Strain Hardening Behavior Prediction Model For Automotive High Strength Multiphase Steels

The microstructural refinement by thermal cycling and its effects on the enhancement of mechanical properties and work-hardening response of a typical C-Mn dual phase (DP) steel having the banded ferritic-martensitic morphology is evaluated. It is revealed that the band spacing is reduced by decreasing austenitization temperature and applying thermal cycles to intercritical region, where a saturated spacing will be reached. This results in the enhancement of work-hardening capacity of DP steels as demonstrated based on the instantaneous (incremental) work-hardening rate exponents, modified Crussard-Jaoul analysis, and evaluating the yield ratio after tensile tests. These observations justify the potential of this simple heat treatment route for microstructural control of DP steels. Figure 8. a) Dependence of UTS and total elongation on band spacing and b) Dependence of yield ratio and UTS-YS on band spacing.www.advancedsciencenews.com www.steel-research.de steel research int. 2018, 89, 1700531

\ln σ = \ln k + n \ln ϵ

, and at a given strain, the slope of the plot of

\ln σ

versus

\ln ϵ

was determined. Simply, it can be expressed as

n = d \ln σ / d \ln ϵ

.…”

Section: Methodsmentioning

confidence: 99%

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

Ghaemifar

Mirzadeh

2018

“…Typically, dual phase (DP) steels are low carbon steels, which consist of a ferritic matrix and a martensitic second phase . They possess high ultimate tensile strengths while maintaining good percent elongation to failure values, high initial work hardening rate, continuous yielding behavior, and good weldability with all conventional welding techniques . These properties make them suitable for automotive and other industries …”

Section: Introductionmentioning

confidence: 99%

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

Maleki

Mirzadeh

Zamani

2017

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

“…The Crussard–Jaoul (C–J) analysis based on Ludwik relation, which can better demonstrate characteristic behavior of the different strain stages . The C–J model takes into account the yield strength, thus allowing to better model the plastic regions.…”

Section: Resultsmentioning

confidence: 99%

Effect of ART-Annealing Conditions on Microstructural Regulation and Deformation Behavior of 0.17C-9Mn-3.5Al TRIP-Aided Steel

Zhang

Huang

Guo

et al. 2017

The effects of annealing conditions on the microstructure and deformation mechanism of 0.17C-9Mn-3.5Al steel have been investigated. Through austenite reverted transformation (ART) annealing, a multiphase microstructure composed of d-ferrite, a-intercritical ferrite, g-austenite, and a'-martensite is obtained in as-forged specimens. For the specimen annealed at 750 8C for 60 min, a high volume fraction (42.19%) of retained austenite is attained, yielding a large total elongation (TE) of %38% and tensile strength (Rm) of %810 MPa and a two-stages work hardening behavior. The work hardening behavior analysis using the differential C-J model clarifies that the multistage can be mainly attributed to the discontinuous transformation induced plasticity (TRIP) effect, which is related to the volume fraction of retained austenite and its different stability levels as well as cooperative deformation of the multiphase microstructure. Thus, the active TRIP effect predominately affects the high strain stage, resulting in a higher work hardening ability and a increased plasticity.[ Ã ] X.