Influence of the Quenching and Partitioning Process on the Transformation Kinetics and Hardness in a Lean Medium Manganese TRIP Steel

Self Cite

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.

Section: Influence Of Heat-treatment Parametersupporting

confidence: 89%

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

Kaar

Križan

Schneider

et al. 2019

Self Cite

“…Most papers using the ART effect deal with applications for sheet products, as the necessary heat treatment can be best tailored by continuous strip annealing treatments. Thus, the composition requirement and the process parameters have been studied for a wide range of medium manganese steels [17][18][19][20]. As the time-temperature profiles of sheet products cannot be applied on forging parts because of the complex geometries and great cross sections, only simple and robust heat treatments can be used to modify the microstructure.…”

Section: Introductionmentioning

confidence: 99%

Austenite Reversion Tempering-Annealing of 4 wt.% Manganese Steels for Automotive Forging Application

Gramlich

Emmrich

Bleck

2019

New medium Mn steels for forged components, in combination with a new heat treatment, are presented. This new annealing process implies air-cooling after forging and austenite reversion tempering (AC + ART). This leads to energy saving compared to other heat treatments, like quenching and tempering (Q + T) or quenching and partitioning (Q + P). Furthermore, the temperature control of AC + ART is easy, which increases the applicability to forged products with large diameters. Laboratory melts distinguished by Ti, B, Mo contents have been casted and consecutively forged into semi-finished products. Mechanical properties and microstructure have been characterized for the AC and the AC + ART states. The as forged-state shows YS from 900 MPa to 1000 MPa, UTS from 1350 MPa to 1500 MPa and impact toughness from 15 J to 25 J. Through the formation of nanostructured retained metastable austenite an increase in impact toughness was achieved with values from 80 J to 100 J dependent on the chemical composition.

“…However, the role of precipitates in improving hydrogen embrittlement is still a matter of discussion [20][21][22]. Recently, medium manganese steels (MMnSs) with a duplex microstructure have received significant attention due to their excellent mechanical properties and reduced production costs compared to HMnS [23][24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Development of a Cr-Ni-V-N Medium Manganese Steel with Balanced Mechanical and Corrosion Properties

Allam

Guo

Sevsek

et al. 2019

A novel medium manganese (MMn) steel with additions of Cr (18%), Ni (5%), V (1%), and N (0.3%) was developed in order to provide an enhanced corrosion resistance along with a superior strength–ductility balance. The laboratory melted ingots were hot rolled, cold rolled, and finally annealed at 1000 °C for 3 min. The recrystallized single-phase austenitic microstructure consisted of ultrafine grains (~1.3 µm) with a substantial amount of Cr- and V-based precipitates in a bimodal particle size distribution (100–400 nm and <20 nm). The properties of the newly developed austenitic MMn steel X20CrNiMnVN18-5-10 were compared with the standard austenitic stainless steel X5CrNi18-8 and with the austenitic twinning-induced plasticity (TWIP) steel X60MnAl17-1. With a total elongation of 45%, the MMn steel showed an increase in yield strength by 300 MPa and in tensile strength by 150 MPa in comparison to both benchmark steels. No deformation twins were observed even after fracture for the MMn steel, which emphasizes the role of the grain size and precipitation-induced change in the austenite stability in controlling the deformation mechanism. The potentio-dynamic polarization measurements in 5% NaCl revealed a very low current density value of 7.2 × 10−4 mA/cm2 compared to that of TWIP steel X60MnAl17-1 of 8.2 × 10−3 mA/cm2, but it was relatively higher than that of stainless steel X5CrNi18-8 of 2.0 × 10−4 mA/cm2. This work demonstrates that the enhanced mechanical properties of the developed MMn steel are tailored by maintaining an ultrafine grain microstructure with a significant amount of nanoprecipitates, while the high corrosion resistance in 5% NaCl solution is attributed to the high Cr and N contents as well as to the ultrafine grain size.