Dimensional stability of cryotreated diaphragms of pressure transducers

Abstract Accurate data of propellant pressures are very critical for the successful propulsion of launch vehicles. These pressures are measured using the integral diaphragm pressure transducers machined from precipitation hardened martensite stainless steel (APX4). The thin diaphragms of these transducers gradually develop dimensional changes with time due to the conversion of residual austenite to martensite, resulting in drift in output pressures. This situation calls for enhancement of dimensional stability of the diaphragms which is carried out by cryotreating them at 98K for 36 hours followed by tempering at 673K for one hour in vacuum furnace. The dimensional studies were carried out on three categories of diaphragm materials viz. normal, cryotreated and cryotreated followed by tempering using the Thermo Mechanical Analyser (TMA). The dimensional changes of the test specimens were determined at intervals of 5K in the temperature range from 123K to room temperature. The results are analysed and presented in this paper.