Evaluating quenchants and facilities for hardening steel
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The effects of agitation and quenchant temperature on the ability of a fast oil, water, and a 16 pct solution of a polyglycol in water to remove heat from steel during quenching have been determined using instrumented probes and bars of known hardenability. The fast oil was relatively insensitive to quenchant velocity in the range of 0 to 1 m/s (200 fpm) or to temperatures of 25° to 70 °C (85° to 160 °F). The oil produced quench severity factors of 0.3 to 0.6 under most conditions examined.
Water was more sensitive to both agitation and temperature variations than oil. No agitation resulted in quench severity factors in the range of 0.20 to 1.8, depending on the water temperature. Agitation of 25° to 50 °C water to produce velocities of 0.5 m/s (100 fpm) or higher produced quench severity factors of 1.5 to 2.8, depending on the actual velocity and section thickness. Quench severity factors of about 0.50 were obtained with 70 °C water with velocities up to 1 m/s.
The polyglycol solution examined was the most sensitive to temperature control and agitation. Proper usage at a temperature of about 25° to 30 °C, with agitation to produce velocities of 0.5 to 1.0 m/s, produced quench severity factors of 1.1 to 1.3. These values were higher than those produced by oil but lower than those achieved with water at the same temperatures and velocities. Higher bath temperatures or inadequate agitation resulted in lower quench severity factors, in the range of 0.15 to 0.5.
Instrumented probes and bars of known hardenability were used to evaluate quenchant performance in two commercial heat-treating facilities. High cooling rates and quench severity factors produced high hardnesses at the center of steel bars placed in quenching trays. The instrumented probes were more sensitive in their ability to detect changes in bath conditions than bar center hardness.
The techniques used allow individual quenchants to be evaluated for their ability to extract heat from metal parts as a function of operating conditions. They also permit the best operating conditions for a particular quenchant to be determined, in terms of both the agitation and temperature. This information can be used to specify operating conditions and to aid in sizing quenchant pumps and cooling towers. The causes of incomplete hardening can be defined and eliminated.
KeywordsCool Rate Tray High Cool Rate Cooling Tower Quenchant Temperature
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