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Vol.33, No.1, 42 ~ 49, 1995

Title

Mechanical Properties of Ultrafine Grain ( α' + γ ) Two Phase Stainless Steels

김영환 , 안용식 , 정해용 , 강창용 , 정병호 , 김창규 Y . H . Kim , Y . S . Ahn , H . Y . Jeong , C . L . Kang , B . H . Jeong , C . G . Kim

Abstract

The mechanical properties in a series of low carbon Fe-(15.5∼18.5)%Cr-10%Ni ternary stainless steels with two phase structure of deformation-induced martensite(α′) and reversed austenite(γ) after annealing for 0.6ks in the temperature range of 750 to 1100K were investigated as a function of α′ content and γ stability with transformation-induced plasticity(TRIP). All the steels almost transform to lath α′ from γ by 90% cold rolling and show α′ structure below γ content of 10%. The increase of Cr contents increases γ stability and hence decreases γ′ content in the same reduction of area. The deformed α′ rapidly reversed to γ in the temperature range of 773 to 873K and then the reversion was completed at about 1073K. The reversed γ has a ultrafine grain diameter of 0.5㎛. As a result of ultrafine grain structure of γ, the (α′ + γ) mixed structure was more stabilized. The good combination of high strength and elongation was obtained from the mixed structure containing a higher amount of retained α′ with decreasing Cr content. For example, for 15.5%Cr-10%Ni steel the proof stress of 0.79GPa and ultimate true tensile stress of 1.06GPa were obtained with elongation of 30%. The elongation caused by TRIP in the mixed structure was greatly affected by transformation behavior to α′ from γ in the initial stage of deformation.

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