The Study On Elevated Temperature Phase Transfromation And Thermal Physical Properties Of Two Stainless Steel

During production process of stainless steel,there are some problems that can't be ignored,such as hot-rolled edge loss,rolling cracks and other defects.These problems will make a significant adverse impact to products,productivity and economic benefits.At present,microstructures and properties at room temperature for stainless steel have been widely studied by researchers at home and abroad,but the study on microstructure and properties at elevated temperature is still not enough and without systemic.In this paper,distribution,morphology and the number ofδ-ferrite in microstructures of the two austenitic stainless consecutive casting blanks have been observed and analyzed at room temperature.In solidification process of stainless steel 304,most ferrite is punctate at edge position.In addition,there are some parts of the island-shaped ferrite.The remaining parts of ferrite are island-shaped or net-shaped.In solidification process of E01 stainless steel,first-shaped ferrite nucleus shape and grow up sufficiently,therefore,ferrite is well-developed to dendrite.Mn works as austenite formation element which substitutes for Ni.The nuclear formation ability of Mn is weaker than Ni.During theδ→γsolid phase transition,developed first-shaped ferrite is difficult to transform into austenite completely.Net-shaped 8 ferrite organization is observed at the boundary of austenite grain at room temperature.Ferrite distribution in 304,E01 stainless steel of consecutive casting blanks along the thickness direction is "W" distribution,the distribution along the width of the distribution is not clear.The process of carbide precipitation is observed by use of high temperature microscope.The temperature of carbide precipitation is 550℃.Carbide precipitates at inherent carbide by non-homogeneous nucleation.Carbide precipitation is mainly in the grain boundary.There is no phase boundary carbide precipitation observed, ferrite transformation is also not be observed during heating process.Carbide precipitation is from the decomposition of ferrite:δ→M23 C6 +δ'(δ' for the poor chromium ferrite).Carbide precipitation reduces inter-crystal corrosion resistant of stainless steel seriously,which also has effect on elevated-temperature mechanical properties.On the basis of elevated temperature phase transformation,the effect of heating temperature on carbide precipitation and 8 ferrite is studied through solution heat treatment.Mechanical properties data at the same temperature are tested.The results show that with the solution treatment temperature increasing,the number of 5 ferrite in two kinds of stainless steels is gradually increases.Tensile strength decreases rapidly.The elongation of 304 stainless steel changes rapidly with temperature increasing,and its reduction of area is more than 90%.At the same condition,the elongation of E01 stainless steel changes slightly while its reduction of area is lower than 50%.Thermal physical properties of two stainless steels at elevated temperature are measured through thermal analysis means,some basic performance data related to stainless steel production closely are obtained.Thermal expansion coefficient of stainless steel 304 and E01 is 21.2×10 - 6/℃,26.2×10 - 6/℃form room temperature to 1200℃respectively.There is no phase transformation in the expansion process of stainless steel 304.At 1147℃,the thermal expansion rate of E01 stainless steel increases suddenly,and thermal expansion coefficient increases discontinuously,which shows the occurrence of austenite to elevated temperature ferrite transformation.At 1000℃,steel heat capacity of 304 stainless is 1.21J/(g * K),its thermal conductivity,is 53.4w /(m * k).For E01,its heat capacity is 1.06J / (g * K),and thermal conductivity coefficient of which is 45.2w /(m * k).