Microstructure Evolution and Dynamic Softening Mechanism of 00Cr22Ni5Mo3N DSS During Hot Compression

Through plane strain compression, hot ductility of 00Cr22Ni5Mo3N DSS is studied under plane strain con dition, and the dynamic softening mechanism is investigated through microstructure observation under TEM. The results show that the deformation temperature can markedly influence the peak stress of 00Cr22NiSMo3N specimens. And being different from DSS softening mechanism generally reported, ferrite can be softened through dynamic re eovery and recrystallization, hut austenite can he softened only through dynamic recovery during hot deformation. The unfavourable effect of N on softening capacity of austenite is greater than that of Ni.

Flow behaviour constitutive model of CuCrZr alloy and 35CrMo steel based on dynamic recrystallization softening effect under elevated temperature

In order to study the effect of dynamic recrystallization on the metal flow behavior during thermal deformation,the elevated temperature compression experiments of CuCrZr alloy and 35CrMo steel are carried out using Gleeble-3810 thermal simulator.It is proved that the samples underwent obvious dynamic recrystallization behavior during thermal deformation by microstructure observation of deformed specimens.The size of recrystallized grains increases as the temperature improved and the strain rate decreased.Meanwhile,the net softening rate caused by dynamic recrystallization is determined based on the stress-dislocation relationship.It can be found that the value of net softening rate increases quadratically as the Z parameter decreases,and the dynamic recrystallization net softening rate of CuCrZr alloy and 35CrMo steel are calculated to be 21.9%and 29.8%,respectively.Based on the dynamic recrystallization softening effect proposed,the novel elevated temperature flow constitutive models of two different alloys are proposed,and the related parameters are well defined and solved in detail.The predicted values of the obtained models are agreed well with the experimental values.

DYNAMIC BEHAVIOR OF THIN RECTANGULAR PLATE ATTACHED TO MOVING RIGID

A nonlinear dynamic model of a thin rectangular plate attached to a moving rigid was established by employing the general Hamilton＇s variational principle. Based on the new model, it is proved theoretically that both phenomena of dynamic stiffening and dynamic softening can occur in the plate when the rigid undergoes different large overall motions including overall translational and rotary motions. It was also proved that dynamic softening effect even can make the trivial equilibrium of the plate lose its stability through bifurcation. Assumed modes method was employed to validate the theoretical result and analyze the approximately critical bifurcation value and the postbuckling equilibria.

Hot deformation behavior and constitutive modeling of Q345E alloy steel under hot compression

Q345E as one of typical low alloy steels is widely used in manufacturing basic components in many fields because of its eminent formability under elevated temperature. In this work, the deformation behavior of Q345E steel was investigated by hot compression experiments on Gleeble-3500 thermo-mechanical simulator with the temperature ranging from 850 ℃ to 1150 ℃ and strain rate ranging from 0.01 s-1 to 10 s-1. The experimental results indicate that dynamic softening of Q345E benefits from increasing deformation temperature and decreasing strain rate. The mathematical relationship between dynamic softening degree and deformation conditions is established to predict the dynamic softening degree quantitatively, which is further proved by some optical microstructures of Q345E. In addition, the experimental results also reveal that the stress level decreases with increasing deformation temperature and decreasing strain rate. The constitutive equation for flow stress of Q345E is formulated by Arrihenius equation and the modified Zener-Hollomon parameter considering the compensation of both strain and strain rate. The flow stress values predicted by the constitutive equation agree well with the experimental values, realizing the accurate prediction of the flow stress of Q345E steel under hot deformation.

MODAL TEST AND ANALYSIS OF CANTILEVER BEAM WITH TIP MASS

The phenomenon of dynamic stiffening is a research field of general interest for flexible multi-body systems.In fact,there are not only dynamic stiffening but also dynamic softening phenomenon in the flexible multi-body systems.In this paper,a non-linear dynamic model and its linearization characteristic equations of a cantilever beam with tip mass in the centrifugal field are established by adopting the general Hamilton Variational Principle.Then,the problems of the dynamic stiffening and the dynamic softening are studied by using numerical simulations.Meanwhile, the modal test is carried out on our centrifuge.The numerical results show that the system stiffness will be strengthened when the centrifugal tension force acts on the beam (i.e.the dynamic stiffening).However,the system stiffness will be weakened when the centrifugal compression force acts on the beam (i.e.the dynamic softening). Furthermore,the equilibrium position of the system will lose its stability when the inertial force reaches a critical value.Through theoretical analysis,we find that this phenomenon comes from the effect of dynamic softening resulting from the centrifugal compression force.Our test results verify the above conclusions and confirm that both dynamic stiffening and softening phenomena exist in flexible multi-body systems.

Quantitative analysis of influence of α-Al(MnFeCr)Si dispersoids on hot deformation and microstructural evolution of Al-Mg-Si alloys

The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.

Microstructural evolution of a superaustenitic stainless steel during a two-step deformation process

Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^（-1）. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.

Dynamically softened substrate regulates malignancy of breast tumor cells

It has long been hypothesized that an increase in the extracellular matrix(ECM)stiffness mechanoactivates malignant phenotypes of breast tumor cells by regulating an array of processes underlying cancer biology.Although the contribution of substrate stiffening to drive malignant phenotype traits and other biological functions of a tumor is increasingly understood,the functional role of substrate softening on breast cancer cellular responses has rarely been investigated.Herein,we employed matrix metalloproteinase(MMP)-sensitive film to perform assays to explore the consequences of lowering stiffness on the biological behaviors of breast cancer cell MDA-MB-231.We demonstrated that cells underwent dramatic changes in migration,cellular conjunction,and expression of malignance-associated proteins and genes when the substrate stiffness decreased.Based on RNA sequencing and analysis,we found that hub genes including TP53,CCND1,MYC,CTNNB1,and YAP were validated to play central parts in regulating stiffness-dependent cellular manner change.Moreover,through visualization of differentially expressed genes(DEGs),cells on dynamically softened substrate appeared less influenced by transfer to tissue culture polystyrene(TCPS).These results suggest substrates with decreasing stiffness could normalize breast tumor malignant phenotype and help cells store the mechanical memory of the consequential weaker malignance.