Effect of Intercritical Annealing on Mechanical Properties and Work‐Hardening Response of High Formability Dual Phase Steel

Abstract

The effect of austenitization and intercritical annealing temperature on mechanical properties and work-hardening response of high-formability dual phase (DP) steel with low C and Mn content is studied. Different mechanisms of microstructural development are characterized. At intercritical temperature range, austenite forms in the ferritic matrix, which will transform to martensite during quenching. However, at austenitization temperatures, the material becomes completely austenitic with low hardenability. As a result, during quenching, there will be some ferrite phase in the martensitic matrix of the resultant DP steel. These differences are found to have important effects on the mechanical properties. The yield strength decreases at low martensite fraction due to the disappearance of the yield-point phenomenon and the presence of martensite-induced dislocations that move at low stresses. However, the yield strength rapidly increases by the dominance of the martensitic matrix at high martensite fractions. Moreover, the dependence of the ultimate tensile strength on martensite volume fraction is discussed based on the work-hardening capacity of the DP steels. Finally, the mechanical properties are summarized by consideration of strength-ductility trade-off seen for DP steels. Figure 8. The strength-ductility balance of DP steels [1] and its extension to high ductility region by including the results of the present study and results of Mirzadeh et al. [24] www.advancedsciencenews.com www.steel-research.de steel research int. 2018, 89, 1700412 www.advancedsciencenews.com www.steel-research.de steel research int. 2018, 89, 1700412

Spheroidization heat treatment and intercritical annealing of low carbon steel

“…2 shows the evolution of starting microstructures during spheroidization treatment at 700 o C along with the variation of hardness. The fully annealed sample (denoted as 0 h) had a well-defined banded microstructure, as expected [38]. During spheroidization treatment, the spheroidized carbides started to appear in the pearlite bands, and after 24 h, they were easily identified.…”

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

“…Figure b shows the work‐hardening rate plots based on the modified Crussard–Jaoul analysis. For the DP steels, three stages of work‐hardening can be detected: The transient Stage I represents the glide of mobile dislocations in ferrite present near the martensite regions, Stage II belongs to the deformation of constrained ferrite, and Stage III is related to the concurrent deformation of martensite and hardened ferrite . It can be seen that at each given flow stress, the curve corresponding to DP3* falls above others, which reveals that the work‐hardening capacity of this steel is higher.…”

“…The initial material was a cold rolled sheet subjected to the normalizing heat treatment and had an equiaxed ferritic‐pearlitic microstructure, as shown in Figure . The A 1 and A 3 temperatures were, respectively, estimated as ≈726 and ≈865 °C based on Trzaska and Park equations as shown in Equation : …”

The effects of primary thermo-mechanical processing routes and intercritical annealing on the mechanical properties of st37 low carbon steel

“…For the DP steels, the initial work-hardening rate is much higher as discussed above. Moreover, three stages of work-hardening can be detected: The transient Stage I represents the glide of mobile dislocations in ferrite present near the martensite regions, Stage II belongs to the deformation of constrained ferrite, and Stage III is related to the concurrent deformation of martensite and hardened ferrite [13,41,51,52]. For a major part of the curves, it can be seen that the workhardening curve corresponding to DP2 locates above DP1 at each given flow stress, which reveals that the work-hardening response of DP2 is better.…”