Quenching of steels consists in heating a component such as it goes into an austenitic state and then applying a cooling to transform the austenite. A rapid quenching process produces a martensitic transformation, a slow one is likely to generate pearlite, with the remaining austenite corresponding to a partly hard structure. Heat treatment gives the material its final properties and microstructure depending on its cooling rate. Different quenching methods exist: immersing into a bath, jet impingement and spray quenching.
Spray quenching is a heat treatment process based on the quenching method, where the metal part is spray-cooled with a quenchant. After heating, the part’s hot surface is sprayed with a jet of gas carrying small droplets to be cooled to the desired temperature. The quenchant used can be water or oil media.
Compared to other quenching techniques, spray quenching has the advantages of providing high heat transfer and achieving uniform heat removal. It is also a very flexible method as it is possible to apply a wide amplitude of cooling rates by simply adapting the water flow rates.
In spray quenching, the heat transfer coefficient (HTC) varies with:
SIMHEAT® simulation software can be used to:
Modeling of vertical spray quenching with SIMHEAT®
A case study developed in collaboration with the Italian company Ofar (Giva Group) on the spray quenching of a large shaft is presented below.
Figure 1 - Heat transfer coefficient distribution
A sensor was used to record the temperature evolution on the shaft’s surface. In the following graph, we see the temperature evolution during quenching. We can observe how the temperature recorded by the sensor decreases over time.
Figure 2a – Sensor defined to record the temperature evolution of the shaft’s surface
Figure 2b – Temperature evolution during quenching
Figure 3 shows the phase distribution after quenching. A bainite phase is present in the center of the shaft. On the boundary, since the cooling is faster, we can observe the appearance of a martensite phase.
Figure 3 - Phase distribution (bainite and martensite) after spray quenching: bainite (left) and martensite (right)
Figure 4 presents the effect of quenching on the first principal stress:
Residual stresses can be observed in the final step of the animation.
Figure 4 - First principal stress evolution during quenching
In this animation, displacement has been amplified by 10 in order to show the distortions induced by the spray quenching process. Thus, it is possible to easily compare the non-deformed model with the final distorted geometry obtained after quenching.
To compensate the distortions, machining is applied in almost all circumstances and our teams are working on modeling for this specific stage. In the near future, it will be possible to model residual stress relaxation after machining.