I answered a similar question here a while back.
/u/alriclofgar answered [a related question] (https://www.reddit.com/r/AskHistorians/comments/98akpu/were_there_differences_in_the_quality_of/e4kl6lw/) a few weeks ago regarding the quality of metal during and after the Roman Empire. It doesn't directly answer your question but you may be able to draw useful inferences from it.