High strength bolt has bainite structure produced by austempering which extends across whole cross-section of the bolt and increases its tensile strength

摘要

High strength bolt (2) has a bainite structure produced by austempering. This extends across the whole cross-section of the bolt and gives it a tensile strength of at least 1400 N/mm 2>. Independent claims are included for: (A) bolted joints comprising the bolt and components (3, 4) held together by it; (B) a method of making the bolt comprising austempering to produce the desired bainite structure; and (C) a method for assembling the bolted joint in which the bolt is first tightened above its elastic limit, producing an increased elastic limit, and then tightening to this new elastic limit.