International Journal of Iron & Steel Society of Iran

International Journal of Iron & Steel Society of Iran

Effect of Intercritical Annealing Temperature and Time on Microstructure and Tensile Properties of a Step-Quenched Dual Phase Steel

Document Type : Research Paper

Authors
H. Ashrafi
Z. Soleimani Bistegani
Faculty of Chemical and Materials Engineering, Shahrood University of Technology, Shahrood, Iran
10.22034/ijissi.2025.2052973.1318
Abstract
 A heat treatment cycle involving step-quenching followed by intercritical annealing (IA) at 740°C, 770°C and 800°C for times between 2-12 min was utilized to produce dual-phase (DP) steels. The microstructural analysis revealed that the martensite islands formed during step-quenching were refined significantly after IA. The final DP steels contained ferrite grains of two sizes distribution: coarse grains ranging from 10 to 25 µm and ultrafine grains smaller than 2 µm. The martensite islands displayed two morphologies: fine and fibrous martensite in samples annealed at 740°C and 770°C and equiaxed martensite islands in all samples. Continuous yielding behavior was observed in all samples except those annealed at 740°C for 2- and 4-min. IA at all temperatures led to a decrease in yield stress and ultimate tensile strength, with enhancements in uniform elongation and total elongation only observed after IA at 740°C and 770°C. The sample annealed at 770°C for 12 min exhibited the best combination of tensile properties for auto body applications. The samples displayed a three-stage work-hardening behavior based on the modified Crussard–Jaoul analysis, however the third stage was absent in samples annealed at 740°C for 7 and 12 min due to the high carbon content of the martensite. 
Keywords
Dual phase steel
step-quenching
intercritical annealing
microstructure
tensile properties

Subjects

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