A 2400 cals power source is used to weld thick plates of SAE

A 2400 cal/s power source is used to weld thick plates of SAE 4140 steel. The centerline hardness on the top surface should be less than 50 Rc. Estimate the critical welding speed which will just satisfy this requirement? (based on the hardenability curves given below, assuming that the metal thermal conductivity is 30 W/mK) Is this critical speed a maximum or minimum speed limit? Explain. In general, what effect would preheating the weld plates have on the amount of martensite formed in the heat affected zone when welding a steel alloy with very high hardenability? Provide an equation and use it to explain your answer.

Solution

The given speed is critical speed while the at this speed the value is maximum possible value of attained after the long decrement.