Distortion in quenching an AISI 4140 C-ring – Predictions and experiments

Heat treatment processes are used to enhance the material properties of a wide range of mechanical steel components, according to their final application. Quenching is a common step in these heat treatments, involving the fast cooling of previously austenitized parts and leading to a phase transformation from austenite to hard martensite in the material. Quenching commonly causes a geometric distortion in the parts, associated with the thermal contraction and with the change in the mechanical and geometrical properties of austenite and martensite. It is of importance to predict these distortions, so that one can design corrective post-heat treatment shape corrections or include them in the pre-heat treatment part dimensions, thus leading to a final part with adequate shape and dimensions. This study presents the results of a finite element (FE) simulation of the quenching of an AISI 4140 steel C-ring in oil, covering the analysis of the distortion caused by both thermal contraction and phase transformation. Furthermore, the distortion behavior during the cooling stage is analyzed, as well as the hardness and martensite volume fractions. Experiments were also conducted in order to obtain the geometric distortion, the microstructures and hardness of the C-rings. The FE modeling results are in good agreement with the experimental values and, to the knowledge of the authors, this is the first time that such an agreement has been obtained for the distortion caused by quenching of C-rings. The design of new products and quenching processes should consider the studied aspects, and may also be assisted by the methodology applied to this work.

During quenching process, thermal gradients and phase transformation may induce geometrical distortions. In the C-ring case, the distortion occurs due to the martensite formation throughout the fast cooling procedure, where the thicker specimen’s volume increase results in the C-ring opening, as illustrated in the figure (displacement magnified 20×).Figure optionsDownload as PowerPoint slideHighlights
► AISI 4140 C-rings are quenched in oil.
► The quenching process is simulated using a FE code.
► Distortion, hardness and microstructure are predicted.
► Simulations agree with experiments.
► Distortion may be taken into consideration in the design and manufacturing steps.