Study On The Effect Of Mn On The Large Deformation Hot Compression Behavior Of 18%Cr Nickel-saving Duplex Stainless Steel

Duplex stainless steel is widely used in petrochemical,chemical,seawater and paper industry as a high performance structural material because of its characteristics of austenite and ferrite.The Ni-saving duplex stainless steel studied in this paper stabilizes austenite phase by substituting Mn for Ni.Because of the different mechanism of stabilizing austenite with Mn and Ni,the stacking fault energy is affected differently,which leads to the difference of the effect of different Mn-Ni content on its hot deformation behavior at high temperature.By controlling the content of Ni and changing the content of Mn,the effect of Mn addition on the high temperature compression deformation behavior of 18%Cr low Ni duplex stainless steel was studied.The aim is to improve the hot working performance of 18%Cr nickel-saving duplex stainless steel,to provide the necessary theoretical basis for the optimization of forging process,plate rolling and hot extrusion,and to provide guidance for practical production.In this paper,the hot compression experiments of 18%Cr nickel-saving duplex stainless steel with different Mn content were carried out by Gleeble-3800 thermal simulator under the hot deformation conditions of 1123-1423 K/0.01-10 s^-1.Through the analysis of its microstructure,thermodynamic constitutive equation,recrystallization kinetics and hot working diagram,it can be known that:1.At a lower strain rate(0.01-0.1s^-1),the austenite recrystallization effect is good.With the increase of hot compression temperature,the austenite grains gradually change from very tiny primary grains to equiaxed grains with balanced size.When the strain rate is 10s^-1,the recrystallization effect of austenite is undesirable at low temperature.With the addition of Mn,the austenite changes from partial recrystallization to dynamic recovery at the same low deformation temperature.The recrystallization effect of ferrite is generally good at low temperature?1123-1223K?.The strain rate has little effect on the recrystallization of ferrite at the same hot deformation temperature.2.In the thermal deformation conditions of 0.01s^-1/1223K and 0.1s^-1/1123K,the grain size of the rotation angle and the difference of the orientation angle of the adjacent grain boundary are found that the continuous dynamics of austenite at 0.01s^-1/1223K Recrystallization,the grain refining effect is good.In the condition of 0.1s^-1/1123K,in addition to austenite,the grain recrystallization of ferrite recrystallized well.And under the condition of 0.01s^-1/1223K,the?3twin content in the austenitic phase of the experimental steel with high Mn content?8.97%?is higher than that of the experimental steel with low Mn content?5.77%?.3.With the increase of Mn content to 5.77%,the activation energy of hot deformation of the experimental steel increases greatly,from 423.67 kJ/mol to 548.28 kJ/mol,which increases by29.4%.With the further increase of Mn content,the activation energy of thermal deformation decreases to 514.29 kJ/mol.In homology,excessive Mn content will increase the activation energy of therIVmal deformation and increase the difficulty of deformation.4.By comparing and analyzing the recrystallization critical conditions of three experimental steels with different Mn content at 1223-1323K deformation temperature at low strain rate,it is found that the critical strain increases with the increase of Mn content from 3.12%to 8.97%.)increases as the Mn content increases.That is to say,at low strain rate,the increase of Mn content will delay the occurrence of dynamic recrystallization to some extent.Under the thermal deformation conditions of 10s^-1/1123K and 1423K,the critical strain increases first and then decreases with the increase of Mn content.5.The addition of Mn is beneficial to the enlargement of the safe zone in the hot working process of the experimental steel.In the hot processing map of the experimental steel with 3.12%Mn content,it is found that the optimum processing area gradually changes from low strain rate zone at medium temperature to medium strain rate zone at high temperature with the increase of deformation.In the experimental steels with 5.77%and 8.97%Mn content,the ideal processing area is always concentrated in the low strain rate region at high temperature and the high strain rate region at high temperature,and with the increase of strain,it is mainly concentrated in the high temperature and low strain rate region.In addition,under the same strain,the maximum value of the power dissipation factor decreases first and then increases as the Mn content increases.