About the Memory of Transformation-Induced Plasticity in 35NCD16 Carbon Steel Subjected to Various Thermomechanical Histories

This study deals with Transformation-Induced Plasticity (TRIP) observed in the martensitic transformation of 35NCD16 ferritic steel. In this study, TRIP tests were carried out for two different cases: First, after only free dilatometric (FD) tests, which is used as the reference test for the considered applied stress; second, with TRIP tests being performed similarly to the first case (same thermal cycle, same applied stress) but with pre-thermomechanical loading histories applied. Such histories may be FD tests, TRIP tests, elastoplastic history, etc. The comparison between the results of TRIP test (a) and TRIP test (b) indicates if TRIP holds the memory of the applied loading histories. The current obtained results tell us that TRIP does not hold any significant memory. During the martensite à austenite transformation, the material may present recovery from strain hardening. Waiting for more details about the physical phenomena responsible for the absence of TRIP memory, one can point out the importance of this result as it enables one to use the same specimen for several TRIP tests. However, this result must be validated using other combinations of loading histories (such as multiaxial and cyclic, among others).

Modeling of Critical Cutting Speed of White Layer Formation in Hard-Cutting Process

White layer exists on the machined surface of the hard-cutting and affects the surface quality and mechanical properties of a workpiece. Accurate predicting the critical cutting speed of white layer formation is of great significance for controlling the surface quality and selecting appropriate cutting parameters. In this work, an austenite transformation driving force calculation model of the white layer formation was established based on phase transformation thermodynamics theory, in which the influence of cutting temperature, stress and strain on the austenite transformation driving force in the hard-cutting process was taken into account. Second, a finite element (FE) model of the hard-cutting process was built by using hardened AISI52100 steel as cutting material. Then, a prediction model of critical cutting speed of the white layer formation was developed in combination with the austenite transformation driving force model and the hard-cutting FE model. Finally, the critical cutting speeds of the white layer formation at different chip thicknesses, tool rake angles and different levels of flank wear were simulated by using the critical cutting speed prediction model.

Weld thermal simulation of API 5CT L80 grade steel

The microstructure and mechanical properties of an API 5CT L80 casing grade steel (0.24C 0,4Si 1.4Mn CrNiCu) have been studied after performing weld thermal simulations (with and without subsequent tempering) applying a thermal cycle weld simulator. Specimens were subjected to three different peak temperatures (1300 °C, 1150 °C, 950 °C) and five different cooling rates (1 °C/s, 3 °C/s, 5 °C/s, 10 °C/s, 60 °C/s) through the austenite transformation temperature range. Based on the microstructure, hardness values, and toughness properties of the simulated specimens, thermal cycles were selected and recommended for welding of L80 components by the SAG-FW (shielded active gas forge welding) method.