The Impact Of S On Inclusions And Organization For Ship Plate Steel

As the development of ship plate industry and the continuous application of high heat input welding technology, the steel for ship plate needs the performance of high strength, high toughness and could be welded by high heat input welding. In high heat input welding condition, Grain coarsening occurs in welding heat affected zone (HAZ) of plate, causing the reduction of toughness and the appearance of weld cracks. Tiny inclusions grains were used to promote the nucleation of IGF in order to reduce the size of grains and improve the organization of HAZ. This method has been an effective way to improve the toughness of HAZ.In this paper, different contents of S were taken into consideration to investigate the impact of S by using the idea of oxide metallurgy technology. Five groups of experiments were performed by using molybdenum silicide furnace. The influences of S were studied by changing the content. Optical Microscopy (OM) and Image Pro Plus (IPP) software were used to analysis the size and number of inclusions in steel. Morphology and composition were analyzed by SEM and EDS. Confocal Laser Scanning Microscopy was used to observe the change of the organization. The following results were got:(1)The content of S in steel affect the content of S in inclusions and the ratio of MnS area in inclusions, the S content in inclusions and the area ratio of MnS in inclusions increase with the raising content of S in steel.(2)The ending samples were electrolyzed to analysis the inclusions and the results were nearly the same with the results got by directly using SEM and EDS. The types of inclusions were nearly the same. But there are some differences between them on the size(3)In the thermal simulation experiment, size of grains while w[S] is0.0015%is the largest, the size while w[S] is0.011%is the smallest, and the size while w[S] is0.0075%is between the two mentioned above. (4)When the heat input was100kJ/cm, it can be clearly seen that a lot of acicular ferrite appear in the grains, some appear by using inclusions as nucleation core. However acicular ferrite while w[S] are0.0015%and0.011%is less than that while w[S] is0.0075%.and the amount of acicular ferrite while w[S] is0.0015%is more than that while w[S] is0.011%.