Abstract. Machinability is the one of the criteria in determining the life span of the cutting tool. In this experiment, hard and difficult to cut materials like hard AISI 440 C stainless steel and hard S C M 440 alloy steels were discussed. However, machinability of the material is considered to be poor due to its inherent characteristics. Machinability studies on AISI 440 C stainless steel and SCM 440 alloy steels had not been carried out by researchers. Machinability indices used in such cases have the characteristics such as cutting force, surface roughness, tool wear etc. In the case of highspeed machining of said materials machinability indices such as chip thickness (Rc), shear angle (a), surface integrity, and chip analysis are of prime importance. In this work, an experimental investigation was carried out to understand the behavior of difficult to cut materials, when machined using Cubic Boron Nitride (CBN) insert tool. The results and analysis of this work indicated that the above-mentioned machinability indices are important and necessary to assess the machinability of said materials effectively. The operating parameters used were cutting speed 100, 125,150, 175 and 200 mimin with feed rate of 0.10, 0.20 and 0.30 mm rev" with constant depth of cut of 1.0 mm. The length of turning was 150 mm and 300 mm. Machinability of both materials and tool was evaluated in terms of roughness, flank wear, cutting force, chip thickness ratio and shear angle. IntroductionMachining of hard materials is difficult by high speed steel tools, ceramic tools, even more difficult on material like titanium alloy, Inconel 718 and martensitic stainless steel etc. Few attempts have been made on the machinability of hard martensitic AISI 440 C and SCM 440 alloy steel with respect to chip thickless ratio, shear angle, and flank wear. Machinability is poor in turning stainless steel owing to low thermal conductivity, high ductility, high strength, high fracture toughness and high rate of work hardening. Work hardening of stainless steel occurred after a previous severe cutting operation by worn tools [I]. Sethikumar et al.[2] turned hard martensitic stainless steel and found that it produced saw tooth chips in all operating parameters which increased the cutting forces. Liew et al. [3] conducted study on cutting AISI 420 steel using PCBN tool. The tool wear was found due to abrasion and cutting temperature. The porosity, ductility, and the bonding strength of the grains in the tool, apart from its thermal conductivity which have great influence on the fracture resistance of the tool. Fig.1. shows tool wear on single point tool. Machinability indices used here are chip thickness ratio, shear angle, tool wear, chip analysis was important. Experimental work was carried out to study the behavior difficult to cut materials like AlSI 440 C martensitic stainless steel and SCM 440 alloy steel. There were no attempts or little consideration was given to evaluate the machinability with respect to chip thickness ratio and chip compression rat...

Electric discharge coating is an alternative process for surface modification/alloying/coating requirements to improve mechanical and metallurgical properties of the materials. The high-pressure compacted electrode is made of the semi-sintered nickel and tungsten during the electric discharging process which influences the material migration towards substrate. In this proecess addtiton of pyrolysis carbon from dielectric togeather with the alloying elements and substrate material results in formation of metal matrix composite coating. It depended on the stabilization pressure of spark which increases the deposition rate of alloying materials and reduces the carbon, brittleness, cracks, voids, blowhole on the surface and made the layer to be desired metallurgical properties. Modified layer shows higher in hardness value of 1100 HV0.5 and reduction in specific wear to 0.082 × 10 −5 mm 3 /Nm compared with uncoated substrate material. Inclusion of the alloying material and reduction of the carbon percentage consequences in self-lubricant properties which alter the wear rate and coefficient of friction. Surfaces topography obtained during alloying, material migration and the mechanism have been characterized through scanning electron microscopy and energy-dispersive X-ray spectroscopy. The wear behaviour has been analysed by using pin-on-disc tribometer.

Hard turning of materials is a process where dimensional accuracies, dimensional controls and surface roughness are easily obtained. Currently hard components are produced by hard machining in a very short time which also saves on cost. Martensitic stainless steel is difficult to cut due to the presence of high amount of chromium and makes the material harder. AISI 440 C hardness is maintained through induction hardening process. The cutting tool used for this material is normally a super hard cutting tool like CBN and PCBN tools and less tool wear is possible. Minimising tool wear is the main criteria of the machining process. The influence of flank wear was due to abrasive action of hard martensitic carbides of the work material at low cutting speed, and low feed rate. The crater wear also formed and was due to abrasive action of the saw tooth chips and also by heat at cutting zone. Saw tooth chips were produced by while machining martensitic stainless steel and the rough surface of the chips responsible for occurrence of the crater wear.

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Hard turning technique is new and the management of this process is still limited. AISI 440 C martensitic stainless steel and SCM 440 are alloy steel used as work piece materials for this research work. The stainless steel is difficult to cut material, low thermal conductivity, tendency to form built up edges at tool edge and less corrosion resistant where as SCM 440 is high strength material. The flank wear formed on CBN by stainless steel was more than alloy steel. The crater wear formed on CBN tool while turning stainless steel than alloy steel. The chips produced by stainless steel were saw tooth form and SCM 440 alloy steel did not produce saw tooth chips. Flank wear and crater wear were caused by severe abrasion and also by high heat generated during turning on stainless steel. The flank wear and temperature also contributed on cutting forces on both materials, but very little on stainless steel and more on alloy steel.

the cutting forces and also causes the heat generated at tool tip and work surface interface. High cutting forces are identified and this may be due to heat and flank wear combinations. Flank and crater wear on the rake face and hard metal deposition due to diffusion of metals on the cuttiug tool surface are the damages occurred during process. mRODUCTIONHard turning has been applied in Inany areas like production of bearings, gears, shafts, axles, and other mechanical components [l-21. ATSI 440 C martensitic stainless steel is pronounced as difticult to cut materials and t l~i s~a r d e n e d %~~r i k e~-d~s * R r m i~ of these types of materials require hard and tough cutting tools like CBN and PCBN tools. These types of cutting tools will reduce flank wear and withstand the heat generation. The generatlon of heat will produce low cutting forces due to thermal softening of the chips. It is known that 60 % of the heat generated by the turning is c a~i e d away by chips and the remaining is retained by work material and tool cutting edges. However, stainless steels are low thermal conductivity material and very small percentages of heat retained by the work material. Tool wears are complex phenon~enon.Tool wear is common in all the machining processes and depend very much on the hardness of the work materials, type of tool, rigidity of the machine, hardness of the work materials heat All rights reserved. No pan of contents or this paper may be reproduced or tnnsmined in any brm or by any means wimoufthe wrnten permissionof TTP.

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Deep cryogenic treatment produces a significant enhancement in the mechanical properties of metals. In this research paper, the mechanical properties of Aluminium Silicon composite were studied when they were subjected to deep cryogenic treatment. Samples were prepared from two different compositions of Aluminum silicon composites (Al 2024_5%SiC & 10%SiC). The samples were given controlled cryogenic treatment at -186oC. Treated samples were compared with un-treated samples for their compressive strength, hardness and metallurgical changes. The treated samples have shown an improved compressive strength. The improvement is supplemented by the hardness survey and micro-structural changes.