Ah... my first reply lol. Albeit, very late on this thread, but in case the OP hasn't figured it out, I'm happy to lend some expertise here. This is 100% textbook manmade slag. There are expanding gas bubbles in your sample, the scratch test is correct for slag and the overall appearance is that of slag as well. Shiny, heavy, magnetic in spots, different streak colors, bubbles... all conclusive that this is slag. Cheers ?
ps - here is a great link on meteorwrongs, many of which are different examples of slag. https://sites.wustl.edu/meteoritesite/items/meteorwrongs/