Hi Doug. You obviously have a very good knowledge of this subject and I hope you will not mind if I copy your piece for my records.
I have really only been concerned with making new items, mostly for production machinery and tooling. You assess the duty the piece should withstand, make the design that is the best effective compromise of all the conflicting requirements and then select the appropriate material.
I am always interested to see a failure, because it can tell much about the nature of the loadings that have eventually brought about the breakage, but actually I look to the replacement with modern materials as a new problem. Optimise the design, select the most suitable material, ensure heat treatment is correctly specified and carried out, test the results before final machining.
I was very heartened that you chose to cite 300M as an ultimate through hardening material. It is this exact material that, after considerable study, I chose to make replacement Scott long stroke cranks in 1997.
I send my sincere respect and kindest regards
Roger
