“Bang.” “Bang.” “Turn.” “Brush.” Apparently that’s how steel gets made, or got made in World War II, with two men pounding it, one positioning it, and one more readying it for the next step. And a lot of steel gets made in Operation Crucible, Kieran Knowles’s vigorous retelling of the Sheffield Blitz, a 1940 calamity in the South Yorkshire town. Part-documentary, part-character study, and all-teamwork, this four-man entry into 59E59’s Brits Off Broadway series is energetic and affecting, and a little disorganized.