Authors: Masayuki Wakita, Yoshitaka Adachi, Yo Tomota
Abstract: This study aims at examining thermomechanical controlled process to realize ultrafine
TRIP-aided multi-phase microstructures in low carbon steels. Heavy deformation at a supercooled
austenite region was found to lead the formation of 2 μm ferrite as well as retained austenite with
high volume fraction. The morphology of retained austenite was changed from film-like shape to
granular shape with lowering finish rolling temperature in austenite field. This ultrafine TRIP-aided
multi-phase steel showed good balance of tensile strength with total elongation, ie. 1080MPa and
26.9%. A novel in-situ neutron diffraction measurement demonstrated that the retained granular
austenite transformed to martensite at a relatively large strain compared with the retained film
austenite. The therein-underlying mechanism of the good mechanical properties was discussed from
the view points of the morphological and thermodynamical stabilization of retained austenite.
4351
Authors: Sophie Lubin, Anne Francoise Gourgues-Lorenzon, Brigitte Bacroix, Hélène Réglé, Frank Montheillet
Abstract: The effect of the metallurgical state of austenite (undeformed vs. deformed vs. deformed + recrystallised) on the properties of the austenite to bainite transformation were investigated thanks to thermal (Gleeble simulations) and thermomechanical (hot torsion) treatments. No obvious influence of the state of austenite was found, using electron backscatter diffraction, on the resulting microtexture. Advantages and drawbacks of using misorientation angle histograms vs. axis-angle pair distribution are discussed regarding investigations of local variant selection. For an austenite grain size higher than about 50 µm, a strong effect of the transformation temperature was evidenced, bainite formed at lower temperature (530°C) exhibiting a microtexture close to that of lath martensite in the same steel.
772
Authors: Petr Kawulok, Rostislav Kawulok, Ivo Schindler, Jaroslav Sojka, Martin Kraus, Karel Milan Čmiel, Miroslav Legerski, Stanislav Rusz
Abstract: A physical simulation of the thermomechanical processing of the Mn-Ni-Cr-Mo low-alloy steel was performed in the laboratory rolling mill Tandem in the Institute of Modelling and Control of Forming Processes at VŠB – Technical University of Ostrava. The task was to determine the influence of the finish rolling temperature on the structural and mechanical properties of the rolled products. After different modes of rolling and slow cooling in the furnace, the final structure of the tested samples was in all cases composed of ferrite, bainite and islands of martensite. The finish rolling temperature markedly influenced a part by volume of the individual phases as well as the structure homogeneity. The results of the tensile tests at room temperature indicated that the studied steel did not show any pronounced dependence of the yield stress on the finish rolling temperature in the investigated range of values (750 – 1000 °C). On the other hand, the closely corresponding dependences of the ultimate tensile stress and elongation exhibited a considerable and very complex course, which can be explained mainly by the martensite fraction originating during the last stage of the final air cooling from temperature 600 °C.
386
Authors: Xiao Yu Ye, Kai Hua Zhang, Jun Zuo
Abstract: In Formastor-Ⅱ thermal expansion phase transition instrument, determine test steel's thermal expansion curves with different cooling rates during continuous cooling. Using thermal expansion combined with metallographic-hardness method to draw the continuous cooling transformation curve (CCT).According to the test results draft thermal simulation program, in Gleele-3500 thermal simulation test machine, conduct thermal simulation experiment for vanadium microalloying X70 grade pipeline steel at different deformation temperature, deformation extent and coiling temperature. Analysis that the microstructure was influenced by different rolling process.The results showed that: in industrial production, the experiment steel's rough rolling temperature should be controlled more than 1020°C, finishing temperature controlled in 820±20°C and coiling temperature controlled in 500～530°C to obtain acicular ferrite.
1033
Authors: Zhuang Li, Di Wu, Wei Lv, Shao Pu Kang, Zhen Zheng
Abstract: In this paper, ultra-high strength dual phase steel was investigated. Thermomechanical processing was conducted by using a laboratory hot rolling mill. The results have shown that the main transformation products at three different kinds of thermomechanical processing were ferrite, bainite, and small amounts of martensite. Laminar cooling led to ferrite grain refinement. The mechanical properties of specimen 1 which was controlled cooling after a relative lower temperature rolling are much higher than that of specimen 2. The presence of martensite islands and precipitates contributed to the enhancement of strength of the present steel. And the presence of retained austenite resulted in higher toughness. As a result, these specimens exhibited satisfactory mechanical properties.
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