Effect Of Co Content On Hot Deformation Behavior Of Maraging Stainless Steel

Maraging stainless steel combine excellent strength with good fracture toughness and corrosion resistance,have become one of the main materials in aviation,aerospace and navigation.As an element to improve the strength and toughness of maraging stainless steel,the effect of the content of cobalt(Co)on the thermal processing properties of maraging stainless steel is not clear.Hot compression test can optimize the technological parameters and explore the evolution of hot deformation of materials and be applied to many kinds of materials.In this paper,the internal relationship between the hot deformation parameters(temperature,strain rate,Co content),microstructure and hot processing properties of the as-cast maraging stainless steel with different Co content through the hot compression test.The corresponding deformation mechanism is revealed from the study results.The experimental data and related theories of thermal deformation behavior and mechanism of maraging stainless steels are also enriched.Hot uniaxial compression tests of the four kinds of different content of Co(0,3,6 and 9 wt.%)maraging stainless steels were carried out at deformation temperatures of 950?1150? and strain rates of 0.01?10 s-1.The hot deformation behavior and microstructure evolution under different deformation conditions were studied,and the effect of Co content on the hot deformation of maraging hardened stainless steel was analyzed,and the following conclusions were obtained:The flow stress curves of four kinds of test steels at 950?1150? and 0.01?10 s-1 show that the flow stress decreases with the decrease of deformation temperature and the increase of strain rate,and increases with the increase of Co content.With the decrease of strain rate,the influence of Co content on flow stress decreases,and the difference of flow curves between the four kinds of steels is reduced.At the same deformation temperature and strain rate,the increase of Co content will promote the dynamic recrystallization of the maraging stainless steel,and the dynamic recrystallization volume fraction and grain size will increase.The effect of Co content on the volume fraction of dynamic recrystallization is more obvious than influence on the dynamic recrystallization grain size.Especially when the temperature is lower and the strain rate increases,the higher the Co content,the greater the dynamic recrystallization degree of maraging stainless steel.Based on the flow stress data of maraging stainless steel with different Co content,the Arrhenius constitutive model and the BP neural network model were established.The structure of BP network model is {4-12-3-1-1} and the Arrhenius constitutive equations are:? =1.82×1018[sinh(0.0095?)]6.64 exp(-476457/RT)(0Co steel);? = 1.55 ×1017[sinh(0.0091?)]6.89 exp[-449417/RT)(3Co steel);? =3.24×1015[sinh(0.0086?)]6 33 exp(-407019/RT)(6Co steel);? = 1.88×1015[sinh(0.0080?)]6.20 exp(-401320/RT)(9Co steel).Through the comparison of the Arrhenius constitutive model and the BP neural network model,it is found that the BP neural network model is more convenient and faster than the traditional Arrhenius constitutive model on the premise of good prediction ability of the two models.And the BP network model can consider more factors,not only the traditional regression model of temperature and strain rate,the establishment of the the model is more accurate.Based on the dynamic material model and the Murty criterion,hot processing maps of maraging stainless steels with different Co content at 0.8 strain were established.Under the condition of 1130?1150? and 0.01?0.1 s-1,the test steels can obtain full and uniform recrystallized structure,which is suitable for hot processing.The instability regions are all located at high strain rates and low temperatures:Local recrystallization,inhomogeneous deformation and mixed crystal structure are the main instability mechanisms of maraging stainless steel.