• Saldaña Garcés, Rocio
• Galicia-Ruiz, Carlos
• Hernández-Hernández, Lorena
• Torres-Castillo, Alberto
• Aguilar-Carrillo, Javier
• Gutierrez, Emmanuel
• Lange, Dirk Frederik De
• Deaquino-Lara, Rogelio
• Salinas Rodriguez, Armando
• Reyes, Iván

Abstract

<jats:p>In the present work, a Cr+Mo+Si low-alloyed low-carbon steel was fabricated at laboratory scale and processed to produce multiphase advanced high-strength steels (AHSS), under thermal cycles similar to those used in a continuous annealing and galvanizing process. Cold-rolled steel samples with a microstructure constituted of pearlite, bainite, and martensite in a matrix ferrite, were subjected to an intercritical annealing (817.5 °C, 15 s) and further isothermal bainitic treatment (IBT) to investigate the effects of time (30 s, 60 s, and 120 s) and temperature (425 °C, 450 °C, and 475 °C) on the resulting microstructure and mechanical properties. Results of an in situ phase transformation analysis show that annealing in the two-phase region leads to a microstructure of ferrite + austenite; the latter transforms, on cooling to IBT, to pro-eutectoid ferrite and bainite, and the austenite-to-bainite transformation advanced during IBT holding. On final cooling to room temperature, austenite transforms to martensite, but a small amount is also retained in the microstructure. Samples with the lowest temperature and largest IBT time resulted in the highest ultimate tensile strength/ductility ratio (1230.6 MPa-16.0%), which allows to classify the steel within the third generation of AHSS. The results were related to the presence of retained austenite with appropriate stability against mechanically induced martensitic transformation.</jats:p>

Topics

• impedance spectroscopy
• microstructure
• Carbon
• phase
• strength
• steel
• annealing
• tensile strength
• ductility