Numerical analysis applied to thermal and fluid-dynamic quenching simulation of large high quality forgings.

Abstract

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Heat treatments of steels consist in a modification, in hot conditions, of the initial crystal lattice of such alloys
and represent one of the most delicate step in the industrial production of forgings. In this frame, one of the
most critical stages is quenching, which consists in rapid cooling of steel pieces at high temperature, in water
or oil or in a polymer water solution (aquaquench). It is a process which is intrinsically unstable, complex
from a physical point of view, which can be hardly predicted without using suitable simulation software. If not
carefully carried out, this heat treatment can be inefficient or even harmful, causing fracture triggering, or,
worse, directly the breakage of the piece. Of course, the bigger the forging, the greater the importance of
estimating the process dynamics and, consequently, designing the plant configuration to obtain the expected
final results, in order to avoid heavy economical losses deriving from a bad treatment.
In this work a study of the water quenching process of large industrial forgings, made of SA 508 steel and
intended for nuclear applications is presented. This is carried out by means of transient thermo-fluidsimulations
in CFD environment (Computational Fluid Dynamics).
The models have been validated by comparing the numerical results with the ones obtained by experimental
trials carried out on steel test samples, having suitable dimension and properly instrumented: the results have
shown that the average error is below 3%, while the maximum error is below 10%. These results confirm that
the chosen method suitably simulates the physical phenomenon and so it can be extended to study a wide
range of cases, in order to provide a valid and reliable support for large forgings Manufacturers.