FEATURE ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2026 29 Quench distortion of steel parts can be caused by the material, geometry, and process. With the distortion being measured at the end of the processing steps in general, the causes of distortion can be quite complex and difficult to quantify or even to qualify in most causes. In this article, an Almen strip was used to simplify the factors and experiment distortions during different heat treatment stages, and computer modeling is used to make the heat treatment process more transparent. BRIEF DESCRIPTION OF EXPERIMENTAL STUDY AND RESULTS In this study an Almen strip made of Pyrowear 675 is selectively carburized, double normalized, high pressure gas quench (HPGQ) hardened, subjected to deep freeze, and double tempered. The Almen strip sample has dimensions of 100 mm length, 20 mm width, and 5 mm thickness. The heat treatment was conducted at Solar Atmospheres. Before heat treatment, all surfaces are copper plated other than the top surface. With a plated copper layer, the carbon diffusion is blocked, so the copper plated surfaces are not carburized. Figure 1 shows the samples hung in the fixture for processing. UNDERSTANDING CAUSES OF DISTORTION THROUGH MODELING AND EXPERIMENTS A modeling and experimental study using a carburized Almen strip demonstrates that distortion during heat treatment arises from residual stress relations, nonuniform austenitizing, thermal stress, and phase transformations. Charlie Li* DANTE Solutions Inc., Cleveland *Member of ASM International Figure 2 shows the modeled carbon distribution profile, and the effective case depth (ECD) is between 1.7 mm and 2.0 mm using HRC 50 criterion. With 5 mm thickness, the thermal gradient in the thickness direction is negligible, which simplifies the distortion problem by eliminating the stress caused by the stresses from the temperature gradient and the geometry. The measured hardness of one fully processed sample is shown in Fig. 3. The surface hardness is about 64 HRC, and ECD is about 2 mm. The opposite side of the carburized surface is not carburized, and the measured hardness of HRC 43 is considered as the core hardness. Fig. 1 — Photo of samples in the fixture for processing. Fig. 2 — Simulated carbon distribution profile using the lowpressure carburizing process to carburize the top surface selectively. Fig. 3 — Hardness profile of fully processed sample.
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