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A three-dimensional mathematical model of mould electromagnetic stirring (M-EMS) was established. Based on Maxwell's equations, the continuity equation and the momentum equation, the distribution characteristics of electromagnetic and flow fields with M-EMS were numerically simulated by the finite element software ANSYS and the finite volume software CFX. The influence of M-EMS on electromagnetic and flow fields was examined, and the process parameters of M-EMS were optimised by industrial plant trials. By the model verification, there was a good agreement between the calculated results and the measured data. The results indicate that the tangential electromagnetic force increases with the increasing current intensity, and increases at first and then decreases with the increasing current frequency. The tangential velocity increases with the increasing current intensity and current frequency (2-6 Hz). According to statistical results of the centre equiaxial crystal proportion and the macroscopic defects of round billet for different process parameters in industrial plant trials, the optimal process parameters of the M-EMS are as follows: the current intensity is 400 A, and the current frequency is 2 Hz.

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Stress corrosion cracking behaviour of ferritic stainless steels with copper and molybdenum additions in 42 wt-% boiling magnesium chloride at 143¡18C has been determined. The nature of the corrosion products was analysed by X-ray photoelectron spectroscopy (XPS). XPS results show that the presence of Fe(0), Cr(0) and Mo(0) unoxidised states on the crack tips of (copper þ molybdenum) addition ferritic stainless steel cannot form the stable passive film and causes the further corrosion in the chloride solution. The addition of both copper and molybdenum to 19% Cr ferritic stainless steel causes stress corrosion cracking. The susceptibility to stress corrosion cracking increases with the growth of 1-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of 1-copper phases, then propagates to molybdenum atoms, and finally propagates to the other 1-copper precipitations perpendicular to the direction of maximum strain.

The effects of Nb addition on microstructures and formability in Si‐Al‐Mn TRIP cold‐rolled steels were investigated. These steels were intercritical annealed at 770 °C for 5 min, and isothermally treated at 400 °C for 3 min. Microstructural observation, tensile tests and forming limit diagram (FLD) tests were conducted, and the changes of retained austenite volume fraction as a function of tensile strain were measured by using an X‐ray diffractometer. The results showed that Nb addition makes grain size refined, the volume fraction of ferrite increase and that of bainite decrease, however, obviously it does not affect the volume fraction and carbon content of retained austenite. The Nb addition increased the stability of retained austenite owing to grain refinement. With Nb addition, increase in strength, ductility, strain hardening exponent and formability could be achieved simultaneously. These findings indicate that Nb addition can be a new direction of microalloying design for the low carbon TRIP steels with excellent formability and high stability of retained austenite.