Investigation On Microstructure And Properties At High Temperature And Hot Rolling Technology Of 2205 Duplex Stainless Steel

Duplex stainless steel has the excellent mechanical properties?weldability and corrosion resistance,which microstructure comprising almost equal proportion of ferritie and autenite phase.It is concerned one high performance structural material,which is increasingly used in petrochemical,papermaking,fertilizer,marine engineering and other fields.But because of its poor thermal forming properties,which makes the products in the process of forging,hot rolling and other hot working are prone to produce cracks and other defects,which could lead to materials failure,at present,it is difficult to forging,hot rolling and welding process for duplex stainless steel,so the thermoplasticity of duplex stainless steel is one of hot topic in the field of current research of stainless steel.Therefore,based on the experiments including high temperature tensile test,single-pass and multipass hot rolling,wedge hot rolling and annealing heat treatment,the thesis systematically explores the effect of hot working process parameters on microstructure and mechanical properties of 2205 duplex stainless steel.The mainly results of this thesis are as follows:(1)Various schedules of heat treatment are conducted to investigate the microstructure transformation of forged 2205 duplex stainless steel at high temperature.The results indicates that the phase proportion of austenite decreases as the heat treatment temperature increase from 900 to 1200?,while the heat treatment time was fixed.The same variation tendency of austenite phase proportion has been founded when the heat treatment time was extended in a certain temperature,the proportion of austenite has significant influence on mechanical properties of duplex stainless steel at room temperature,the hardness of alloy would increase with the content of austenite decrease.(2)The phase ratio has a significant effect on the tensile mechanical properties of 2205 duplex stainless steel at high temperature,the content of austenite would decrease,the softening mechanism would improve,the tensile strength decreased rapidly and the reduction of area increased significantly when the temperature increase from 600? to 1200?,the microcrack firstly appeared on the phase boundary of austenite and ferrite and have a priority to expend into austenite phase,based on this,the breakage of austenite is faster than ferrite.(3)The effect of deformation reduction on the microstructural evolution of DSS2205 was important,with a relatively small rolling reduction(5?20%),deformation was defined in the surface layer of the rolled plate and the central layer is non-deformable,austenite in the surface layer is smaller than those in the center layer;When the reduction increase,the deformation in the central layer becomes intensified,besides,the grain size of ferrite and austenite would become finer if the reduction is severer.(4)The results of multi-pass hot rolling of 2205 duplex stainless steel indicates that if the previous passes adapt large deformation(30?40%),the uniform microstructure would obtained,otherwise,the cracks would formed in the austenite phase,which leads to the suggestion to steel enterprises that the previous passes should adapt a reduction between 35%to 40%to obtain a finer microstructure of rolled plate and enhance homogeneity in plastic deformation.(5)The ratio of two phase about hot rolled plate of 2205 duplex stainless steel indicates that when the temperature within the range of 900?1200 ?,the low temperature is advantageous to ferrite tramsform into austenite phase,if the temperature higher than 1150 ?,the content of austenite would increase at the beginning of heat treatment,after that,the austenite tramsform into ferrite.