Avaliação de meios de resfriamentos a base de soluções iônicas

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 vapor film formation enhancing the uniformity of heat transfer during the cooling. This work will investigate the cooling performance of different ionic solutions (NaCl, NaOH, NaNO2, Na2SO4, NaHCO3) varying concentration, temperature (25, 35 and 45°C) and agitation of the quenchants (0, 500 and 800 rpm) and their use on quenching a low hardenable steel. The description of these medium and the influence of external factors were made using cooling curves, cooling rates, heat transfer coefficients and heat flux. Samples of SAE 1045 steel were quenched and evaluated by hardness measures and metallography. The use of ionic 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. These solutions were abele to quench SAE 1045 steel.