This paper presents results of a research on hard turning of 9XC and X12M alloy steels to explore the influence of workpiece’s hardness on machined surface roughness and topography at selected cutting conditions. It is evident that the surface roughness was directly proportional to the increase of the workpiece’s hardness from HRC = around 50 to higher than 60. Moreover, lower hardness resulted in worse surface roughness. | The Quang Phan et al Journal of SCIENCE and TECHNOLOGY 127(13): 3 - 8 EFFECTS OF WORKPIECE HARDNESS ON HARD TURNED SURFACES OF ALLOY STEELS The Quang Phan, Dung Thi Quoc Nguyen* and Thao Thi Phuong Phan University of Technology - TNU ABSTRACT Nowadays, hard turning is widely applied in Vietnam industry and it is usually the finished operation so the quality of the machined surface plays a very important role to the use today and in the future. This paper presents results of a research on hard turning of 9XC and X12M alloy steels to explore the influence of workpiece’s hardness on machined surface roughness and topography at selected cutting conditions. It is evident that the surface roughness was directly proportional to the increase of the workpiece’s hardness from HRC = around 50 to higher than 60. Moreover, lower hardness resulted in worse surface roughness. Even though when the cutting speed increased by twice, the best surface roughness still achieved at the workpiece’s hardness of HRC= around 50. The cause is predicted to be involved with a change in chip/ rake face interactions depending on workpiece’s hardness and tools wear. Keywords: Hard turning, furface roughness, topography, workpiece, tool wear. INTRODUCTION* Precision machined components can be manufactured by hard turned or ground operations. Surface integrity is a qualitative and quantitative description of both the surface and subsurface component including surface topography, surface and subsurface hardness, microstructure and residual stresses, etc. The work of Schwach and Gue [1] used a stylus instrument to measured surface roughness created by hard turn stated that surface roughness decreased when feed rate reduced. Decreasing feed rates makes the surface residual stress more compressive and its maximal one closer to the surface. Moreover, tools wear increased surface roughness except at moderate mode. Sharp cutting tool is recommended for hard turn to get better surface integrity. Chou .
