Influence of thermo-mechanical treatment in ferritic phase field on microstructure and mechanical properties of reduced activation ferritic-martensitic steel (original) (raw)
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Bulletin of Materials Science, 2014
This paper presents the results of an experimental study on the microstructural evolution in 9Cr reduced activation ferritic/martensitic steels during short term thermal exposures. Since the microstructure is strongly influenced by the alloying additions, mainly W, Ta and C contents, the effect of varying W and Ta contents on the martensite structure that forms during normalizing treatment and the subsequent changes during tempering of the martensite in the temperature regime of 923-1033 K have been studied. Microstructural changes like subgrain formation and nature of precipitates have been evaluated and correlated to hardness variations. The systematic change in size distribution and microchemistry of M 23 C 6 carbide is studied with variation in W content at different temperatures.
Russian Physics Journal, 2013
ABSTRACT The effect of heat-treatment (HT) modes on the structural-phase state of heat-resistant ferritic-martensitic steel EK-191 is investigated. The use of intermediate (between quenching and tempering) annealing at reduced temperatures is shown to result in a higher dispersion of nanoparticles of vanadium carbonitride than that achieved by traditional heat treatment. The HT modes ensuring high density of nanoparticles and a simultaneous reduction of the martensite tempering intensity are found out.
Microstructure of EK-181 ferritic-martensitic steel after heat treatment under various conditions
Technical Physics, 2012
The effect of heat treatment conditions on the microstructure and phase composition of a low activated high temperature ferritic-martensitic EK 181 steel (Fe-12Cr-2W-V-Ta-Ba) is studied. Addi tional thermal cycling about the austenite-martensite phase transition temperature between quenching and tempering hinders the formation of fine interstitial phases, decreases the phase transformation induced hard ening intensity, retards the formation of a substructure with continuous misorientations, and decreases the brittle-ductile transition temperature.
steel research international, 2013
The microstructural changes and hardness exhibited by ductile iron with dual matrix structure (DMS) are investigated. In particular, DMS microstructures are obtained by continuous cooling in the (ferrite þ austenite) region followed by quenching to transform the austenite into martensite or by austempering at 3758C, to transform the austenite into ausferrite. Additionally, two deformation steps are applied in the austenite region. The structure was produced in a thermomechanical simulator equipped with a dilatometry system. The dilatometry is used to monitor the structure development throughout the thermomechanical processes. The structure was investigated using light optical microscopy and scanning electron microscopy. The influence of introducing ferrite to the microstructure and the deformation magnitude on the structure development and hardness properties are explored.
Metals
The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation by rolling in austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. The features of the grain and defect microstructure of steel are studied by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). It is shown that HTMT leads to the formation of pancake structure with grains extended in the rolling direction and flattened in the rolling plane. The average sizes of martensitic packets and ferrite grains are approximately 1.5–2 times smaller compared to the corresponding values after traditional heat treatment (THT, which consists of normalization and tempering). The maximum grain size in the section parallel to the rolling plane increases up to more than 80 µm. HTMT leads to the formation of new sub-boundaries and a higher dislocation density. The fr...
Materials Science and Engineering: A, 2014
Dual phase (DP) steels was investigated using thermomechanical processes designed to obtain ultrafine/ nanoferrite-carbide aggregates and martensite-ferrite duplex starting structures prior to intercritical annealing. The effects of processing parameters such as intercritical annealing temperature and time on the microstructural evaluations, mechanical properties, strain hardening behaviors and fracture mechanisms have been studied. The ferrite grain size and martensite volume fraction were depended on the initial microstructure and thermomechanical processing parameters. Ultrafine grained DP (UFG-DP) steel with an average grain size of about 2 μm was achieved by short intercritical annealing of the 80% cold-rolled duplex microstructure. Tensile testing revealed an excellent strength-elongation balance (UTS Â UE 4110 J cm À 3 ) in the DP steels. The new UFG-DP steels showed superior mechanical properties in comparison with the commercially used high strength steels. The variations of strength, elongation, strain hardening behavior and fracture mechanism of the specimens with thermomechanical parameters were correlated to microstructural features.
Materialia, 2019
The effect of strengthened elements (Y2O3 and TiO2) on the microstructure has been investigated in Fe-14Cr-1W based ferritic steels. Titanium content and/or volume fraction of yttria range between ~ 0 up to 0.3 wt%. The volume fraction of nanoparticles is shown to control the grain size whereas titanium content has a significant influence on the chemical homogeneity. Martensite phase was obtained on a Fe-14Cr-1W based ferritic steel after consolidation by Hot Isostatic Pressing because of a higher content of carbon. A relationship between martensite phase and chemical heterogeneities was evidenced showing a chemical partitioning phenomenon. This phenomenon was also observed on ODS ferritic steels containing a low content of titanium (≤ 0.05 wt%) however microstructural parameters, such as size and volume fraction of nano-precipitates and grain size, are shown to delay the formation of martensite during cooling by decreasing the value of critical cooling rate. Thermodynamic calculations indicate that the minimal titanium content to get a microstructure with 100% of ferrite is about 0.09 wt%.
Journal of Nuclear Materials, 2011
The Fe-14Cr-2W-0.3Ti-0.3Y 2 O 3 oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steel was fabricated by mechanical alloying of a pre-alloyed, gas atomised powder with yttria nano-particles, followed by hot isostatic pressing and thermo-mechanical treatments (TMTs). Two kinds of TMT were applied: (i) hot pressing, or (ii) hot rolling, both followed by annealing in vacuum at 850°C. The use of a thermo-mechanical treatment was found to yield strong improvement in the microstructure and mechanical properties of the ODS RAF steel. In particular, hot pressing leads to microstructure refinement, equiaxed grains without texture, and an improvement in Charpy impact properties, especially in terms of the upper shelf energy (about 4.5 J). Hot rolling leads to elongated grains in the rolling direction, with a grain size ratio of 6:1, higher tensile strength and reasonable ductility up to 750°C, and better Charpy impact properties, especially in terms of the ductile-to-brittle transition temperature (about 55°C).
IAEME PUBLICATION, 2015
The present work involves the studies on the transformation and micro-structural changes during Thermomechanical treatment (TMT) in 38MnSiVS5 micro alloyed steel with respect to the temperature of isothermal treatment post hot rolling in thermomechanical processing. A second heat treatment cycle with Two Step Cooling with Annealing (TSCA) was carried out to obtain multiphase micro structure of Ferrite Bainite and Martensite (FBM). In the TMT heat treatment cycle, steel after austenitization at 1250°C for 20 minutes was subjected to thermomechanical treatment by hot rolling at a finish temperature of 750oC (in 7-8 passes on two high rolling mill) followed by isothermal treatment in salt bath at a preselected (optimized through experiments) temperature of 365, 400, 435, 470 or 500°C and after holding for 35 minutes quenched in water. The second heat treatment, TSCA, involved 30 mm forged bar of 38 MnSiVS5 soaked at 1200oC (30 min) hot rolled at finish rolling temperature of 800 oC in 6 to 8 passes to 17 mm air cooling up to 700oC followed by water quenching (Two Step Cooling) annealed at 400-550ºC (in steps of 50oC) for 90 minutes. The optimized microstructure obtained was predominantly Acicular Ferrite with Bainite (AFB) in TMT treatment referred as TMT/AFB and multiphase microstructure of Ferrite, Bainite & Martensite (FBM) in Two Step Cooling with Annealing and referred as TSCA/FBM. The structural changes during the two types of heat treatment routes have been investigated using optical microscopy and mechanical testing techniques. The effect of heat treatment temperature on the hardness, UTS, %Elongation and Toughness of steel processed by these two processing routes have also been studied and related to their microstructure.