Introduction
Himax bars are improved machining quality (imq) bars produced by hindustan. The machinability characteristics are primarily influenced by:

• Work hardening rate of chips generated in machining operation
• Nature of sulphide inclusion and their morphology

The effect of these parameters on machinability characteristics is given below:

Work Hardening Rate
The work hardening rate is dependent on Carbon & Nitrogen Levels. Decrease in work Hardening rate increases the Tool Life, but chip ductility also increases & results in the tendency of the tool to stick to the work piece. On the other hand, increased work hardening rate helps in formation of brittle chips, but at the cost of increased tool wear. Therefore, these elements need to be maintained at optimum levels.

Sulphide Inclusion Control
Small addition of sulphur in the region of 0.015 to 0.030% in general grades i.e. 304/316 proves very effective in increasing the tool life. In case of grade 303, the machinability is further improved by achieving sulphur levels of 0.30% min. The sulphide inclusions act as lubricant on the tool-chip interface. This is acheived by special deoxidation using Calcium. Further, calcium has strong affinity for Sulphur and forms as envelope as Calcium sulphide on the surface of manganese Sulphide inclusions.

Sulphur additions are made to achieve targeted sulphur level i.e. Min of 0.30% in case of AISI 303 & 0.015 to 0.030% in case of 304 & 316 grade.