The cap screw/hex head question is answered in the article table. Grade 8 (best shown hex) is medium carbon material. Socket head cap screw is listed as high carbon. This translates into a higher Rockwell hardness and higher yield strength.
The process for manufacturing is very similar for all the bolts. hex or socket head.
Steel in the form of a coil of round stock is drawn through a die to achieve a close tolerance diameter. Then the shape is cold headed ( basically like a cold forging) into a die. The material starts cold, but gets extremely hot (but not red hot) during the forming process. Yes, the granules get shaped and aligned to add strength. During this forming process, the head is also formed, both on socket head and hex head bolts. Even in the hex head, there are two variations, formed and trimmed. The formed ones are the ones with a tapered hex that your wrench slips off of so easily. The ones that are better to wrench on have a straight hex that is trimmed after forming. Then the threads are roll formed between two dies. After that, the bolts are heat treated in a carburized atmosphere to prevent decarburization (weakening) of the threaded area. The critcal strength point dimensionally is the radius under the bolt head. My first quality control job was in a boltmaking plant 35 years ago. Not much boltmaking in the USA now. Mostly CHINA.
