Thermomechanical processing (TMP) involves both thermal and mechanical treatments that define both product shape and microstructure/properties. Since the industrial revolution, machines of augmented power, size and precision have given rise to TMP that challenged explanation of the crystal mechanisms. In wrought iron, lamellar ferrite exhibited high transverse crack resistance due to fine slag stringers that as flux facilitated welding of puddled bars in forging of shafts or rolling of plates for bell-welding into pressure tight pipes; the substructure developed in the iron as working continued below 900°C strengthened it. Patenting of high C steel wire led to an optimum cold-drawn structure for outstanding strength and toughness. Hot forming technology, combined with the refining potential for austenite decomposition gave rise to controlled rolling for enhanced ferrite nucleation, ausforming to refine martensite and intercritical rolling to deform the ferrite or to spheroidize the carbides. Cold rolling and annealing have been scheduled to impart suitable strength, grain size, substructure and texture.