A novel observation of strain-induced ferrite-to-austenite retransformation after intercritical deformation of C-Mn steel

作者：Luo HW^*; Sietsma J; Van Der Zwaag S

来源：Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2004, 35A(9): 2789-2797.

DOI：10.1007/s11661-004-0225-2

It was found that a ferrite-to-austenite retransformation can take place during isothermal holding after deformation in 0.19 pct C-1.46 pct Mn steel at higher intercritical temperatures, but it was not observed at lower intercritical temperatures. This new finding was revealed by the combined techniques of optical observation and quantitative metallographic measurements. Also, two unexpected experimental observations on the quenched microstructure can be interpreted very well by the retransformation: one is that microhardness does not decrease at the end of relaxation as expected; the other is that an experimentally observed X-ray peak gets broader after long relaxation. In contrast, dilatometry measurements on the undeformed specimens show that the thermodynamically induced transformation during the isothermal holding should be from austenite to ferrite. Therefore, the ferrite-to-austenite retransformation after deformation should be strain induced. Such a retransformation can be explained quite well using a validated and quantitative model for the intercritical rolling and softening of both austenite and ferrite. The model presented is based on the fact that in intercritically deformed steel there is a strain distribution over the two phases with the more strain in the softer ferrite. The ferrite dynamically recovers, which leads to a shift in the relative amount of stored energy in the two phases. This phenomenon leads to a shift in the equilibrium fractions of ferrite and austenite.

• 出版日期2004-9
• 单位中国科学院金属研究所