Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching (CROSBI ID 80253)
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Liščić, Božidar
engleski
Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching
The pattern of hardness distribution on round bars' cross-section after quenching was studied in relation to the change of heat transfer on the workpiece surface. It was found that a "delayed quenching", producing a discontinuous change of cooling rate, may result in higher hardness in the core, than at the surface. This phenomenon called "inverse hardening" has been theoretically expllained by Shimizu and Tamura. It depends on: hardenability of the steel, cross-section size of the workpiece and on quenching condition, and is related to the incubation period consumed before the cooling rate was changed. own experiments using cylindrical specimens of 50 mm Dia, made of AISI-4140 steel, have shown that Controllable Delayed Quenching (CDQ) technology has a great potential to increase the depth of hardening, compared to conventional quenching practice. Bending fatigue tests with inverse hardened and tempered specimens have shown a significant increase of the fatigue life compared to specimens having normal hardness distribution after quenching. CDQ-technology and "inverse hardening" can reproducibly be realized using adequate steel hardenability and cross-section size of the workpiece, by quenching in PAG polymer-solution of high concentration, or high pressure-circulated gases.
Quenching; Heat Transfer
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