Research On High-temperature Physical Properties And Mechanical Properties Of Stainless Steel

As an important structure material in modern industry, stainless steels have been widely used in aviation, chemical industry and energy industry, et al.In this paper,the physical and mechanical properties in high temperature of continuous cast slabs were investigated for three kinds of stainless steels of 1#,2#,3#. The research results provided the necessary data for continuous casting production of the stainless steels. The application of the data in continuous casting production was discussed. The results showed as follow:(1)The as-cast microstructure of 1#,2#,3#stainless steelsThe as-cast microstructure and elements distribution were researched by metallurgical microscope and electron probe analysis.It shows that:the as-cast microstructure of 1# slab is composed of martensite-ferrite and the amount of martensite is influenced by C,N content; the matrix of 2# slab structure is ferrite, in which lots of carbonitrides and a small amount of silicates and titanium nitrides are dispersively distributed; the matrix of 3# slab structure is austenite, in which lots of variably sized carbonitrides are distributed.(2) The physical properties in high temperature of 1#,2#,3# stainless steelsThe thermal expansions of the three stainless steels were measured by NETZSCH DIL402EP thermal expansion analyzer and the thermal expansion coefficients were gotten using Least-square method. The Cp-T curve, DSC curve and DTA curce were gotten by the STA449C thermal analyzer for three stainless steels.The regression equation of specific heat capacity was gotten by Least-square method. The obvious crystal form transition temperatures were determined by the DSC differential thermal analysis curves:transition temperatures of 1#,2#,3# are 851℃,800℃and 877℃, respectively. The liquidus temperatures were determined according to DTA curve and the solidus temperatures were calculated by calculation formula. The liquidus temperatures of 1#,2#,3# are 1508℃,1506℃and 1467℃, respectively. The solidus temperatures of 1#,2#,3# are 1497℃,1490℃and 1394℃, respectively.(3) The mechanical properties in high temperature of 1#,2#,3# stainless steels The mechanical properties in high temperature were tested by Thermechastor. The temperature of zero intensity and temperature of zero plasticity were obtained. The temperature of zero intensity of 1#,2#,3# are 1430℃,1400℃and 1390℃,respectively. The temperature of zero plasticity of 1#,2#,3# are 1410℃,1370℃and 1330℃, respectively. The thermoplastic curves ((?)-T)and the heat strength curves(σb-T)were obtained.The variation of section contraction rate was gotten and the brittle area was determined.The first brittleness area of 1# is from 1350℃to melting point and the third brittleness area is from 800℃to 930癈; the first brittleness area of 2# is from 1350癈 to melting point and the third brittleness area is not appeared; the first brittleness area of 3# is from 1300癈 to melting point and the third brittleness area of 3# is from 800癈 to 950癈.(4) the application guide of the physical and mechanical properties in high temperature for actual production process of continuous castingThe straightening temperature of casting billet should avoid the low temperature brittleness area. According to the test results of the mechanical properties, the variation of section contraction rate of 1# from 800癈 to 900癈 is very low and the plastic is poor((?)=40%), so the cracks will be promoted if straightening process is done in this temperature point. Therefore, straightening slab should be avoided in the third brittleness temperature range in the production process.There is no obvious third brittleness area for 2# in high temperature,so the cracks are lower in practical production.The research work are mainly concentrated on increasing the strength of 2# by controlling the size of the grain fineness. The reduction of cross section of 3# is lower than 40%between 800-950癈 and the third brittleness area is wider than other stainless steels. Therefore, in order to increase the internal and external quality of 3#, the third brittleness area should be avoided between 800-950癈 and strengthening temperature should set above 950癈. In this process, the surface cracks would be reduced.