Abstract
The effects of surface roughness, presence of nitrided diffusion regions, and magnetron sputtering of Cr2N–6Ag thin films on the toughness of Cr–V ledeburitic Vanadis 6 die steel were investigated by using the flexural strength measurement method, which was coupled with careful microstructural investigations and analyses of fractured surfaces. The results undoubtedly show that enhanced surface roughness reduces the material toughness, since the cusps formed on the metallic surface as a result of the machining act as preferential sites for crack nucleation and growth. The presence of nitrided regions on the surface, on the other hand, forms a structural notch there, which has a strong detrimental effect on toughness. Deposition of Cr2N–6Ag thin films has only marginal effect on the steel toughness. Practical recommendations for the designers, heat treaters, and coaters of the tools are thus that they should maintain the surface finish quality of the tools as high as possible, avoid too thick and supersaturated nitrided regions, and that there is almost no risk of tool embrittlement due to physical vapor deposition (PVD) coating.
Highlights
High-carbon, high-chromium, and high-vanadium cold work tool steels have been frequently used in modern industries in applications where superior wear resistance and strength are required
The microstructure of magnetron-sputtered thin films was examined on the fractured surfaces of specimens prepared as follows: After deposition, the specimens were immersed into liquid nitrogen, held there for 15 min, and broken down
These results suggest that the diffusion regions on the surfaces reduce the flexural strength of the examined steel dramatically, and that this reduction increases with increasing the thickness of the nitrided region, its increasing saturation with nitrogen, hardness, etc
Summary
High-carbon, high-chromium, and high-vanadium cold work tool steels have been frequently used in modern industries in applications where superior wear resistance and strength are required. The high strength and hardness, and excellent wear resistance of these tool steel grades are a result of the standard heat treatment procedure It comprises vacuum austenitizing, holding at the desired temperature for a pre-determined duration, and inert gas quenching, followed by immediate tempering. The specimens were cleaned and degreased in an ultrasonic acetone bath for 15 min They were moved to the plasma nitriding device, where they were heated up to the pre-determined temperature, and sputter cleaned for 30 min in a pure hydrogen atmosphere in order to activate the surface. The microstructure of magnetron-sputtered thin films was examined on the fractured surfaces of specimens prepared as follows: After deposition, the specimens were immersed into liquid nitrogen, held there for 15 min, and broken down They were reheated slowly to room temperature, cleaned ultrasonically in acetone, and dried before inserting into the SEM. The fracture surface morphology was investigated by a JEOL JSM 7600F scanning electron microscope
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