/Warren-Averbach method

Details

• CRID: 1390282681463508224
• NII Article ID: 130005264625
• DOI: 10.2355/isijinternational.isijint-2016-140
• ISSN: 13475460
• ISSN: 09151559
• Web Site: https://www.jstage.jst.go.jp/article/isijinternational/56/9/56_ISIJINT-2016-140/_pdf
• Text Lang: en
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
  • KAKEN
• Abstract License Flag: Disallowed