Studies of Cooling Processes in the Cases of Welding with Coated Electrode and Submerged Arc Welding

Studies of Cooling Processes in Various Arc Welding (Report 1)

Abstract

Cooling time, which has an immediate connection with root cracking in a high strength steel weld with its strength level of 60 kg/mm² and below, from 800 to 300°C was measured for various welding conditions in the cases of welding with coated electrodes and submerged are welding, respectively. Experimental formulas for the estimation of the cooling time were obtained and these nomographs were shown.
The main conclusions are summarized as follows:
(1) Dimensions of heat flow in a weld were varied by any particular combination of welding condition, plate thickness and the shape of penetration.
For the cooling process with two-or three-dimensional heat conduction in a weld, a relation between temperature T on a weld and cooling rate (dT/dS) as the temperature T is shown as follows :(dT/ds)_T∞(T-T₀)ⁿ
where T0: initial temperature of plate
n: the exponent which is varied with dimensions of heat flow in a weld
Hence, the dimensions of heat flow was clearly shown as the gradient of a line in a logarithmic groph of (dT/dS) VS. (-T-T₀).
(2) In a finite plate, it was able to determine a minimum size of specimen, which is equivalent to an infinite plate for the given weld heat input, according to the temperature range of a weld thermal cycle to be considered. When they consider the cooling process to 500 and 300°C, the Value of T in the following formula should be chosen as, T^*≤320 for 500°C and T^*≤210 for. 300°C, respectively.
Where T^*=0.24ηJl/mc+T₀(°C)
η: thermal efficiency of arc, j: heat input (Joule/cm)
l: bead length (cm), m: weight of plate (gr) and
c: specific heat (Cal/gr.°C)
(3) If thickness (t), initial temperature (T₀) of plates and weld heat imput (J) are given in the case of single bead-welding, cooling time (s) from 800 to 300°C at manual arc welding and submerged arc welding can be estimated with the following experimental formula or nomographs by the present authors;
S=K·Jⁿ/(40-T₀)²{1+2/πtan^-1(t-t₀/a)}