International Journal of Research in Engineering and Science (IJRES) ISSN (Online): 2320-9364, ISSN (Print): 2320-9356 www.ijres.org Volume 6 Issue 9 Ver. I ǁ 2018 ǁ PP. 01-08 www.ijres.org 1 | Page Investigation of Machinability in Heat Treated SAE 1040 Steel by Experimental Design Method Ayhan Aytaç* 1 , Muhammed Ilivan 2 1 (Dr., Turkish Military Academy/ National Defence University, Turkey) 2 (Lecturer, Dumlupınar University, Turkey) Corresponding Author: Ayhan Aytaç ABSTRACT: The purpose of design in engineering experiments is not only to investigate effects of the variables on production, but also to investigate effects of interactions between them. Especially statistical-based experiment design techniques are quite useful for improving the manufacturing process performance in the engineering world. It can be decided to subset of process variables that are the most effective ones by using experimental design. Using experimental design offers advantages such as easier production, better performance, more reliable and shorter design, development and production. In problems that two or more problems are considered, factorial experiment design is a powerful technique. Double-phase steels are widely used in the automotive industry, especially due to their high strength / weight characteristics. These steels provide high strength with the hard martensite phase that is dispersed in the ferrite phase. When the heat treatment parameters are applied correctly between the critical temperatures, a double phase structure is obtained. In this study, the bars prepared from SAE 1040 steel were cooled in water after annealing process between critical temperature, and specimens having double phase microstructures were obtained with two different martensite volume ratios. In the machinability study, the experiments were carried out with full factorial experiment design technique as three factorials (k = 23 and 8 experiments). Type of cutter (CBN and Ceramic cutter), feed rate (0.02 and 0.06 mm / rev) and martensite volume ratio (55% and 78) was used as independent variable (factor) in the experiments, average surface roughness value (Ra) that is dependent variable was determined by measurement from 6 different points with three experiments. Experiments were performed in dry cutting conditions in CNC Turning Table that has 1.5 kW power and rotates with maximum 2000 rpm.As a result, these three factors are effective in turning these steels on their own. The most effective parameters on the surface quality were the cutter tool, the martensite volume ratio, dual interaction of the cutter tool-martensite volume ratio (material hardness), respectively. The results obtained were interpreted together with evaluations that were previously included in the literature. KEYWORDS: Full Factorial Experiment Design, DOE, Dual Phase, Surface Quality, Machinability. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 18-12-2018 Date of acceptance: 31-12-2018 --------------------------------------------------------------------------------------------------------------------------------------- I. INTRODUCTION It has enumerated the heat-treatment practices of the steels of commercial importance like low-carbon lean-alloy steels, medium-carbon high-alloy steels, structural steels, and ultra high-strength maraging steel (1). Heat treatment; It is a term that defines the controlled heating and cooling processes applied to material in solid form and to change mechanical properties of the material (2). The purpose with these processes is to change microstructure and / or mechanical properties of the material. It is generally aimed to achieve better mechanical properties such as better tensile strength, higher impact toughness or high wear resistance by heat treatment in many applications. In practice, however, the heat treatment applied to a material causes the simultaneous change of more than one mechanical property of the material (1-3). Two-phase ferritic martensite steels are obtained by heat treatment performed in the ferrite austenite phase region to the martensite structure obtained by tempering after austenite conversion. By simply changing the heat treatment temperature in these steels, a wide range of strength and ductility can be provided. Strength enhancing mechanisms can be calculated by the morphology and amount of the second phase (4). One of the main purposes in machining is to bring surface roughness to the top level. Being surface quality of material well has a positive effect on mechanical properties of material. It is required to choose cutting parameters the most suitable to get a good surface quality (5). Alloy steels are preferred for manufacturing of machine parts owing to their physical and mechanical properties. However, these parts require turning operation to be carried out in order to obtain desired quality product. Components can be machined at minimum lead time, with higher machining parameters such as cutting speed, feed/revolution and depth of cut, which leads to increase in cutting force and surface roughness (6).