Enhancement of Cavitation Erosion Resistance of Cast Iron with TIG Remelted Surface
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NODULAR graphite cast iron has an excellent casting capacity (comparable with the one of the widely used gray cast irons), good machinability, and a lower price compared to steels. Due to the spherical shape of the graphite, the tendency to propagate cracks is reduced, leading to mechanical strength and toughness characteristics comparable to the ones of unalloyed steels with a similar structural matrix (ferrite and pearlite content). These materials are used for the manufacture of crankshafts for automotive engines, presses, rolling mills, as well as pump and valve bodies used in corrosive environments. As a result of the good anti-friction and high wear properties, they are used in the manufacture of machine tools and presses and in
I. MITELEA, T. BENA, I. BORDEASU, I. D. UTU are with the Department of Materials and Manufacturing Engineering, Politehnica University of Timisoara, Timisoara, Romania and also with the Department of Mechanical Machines, Equipments and Transportation, Politehnica University of Timisoara. C. M. CRA˘CIUNESCU is with the Department of Materials and Manufacturing Engineering, Faculty of Mechanical Engineering, Politehnica University Timisoara, Bd. Mihai Viteazul 1, 300006 Timisoara, Romania and also with the Department of Mechanical Machines, Equipments and Transportation, Politehnica University of Timisoara. Contact e-mail: [email protected] Manuscript submitted May 8, 2019. Article published online May 30, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
forging machine parts. However, they face severe erosion when used in many installations, such as air pressure pumps, gas pipes (with or without vapors), and automatic sand forming equipment in the foundry industry.[1–3] The importance of graphite morphology and matrix structure (i.e., pearlite/ferrite ratio) for cavitation erosion resistance has been extensively highlighted. Ba˘lan et al.[2] reported that the gray cast-iron graphite shows a much lower erosion resistance compared to the nodular cast iron and that by the application of the annealing and quenching heat treatment no improvement occurs. A comparative analysis of the cavitation resistance of gray cast iron and steels with the same structural matrix was performed by Okada et al.[3] It was concluded that graphite acts as a surface tension concentrator and thus reduces cavitation erosion resistance.[3–8] In recent years, high-energy techniques (usually in the range of 500 W to 3 kW), such as electron,[10–12] laser,[6,13–17] and plasma,[11,12] have been tested to alter the physical state of the metal alloys surfaces. By such techniques, the surface of the material is remelted, and by rapid solidification, a microstructural refinement occurs and, implicitly, an improvement in wear resistance. Due to the high cost of laser equipment and the need for vacuum in electron beam chambers, our attention has been focused on the use of affordable, flexible, and easy-to-operate welding machines for melting the surface of cast iron parts. The TIG process uses a nonconsumable
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