Q: I have come across an unusual defect several times in various places I have worked. It has appeared in upset forgings and also in forgings produced at slow speeds on hydraulic presses. The defect size is about 2 to 3 in. in a round or hex upset . The material, in most cases, is 1045 or 4140 steel, forged at recommended forging temperatures. Do you have any ideas as to what may cause such a defect?
A: I have seen these types of transverse defects in headed or upset forgings from stainless alloys, but not in 4140 or carbon steel. In one case with 17-PH stain less, the upset ratio was close to the maximum and a small percentage of parts cracked in the central part of the head much like that shown in your example. It was eventually proven to be somewhat of a shear crack where the shearing action took place in the upsetter.
A punch- in-die alignment system was being used. For the perform blows, the preformed cones were out of line by about 1/16 in. The lateral shearing action that occurred when the rugged finish die pulled the out of line preform back into alignment seemed to be the culprit in that case. Once the upset ratio was reduced and the tool alignment was corrected for the first two blows, the problem was resolved. You may be seeing the results of a similar problem.
For more than 40 years H. James Henning held key technical positions in the forging industry, including as director of technology for the Forging Industry Association, and as president of Henning Education Services, a Columbus, OH, firm specializing in customized education and training in forging technologies.
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