Residual mechanical properties of high-strength steel bolts after exposure to elevated temperature

This paper presents results from experimental studies on residual mechanical properties of Grade 10.9 bolts exposed to elevated temperatures. The effects of various target temperatures on the residual mechanical properties, including ultimate and yield strengths, stressstrain response, and the failure modes of bolts, were investigated. Furthermore, the influence of temperature level, chemical composition of feedstock steels, and heat treatment parameters in the fabrication process of Grade 10.9 bolts on residual mechanical properties was studied. Data from the experiments indicate quick reduction in residual strength of the bolts when heated up to temperatures greater than 400°C, reaching to 50% of its ultimate strength when exposure temperature reaches 800°C. Tempering the temperature in the bolt manufacturing process and carbon content in steel are two other important factors besides exposure temperature that have a great influence on residual properties of Grade 10.9 bolts. Based on the experimental results, a set of predictive equations is also proposed for assessing the temperaturedependent residual mechanical properties in Grade 10.9 bolts.