Development of 3rd generation Medium Mn duplex steels for automotive applications

Abstract

The mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

“…Figure 36 shows the M(H) curves for a high-Mn steel cold rolled to several logarithmic strains (e), as reported in our preceding work [403] and provide us important parameters, such as the saturation magnetization (M s ) and the coercive field (H c ). The M s values mirror the volume fraction of ferromagnetic phases present in the specimen and thus they have extensively been used for tracking phase transformations in TRIP-assisted, [62,402] medium-Mn, [404,405] and high-Mn steels. [403,406,407] Figure 36, as an example, reveals the increase of the M s values as a function of plastic deformation, thus revealing the formation of strain-induced a¢-martensite upon rolling as confirmed by the EBSD maps displayed in Figure 36(b).…”

“…Medium-Mn steels are generally composed of ferrite and metastable austenite which may undergo martensitic transformation upon straining. Perlade et al [404] tracked the evolution of the austenite fraction during tensile testing of a 5Mn-2.47Al-0.208C (wt pct) steel that was intercritically annealed at various temperatures (T IA = 740°C, 760°C, 780°C), Figure 38. They observed that the rate of the martensitic transformation increased with increasing T IA for the investigated steel.…”

A Review on Measurement Techniques of Deformation‐Induced Transformation Kinetics in Transformation‐Induced Plasticity and Transformation‐Induced Plasticity‐Assisted Steels

“…The impedance coil responds to the change in AC permeability of the specimen as its ferromagnetic content, that is, martensite content increases. Two methods are used to measure the permeability change, 1) by voltage measurement (transformer method) [112][113][114] or 2) by frequency measurement (resonant circuit method). [47,73,74,115,116] In the transformer technique, the magnitude of the phase of the induced AC voltage is measured in the sensing coil (that surrounds the specimen) as the secondary winding of a transformer for a known AC reference voltage.…”

“…[47] AC magnetic permeability Does not require extra sample preparation. [110][111][112][113][114][115][116][117] www.advancedsciencenews.com…”

New Developments and Future Trends in Low-Temperature Hot Stamping Technologies: A Review

“…For instance, with a reduced heating temperature, it is not possible to achieve high strength with thinner components; while with a reduced forming temperature only, thick oxidation and decarburisation layers cannot be avoided and the ductility is still not high enough to widen application in the automotive industry. Therefore, in recent years, attention has been focused on improving the steel grades to overcome these issues [80].…”