As memo serves the BR42 steam locomotive was a more powerful variant of the BR52 war one ( Kriegslokomotive ), by combining the boiler of heavy BR44 machine with the chassis of the very universal BR52. The boiler of the new locomotive differed from the original with slightly shortened fire tubes, thanks to which the locomotive had a lower axle load required when operating lines with poor surface. Also I have read that the BR42 locomotive had a steram boiler of very poor quality steel. It couldn't be patched by welding becuase stresses around the welds caused cracks. It led to the explosion of the boiler in two cases what, among other defects, resulted in withdrawing of the BR42 from the DB railway very quickly and replaced with the BR52.
The BR42 steam locomotives were produced by the Esslingen, Schwartzkopf, WLF, Floridsdorf factories and the Schichau Werke in Elbląg ( in German - Elbing ) in cooperation with the Cegielski plant in Poznań.
After the war the BR52 was marked as the Ty2/Ty42 and the BR42 as Ty3/Ty43 here in Poland. The Ciegielski factory and Fablok plant in Chrzanów continued their assembling for a couple of years. Initially they used the German abandoned parts from the Schichau Werke in Elbląg and then, in 1948, started the own production of subsequent steam locomotives of the 42 series.