In the present study, the effects of Al content on the evolution of inclusions formed in Fe-16Mn-xAl-0.6C high Mn TWIP steels were investigated experimentally and discussed based on the thermodynamic calculation with FactSage. The results showed that with the increase of Al content from 0.002 to 2.1 wt-% in the steels, the evolution route of the main oxide inclusions is MnORAl 2 O 3 RMgAl 2 O 4 RMgO, the main sulphide inclusion is changed from MnS to MgS, and the dominant stable inclusion changes along the route of MnORAl 2 O 3 /MnSRMnSRAlN. The main inclusion types in thermodynamic calculation results with FactSage are consistent with the observed results in the present experimental steels.
In order to control central cracks in continuous casting of microalloy 49MnVS3 steel, the formation mechanism of central cracks has been studied by analysing the element segregation, crack morphology, hot ductility, precipitates and centre macrosegregation. It was found that the centre macrosegregation of carbon and sulphur and the precipitation of (Mn, Fe)S in grain boundary at the later stage of solidification could decrease the solidus temperature and enlarge the high temperature brittle zone, meanwhile, the precipitations of MnS and Ti(C, N) in grain boundary could make cracks easier to propagate, both of which lead to the formation of central cracks. Based on the above analysis, the centre macrosegregation of carbon and sulphur and the inclusions including MnS and the total in the centre of bloom were decreased by using final electromagnetic stirring and machine soft reduction together, thus, the central cracks of bloom were controlled successfully.
The time-temperature-transformation (TTT) curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on σ precipitation was studied by metallographic observation, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000°C, especially in the range of 800-900°C. The longer the aging time, the higher the amount of σ precipitation. The area fraction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850°C is the most sensitive transaction temperature, the incubation time for the formation of σ precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The σ phase is formed preferentially at the α/α/γ junction, and then grows along the α/α boundary in the matrix.
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