steel

For those more knowledgeable of the history of metallurgy, at what points in time could the Siemens-Martin process and the Open Hearth Furnace design have been invented before the time it was in OTL?

THE UNBROKEN REED: INTRODUCTION Flowers spring along songs in Mexico and Tlatelolco, in the hearts of warriors and wise men. We know it is true that we must perish, for we are mortal men. You, our Blessed Progenitor, you have ordained it. We follow your command, and work these blessings...