High Versatility of Niobium Alloyed AHSS

Abstract

The effect of processing parameters on the final microstructure and properties of advanced high strength CMnSiNb steel was investigated. Several processing strategies with various numbers of deformation steps and various cooling schedules were carried out, namely heat treatment without deformation, conventional quenching and TRIP steel processing with bainitic hold or continuous cooling. Obtained multiphase microstructures consisted of the mixture of ferrite, bainite, retained austenite and M-A constituent. They possessed ultimate tensile strength in the range of 780-970 MPa with high ductility A 5 mm above 30%. Volume fraction of retained austenite was for all the samples around 13%. The only exception was reference quenched sample with the highest strength 1186 MPa, lowest ductility A 5 mm = 20% and only 4% of retained austenite.

Austenite Decomposition and Precipitation Behavior of Plastically Deformed Low-Si Microalloyed Steel

“…Therefore, industrial requirements prefer low-Si grades in TRIP-aided steels [16,17]. The decrease of the solid solution potential of silicon and a resulting decrease of the strength level (Al has a smaller solid solution strengthening effect) can be compensated by Nb, Ti, and/or V microalloyed additions [18][19][20][21][22]. These elements form stable nitrides and carbonitrides during hot working in the austenite region.…”

Numerical Model for Mechanical Nonlinearities of High Manganese Steel Based on the Elastoplastic Damage Model

“…When the Newton-Raphson method is introduced to obtain a proper numerical approximation, it is normal to set the initial value of ∆γ to 0. To improve convergence, however, ∆γ (0) is defined as shown in Equation (28).…”

“…Moreover, one should note that the rapid degradation represented by a necking-failure phenomena occurred immediately after reaching the tensile strength. Earlier studies reported that microstructural effects such as martensite formation and mechanical twinning contributed to the strengthening of high manganese steel and delayed the onset of necking, which is associated with large uniform elongation [24][25][26][27][28][29]. Based on these features, strength-based design is typically performed for industrial structures and can lead to structural safety problems with respect to excessive deformation and rapid necking-fracture in high manganese steel.…”

Dilatometric Study of Phase Transformations in 5 Mn Steel Subjected to Different Heat Treatments

“…The presence of retained austenite is due to its high thermal stability revealing during heat treatment. Its stability is influenced by carbon and manganese contents in the austenite, a morphology, dislocation density and the neighborhood of soft or hard phases [7][8][9]. These factors determine the amount of retained austenite present in the microstructure and resulting mechanical properties.…”