INFLUENCE OF MICROSTRUCTURAL CHANGE IN AISI 4340 STEEL SPRING MATERIAL HAVING IDENTICAL HARDNESS LEVEL ON THE HYSTERESIS ERROR OF FORCE TRANSDUCER
Sinan Fank
Abstract:
Different heat treatment processes can be applied on the spring element of a force transducer in order to obtain good and satisfactory performance. The manufacturers are generally focused on the improvement of performance by applying different heat treatments on spring material, and no information is in free circulation regarding the process-performance relationships of transducers due to tight competition in the market. The study covers the attempts of different heat treatments on spring element using AISI 4340, which is regarded as one of the best spring materials for force transducer applications. The steel was quenched and tempered at predetermined temperature, and 45 Rockwell-C hardness values was reached to obtain fine martensite structure. In order to obtain coarse martensite structure having identical hardness from spring material, some specimens were subjected to high temperature during austenite transformation in 1000°C in 4.5 hours priority. In order to produce bainitic structure different heat treatment was applied on the specimens to have identical hardness level. It was observed that different heat treatments influenced the transducer performance, particularly hysteresis behaviour point of view. To minimize the hysteresis error of force transducers has prime concern and best result was obtained in the bainitic- structured specimen. After building the force transducers with differently heat-treated spring materials, their performances were recorded by using a dead weight force standard machine, concentrating on hysteresis characteristics. The results were compared with each other and analysed regarding the structural properties of spring materials and a process path was proposed to obtain the best performance in force transducers.
