Residual mechanical properties of high strength steel bolts subjected to heating-cooling cycle

This paper presents results from experimental studies on residual mechanical properties of Grade 8.8 bolts exposed to elevated temperatures. The residual mechanical properties including stress-strain response, elastic modulus, yield and ultimate strengths, as well as failure modes of bolts are evaluated after exposure to various target temperatures. The effect of temperature level, chemical composition of feedstock steels and heat treatment characteristics in production process of Grade 8.8 bolts on residual mechanical properties is studied. Data from the tests indicate that bolts experience rapid reduction in residual strength when heated to temperatures beyond 400 °C and reaches to 50% of ultimate strength after exposure to 800 °C. Apart from temperature amount of carbon content in steel and tempering temperature in bolt production process significantly influence residual properties of Grade 8.8 bolts. Data from the tests is utilized to propose a set of predictive equations for evaluating temperature dependent residual mechanical properties of Grade 8.8 bolts.