Investigation of mechanical properties, microstructures and cutting performances of cutting tools produced from surface hardened and coated AISI 1070 steel

ABSTRACTPhD ThesisINVESTIGATION OF MECHANICAL PROPERTIES, MICROSTRUCTURES ANDCUTTING PERFORMANCES OF CUTTING TOOLS PRODUCED FROM SURFACEHARDENED AND COATED AISI 1070 STEELAhmet ÇAKANFırat UniversityGraduate School of Natural and Applied SciencesDepartment of Metallurgy Education2006, Page: 125The production of valuable machine parts from materials which are not expensive andhave good mechanical properties in materials technology is very important. Use of cutting toolsin production industry and their consumption in metal workshop are expanding every year. Theproduction costs of cutting tools in countries, which are not fully developed such as Turkey,play an important role in total manufacturing costs. The extra costs for cutting tools add to thecost of products directly, raising their costs, and thus decrease the competitiveness of countries.The use of cheaper new-type cutting tools, which have been produced by means ofsurface coating techniques, instead of expensive and classic cutting tools, has become a rule inlast ten years. Use of these new, cheap, useful and novel materials in the production of cuttingtools has brought about an innovation in the manufacturing industry. Introduction of suchcutting tools, which have suitable mechanical properties, to chip removal industry is veryimportant as they offer various advantages over more conventional cutting tools, such as lowercost and longer service life.In this study, the cutting tools have been produced from medium-carbon steelcontaining 0.7-0.8 % C, which is not expensive and not easy to heat treat, and generally used assimple classic cutting tool due to its low cutting performance and short service life, usingmodern surface coating techniques. This tool material can be found easily in the market andshows good tool material properties. As well known, the interior parts of cutting tools must bereasonably tough and possess acceptably high tensile strength and, on the other hand, thesurfaces must be hard and exhibit a good wear resistance. The cutting tools produced frommedium carbon steel with surface coating methods have been shown to be less costly andvaluable, and exhibited long service life.In this study, raw cutting tools have been cut from a medium carbon steel with 0.7 % C.These tool parts have been then water hardened and tempered at 180 ºC for stress-relieving,followed by nitriding in a liquid cyanide salt bath. Finally, the tips of the tool parts have beencoated by cathodic arc vapour deposition method which is a special type of PVD coatingtechnique. By this technique, TiN, TiCN and CrN thin coating layers have been produced on thesurface of cutting tools.The cutting performance of such produced cutting tools has been tested at 190, 240 and320 rev/min turning cycles with feeding rates of both 0.052 and 0.081 mm/rev for each turningcycle. The wear behaviour of cutting tools has been investigated by using an on-line monitoringtechnique. The results of wear tests conducted under different conditions have been comparedwith each other comprehensively.TiN-coated specimens have exhibited the best wear performance under the conditions of190 rev/min turning cycle and 0.052 mm/rev feeding rate. The microstructures of the tips of thecutting tools were investigated by means of scanning electron microscopy (SEM). Themicrostructures indicated that the heat treatments and coating processes were successful. Thephases present in the coating layers are uniform, homogeneous and well-dispersed in the coatedzone. The coated layers show a small amount of porosity and a good binding to substratematerial and are not brittle.Keywords: Surface modification, PVD, On-line monitoring, Modern cutting tools, TiN coating, TiCNcoating, CrN coating.