Development of a New Concept for Hot-Rolled Weathering-DP Steel: Thermo-mechanical Simulation, Microstructure Adjustment, and Mechanical Properties

• Published in: Steel research international Vol. 87; no. 1; pp. 68 - 78
• Main Authors: Allam, Tarek, Bleck, Wolfgang
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 01-01-2016; Wiley Subscription Services, Inc
• Subjects: Cooling; cooling strategies; Hot rolling; Mechanical properties; Microstructure; pilot hot rolling; Simulation; Steel alloys; thermo-mechanical simulation; weathering-DP steels
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.201500108

A new alloying concept is proposed to develop a hot‐rolled weathering steel with a dual‐phase microstructure in order to combine good anticorrosion and good forming properties. The chemical composition in wt% comprises 0.11C, 0.5 Si, 1.52 Mn, 0.055 P, 0.4 Cr, 0.3 Ni, and 0.3 Cu. The phase transformation behavior is investigated by means of continuous cooling transformation diagrams. Different cooling strategies are applied in thermo‐mechanical simulation experiments for proper adjustment of the dual‐phase microstructure. The laboratory‐scale processing parameters are transferred to a pilot hot rolling plant. The hot‐rolled sheets are characterized by tensile testing and quantitative metallography. The produced hot‐rolled steel sheets consist of a microstructure with 71 vol% ferrite, 2 vol% pearlite, and 27 vol% martensite achieving average mechanical properties of 375 MPa for Rp0.2, 740 MPa for Rm, and 14% for A50. A delayed ferrite transformation makes step cooling unnecessary and enables easy processing by continuous cooling after hot rolling. The tendency to microstructural banding decreases as the cooling rate increases.
The current work aims at developing a hot‐rolled weathering steel with typical microstructure and mechanical properties of DP steels. A new alloying concept is proposed and cooling strategies are applied in thermo‐mechanical simulation experiments for proper adjustment of the DP microstructure. Afterward, the laboratory‐scale processing parameters are transferred to a pilot hot‐rolling plant and the produced sheets are characterized.