Reynolds 853 is a low-carbon steel alloy containing manganese, chromium, molybdenum, copper and silicon. 853 tubes are manufactured in very thin wall thicknesses, like 0.5 mm to 0.4 mm. They are weldable by conventional tungsten-inert-gas (TIG) welding and gas-metal-arc-welding (GMAW). Tubes are seamless (no joints) and cold worked to increase the tensile strength by work-hardening. Reynolds 853 tubes are also available in the quenched and tempered condition.
The resistance to bending of a steel tube is a function of the Ultimate Tensile Strength (UTS) and the geometry of the tube (diameter, wall thickness and ovality).
There is only so much that the tube manufacturer can do to reduce fatigue cracking. Fatigue resistance of steel bicycle frames is a function of the quality control exercised during frame manufacture, in particular elimination of any sharp corners or notches that act as stress raisers, careful blending of welds, and double-butting of tubes so that extra thickness is provided at the joints where it is needed most. Reynolds 853 tubes are double-butted.
The chemical composition of Reynolds 853 is fine-tuned to the rapid thermal cycle of TIG welding to produce an austenite to bainite phase transformation in the heat-affected zone (HAZ) upon cooling between 800
oC to 400
oC. This ability to air-harden in the HAZ gives frame builders an economic advantage, and removes the need for any subsequent heat treatment.
Here is a chart taken from Reynolds website comparing the mechanical properties of their products. Notice that the stiffness (Young's Modulus) of steel alloys are all the same. That is because Young's Modulus is determined by the iron content and not by the alloying elements or the heat treatment.
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