Model prediction of the effect of in-mold electromagnetic stirring on negative segregation under bloom surface

Aiming at the problem of negative segregation under a bloom surface, a coupling macrosegregation model considering electromagnetic field, flow, heat, and solute transport was established based on the volume average method to study the effect of in-mold electromagnetic stirring(M-EMS) on the negative segregation under the bloom surface. In the model, the influence of dendrite structure on the flow and solute transport was described by the change of permeability. The model was validated by the magnetic induction intensity of M-EMS and carbon segregation experiment. The results show that the solute C in the solidified shell in the turbulent zone of the bloom undergoes two negative segregations, whereby the first is caused by nozzle jet, and the second by the M-EMS. The severities of the negative segregation caused by M-EMS at different currents and frequencies are also different, and the larger the current is, or the smaller the frequency is, the more serious will be the negative segregation.With the M-EMS, the solute C distribution in the liquid phase of the bloom is more uniform, but the mass fraction of C in the liquid phase is higher than that without M-EMS.

Optimization of Low Phosphorus Steel Production With Double Slag Process in BOF

To produce the steel with phosphorus less than 0. 007% （mass percent）, the double slag process has been optimized in basic oxygen furnace （BOF）. Dephosphorization and decarburization are performed in sequence in the same converter. Deslagging is conducted twice, each at the end of dephosphorization and decarburization, by tilting the BOF. Production was tested in a 180 t BOF. Mass percent of phosphorus in steel at BOF blow end has been made to as low as 0. 004 2 % after optimizing operational parameters. Factors affecting dephosphorization performance were studied. Before intermediate deslagging, dephosphorization is determined by the mass transfer of phosphorus from metal/slag interface to bulk slag phase rather than equilibrium thermodynamic conditions. After intermediate deslag-ging, dephosphorization is deter/nined by the equilibriurn thermodynamic conditions such as slag composition and temperature.

Effect of Martensite Fine Structure on Mechanical Properties of an 1100 MPa Grade Ultra-high Strength Steel

An 1100 MPa grade ultra-high strength steel with different martensite fine structures, characterized by prior austenite grain size, martensite packet size, block width and lath width, was studied by various heat treatment processes. The result shows that with decreasing prior austenite grain size, both the packet size and block width decrease, while the lath width has virtually no change. Accordingly, both strength and toughness increase, while total elongation decreases. The yield strength has a Hall Petch type relationship with the prior austenite grain size, packet size and block width, and the block width may be regarded as a key factor influencing strength. On the other hand, the ductile to brittle transition temperature （DBTT） is found to be more related lo the packet size, which may be considered as a dominant factor influencing toughness.

Weldability of 610MPa Grade High Strength Plate Steel 12MnNiVR for Oil Storage Tanks

The weldability of 12MnNiVR was examined in terms of the simulated HAZ continuous cooling transformation (SH-CCT) diagram,microstructure and mechanical properties of the simulated coarse grain heat-affected zone (CGHAZ).When t 8/5 is shorter,the microstructure mainly consists of lath bainite.When t 8/5 is 60 s,the microstructure becomes coarser bainite.Some acicular ferrite appears beside lath bainite when t 8/5 =100s.Finally,a microstructure composed of polygonal ferrite,acicular ferrite,and small amount pearlite is obtained with a small amount of bainite at t 8/5 】100s.With the increase of t 8/5,the hardness of CGHAZ decreases considerably.The minimum impact toughness of CGHAZ appears at t 8/5 =100s.The hardness and the toughness of CGHAZ remain above the specified values for steel 12MnNiVR.

Effect of Nb on corrosion behavior of inner bottom plate of cargo oil tankers

The effect of Nb on the corrosion resistance of steels in simulating an oil-corrosion environment was investigated by means of microstructure observation, electrochemical test, dissolved Nb content measurement and Nb segregation observation. The results show that the microstructure of the experimental steels is mainly ferrite with a little pearlite. The dissolved Nb contents of the experimental steels are 0.0235 and 0.0458 wt.%, respectively, while the undissolved Nb content is nearly the same. In addition to enhancing mechanical properties of the steel, dissolved Nb improves the corrosion resistance by enriching Nb in the rust layer. Nb oxides in the rust layer cause a decrease in the corrosion rate due to a decrease in the anodic reaction kinetics. The segregation of Nb at the grain boundaries suppresses the corrosion. Moreover, Nb is enriched at the bottom of the corrosion pit and prevents any further corrosion.