Hardness and Tensile Strength

Hardness

Hardness is the ability of a material to resist penetration by another body. Hardness is often measured in the Brinell or Rockwell scale. As higher hardness implies higher strength, greater cutting force and power are required for machining a harder material. Greater hardness means greater tool wear under a given cutting condition. For optimum tool life the cutting speed will have to be lower and hence productivity will be lower. Normally a harder material gives better surface finish than a softer material as the harder materials have less tendency to form built up edge.

Tensile Strength

Tensile strength of a material is the ultimate strength or the maximum stress the test specimen in a tensile test could sustain during the test. Increased tensile strength calls for higher cutting forces during machining as the specific cutting pressure increases with increasing tensile strength. Also to withstand the increased impact loads at entry, the cutting edge must be made stronger to achieve reasonable tool life. The surface finish is better with increased tensile strength of work material due to reduced tendency to form built up edge.