Study Of Structure Refining Mechanism Of Inclusions On High Strength Ship Plate Steel

With the development and application of large-wire energy welding technology,the shipbuilding efficiency has been improved significantly,and the welding performance of ship-plate steel has put forward higher requirements.Combined with the mechanism of oxide metallurgy,the mechanism of inclusions refinement of high-strength steel reinforced ship plate steel was studied by analyzing the ferrite-induced phenomena in different samples.First of all,according to the optimized ship steel design components the smelting experiment was conducted,and carry out a series of studies on the obtained test steel.The results show that a large amount of IAF structure is found in the heat-affected zone of the typical sample,and the impact energy is much higher than that of other heats.The shape of the inclusions that can induce IAF is round and irregular mainly,and the size of the inclusions in the heat-affected zone were different significantly,the concentrated area is between 5μm~10μm and 2μm~5μm respectively.The compositions of the samples were the same as Ti Ox,Al2O3,Mn S and a few carbon and nitrogen compounds basically.Secondly,heat treatment tests were carried out on as-cast and as-rolled structures of industrial shipboard steel respectively.The results show that the microstructure changes of the samples under different heat treatment temperature are different obviously.The temperature range of IAF induction in as-cast samples is 700℃~750℃ and 1150℃~1300℃,and the temperature range of IAF induction in the rolled samples is 1100℃~1300℃.The shapes of IAF inclusions are mainly round and irregular with the same composition.The size of the inclusions in IAF can be concentrated between 5μm~10μm,and the inclusions in the 40 mm thick steel plate are more than 5μm.Finally,the size of IAF inclusions and the size of the austenite grain are calcuiated by aggregated with different grain sizes.It is concluded that the size of inclusions gradually decreases with the increase of austenite grain size.The obtained data were fitted and analyzed by least-squares method,and the fitted function that can reflect the matching relationship between the inclusions and the original austenite grain size was obtained.It provides the guidance for controlling the grain size and controlling the inclusions in the smelting process.