Re: Re: Welding Rod #'s

Posted by Gavin M on December 10, 2003 at 23:49:42 from (161.184.204.34):

In Reply to: Re: Welding Rod #'s posted by Jon on December 10, 2003 at 19:20:24:

Jon, A-36 is the most common structural grade of steel for plate and rolled shapes such as angle, channel, and wide flange. It is semi-obsolete in that most structural steel is produced to a CSA 44W chemistry, which is stronger with no compromises on ductility. 44W also meets A-36 specs. A-36 has a yield strength of 36 ksi min. and an ultimate tensile strength of 58ksi min./80 ksi max. A yield strength of 50ksi would imply a medium carbon steel or a low alloy steel, and this would require a specified heat treatment process in order to accomplish the required strength along with sufficient ductility to avoid cracking. Welding such steels requires careful pre & post weld heat treatment to avoid problems. I recently did a failure analysis on a low-alloy pintle hitch that had experienced a catastrophic failure; the towed air compressor separated completely from the towing truck & was destroyed. The failure was directly due to improper welding used to build up a worn area on the hitch. The weldment had underbead cracking from brittleness in the heat-affected zone. My understanding is that until recently, vehicle frames were made out of a cap or rim steel with very high ductility (to aid forming) and consequent lower yield strength. This makes a much more robust frame (for machinery) or unibody (for cars) than a high strength, thin, brittle frame section. With advances in robotics, it is now possible to heat-treat to high precision on an assembly line, so many manufacturers are building frames out of thinner, stronger steel, relying on the heat-treatment to provide adequate ductility. This saves a few pounds but sends many new cars & trucks to the scrap heap because of frames that are uneconomic to repair.

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• Re: Re: Re: Welding Rod #'s Jon 02:42:06 12/11/03 (0)

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