THE EFFECTS OF VARIATIONS IN HEAT TREATMENT ON THE STRENGTH AND TOUGHNESS OF RAIL STEEL

Because of the growing number of incidents due to rail failures, research is being made into possible improvements. The AAR and Carnegie-Mellon University have jointly sponsored a research programme into the possiblity of improving rail strength (which determines what axle load can be supported without any permanent rail deformation), and toughness (defined as the measure of the steel's resistance to brittle fracture or the slowness with which a defect spreads) by simply altering the heat treatment conditions (rolling or austenization temperature, isothermal transformation temperature or cooling rate). The general tendencies of the phenomenon have been determined. Strength and hardness are unaffected by austenization temperatures between 1470 degrees F and 1830 degrees F but toughness decreases. Resistance increases as isothermal transformation temperature rises (between 1010 degrees F and 1155 degrees F and toughness would reach its maximum at about the lowest temperatures tested). This unfinished study should make it possible to decide whether the improvements that can thus be obtained are adequate for justifying a transformation of the heat treatment process or whether this line of research is pointless.