Static Softening Behaviour of Hot-worked Austenite in Microalloyed Structural Steel StE460

Double-hit compression tests were performed on StE460 steel containing microalloying elements niobium and vanadium over a range of temperatures and strain rates penment to hot rolling. The fractional softening was evaluated by use of the offset method, which was confirmed to be a very reasonable method. Appropriate expressions are given for the static recrystallization kinetics as a function of temperature and strain rate. Particular attention is paid to the effect of strain rate on static recrystallization. It can be shown that the static softening is apparently accelerated by strain rate. Recrystallization in low temperature austenitic region is stopped due to precipitation of carbonitrides of microalloying elements, which is reflected in the form of a plateau in the curves of static softening.

Static Softening Characteristics and Static Recrystallization Kinetics of Aluminum Alloy A6082 After Hot Deformation

The static softening behavior of aluminum alloy A6082 was investigated by interrupted hot tests conducted on Gleeble-1500 simulator at deformation temperatures from 573 to 773 K and strain rates from 0.1 to 10 s-1,with a pre-strain from 0.3 to 0.7 and variable inter-pass delay times.The offset method was applied to convert the changes in flow stress between two passes to static softening fraction.The microstructural changes were characterized by the quantitative metallography of quenched specimens.The results showed both static softening and static recrystallization curves exhibited a simple sigmoidal shape;the static softening is related to the static recrystallization in a nonlinear manner with 50% static recrystallized volume fraction corresponding to 80% static softening fraction;an increase in temperature,strain rate or pre-strain yields a decrease in the time for 50% static recrysallized volume fraction,on which the temperature has the most remarkable influence;Si and Mn additions accelerate the process of static recrystallization.Finally,the equations of static recrystallization kinetics of this alloy were developed with a good agreement between the predicted and experimental results.

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.

Static Recrystallization Behavior of SA508-III Steel during Hot Deformation

The static recrystallization behavior of SA508-III steel was investigated by isothermal double-hit hot compression tests at the deformation temperature of 950-1 250 ℃,the strain rate of 0. 01-1 s^（-1）,and the inter-pass time of 1-300 s.The effects of deformation parameters,including forming temperature,strain rate,degree of deformation（ pre-strain） and initial austenite grain size,on the softening kinetics were analyzed. Experimental results show that static recrystallization kinetics is strongly dependent on deformation temperature and degree of deformation,while less affected by the strain rate and initial grain size. The kinetics and microstructural evolution equations of static recrystallization for SA508-III steel were developed to predict the softening behavior and the statically recrystallized grain size,respectively. Based on the comparison between the experimental and predicted results,it is found that the established equations can give a reasonable estimate of the static softening behavior for SA508-III steel.