Does the manufacturing route for steel affect its elevated temperature strength?
A. Yes. Any process that raises the strength of steel by a mechanical or heat treatment process will result in a greater loss in strength in proportion to hot rolled structural steels. For example, reinforcing steel achieves much of its strength by cold working at ambient temperature. Under fire conditions stress relieving occurs at temperatures above 400°C, which results in a more rapid loss in strength. High strength bolts (Strength grades 8.8 and 10.9) achieve much of their strength by a quench and temper process. Bolts are quenched from around 850°C and this creates an extremely hard but brittle structure. They are then subsequently tempered between 475°C to 600°C to restore some ductility but with a measured loss in strength. If these temperatures are then exceeded during a fire the bolts over temper with a resulting sharp drop in strength. Further information is given in the publication available from Sirius Fire Safety Consultants ‘The behaviour of high strength bolts at elevate
