Effect of Preheating on Martensitic Transformation in the Laser Beam Welded AH36 Steel Joint: A Numerical Study

In this work, the effects of preheating temperatures on martensitic transformations in a laser beam-welded AH36 steel joint were observed using a numerical study. In the same weld, the martensitic contents increased slightly from the upper area, the middle area to the lower area, and simulated martensite contents in the fusion zone were slightly lower than that in the HAZ (Heat Affected Zone). Under different preheating temperatures, simulated martensitic contents decrease with the increase of the preheating temperature. According to the simulated results, the average cooling rate and the CCT (Continuous Cooling Transformation) diagram were drawn to analyze the relationships between preheating temperatures and martensitic transformations. Simulated martensitic contents agreed well with the experimental metallographic microstructures. Moreover, the measured microhardness was reduced with the increasing preheating temperature, and measured microhardness in HAZ was higher than that in the fusion zone. The accuracy of the simulation results was further confirmed. The main significance of this work is to provide a numerical model to design martensitic contents in order to control the performances of the weld, avoiding many tests.

Local chemical fluctuation mediated ultra-sluggish martensitic transformation in high-entropy intermetallics

Superelasticity associated with the martensitic transformation has found a broad range of engineering applications such as low-temperature devices in aerospace industry. Nevertheless, the narrow working temperature range and strong temperature...

Влияние предварительной сжимающей нагрузки на работу, производимую монокристаллами Cu-Al-Ni при взрывном восстановлении деформации памяти формы

The ability of martensitic single crystals Cu 82.5 wt.% - Al 13.5 wt.% - Ni 4.0 to perform work has been investigated. It is shown that weight placed on the crystal is transferred smoothly or by impact during shape memory strain recovery (SMS) Moving depends on the preliminary deformation of the crystal. An influence of the preload on this work is studied. It was found that the transition to the impact mode occurs after preliminary compression of the crystal to the full SMS (~ 9%), when the load is more than twice the stress of the detwinning of martensite. DSC calorimetry showed that after compression to 200–250 MPa and higher sharp narrowing of reverse martensitic transformation (RMT) peak takes place.

Decoupling the Impacts of Strain Rate and Temperature on TRIP in a Q&P Steel

The individual effects of strain rate and temperature on the strain hardening rate of a quenched and partitioned steel have been examined. During quasistatic tests, resistive heating was used to simulate the deformation-induced heating that occurs during high-strain-rate deformation, while the deformation-induced martensitic transformation was tracked by a combination of x-ray and electron backscatter diffraction. Unique work hardening rates under various thermal–mechanical conditions are discussed, based on the balance between the concurrent dislocation slip and transformation-induced plasticity deformation mechanisms. The diffraction and strain hardening data suggest that the imposed strain rate and temperature exhibited dissonant influences on the martensitic phase transformation. Increasing the strain rate appeared to enhance the martensitic transformation, while increasing the temperature suppressed the martensitic transformation.

The strain variation during the isothermal B2→B19’ martensitic transformation in the quenched or annealed Ni51Ti49 alloy

The strain variation during the isothermal holding under constant stress was studied in the quenched or annealed Ni51Ti49 alloy samples. The isothermal strain variation was found in both samples and this strain was completely recovered on subsequent unloading and heating. This allowed to conclude that the strain variation on holding was caused by the isothermal martensitic transformation. It was found that the maximum value of isothermal strain depended on the alloy heat treatment. This value was equal to 0.5 % in annealed sample and it was equal to 6 % in quenched sample. It was assumed that the formation of the Ni4Ti3 phase during annealing led to a decrease in concentration of substitutional Ni atoms in NiTi phase that were responsible for the isothermal transformation. As a result, the less volume fraction of the martensite formed during holding that supresses the strain variation in annealed samples.