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The Effect of Two-stage Heat Treatment Temperatures on Initial and FSSWed Properties of TRIP Steels
international journal of iron and steel society of iran, 2017
In this paper, a 0.2 C–1.6 Mn–1.5 Si wt. % TRIP-aided cold-rolled steel sheet was fabricated and the optimal heat treatment conditions (Intercritical Annealing “IA” and Bainitic Isothermal Transformation “BIT”) were investigated to maximize the volume fraction and stability of the retained austenite. The effects of temperature on IA (770, 790 and 810 oC) and BIT (330, 350 and 370 oC) were studied via optical microscopy, SEM and XRD. Its tensile properties and formability were also evaluated. It is obtained that under conditions of 790 oC /330 oC and 770 oC /350 oC, the maximum and minimum amounts of the retained austenite resulted in a microstructure. Also, for the case which heat treated under 790 oC /330 oC condition obtained the best formability by showing the highest elongation ( more than 40%) and the case that heat treated under 810 oC /350 oC condition had the highest tensile strength (more than 800 MPa). The cases with the maximum (12.1 %) and minimum (8.1 %) volume fracti...
Materials, 2014
A medium Mn steel has been designed to achieve an excellent combination of strength and ductility based on the TRIP (Transformation Induced Plasticity) concept for automotive applications. Following six passes of hot rolling at 850 °C, the Fe-7.9Mn-0.14Si-0.05Al-0.07C (wt.%) steel was warm-rolled at 630 °C for seven passes and subsequently air cooled to room temperature. The sample was subsequently intercritically annealed at various temperatures for 30 min to promote the reverse transformation of martensite into austenite. The obtained results show that the highest volume fraction of austenite is 39% for the sample annealed at 600 °C. This specimen exhibits a yield stress of 910 MPa and a high ultimate tensile stress of 1600 MPa, with an elongation-to-failure of 0.29 at a strain rate of 1 × 10 −3 /s. The enhanced work-hardening ability of the investigated steel is closely related to martensitic transformation and the interaction of dislocations. Especially, the alternate arrangement of acicular ferrite (soft phase) and ultrafine austenite lamellae (50-200 nm, strong and ductile phase) is the key factor contributing to the excellent combination of strength and ductility. On the other
Jurnal Sains Materi Indonesia, 2023
Austenitic manganese steel (AMS) is widely used in the mineral and mining industry under high workload condition due to its remarkable work-hardening capacity under impact. However, AMS typically has an austenitic matrix with carbides precipitated resulting in low hardness and brittle properties, which impaired its wear performance. In this study, cold deformation followed by flash annealing were conducted to improve the mechanical behavior of AMS. The experimental was carried out by solution treatment (ST), cold rolling (CR) with deformation degrees of 10% and 20%, and flash annealing (FA) at 915°C with holding times of 90 and 150 seconds. The microstructure evolution and mechanical behavior were studied. The ST produced a completely austenitic microstructure which was free of carbide, resulting in a decrease in strength and hardness, as well as improved ductility. After cold deformation, both of strength and hardness were substantially improved, followed by loss in ductility. Optical microstructures reveal the formation of deformation twin (DT) and annealing twin (AT) after cold deformed. Higher intensity of DT results in AMS with considerable strength and hardness but decrease in ductility. After FA process, cold deformed structures undergo microstructural restoration, which manifests by recovery stage at 90 s and recrystallisation stage at 150 s annealing time. At the same FA time, higher degree of deformation led to increase the hardness, while at the same degree of strain, longer annealing time led to a decrease of hardness. Moreover, both of higher degree of strain and longer annealing time during flash annealing were contributed to grain refinement, even though did not affected to the increase of tensile and hardness. In addition, 20% cold rolling followed by 150 s annealing time (CR20FA150) could be considered as an effective method to obtain the most optimum combination of strength and ductility with finer grain.
Kovove Materialy-Metallic Materials
The structure and mechanical properties of two 0.2 wt.% C TRIP-assisted steels (Transformation Induced Plasticity) were compared to evaluate the effect of additional (Cr, Mo, V)-alloying on transformation kinetic and tensile/impact behavior after isothermal bainite transformation (bainitizing) and Q&P (Quenching-and-Partitioning) treatment. The work was performed using SEM, XRD, tensile/impact testing, and computer simulation. It was found that adding 0.55 wt.% Cr, 0.2 wt.% Mo, and 0.11 wt.% V into Mn-Si-Nb steel increased the incubation time in pearlite and bainite temperature ranges by 5.6 and 4.4 times, respectively. More heavily alloyed steel performed an improved combination "Strength/Ductility/Impact Toughness": its maximum PSE (Product of Strength and Elongation) value of 24 GPa• % referred to bainitizing treatment, whereas the highest KCV 20 • C values (220-225 J cm −2) corresponded to Q&P treatment. Improved mechanical properties of (Cr, Mo, V)-alloyed steel were attributed to a higher amount of retained austenite and a slower rate of TRIP-effect.
Hot rolled and cold rolled medium manganese steel: Mechanical properties and microstructure
Materials Science and Engineering: A, 2017
The current work aims at obtaining optimum amount of austenite after processing of a medium manganese steel in order to invoke partial twinning induced plasticity (TWIP) mechanism during deformation and to maximise elongation. Steel chemistry was optimised using thermodynamic calculations and the same was processed in different ways which includes continuous cooling from single phase austenitic region, quenching + austenite reverted transformation (ART) annealing and austenite reverted transformation (ART) annealing. DICTRA and Thermo-Calc simulation was done to understand the austenite to ferrite transformation kinetics during continuous cooling and the mode of equilibrium that is operative. The study suggests that quenching + austenite reverted transformation (ART) annealing is the ideal approach for processing this material in order to get the desired microstructure and properties. Thermo-Calc and Koistinen and Marburger's (KM) equation was coupled to estimate the fraction of austenite to be retained after isothermal holding at different intercritical temperatures and the optimum temperature found was used for annealing this steel. Microstructural characterization along with tensile test was done to ascertain the effect of processing route, initial microstructure on the mechanical properties. It was found that the morphology of austenite was greatly affected by the initial microstructure of the steel. Mechanical properties obtained after cold rolling (CR) and austenite reverted transformation (ART) annealing was found to be superior to that of hot rolling (HR) and austenite reverted transformation (ART) annealing. The difference in mechanical properties was correlated with the austenite morphology and the final microstructure.
Microstructure and tensile behaviour of cold-rolled TRIP-aided steels
Journal of Materials Processing Technology, 2004
The transformation of austenite to martensite is fundamental to the hardening of carbon steels. This transformation plays an important role for the mechanical behaviour of lowcarbon ferrous alloys containing about 10 vol.% retained austenite. The effect, known as transformation induced plasticity, is manifested by unusual high work hardening and high uniform elongation -properties very desirable for thin sheets applied for automobiles parts. Tensile tests of cold-rolled sheets at room temperature allowed to study the retained austenite stability against strain induced martensitic transformation. The influence of the processing texture (specimen orientation) and the strain rate (2·10 -2 , 2·10 -3 s -1 ) on the uniform elongation were observed experimentally. Results show that a homogeneous microstructure and the absence of initial blocky martensite ensure a long deformation paths. At the same time, tensile data reveal only a small influence of deformation parameters on the ultimate strength.
steel research international, 2015
High Mn steels, alloyed with Si and Al, present large plasticity when deformed due to the TRIP/TWIP effect. The present work studies the microstructural evolution and its influence on the mechanical behavior of a steel containing 17%Mn and 0.06%C after cold rolling to 45 and 90% reduction and subsequent annealing at 700 8C for different times. The microstructural analysis is performed by X-ray diffraction (XRD), scanning electron microscopy (SEM)-electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). It is observed that cold reduction induces the formation of eand a 0 -martensite. The material exhibits yield and tensile strength around 700 and 950 MPa, respectively, with a total elongation around 43% and a work hardening exponent of around 0.30 after 45% cold rolling and subsequent annealing and a yield and tensile strength of 750 and 950 MPa, respectively, with a total elongation of almost 50% when 90% cold rolling and subsequent annealing. The austenite texture contains brass, copper, and Goss components, while the a 0 -and e-martensite textures mainly consist of rotated cube and prismatic and pyramidal fibers, respectively.
Analysis of medium manganese steel through cold-rolling and intercritical annealing or warm-rolling
Materials Science and Technology, 2018
Medium manganese steel is typically fabricated from hot-rolling followed by cold-rolling and intercritical annealing processes. However, a singular process, warm-rolling, is an appealing prospect. The microstructure, mechanical properties and texture of a 8 wt-% Mn-0.08 wt-% C steel was investigated by cold-rolling followed by intercritical annealing or warm-rolling. The product from both processes exhibited a highly refined microstructure as well as a large volume fraction of austenite. However, a slightly larger volume fraction as well as a more heterogeneous austenite morphology resulted from the warm-rolling process, associated with a higher workhardening rate. Microstructural analysis revealed intense α-fibre components due to a higher strain following the warm-rolling process as well as a considerably high-angle grain boundary number which was associated with dislocation accumulation.
Metals
The quenching and partitioning (Q&P) process of lean medium Mn steels is a novel approach for producing ultra-high strength and good formable steels. First, the steel is fully austenitized, followed by quenching to a specific quenching temperature (TQ) in order to adjust an appropriate amount of initial martensite (α’initial). Subsequently, the steel is reheated to a partitioning temperature (TP) in order to ensure C-partitioning from α’initial to remaining austenite (γremain) and thus retained austenite (RA) stabilization. After isothermal holding, the steel is quenched to room temperature (RT), in order to achieve a martensitic-austenitic microstructure, where the meta-stable RA undergoes the strain-induced martensitic transformation by the so-called transformation induced plasticity (TRIP) effect. This paper systematically investigates the influence of the Q&P process on the isothermal bainitic transformation (IBT) kinetics in a 0.2C-4.5Mn-1.3Al lean medium Mn steel by means of d...