Enhancement of micro-drilling performance by cryogenic treatment of drill bit

Abstract

Cryogenic treatment is one time permanent treatment that affects the entire section or bulk of the component unlike coatings. The cryogenic treatment is an add on process over conventional heat treatment in which the samples are cooled down to prescribed cryogenic temperature for a long time and then heated back to room temperature. The process is not a substitute for heat treatment but rather an extension of the heating/quenching/tempering cycle. In most instances the cryogenic cycle is followed by a heat tempering procedure[1]. Two major changes in micro-structure of steel occur as a result of cryogenic treatment[2,3], which play the principal role for dramatic improvement in wear resistance. The retained austenite are transformed to wear resistant martensite to achieve more uniform hardness. Fine carbide precipitates are formed during the long cryogenic soak. These fine particles along with large particles form a denser, more coherent and much tougher matrix in the material. Yun et al.[4] verified the changes in the microstructure of M2 high speed steel when the materials was submitted to different cycles of cryogenic treatment at -196 degree Celsius. Dong et al.[5] investigated in detail an effect of varying the deep freezing and tempering cycles on high speed steels and concluded that improvement of wear resistance in tool steels because of elimination of retained austenite and initiation of nucleation site for precipitation for large number of very fine carbide particles. Empirical investigations have demonstrated that the tool life of cutting tools like high speed steel and tungsten carbide can be enhanced by cryogenic treatment