Investigation of microstructural characteristics and cutting performance of hardened cutting tools from DIN 115CrV3 steel coated with TiN and CrN

DIN 115CrV3 steel is a low alloyed cold working tool steel which has sufficient strength and ductility. It uses to produce machine tools such as spiral and tap drills, broaching tools, metal saws. It is possible that from these low-alloyed and cheaper cost steel, after an appropriate heat treatment process and then ceramic coatings to produce very valuable cutting tools. Normally, the wear and cutting performances of a DIN 115CrV3 steel in thermal processless and uncoated condition is very low and insufficient. To improve cutting performance and wear resistance, these steels need a thermal processes such as hardening and stress relieving tempering, and also coating with a thin seramic layer respectively.In this work, cutting tools made of DIN 115CrV3 steel have been as first hardened, stress free tempered and then surface coated by using a physical vapor deposition method. As a last step the abrasive and adhesive wear behavior, and cutting performance tests were performed. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis techniques have been used to analyse microstructures of produced cutting tools and to determine the surface roughness. In addition, the alteration of hardness and wear characteristics have been investigated.In experimental studies it was identified that DIN 115CrV3 steel which has been obtained from market had a hardness of 372 HV was already heat treated and its microstructure consists of nodular annealed pearlite. In hardening process, the highest hardness value have been obtained as 820 HV after annealing at 780 °C temperature and quenching into the cold water. TiN and CrN coating layers cover the surface of substrate uniformly and the surface roughness of TiN layer in comparison with CrN layer has been found thinner and less than 10 nm. Experiment results under a constant or an increasing load the adhesive wear behaviors of coated or uncoated cutting tools were found differently. Under an increasing load TiN and CrN coated cutting tools have been given a higher friction coefficient than the hardened and stress free tempered martensitic steel. However, the tests carried out that the friction coefficient of the hardened martensitic steel under constant load was higher than the other coated tools. In addition, the CrN coated cutting tools under high loading has been shown an adhesion disorder and delamination in comparison with TiN coated cutting tools. Accustic emission experiments shows that there is internal stress in hardened martensitic steel tool than the others. The lowest internal stress has been found in TiN coated cutting tools. After adhesive wear test under a constant load, trace of W metal abrasive particles was identified on the surface of hardened martensitic steel tool and CrN coated cutting tools, but it wasn?t found any W metal traces on the surface of TiN coated cutting tools. At abrasive wear, weight loss was observed when the load increased. According to the abrasive wear results, the hardened martensitic steel cutting tools had a higher weight loss in comparison with other coated cutting tools. In addition, the microstructure and EDS analysis of each three cutting tools has been shown that there are high amounts of the Mn element contents on the surface of cutting tools which came from work pieces. It means that abrasive and adhesive wear occurs on the surface. On-line monitoring method gives an information about the performance of cutting tools based on the dimensional change during machining of the work piece surface. Accordingly, at the low-speed machining, TiN coated tools have been shown lower abrasion. Likewise, according to high speeds machining results, CrN coated cutting tools have been shown a slightly superiority in comparison with TiN coated cutting tools. The microstructural analysis of each three cutting tools after abrasion tests had been shown fracture and galling.According to results of this experimental thesis it has been found that the best cutting performance has been attained by TiN coated tools which made from DIN 115CrV3 cold work steel, and can be used for industrial purposes. As well CrN coated tools had been shown enough good performance, so that its performance was better than hardened and stress free tempered uncoated tools which can?t be used so good for industrial purposes.