Complex sentence: These'cops' are converted into bars by exposure for several hours to a charcoal fire not hot enough to melt them: they are then turned over before the blast, and thus the too highly carburised steel is oxidised.
Split into simpler sentences: These'cops' are converted into bars by exposure for several hours to a charcoal fire not hot enough to melt them. They are then turned over before the blast, and thus the too highly carburised steel is oxidised.