I have a need to design a custom wrench for my company's assembly line. My first prototype was made from 4140 steel, hardened to RC 50-53 and black oxide coated. I thought for sure this would be strong enough as it the same material we use for other custom wrenches. However due to the high torque load on this wrench (220 ft-lbs), it broke after just 3 uses. See attached picture. Unfortunately, due to the size constraints of the product, I cannot significantly change the geometry of the wrench in order to help with strain relief. Anyone have any suggestions of another material that may be more durable for this application? Obviously we want to keep the cost to produce relatively low as well.