Abstract
Quench distortion in medium-carbon steel components — ovality and longitudinal bow in shafts, warpage in flat plates — is driven fundamentally by spatial non-uniformity in the local heat-transfer coefficient h(t) across a component's surface during immersion cooling, which desynchronises the timing of the martensitic transformation between end, mid-section, edge, and core regions (Canale & Totten, 2005; Şimşir & Gür, 2008). This paper presents a reproducible mechanism-and-protocol framework for evaluating a passive, perforated flow-masking fixture as a heat-transfer-redistribution strategy during oil quenching. The fixture is designed to modify local heat-transfer-coefficient histories — suppressing high-velocity impingement and edge-dominated cooling at selected zones — without inducing sustained vapour blanketing at the masked zone. The design objective is not uniform flow velocity around the part, but controlled synchronisation of transformation timing across end, mid-section, edge, and core regions. We specify: the fixture mechanism and its theoretical boundary conditions, including two explicit failure modes (over-masking and under-masking) that bound the design space (Section 3); a six-cell perforation design-of-experiments (DOE) spanning unmasked, four intermediate open-area fractions, and a deliberately over-masked solid-shroud control (Section 5.3); a phased validation architecture that separates an initial pilot-scale feasibility phase from the full DOE (Section 6); a randomised, position-controlled experimental protocol for oil-quenched EN8/AISI-1040 shafts and medium-carbon steel plates, covering four-point thermocouple logging, distortion metrology, surface-to-core hardness mapping, and microstructural and residual-stress characterisation (Section 5); an inverse heat-transfer-coefficient estimation method and a transformation-timing (Ms–Mf interval) extraction method (Sections 3.2–3.3); a sample-size and statistical-power rationale (Section 5.6); and a risk register covering over-masking, under-masking, hardness loss, and instrumentation failure modes (Section 5.8). This manuscript does not report completed experimental outcomes, and no percentage distortion reduction, p-value, or effect size is claimed for the present fixture design. Instead, it establishes a falsifiable validation framework — mechanism, DOE, phased protocol, and analysis plan — for future experimental execution. A resource-constrained manufacturing context (MSME heat-treatment operations) is used only to motivate the fixture's low-cost, retrofit-only design constraints and to frame a subsequent field-trial component; it is not the paper's scientific contribution.