Research On Anelasticity Of 40CrNiMo Steel Spring Element In Load Cell

Spring element is one of very important sensor elements in the world of resistance strain gage load cells.And it has a very important role on the accuracy and stability of the load cells. The performance of spring element material impacts the sensor’s.This article researches creep and hysteresis of 40CrNiMo steel with different heat treatment process,and analyses the reasons for anelasticity by means of optical microscope(OM),scanning electronic microscope(SEM), transmission electron microscopy (TEM), X diffraction (XRD) and other test equipment and ANSYS finite element analysis etc.Creep and hysteresis of 40CrNiMo steel with different heat treatment process are researched. The results show that the strength and hardness of spring elements increase with with the tempering temperature increasing,but the plasticity reduces at the same quenching temperature. With low-temperature tempering,the microstructures contain about 4.1% residual austenite, so that the resistance of micro-plastic deformation decreases and the creep and hysteresis increases. In addition,the tempered martensite retains the high-density vacancy, this makes microstructures unstable, causes stress-induced order, leads to internal friction increase. Tempered martensite has a large residual stress, so that elastic limit decreases, resulting in stress relaxation and elastic body anelasticity worst. After the average tempering, the high-density dislocation and dispersive carbides in temper troostite improve the comprehensive mechanical properties and resistance of micro-plastic deformation, reduce internal friction, make the creep and hysteresis decrease, and anelasticity better. The vacancies are very few in high-temperature tempering microstructures,so that the creep resistance improves and creep is very little. Dislocation cell boundaries and these random dislocations at the borders disappear and new block or sheet restoring structures appear because of the emergence of the tempered sorbite that is composed of equiaxed ferrite and small rod-like carbide distribution in the ferrite matrix,so that internal friction and hysteresis increases, anelasticity breaks up.The lower bainite after isothermal quenching has the best over-all mechanical properties.Residual austenite content is less than 0.5%, and elastic limit and resistance of micro-plastic deformation are very high. There is a certain degree of residual compressive stress, so that creep and spring element lag are very small, anelasticity is the best. The mechanical properties are better after sub-crucial quenching. But the microstructures contain a small amount of ferrite, so that the creep and hysteresis increase, anelasticity is worse. After high-temperature quenching, the grains growth coarsing, and dislocation pileup near the grain boundary cause a larger stress concentration,so the plasticity reduces.When loading coarse grain and carbide are prone to induce moving dislocations and produce larger internal stress. So that internal friction, creep and hysteresis increase, anelasticity is poor.ANSYS analysis results show that elastic body with transition arc has a small strain gradient.The stress and strain distribute uniform in workspace of spring element, and the maximum strain is in the working area.The maximum stress and strain are in line with the design requirement. With different loads,strain and lag test results are consistent.