Submitted on: 12 April 1999.
Revised on: 09 May 1999.
Accepted on: 02 June 1999.
___________________HTM-Journal of Heat Treatment and Materials
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Submitted on: 06 April 1998.
Revised on: 25 June 1998.
Accepted on: 13 July 1998.
___________________HTM-Journal of Heat Treatment and Materials
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