Quenching power of aqueous salt solution

Abstract

Abstract The mechanical properties of steel components are influenced by the microstructure that is determined by the heat treatment cycle. In the quenching of the steel: water, oil, aqueous polymer solutions and aqueous salt solutions (brine) can be used as quenchants that exhibit different characteristic on cooling mechanisms. For example: when water is used as the cooling media, a stable vapor film is formed around the hot component resulting in non-uniformity of surface heat transfer during the cooling process which is often responsible for distortion and cracking. Salt addition can reduce or inhibit this vapor film formation, enhancing the uniformity of heat transfer during the cooling. This work will investigate the cooling performance of different salt solutions (NaCl, NaNO2, Na2SO4, NaHCO3) varying concentration, temperature (25 and 45\u202f°C) and agitation (0 and 800\u202frpm). The description of these medium and the influence of external factors were made using cooling curves, cooling rates and heat flux. Metallurgical tests were performed in samples of SAE 1045 steel which were quenched in such solutions and hardness were analyzed. The use of aqueous salt solutions, in general, has proved to be effective in to inhibit the vapor blanket, to increase heat extraction and keeping a high heat flux during the most part of the drop of the temperature that results in a homogeneous cooling able to avoid distortions. NaCl, NaNO2, Na2SO4 solutions were able to quench SAE 1045 steel.