Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： In order to obtain the optimal corrosion resistance, the characteristics of microstructure and alloy elements distribution of S32760 duplex stainless steel were studied after solid solution treatment at various temperatures from 1000 ℃ to 1300 ℃ by means of OM, EPMA, SEM, EDS and TEM. In addition, the pitting corrosion resistance was measured by the electrochemical workstation. The results show that the N atoms diffused into d phase from g phase during solution treatment when the temperature was higher than 1080 ℃. N atoms migrated back into g phase when the subsequent cooling was slow enough. However, Cr2N phase in situ precipitated during quenching because there was not enough time for the N atoms to diffuse back into g phase. Cr2N particles increased with the solution temperature increasing. Furthermore, s phase precipitated when the tested sheet was heat treated at or below 1040 ℃ due to the high content of N. Thus it is obvious that the solution temperature range of the S32750 duplex stainless steel is quite narrow, which is between 1040 ℃ and 1080 ℃, and it is confirmed that the optimal temperature is 1060 ℃. After treated at 1060 ℃ for 60 min, the Brinell hardness of S32760 steel is 249 HBW, pitting potential is up to 1068 mV and the passive current density is as low as 1.48×10-4 A/cm2.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Austenite-ferrite transformation in low carbon steels has a fundamental role in phase transformation and is industrial importance. The kinetics of austenite transformation can be described by the kinetics of austenite-ferrite interface migration. Two classical models, the diffusion- controlled growth model and the interfacecontrolled model, can be used to describe the growth of proeutectoid ferrite during g→a isothermal transformation. The austenite transformation in continuous cooling process is more common in production. In continuous cooling process, the equilibrium carbon concentrations in austenite and ferrite change with temperature and the kinetics of austenite transformation is different from that in isothermal process. Based on the models for g→a isothermal transformation, a diffusion control model is established for the growth of proeutectoid ferrite during the decomposition of supersaturated austenite in continuous cooling process. The interface position of proeutectoid ferrite varying with temperature is described with the model. The soft impingement effect at the later stage of transformation is considered. The carbon concentration at the austenite side of interface is difficult to reach the equilibrium carbon concentration when the cooling rate is high. A parameter as the function of cooling rate is proposed to modify the carbon concentration at the austenite side of interface. The polynomial diffusion field approximation is assumed in front of the interface. Simulation is done by utilizing the model to analyze the growth of proeutectoid ferrite in continuous cooling process with different bulk concentrations, austenite grain sizes and cooling rates. The interface position of proeutectoid ferrite as a function of temperature or time is obtained under different cooling conditions. Also, carbon diffusion length at the austenite side of interface as a function of time and carbon profile as a function of interface position are obtained under different cooling conditions. Furthermore, the proeutectoid ferrite fraction as a function of temperature can be acquired. The change law of carbon diffusion length with interface position and the change law of interface position with square root of time are discussed. The simulation results of diffusion control for austenite transforming in Fe-0.17C (mass fraction, %) alloy with grain size of 17 mm and different cooling rates show a good agreement with the literature results previously reported.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Nanostructured bainite steel with an ultimate tensile strength of 2127 MPa, elongation of 4% has been obtained by warm rolling followed with isothermal heat treatment.The effect of deformation temperature on transformation of nano bainites has been investigated. The results show that with a proper warm defromation, the time required for the transformation of the supercooled austenite into bainite can be shortened from 50 h to 20 h. The deformation rates of supercooled austenite adopted at all temperatures in the experiments can accelerate the low temperature nanobainite transformation, while the transformation rate increased with the decreasing deformation temperature. With a deformation rate above 30%, the retained austenites were sharply refined and the blocky austenites were diminished. The low temperature nano bainite transformation can be accelerated by warm rolling process without harm to the strength, thus shortening the time of heat treatment resulting in cost saving of the steel production.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： The high temperature mechanical properties of P-contained high strength interstitial free (IF) steel were investigated using Gleeble3500 thermal simulation testing machine, in terms of zero ductility temperature (ZDT), zero strength temperature (ZST) and the relationship of tensile strength with temperature. The fractured surfaces at different tensile temperatures were characterized by means of scanning electron microscope. The phase transition temperature interval was deduced by the THERMOCALC software. The results show that the ZDT and ZST of the steel are 1420℃ and 1445℃, respectively. The brittleness temperature interval Ⅰ is from 1400℃ to the melting point, and there is no the brittleness temperature interval Ⅲ. The transverse cracks on the surface of casting blank did not occur during the straightening process. The tensile strengths decrease with the increasing temperature in the test temperature range, and which are lower than 5.3 MPa above 1300℃. The result of THERMO-CALC calculation shows that, with the specimens cooling from 500℃ to 400℃, Fe3P precipitates out in the α-Fe matrix, which may results in cold short. The transverse cracks on the continuous casing (CC) slab could dramatically be reduced by Hot-charging Technology.
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