Effect of Layers Position on Fracture Toughness of Functionally Graded Steels in Crack Divider Configuration

In the present study, fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steels slices with various thicknesses and arrange- ments as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels in crack divider configuration has been found to depend on the composites’ type together with the volume fraction and the position of the containing phases. According to the area under stress-strain curve of each layer in the functionally graded steels, a mathematical model has been presented for predicting fracture toughness of composites by using the rule of mixtures. The fracture toughness of each layer has been modified according to the position of that layer where for the edge layers, net plane stress condition was supposed and for the central layers, net plane strain condition was presumed. There is a good agreement between experimental results and those acquired from the analytical model.     

Wear Behavior of Deep-Cryogenic Treated High-Speed Steels at Different Loads

Tools for the cold-working applications are typically made from the high-speed steels. However, due to wear and plastic deformation their performance in several applications is not adequate and should be further improved. By using appropriate combination of vacuum heat-treatment in conjunction with a deep-cryogenic treatment (duplex treatment) the microstructure of high-speed steel matrix can be substantially changed and the hardness and fracture toughness can be modified and optimised. In the present work we have investigated the effect of four different tempering temperatures of vacuum and cryogenically treated ESR AISI M2 high-speed steel on the resulting combinations of microstructure, hardness and toughness and their effect on the wear mechanisms at different loads. The results showed that at relatively high loads the different treatments resulted in an order-of-magnitude difference of wear resistance, while at low loads the selected treatments were efficient enough to keep the wear within the mild wear regime and small variations between the samples. However, the overall wear transition did not occur at any load used or any sample treatment, although some small differences in wear mechanisms can be seen, primarily depending on the fracture toughness of the samples.