Papers by Keyword: Continuous Cooling Transformation

Abstract: The continuous cooling transformation behavior of high-carbon pearlitic steel was studied by employing optical microscopy, scanning electron microscopy, and the Vickers hardness test. The results show that the microstructure of the test steel is composed of proeutectoid cementite and lamellar pearlite in the cooling rate range of 0.05–2 °C/s and lamellar pearlite in the range of 2–5 °C/s. Further, martensite appears at 10 °C/s. With the increase in the cooling rate, the Vickers hardness of the test steel first decreases and then increases. In the industrial production of high-carbon pearlite steel, the formation of proeutectoid cementite at a low cooling rate needs to be avoided, and at the same time, the formation of martensite and other brittle-phase at a high cooling rate needs to be avoided.

Abstract: The present work was undertaken to understand the phase transformation behaviour in a third generation steel 0.22C-2.1Mn-1.0Si during continuous cooling. The microstructure at various cooling rates were examined by using different techniques, such as optical microscopy, scanning electron microscopy, dilatation test and X-ray measurement. The results show that the amount of bainite that forms during continuous cooling is limited and there is a bainitic transformation stop temperature for this kind of steels. A continuous cooling transformation diagram of the steel is established.

Abstract: Continuous cooling transformation (CCT) diagram of a high strength weathering prefabricated building steel was determined using a DIL805L thermal dilatometer by means of the expansion method combined with metallography hardness method. Effect of cooling rate on microstructure and hardness of the steel was also studied. The results show that the austenite transformation products of the steel are ferrite and pearlite when cooling rate is lower than 3°C/s. In the cooling rate range of 3 to 20°C/s, the mixed microstructure of ferrite, pearlite and bainite can be obtained. When cooling rate is higher than 20°C/s but lower than 100°C/s, the microstructure is composed of ferrite, bainite and martensite. When cooling rate is above 100°C/s, ferrite disappeared completely, and transformation products are bainite and martensite.

Abstract: The diagrams of continuous cooling transformation (CCT) of β-phase decomposition for hot-rolled VT8M titanium alloy were obtained using the differential thermal analysis, scanning electron microscopy, and X-Ray diffraction (XRD) analysis for heating temperatures from 880 to 960 °C. The decomposition process was found to occur with several distinguishable stages. The transformation begins from high-temperature stage of the growing of primary alpha precipitates. At lower temperatures, it is followed by the medium-temperature stage accompanied by precipitation of grain-boundary alpha and the formation of coarse secondary alpha-lamellae. The low-temperature stage has been established to be characterized by the formation of dispersed alpha-platelets within beta-grains.

Abstract: Digitization of CCT curves by systemically using common softwares was studied and practiced to rebuild the digital patterns for teaching purpose. As treated in PC procedure, the CCT images printed in books were transformed into the digital data points, which can be read and record clearly and precisely in computer, extremely changing the appearance and precision of raw images. As the digital data, this digitized CCT curves can be conveniently introduced into the courseware, drawing more attendance and interesting from students than raw images. On the other hand, these digitized data also can be used as the CCT database for industrial applications, which can introduce automation into the thermal treatment industry. That is, the digitization of CCT curves will take great advantage of the improvement of teaching and promote the producing depth.

Abstract: Through the thermal simulation test of the Nb-Ti micro-alloyed steel austenite cooling process and microstructure observation & microhardness test, the tests indicate cooling rates have effect on the phase transition and microstructure of tested steel, the critical quenching speed of Nb-Ti micro-alloyed steel is about 23°C/s with very good hardenability. With the increasing of the cooling rate, the beginning and ending temperature of phase transformation decrease and the ferrite structure content was decreased at room temperature. It’s easy to happen Bainite transformation at the beginning, and make the M block or flake M fine, which is to increase the strength and toughness of the steel.

Abstract: Through the thermal mechanical simulation experiment，combined with the metallographic analysis and microhardness test on the Nb-Ti micro-alloyed steel for the austenitic continuous cooling process. The results shows that: with the increasing of the cooling rate, the phase transformation starting and ending temperature decrease and the ferrite content was decreased at room temperature. In less than 5°C/s low cooling speed region, with the increasing of the cooling rate, the grain size of tested steel obviously increases; In more than 17°C/s high cooling speed region, the grain size and vickers hardness of tested steel change and tends to be smoothly.

Abstract: The paper examines the effect of boron (B) on the dynamic recrystallization and continuous cooling transformation (CCT) behavior in Nb-Ti microalloyed high strength interstitial free (IF) steels. For this purpose, two Nb-Ti microalloyed IF steels containing 0.003wt.% and 0.0005wt.% B, respectively, and one IF steel without B were chosen. The dynamic recrystallization behavior was investigated using hot compression testing. The character of the austenite to ferrite transformation during continuous cooling was studied by dilatometry test and CCT diagrams for the IF steels have been constructed. It was found that the initiation of dynamic recrystallization is delayed as the amount of boron increases. Addition of B retards the austenite to ferrite transformation as well. Under cooling rates of 0.5 and 1oC s-1, which correspond to slow cooling rates in the hot strip mill, the addition of B leads to the development of acicular ferrite and bainite phases. On the other hand, at similar cooling conditions the B free IF steel was observed to have a polygonal ferrite microstructure.