Measurement of the Cooling Power of Polyethylene Glycol Aqueous Solutions Used as Quenching Media

Abstract

Solutions of high molecular weight polymers are used widely in the heat treatment of metal alloys known as quenching. Water-soluble polymers offer a number of environmental, economic, and technical advantages, including eliminating the quench-oil fire hazard. The cooling power of water-soluble polymers such as polyethylene glycol (PEG) and salts aqueous solutions is studied with a cylindrical test probe of Inconel 600 by using a quenchometer. The dependences of the cooling rates, at each bath temperature, on polymer concentration and agitation are established. The present paper describes, through an understanding of the quenching mechanism, the effect that some parameters concerning the control of polymer quenchants have on their behavior. The effect of the salts on the quenching characteristics has also been studied. A study has been made of the relationship between the concentration of PEG, bath temperature, agitation, and cooling power in aqueous quenchants that contain up to 20 % of PEG. The presence of 5 % or less of the polymer in solution increased the cooling power of the quench in comparison with the water quenchant. However, increasing polymer concentration will decrease the cooling power as well as the maximum cooling rate because of the formation of the vapor blanket in the first phase of the quenching mechanism. The hardening power (HP) of the PEG quenchant solution was characterized on the cooling curve by the two critical points, CRF (the cooling rate at the ferrite/pearlite nose) and CRM (the cooling rate at the martensite start transformation), using an empirical relation giving HP in function of the measured polymer quenchant cooling characteristics. The highest HP was obtained in dilute solution of PEG having a concentration of 2.5 %, which reaches a value of 2051 at 20°C and 1951 at 45°C, under agitation.

Cooling Characteristic of Polymeric Quenchant: Calculation of HTC and Prediction of Microstructure and Hardness

“…Quenching in polymeric aqueous solutions modifies the cooling mechanism and the kinetics of heat transfer, although the three stages during quenching (vapor blanket, boiling, and convection stages) still occur, as shown in Fig. 1 (Ref 19,26,27).…”