Study On Solidification Segregation And Homogenization Process Of 15-15ti Austenitic Stainless Steel

15Cr-15Ni Ti-containing austenitic stainless steel(15-15Ti)is a structural material for preparing the cladding tube in the sodium cooled fast reactor core assembly,and the alloying degree is high,and elements are prone to segregation.In the industrial production,3?6 tons of 15-15Ti austenitic stainless steel ingots are used to prepare the cladding tubes.As the size of the alloy ingots increasing,the degree of segregation of alloying elements will be further aggravated.In order to realize the industrial production of high quality 15-15 alloy cladding tubes,this paper systematically studied the segregation law and homogenization process of solidification elements of 3t alloy self-consumption ingot,and carried out engineering verification.The main findings are as follows:(1)The whole structure of solidification structure of 3 tons of industrial 1515Ti austenitic stainless steel self-contained ingot was obtained.The as-cast micro structure of the self-consumption ingot longitudinal section can be divided into starting zone,steady state and final solidification zone from bottom to top according to macroscopic features.The starting zone is located at the bottom of the consumable ingot and consists of columnar crystals that grow vertically upward.The steadystate zone is in the middle part of the consumable ingot,which is the main part of the self-consumption ingot.It is mainly composed of developed columnar crystals arranged in an inverted "V" shape,with an angle of less than 45° with the longitudinal axis of the ingot,and the structure is uniform and dense.The final condensation zone is located at the head of the consumable spindle,and the axial heat dissipation of the ingot is also relatively fast,so it has a certain similarity with the structure of the starting zone,it is composed of the upper and lower growth columnar crystals.(2)The head,middle and bottom of the 3 ton 15-15Ti consumable steel ingot corresponded to center,1/2 radius and edge have no macrosegregation of elements.In the interdendritic region of the micro structure of the ingot in head,middle and bottom,the elements of Mo,Ti,C,Si and Mn are enriched,the Fe element is depleted,and the Cr and Ni elements have no segregation behaviors,and the degree of segregation of element Ti is highest.(3)The residual segregation index of Mo and Ti elements in different parts of the sample after homogenization at different temperature time indicates that the element segregation at the center of the ingot is the most difficult to eliminate.As the homogenization treatment time is prolonged at 1200?,the white dot-like and long-length MC carbide phases between the dendrites in the as-cast structure gradually dissolve back into the matrix.According to the segregation coefficient,residual segregation index and precipitation phase of the element after homogenization treatment,the optimal homogenization process was determined to be kept at 1200? for 25h.(4)The self-consumption ingot was subjected to high temperature homogenization treatment after 1200? Celsius forging 25h,and no fine-grained strips and strip-shaped carbides were found after forging,High temperature homogenization treatment is an effective process for improving the uniformity of 15-15Ti organization.