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

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2001-03, Vol.32 (3), p.505-514
• Main Authors: KIM, Sung-Joon, CHANG GIL LEE, ILDONG CHOI, SUNGHAK LEE
• Format: Article
• Language: English
• Subjects: Alloying elements; Annealing; Applied sciences; Cold rolling; Cold-rolled steel; Cross-disciplinary physics: materials science; rheology; Dual phase steels; Elongation; Exact sciences and technology; Heat treatment; Isothermal treatment; Manganese; Materials science; Mechanical properties; Metal sheets; Metals. Metallurgy; Microstructure; Physics; Plastic properties; Retained austenite; Solid solution hardening, precipitation hardening, and dispersion hardening; aging; Solid solution, precipitation, and dispersion hardening; aging; Steel; Tensile strength; Tensile tests; Treatment of materials and its effects on microstructure and properties
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-001-0067-0

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.