Development of Low-Alloyed Low-Carbon Multiphase Steels under Conditions Similar to Those Used in Continuous Annealing and Galvanizing Lines

• Published in: Metals (Basel ) Vol. 12; no. 11; p. 1818
• Main Authors: Gutiérrez-Castañeda, Emmanuel, Galicia-Ruiz, Carlos, Hernández-Hernández, Lorena, Torres-Castillo, Alberto, De Lange, Dirk Frederik, Salinas-Rodríguez, Armando, Deaquino-Lara, Rogelio, Saldaña-Garcés, Rocío, Bedolla-Jacuinde, Arnoldo, Reyes-Domínguez, Iván, Aguilar-Carrillo, Javier
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-11-2022
• Subjects: AHSS; Analysis; Annealing; Bainite; Carbon; Carbon content; Carbon steel; Chromium; Cold; Cold-rolled steel; Continuous annealing; Cooling; Ductility; Ferrite; Galvanizing; High strength steels; Hot rolling; in-situ phase transformations; IQ-EBSD; Iron compounds; isothermal bainitic treatment; Laboratories; Low alloy steels; Low carbon steels; Martensite; Martensitic transformations; Mechanical properties; Microstructure; Molybdenum; Multiphase; multiphase steels; Pearlite; Phase transitions; Retained austenite; Room temperature; Solid solutions; Specialty metals industry; Steel; Steel, Structural; Temperature; Ultimate tensile strength; Mexico
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met12111818

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.