Effects of heat treatment and alloying elements on the microstructures and mechanical properties of 0.15 wt pct C transformation-induced plasticity-aided cold-rolled steel sheets |
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Authors: | Sung-Joon Kim Chang Gjl Lee Ildong Choi Sunghak Lee |
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Affiliation: | (1) the Materials Processing Department, Korea Institute of Machinery and Materials, 641-010 Changwon, Korea;(2) the Department of Materials Engineering, Korea Maritime University, 606-791 Busan, Korea;(3) the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, 790-784 Pohang, Korea |
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Abstract: | The main emphasis of this study has been placed on understanding the effects of manganese and silicon additions and of heat-treatment
(intercritical annealing and isothermal treatment) conditions on the microstructures and mechanical properties of 0.15 wt
pct C transformation-induced plasticity (TRIP)-aided cold-rolled steel sheets. The steel sheets were intercritically annealed
and isothermally treated at the bainitic region. Microstructural observation and tensile tests were conducted, and volume
fractions of retained austenite were measured. Steels having a high manganese content had higher retained austenite fractions
than the steels having a low manganese content, but showed characteristics of a dual-phase steel such as continuous yielding
behavior, high tensile strength over 1000 MPa, and a low elongation of about 20 pct. The retained austenite fractions and
mechanical properties varied with the heat-treatment conditions. In particular, the retained austenite fractions increased
with decreasing intercritical annealing and isothermal treatment temperatures, thereby resulting in the improvement of the
elongation and strength-ductility balance without a serious decrease in the yield or tensile strength. These findings suggested
that the intercritical annealing and isothermal treatment conditions should be established in consideration of the stability
of austenite and the solubility of alloying elements in the austenite formed during the intercritical annealing. |
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