Development of novel high strength-ductility steel sheet using nitrogen

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05148
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26050:Material processing and microstructure control-related
• Research Institution: Tohoku University
• Principal Investigator: Sato Mitsutaka 東北大学, 金属材料研究所, 助教 (10547706)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 窒素鋼 / 相変態 / エネルギー散逸 / 機械特性

Outline of Final Research Achievements

The ferrite and bainite transformation of Fe-0.3N-xMn (x=0, 1, 2) alloys was investigated in terms of morphology, crystallography, growth rate and elemental partitioning, and the effects of Mn and Cr additions on those transformation behavior and mechanical properties were investigated. With decreasing transformation temperature, the microstructures of the ferrite changed to AF, WF and BF, and the growth of ferrite was retarded with increasing Mn addition.
The mechanical properties of bainitic transformed Fe-0.3N and 1Mn alloy showed an increase in uniform elongation and work hardening due to the increase in the volume fraction of retained g, confirming the occurrence of the TRIP effect. The strength-ductility balance of the Fe-0.3N and 1Mn alloy was comparable, while the 2Mn1Cr alloy had a higher yield stress due to a larger martensite volume fraction, but no increase in elongation.

Free Research Field

相変態、窒素鋼、組織制御

Academic Significance and Societal Importance of the Research Achievements

本研究では，正変態におけるα/γ界面での元素分配を詳細に測定し，窒素鋼の正変態挙動をα/γ界面の平衡組成からのずれ、すなわち、エネルギー散逸という観点から評価した．Fe-0.3N材およびMn添加材いずれいおいても，変態時にエネルギー散逸生じており，それらを物理的作用および化学的作用にて定量的に説明することが可能であることを明らかにした．また，炭素鋼との比較では，MnとNおよびCとの間の引力的相互作用から説明でき，i-s相互作用とNおよびC自身の偏析エネルギーの観点から理解することが可能であることを明らかにし，従来の炭素鋼の知見を基にして窒素鋼の相変態も理解することが可能であることを示した．