Corner Strengthening by Local Thickening and Ausforming Using Planar Compression in Hot Stamping of Ultra-High Strength Steel Parts

Hot-stamped products are widely used for the body-in-white of an automobile as they are lightweight and improve crashworthiness. A hot-stamping process using planar compression was developed to strengthen corners of ultra-high strength parts by local thickening and hardening. In this process, the corners are thickened by compressing the blank in the planar direction with the upper and lower dies while blocking the movement of both edges with stoppers in the latter stage of forming. Thickening of the corners largely heightens the strength of the formed parts. Not only the thickness but also the hardness of the corner was increased by large plastic deformation and die quenching. For a hot hat-shaped part, a 30% increase in thickness and a 530 HV20 hardness around the corners were attained. The bending rigidity and strength of the formed parts thickened by 30% in the corners increased by 25% and 20%, respectively. In addition, the improvements of the part shape accuracy and the sidewall quenchability were obtained.

Efficiency of Microstructure Refinement in Ti-Based Alloys

The influence of various factors on the efficiency of microstructure refinement in two-phase titanium alloys with respect to a well-known Ti-6Al-4V alloy was discussed. The kinetics of microstructure evolution in titanium alloys with a lamellar type α/β microstructure during large plastic deformation depends mainly on temperature and strain rate, type of the initial microstructure, thickness of the α lamellae, path of deformation and chemical composition. Each parameter should be controlled to provide the most efficient microstructure refinement during conventional metalforming methods.

Influence of Recrystallization Annealing Modes on the Mechanical Properties of Copper Pipes After Large Plastic Deformation

This paper presents the influence of heat treatment modes on product quality parameters. The experiments were carried out on Cu-DHP pipes at various annealing temperature and time. Grain size and mechanical properties dependence on annealing mode were plotted for phosphorus-containing copper. Laboratory results were taken into account for setting process parameters and were industrially tested.

On the thermocyclic tests of corset shape samples as a promising method for studying thermal fatigue

The dynamics of deformation and fracture of the corset shape flat samples under cyclic heating was analyzed. These tests allow us to trace metallographic changes in the substructure of the material that is a result of its plastic deformation. The cracks appear in the first test cycles, regardless of the length of their thermal cycle mode. It means that the material is currently in a state favorable for cracking, according to the commonly accepted terminology. The damage accumulation specific for the development of thermal fatigue was completed in the first few cycles, and possibly in the zero half-cycle of tests. Test results could be explained by an excessively large plastic deformation in the cycle and confirmed by the evaluation calculation. We believe that deformation under cyclic heating in the central part of the corset shape samples is of a different mechanism if compared with cylindrical Coffin samples. Deformation occurs as a result of “external force”, which is created by the shoulders of the sample itself. The analysis showed that the range of plastic deformation changes on corset shape samples is more considerable than in the Coffin method, and it is more consistent with what is happening. It seems that thermocyclic tests of corset shape samples are promising for studying the destruction in real products subjected to cyclic heating, so it is necessary to identify dangerous zones and simulate them in corset samples. Published results of thermocyclic tests of the ZhS32 alloy were used to demonstrate the features of fracture development in corset shape samples. For a visual representation of the process in semi-cycle tests, a deformation diagram has been developed, which is useful when planning the thermocyclic tests.