# Cutting Force When Machining Hardened Steel and the Surface Roughness Achieved
###### Abstract
During their experiments, hardened steel was turned with the (Ti, Al) N-coated CBN tool at cutting speeds of 200 and 300 m\(\cdot\)min\({}^{-1}\), with a feed rate of 0.3 mm\(\cdot\)rev\({}^{-1}\) and a depth of cut of 0.1 mm. In addition, uncoated CBN was also used as a substrate for the (Ti, Al) N coating. [PERSON] et al. [12] tested an ultra-hard cutting material, specifically nanocrystalline cubic boron nitride (BNNC). This material was fabricated using a high-pressure-high-temperature (HP-HT) process. The starting material was a pyrobilically deposited hexagonal boron nitride (PBN), which was transformed at temperatures of 1400-2200 \({}^{\circ}\)C and pressures of 10-20 GPa during direct synthesis without any binder. The average crystallite size of this material was 50-100 nm and it was, therefore, significantly smaller than that of the conventional polycrystalline cubic boron nitride (PCBN) cutting materials. Compared to conventional PCBN cutting materials, this material had an increased hot-hardness and a better temperature resistance. Testing was carried out by turning grooves in hardened steel. Interesting research in this field was also carried out by [PERSON] et al. [13] who studied the cutting forces and stresses on the surface of cutting tools with inserts made from five sets of cubic boron nitride polycrystals. The inserts had different specific surface areas of the base material. The dynamic strength of the super hard polycrystals was investigated under the diametric compression of disk-shaped specimens with a diameter of 10-12 mm and a thickness of 3-4 mm. An algorithm for the calculation of the probability of failure was described, which included the evaluation of the probability of tool failure by analyzing the differential distribution functions for the compressive and tensile stresses that arose during the turning on the front and back faces of the cutting edge and the distribution of the compressive and tensile strengths of the tool material. This algorithm was used in the development of the VarTool software in the Mathcad package to evaluate the probability of the failure of tools or other structures operating under non-stationary loads. Overall tool geometry represents another critical condition leading to an increase in cutting efficiency as [PERSON] et al. [14] point out in their study. Improper tool geometry can result in energy loss and tool wear during the machining of hardened steel, leading to higher production costs. Therefore, the objective of their work was to determine the optimum combination of parameters such as angle of attack, depth of cut, tip radius and feed rate during turning to reduce the cutting force and energy consumption. Apart from the tool geometry, due attention should also be paid to the cutting temperatures. [PERSON] et al. [15] address the problem of the cutting temperatures corresponding to the optimum turning modes in a full range of structural alloy hardened steel (HRC 55) used for the manufacture of machine components included in the design of marine vessels. The radial component of the cutting force and the cutting temperature were used as optimization parameters for machining hardened steel with cutting ceramics. Most of the above-mentioned studies used conventional machining methods while [PERSON] et al. [16] addressed cutting tool wear in machining hard materials and the use of modern machining processes such as ultrasonic assisted turning. In the ultrasonic-assisted turning of hard and brittle materials, the cutting tool failure occurred due to vibration shock. After machining short lengths, microcracks occurred in the tool face, so that sharp cutting edges failed in the initial stages of the machining. Therefore, if the cutting edge is deburred before machining, the cutting edge breakage caused by the vibro-strike condition could be eliminated. The aim of the research was to investigate the flank wear of tungsten carbide tools during the ultrasonically assisted turning of hardened alloy steel and to compare the results with conventional turning.