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To control the process of film boiling during quenching in oils, quench oil makers as a rule manipulate physical properties such as a surface tension and viscosity. However, there is much experimental data showing that special additives can eliminate film boiling in oils without changing their physical properties and which is counterintuitive. Authors explain such phenomenon by showing that the addition of a special additive, for example PIB (polyisobutylene polymer), will create an insulating layer on the surface of steel parts during quenching in oils that will eliminate film boiling without affecting physical properties of the oil. Insulating layer decreases initial heat flux density which becomes less than critical one and of the oil will not begin film boiling during quenching with the PIB additive. Authors believe that such approach will allow engineers to solve effectively the problem of part distortion after quenching. The new oil quenchant containing special additive PIB is patented in Ukraine and is manufactured by Barkor Ltd for needs of the heat treating industry.

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In the paper the results of testing three types of FUCHS oils: Thermisol QH 120, Thermisol QH 10 and Thermisol QB 46 are discussed. The main attention is paid to critical heat flux densities evaluation because they create a basis for optimizing cooling intensity of any liquid quenchant. In the paper is underlined that any film boiling during quenching is undesirable since it is a reason for big distortion and non-uniform surface harness. It is shown that intensive quenching decreases distortion of steel parts during quenching. To eliminate film boiling during quenching in mineral oils, optimal temperature of oil should be chosen which maximize the first critical heat flux density and special additives should be used to decrease initial heat flux by creating surface micro-coating. Along with the evaluation of heat transfer coefficients, critical heat flux densities inherent to liquid quenchant must be measured first to optimize quenching processes. International DATABASE on cooling characteristics of liquid quenchants must include critical heat flux densities, initial heat flux densities, and heat transfer coefficients allowing optimizing and governing quenching processes.