Optimization Design of Insert Hot Stamping Die’s Cooling System and Research on the Microstructural Uniformity Control of Martensitic Phase Transitions in Synchronous Quenching Process

Ultrahigh-strength steel BR1500HS was chosen as the research object. The parameters of insert hot stamping die’s cooling system in the synchronous quenching process were calculated, and the cooling system was designed based on the temperature distribution of formed part. Then, by combining FEM simulation and thermal-mechanical coupling theory of synchronous quenching process of hot stamping, the cooling system was optimized. After that, the punch and die were optimally designed based on the simulation of temperature field of formed part as well as dies, and their temperature decreased by 15°C and 12°C, respectively. Next, the microstructural evolution in austenization and synchronous quenching processes was analyzed. By adopting a synchronous cooling system in hot stamping, by optimizing the parameters and control strategies, and by controlling the water velocity in various inserts, the homogeneity of martensitic phase transitions was improved. The results of the application test show that martensitic phase transitions of major parts are uniform under given working conditions, and hardness difference of each part was small.

Martensitic organic crystals as soft actuators

Being capable of rapid and complete structure switching, the martensitic phase transitions in molecular crystals are thought to hold a tremendous potential as thermally driven organic actuators.

Length scales and pinning of interfaces

The pinning of interfaces and free discontinuities by defects and heterogeneities plays an important role in a variety of phenomena, including grain growth, martensitic phase transitions, ferroelectricity, dislocations and fracture. We explore the role of length scale on the pinning of interfaces and show that the width of the interface relative to the length scale of the heterogeneity can have a profound effect on the pinning behaviour, and ultimately on hysteresis. When the heterogeneity is large, the pinning is strong and can lead to stick–slip behaviour as predicted by various models in the literature. However, when the heterogeneity is small, we find that the interface may not be pinned in a significant manner. This shows that a potential route to making materials with low hysteresis is to introduce heterogeneities at a length scale that is small compared with the width of the phase boundary. Finally, the intermediate setting where the length scale of the heterogeneity is comparable to that of the interface width is characterized by complex interactions, thereby giving rise to a non-monotone relationship between the relative heterogeneity size and the critical depinning stress.

Effect of Mn Doping on Magnetic and Dielectric Properties of Bi2Sn2O7

The Bi2(Sn0.95Mn0.05)2O7 compound existing simultaneously in two polymorphic modifications, namely, orthorhombic and cubic has been synthesized for the first time by solid-phase synthesis. The magnetic, dielectric and electrical properties of the compound have been studied. Anomalies in the temperature dependences of the electrical resistance and magnetic propoties have been found. These features are explained as martensitic phase transitions.