Study On The Mechnical Properties And Thermal Physical Properties Of304Stainless Steel At High Temperature

In the concasting304stainless steel produced by Tai Steel, the surface of slab is liable to cause defects,such as surface crack and pit flaw.In this paper,adopting the304stainless as raw materials,the type Gleeble-1500D thermal simulation testing machine,the DIL402C thermal dilatometer,STA449F3thermal analyzer were employed to test the mechanic properties at high temperature,linear expansion coefficient,DSC and Cp curve of304.At the same time,analysing the effects of the thermology properties and the mechanical properties for the quality of304stainless steel slab,identfying the cracing sensitivity,associating with the processing technique of casting, optimizing the primary processing technique, hoping to achieve decreasing the defects of slab, like surface crack and pit flaw.The results of mechanic properties at high temperature indicated the tensile strength and yield strength decreased with temperature increasing during the7001400℃.The tensile strength was below25Mpa and the yield strength was20Mpa when the temperature was above1200℃.It indicates that the ability of slab to resist twisting at external force bacame worse at high temperature. The first brittleness temperature was1300℃to melting temperature and the third brittleness temperature was950～1050℃.In the range of1050～1250℃,the reduction of area was over65%,the hot ductility was well.The surface defects of slab which was located in the secondary cooling areas and continuous straightening areas can decrease effectively when the surface temperature of slab was controlled above1050℃.The results of thermrology properties at high temperature indicated the range of linear expansion was18.86×10-6～21.34×10-6and the contraction coefficient was18.57×10-6～24.24×10-6.The coefficients of expansion and contraction of304stainless st eel are on the whole greater than2Cr13martensitic stainless steel (α=12.08×10-6) and20CrMo structural alloy steel (α=14.05×10-6). So the304stainless steel belongs to crack sensitivity steel.The curve of Cp waves obviously during the1000~1400℃as temperature raise.Because of the transformation of crystalline shape occurs,the brittleness of slab increased.The curve of Cp generates peak value at1288℃.It indicates that there would be a phase transformation when the slab at this temperature point.The thermal stability became worse and the defects generates more easily when the slab was located in this zone，like the upper levels of the crystallizer where the temperature was1250～1400℃.When the temperature is raised to1402.1℃,a inflexion point on the curve of DSC emerged where the heat abrupt change and the peak value reached1438.0℃.The curve of DSC was unsmooth at these temperature points like1372.7℃、1277.9℃、1231.7℃and the phase change occurs.It causes the volume of shell thickness changed and the thickness of the initial solidified shell non-homogeneous。When the slab located in1450～1100℃,like in the upper and middle levels of the crystallizer，the surface of casting blank causes crackle and pits more easily.