engleski

Benefits of Delayed Quenching

Based on theoretical explanation of "Delayed Quenching" by Shimizu and Tamura, own experiments, using cylindrical specimens of 50 mm Diax200 mm made of steel AISI-4140, have proved that delayed quenching with discontinuous change of cooling rate can yield higher cooling rate below the workpiece surface than at the surface itself. A new method: Temperature Gradient Quenching Analysis System (TGQAS), and a 2-D computer simulation program was used to explain how heat extraction dynamics during quenching can cause "inverse hardness" after quenching. Among all liquid quenchants only solutions of polyalkylene glycol (PAG) copolymer can be tailored or "preprogrammed" for controllable delayed quenching. Specimens having normal hardness distribution after quenching as well as those having "inverse hardness" distribution have been tempered in the same way to show that delayed quenching followed by tempering yields in the core a microstructure of tempered martensite and about 6 HRC higher hardness than conventional quenching in oil. Bending fatigue tests and information about crack growth rate have shown that the fatigue life of specimens having "inverse hardness" distribution is longer than that of specimens having a normal hardness distribution.

Delayed Quenching; Depth of Hardening; Fatigue Resistance

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