超微細粒鉄鋼材料の降伏現象

超细晶钢材的屈服现象

• 批准号: 15J04389
• 负责人: 高 斯
• 金额: $ 1.22万
• 依托单位: Kyoto University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for JSPS Fellows
• 财政年份: 2015
• 资助国家: 日本
• 起止时间: 2015-04-24 至 2017-03-31
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15J04389/
• 关键词: yield point; ultrafine grain material; mechanical property; strain localization

The objectives of the present research for year 2015-2016 have been achieved. The yield point phenomenon in ultrafine grained (UFG) interstitial free (IF)steel has been systematically studied by mechanical tests, microstructure observation and Digital Image Correlation (DIC) technique.Accumulative roll-bonding (ARB) process and subsequent annealing were applied to the IF steel to fabricate the specimens having various mean grain sizes from conventional range (larger than tens micron-meters) to ultrafine range. It was found by the tensile test that discontinuous yielding appeared in the IF steel when the mean grain size was decreased to smaller than 2 micron meters. The yield stress showed an “extra-hardening”. Namely, it became higher than that predicted by the Hall-Petch relationship extrapolated from the conventionally coarse grain size range. Meanwhile, the uniform elongation of the material greatly decreased as the mean grain size became smaller than 2 micron. By the digital image correlation (DIC) technique, it was found that the dramatic decreasing in the uniform elongation is attributed to the initial severe strain localization occurred with the discontinuous yielding.In conclusion, the present work investigated the yield point phenomena in ultrafine grained IF steel in details and deepened the understanding of the grain size effect on the strength and ductility of the materials. Further research works are expected on how to diminish the yield point phenomena and enhance the tensile ductility of the materials having ultra-fine grain sizes.

目前2015-2016年的研究目标已经实现。 通过力学测试、显微组织观察和数字图像相关（DIC）技术系统地研究了超细晶（UFG）无间隙原子（IF）钢的屈服点现象。对IF钢采用累积轧制（ARB）工艺和随后的退火来制造具有从常规范围（大于数十微米）到各种平均晶粒尺寸的试样。 超细范围。 拉伸试验发现，当平均晶粒尺寸减小到小于2微米时，IF钢出现不连续屈服。屈服应力表现出“额外硬化”。即，它变得高于根据传统粗晶粒尺寸范围推断的霍尔-佩奇关系所预测的值。同时，当平均晶粒尺寸小于2微米时，材料的均匀伸长率大大降低。通过数字图像相关（DIC）技术，发现均匀伸长率的急剧下降归因于不连续屈服时发生的初始严重应变局部化。 总之，本工作详细研究了超细晶粒IF钢的屈服点现象，加深了对晶粒尺寸对材料强度和延展性影响的理解。预计进一步的研究工作将涉及如何减少屈服点现象并提高超细晶粒材料的拉伸延展性。

项目成果

Strain localization during tensile test of IF steel with various grain sizes

不同晶粒尺寸IF钢拉伸试验中的应变局部化

• 发表时间: 2015
• 作者: Si Gao;Meichuan Chen;Akinobu Shibata;Naoya Kamikawa;Nobuhiro Tsuji
• 通讯作者: Nobuhiro Tsuji