Locking phenomenon of fasteners

2015-11-26

Fastener users often reflect: why the stainless steel fasteners sometimes have the problem of locking, and the use of carbon steel fasteners does not often occur when similar phenomenon, is not a stainless steel fasteners material more soft, carbon steel fasteners relatively hard reason? Youre right Stainless steel and carbon steel are essentially different. Stainless steel has a good ductility, but its hardness and carbon steel has a certain gap. Austenitic stainless steel grade 316 head and A4-80 of the hardness can actually reach the equivalent of 8.8 grade of carbon steel hardness. However, this argument can only be said to be half. Thread (Galling) is often used in stainless steel, aluminum alloy and titanium alloy fasteners, these types of metal alloy itself has rust, will be damaged in the surface, the metal surface to produce a thin layer of oxide (austenitic stainless steel, is the oxidation of chromium) to prevent further and deeper corrosion. When stainless steel fastening piece is locked, the thread produced by pressure and heat will destroy and wiped out during the chromium oxide layer and the metal thread directly blocking / shear, and thus the occurrence of adhesion phenomenon occurs. When the adhesion phenomenon persists (usually less than a circle of complete tooth diameter), will make the stainless steel fastening parts fully locked, again can not be dismounted or lock.