Mustafa Çöl

Effect of homogenization heat treatment on toughness and wear resistance of plastic mold steel

Abstract In this study, the effect of homogenization treatment on the microstructure, toughness and wear resistance of plastic mold steel was investigated. Homogenization heat treatment was performed at 1150 °C for 3 hours. All specimens were austenitized at 850 °C for 1 hour, quenched in oil and tempered at different temperatures. Wear tests were carried out using a pin-on-disc tribometer under dry sliding conditions. Charpy V notch impact tests were performed to determine the toughness properties. Microstructure, fracture and worn surfaces were investigated by scanning electron microscope. The results show that heat treatment conditions have an effect on the microstructure and mechanical properties of materials. It was determined that homogenization heat treatment causes more homogeneous structure, in particular, it has a positive effect on the toughness properties and wear resistance of the materials which were tempered at low temperatures.

Effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy

Abstract In this study, the effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy was investigated. The influence of cooling rate on microstructure, hardness, electrical conductivity of 7075 aluminum alloy was investigated using a Jominy end quench test. Water at three different temperatures (20 °C, 50 °C, 75 °C) and polymer solutions of varied concentrations (5vol.-% and 25vol.-%) were used as a quenching medium. The changes of hardness, electrical conductivity and microstructure properties of the specimens with an increase in distance from the quenched surface were investigated comparatively for different quenching mediums. Tensile tests were applied to determine the effect of the quenching rate on mechanical properties of the specimens. Residual stress was measured using the ESPI hole drilling technique to understand the influence of cooling rate. The results show that the cooling rate decreases as the distance from the quenched surface, water temperature and polymer concentration increases. The changes in material properties such as hardness, electrical conductivity along the material profile decrease as water temperature and polymer concentration increase. Although the hardness and mechanical properties of the material decrease as the cooling rate decreases, the values obtained are convenient for conditions of industrial usage. Residual stress was significantly eliminated by quenching in hot water or polymer solution at a high concentration.

Examinations of casting cracks in a high alloy steel valve

Abstract High alloy steels are widely used for high temperature and corrosion resistance applications in power plants, e. g., in chemical and petroleum industries. Mechanical properties of these alloys (e. g., hardness and tensile strength) can be altered by suitable heat treatment. This paper deals with failure investigations of a cast valve made of high alloy steel. The samples were taken from valve body and prepared by metallographic techniques. Microstructural defects causing cracking were investigated using light microscopy and scanning electron microscopy/energy dispersive X-ray spectrometry. Segregation areas at the grain boundaries in the microstructure of the material were observed. Casting was repeated by taking necessary measures during the production in order to eliminate these heterogeneous regions and then suitable heat treatment was applied to the part. The samples taken from the last part were also examined. As a result, a homogeneous microstructure was obtained and no macro or micro cracks were observed.