Study On The Mechanism Of Oxide Metallurgy Of Micro Alloying Elements

The appearance of large heat input welding greatly improved the efficiency of ship manufacturing.The coarse microstructure of heat affected zone leads to the decrease of the mechanical properties of the steel.In order to solve the problem of the welding heat affected zone.In this paper,a series of experimental studies have been carried out on industrial production of ship plate steel containing magnesium.For the study on the effect of welding heat input for the HAZ impact toughness of shipbuilding steel,a series of methods including impact testing,fracture analysis and metallographic structure analysis had been carried out in this research.The results show that,at-20 ℃,the HAZ impact energy of steel plate with thickness 16 mm or 40 mm is more than 160 J,but the value of 25 mm is only 57.5 J,the HAZ fractures of 16 mm and 40 mm thickness steel plate are typical ductile fracture,and the HAZ fracture of 25 mm is quasi cleavage fracture.For the HAZ metallographic structure,there are a lot of IGF which could make the microstructure refine in the HAZ,and the HAZ structure is even better than the original plate.The impact toughness of 25 mm thickness steel plate at HAZ is relatively low,because its heat load is largest,and the structure of original plate is also coarser than the other two.For detecting IGF inducing mechanism of casting structure,cooling rate and the size and distribution of inclusions had been studied separately.The results show that,for the experiment steel,the decisive factors for the casting structure of the slab were the size and distribution of inclusions.Compared to the inclusions which are smaller than 3μm and inducing IGF in the structure of steel plate HAZ,the inclusions induced IGF in casting structure were between 5μm and 15μm.For the life of continuous casting machine and the stabilization of bending-straightening technology,the inclusions size should be controlled under 5μm to lower the IGF content of strand casting structure.To study the effect of temperature on Microstructure of cast and rolled steel containing Mg.The results are shown that,the temperature transition interval of the needle like ferrite in the as cast microstructure is between 730 and-760.In this experimental steel,the austenite grain size of austenite grain is not growing up because of the magnesium treatment.