Maybe pictures would help wink

Sulfide and Manganese Sulfide inclusions
https://books.google.com/books?id=rsdbs92yGs4C&pg=PA103&lpg

Manganese sulfide inclusions as fatigue initiation sites
http://www.chalcogen.ro/367_Sohaciu.pdf
Long but interesting failure analysis not unlike the metallurgical study performed for me by METL on the Remington 1894 barrel burst.