Abstract
A new processing route to produce Ultrafine-Grained Dual-Phase steel has been proposed, involving cold-rolling and subsequent intercritical annealing of a fibrous ferrite–martensite starting structure. Ultrafine-grained DP (UFG-DP) steel with an average ferrite grain size of about ~2.7 μm and an average martensite island size of ~2.9 μm was achieved. Tensile testing revealed superior mechanical properties (the ultimate tensile strength of 1267 MPa and uniform elongation of 8.2%) for the new DP steel in comparison with the fibrous DP steels. The superior mechanical properties are attributed to the influence of microstructure refinement on the work-hardening and fracture behavior.
Highlights
The increasing demand for weight reduction with high safety performance in the automotive industry has led to the continuous development of advanced high strength steels (AHSS), such as dual-phase (DP) and transformation-induced plasticity (TRIP) steels [1,2,3,4]
The volume fraction of pearlite was measured as 40%, and the ferrite grain size is 30 μm
The small amount of ferrite is inevitable in this steel grade due to insufficient quenchability
Summary
The increasing demand for weight reduction with high safety performance in the automotive industry has led to the continuous development of advanced high strength steels (AHSS), such as dual-phase (DP) and transformation-induced plasticity (TRIP) steels [1,2,3,4]. It has been well known that grain refinement of DP steels leads to huge strength enhancement without apparent sacrifice of plasticity [9,10,11,12,13,14,15,16,17,18,19,20]. Single-phase UFG materials usually show high strength but limited ductility [19]. Previous studies [16] attributed the benefits of UFG-DP to optimizations of strain hardening rate, martensite plasticity and interface cohesion. A better understanding of the grain refinement is worthy to be studied further to optimize mechanical properties of UFG-DP steels
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