Thermal process for selectively hardening track chain links

A process for selectively hardening a forged track chain link, comprising the steps of:

• providing a forged track chain link having a pad portion, a rail portion, a first side portion, and a second side portion;
• providing a quench tank adapted for receiving said track chain link, said quench tank being adapted for spraying one or more of said track chain link portions with a quenchant at a controlled amount of one or more of a plurality of quenchant flow rates, a plurality of quenchant pressures and a plurality of quench times;
• positioning said forged track chain link within said quench tank;
• spraying one or more of said pad portion, said rail portion, said first side portion and said second side portion, with said quenchant at a controlled amount of one or more of a plurality of quenchant flow rates, a plurality of quenchant pressures and a plurality of quench times;
• wherein said pad portion is sprayed with quenchant at a quenchant flow rate in the range of about 10 g.p.m. to about 50 g.p.m., at a quenchant pressure in the range of about 2 psi to about 5 psi, and at a quench time in the range of about 1 second to about 15 seconds, and said rail portion is sprayed with quenchant at a quenchant flow rate in the range of about 70 gpm to about 100 gpm, at a quenchant pressure in the range of about 5 psi to about 15 psi, and at a quench time in the range of about 90 seconds to about 210 seconds;
• and
• simultaneously hardening said rail portion and said pad portion to respective surface hardnesses, said rail portion being hardened to a surface hardness greater than the surface hardness of said pad portion, said pad portion having a tempered martensitic microstructure up to a depth in the range of about 3 mm to about 12 mm from the surface, and a surface hardness in the range of about R.sub.c 33 to about R.sub.c 41, and said rail portion having a martensitic microstructure up to a depth in the range of about 7 mm to about 25 mm from the surface, and a surface hardness of at least R.sub.c 50.