Effect of Manganese on the Structure-Properties Relationship of Cold Rolled AHSS Treated by a Quenching and Partitioning Process

Abstract

The present work focuses on the investigation of both microstructure and resulting mechanical properties of different lean medium Mn Quenching and Partitioning (Q&P) steels with 0.2 wt.% C, 1.5 wt.% Si, and 3–4 wt.% Mn. By means of dilatometry, a significant influence of the Mn-content on their transformation behavior was observed. Light optical and scanning electron microscopy (LOM, SEM) was used to characterize the microstructure consisting of tempered martensite (α’’), retained austenite (RA), partially bainitic ferrite (αB), and final martensite (α’final) formed during final cooling to room temperature (RT). Using the saturation magnetization measurements (SMM), a beneficial impact of the increasing Mn-content on the volume fraction of RA could be found. This remarkably determined the mechanical properties of the investigated steels, since the larger amount of RA with its lower chemical stabilization against the strain-induced martensite transformation (SIMT) highly influenced their overall stress-strain behavior. With increasing Mn-content the ultimate tensile strength (UTS) rose without considerable deterioration in total elongation (TE), leading to an enhanced combination of strength and ductility with UTS × TE exceeding 22,500 MPa%. However, for the steel grades containing an elevated Mn-content, a narrower process window was observed due to the tendency to form α’final.

Impact of Si and Al on Microstructural Evolution and Mechanical Properties of Lean Medium Manganese Quenching and Partitioning Steels

“…As precisely described in previous studies, [ 27,30 ] T Q is used as a crucial parameter to accurately adjust the volume fraction of α′ prim and thus the remaining microstructural constituents. The present investigations (Figure 2b) have confirmed an increase in RA fraction with decreasing amount of α′ prim , until reaching a pronounced peak at α′ prim = 60–70 vol%.…”

Hot deformation analysis of lean medium-manganese 0.2C3Mn1.5Si steel suitable for quenching et partitioning process

“…The chemical composition of experimental samples was verified by a spectral analyser Q4 TASMAN, and it is presented in Table 1. The microstructure and mechanical properties of the cold-rolled steel subjected to the final Q&P heat treatment are thoroughly described in [18].…”

Performance of Mechanical Properties of Ultrahigh-Strength Ferrous Steels Related to Strain-Induced Transformation

“…One review and nine research articles have been published in this Special Issue of Metals. The subjects of this Issue are roughly divided into four categories: (1) strain-induced transformation behavior [1][2][3], (2) deformation mechanism [4,5], (3) formability [6,7] and (4) mechanical properties [8][9][10] of the ultrahigh-strength ferrous steels. The abovementioned (1) and (2) give important information for improving (3) and (4).…”

“…Third, the formability of the ferrous steels was related to the microstructure and the retained austenite characteristics. Kaar et al [6] studied the structure-ductility relationship in cold-rolled medium manganese bainite/martensite steels subjected to quenching and partitioning processes. Yang et al [7] investigated the springback behavior during the bending process for a quenching and partitioning steel.…”