In the current study, dynamic strain ageing (DSA) phenomena in 316L austenitic stainless steel was investigated under as-received and as-welded conditions. A tensile test was carried out on as-received and as-welded samples for the temperatures of 25-800 • C at a strain rate of 1 × 10 −3 s −1 . Microstructure and fracture surfaces were investigated by optic and scanning electron microscopes (SEM). 316L austenitic stainless steel showed different DSA behavior under as-received and as-welded conditions, which are discussed in terms of microstructure and mechanical properties.

Dynamic strain aging (DSA) behaviour of hot work tool steel (H10) was investigated under asreceived (AR) and as-quenched (AQ) conditions. Hot tensile test was carried out in the temperatures of 25°C-700°C at a strain rate of 1x10 -3 s -1 . The tensile properties indicated that AQ samples showed an increase in yield strength (YS) and ultimate tensile strength (UTS) but a decrease in elongation at 200°C or 300°C consistent with DSA. However, AR samples revealed a decrease in YS and UTS for the same testing temperatures. This indicated the presence of less amount of free C or N in solution of AR samples. Further increase in the testing temperature has increased the elongation. It is believed that DSA occurs in H10 tool steel at different temperatures because of interaction between dislocations and interstitial solute atoms (C or N) or substitutional atoms (Cr or Mo).

The effect of tempering on AISI H10 hot work tool steel  Dynamic strain aging behavior of AISI H10 hot work tool steel  Analysis of microstructure and mechanical properties Figure A. Change in mechanical properties of H10 hot work tool steel at different tempering times and dynamic strain aging behaviorPurpose: This study aims to investigate the changes in the microstructure and mechanical properties of AISI H10 hot work tool steel which is used in many fields of the industry as a result of different tempering times and dynamic strain aging based on optimum tempering time. Theory and Methods:Austenitization and tempering processes were carried out to examine the structural change of AISI H10 hot work tool steel. The experimental steel was quenched after austenitizing treatment at the specified temperature and then tempered at different times. After the process, microstructure and mechanical properties of the material were examined and optimum tempering time was selected for the dynamic strain aging process. Dynamic strain aging was performed at different test temperatures for a determined deformation rate. Results:Increasing the tempering time at 550 °C from 10 minutes to 2 hours resulted in a gradual increase in hardness.The highest hardness was obtained as 393 Hv1 in samples tempered for 2 hours. This is due to the presence of finer precipitates particles in the samples. However, the lowest hardness value was obtained as 290 Hv1 in the samples tempered for 15 hours due to the presence of coarse precipitate particles. According to hot tensile test results which were obtained for the samples tempered at 550 °C for 2 hours, the strength values showed a decrease in the test temperature range of 25-400 °C, however the strength values increased when the test temperature was rised from 200 °C to 300 °C. This indicated that dynamic strain aging takes place in the tempered samples. Conclusion:Dynamic strain ageing and secondary hardening occur in the AISI H10 hot work tool steel under tempered condition which showed an increase in YS and UTS at temperatures 300°C and 400°C corresponding to dynamic strain ageing region. It was also noticed that elongation remained constant as the testing temperature increased from 25 °C to 400 °C. Above 400 °C, tempered samples showed a sharp decrease in strength but a slight increase in elongation. It can be concluded that mechanical properties of AISI H10 hot work tool steel become so poor under tempered condition after tensile testing above 400 °C.

In this work, high-strength low-alloy (HSLA) steel with 0.22 wt% carbon was produced in laboratory scale and hot rolled with a total deformation of 42% via 4, 5, or 6 passes. After multipass hot rolling process, samples were examined either in as-rolled (AR) or as-rolled and heat-treated (ARH) conditions. The results indicated that microstructural and mechanical properties of HSLA steels are influenced by hot rolling conditions for both cases. It was observed that strength values in AR samples have a tendency to increase with increment in rolling pass number. In contrast to AR samples, it was seen that the mechanical properties were slightly decreased in ARH samples that were austenitized at 1150 °C for 45 min and then cooled in still air. Microstructural investigations showed that finer precipitates in AR samples are obviously more than that of ARH samples, as an evidence for higher strength results by precipitation hardening. In addition to precipitation strengthening, refinement of lath bainite and amount of blocky martensite/austenite in AR samples favor the increase in strength.

Highlights• The study focused on the thermomechanical processing behavior for Nb microalloyed steel.• P/M was used as the production method.• Mechanical properties and microstructures were characterized for different conditions.