Abstract
In case of manual arc welding carbon steels or high tensile steels (low alloy steels) with covered electrodes, the cooling time (S sec.) from 800°C to 500°C near fusion line can be calculated by the following experimental formula,
S=1.35(60EI/υ)1.5/β(600-T0)2{1+2/π tan-1(t-1.46/6)}
where, E: arc voltage, Volt
I: welding current, Amp.
υ: proceeding rate of bead, cm/min.
T0: preheating temperature in case of local heating by a flame, °C
t: plate thickness, mm
β: constant{
1 for bead on a plate or final layer of butt joint,
2 for T-fillet joint.
Namely, the cooling time is determined mainly by arc energy per unit bead length J=60EI/υ, preheating temperature T0 and plate thickness t. The other variables, that is, kinds of steel and covered electrode, kind of welding current, AC or DC, and others, have only small effects on the cooling time and it is considered that deviations of measured points from the mean line decided by the above mentioned main factors are due to these small effects. The above formula is applicable at the center parts of a bead, when the bead length and plate width are comparatively larger.
Next, according to the formula, a very convenient nomograph which is used practically was constructed.
