1958 Volume 27 Issue 12 Pages 716-722
It is the purpose of a series of reports to propose the method predicting the cooling time from 800°C to 500°C near fusion line, through a simple procedure from welding conditions for the various usual welding processes. In this report, first, the shape of cooling curve, the nature of cooling rate and cooling time were described. Furthermore, effects of kinds of covered electrode and electric current on the cooling time were observed. The main results are as follows :
1. The theoritical formulas for the temperature distribution and the cooling rate (R) near fusion line of base steels were summarized.
2. The cooling rate R can be expressed generally by the following formula,
R=dT/dS=-k(T-TM0)n, k : Const.
The value of n is about 1.2 for the specimen used to obtain the C-C-T diagram and about 1.8 for the neighbourhood of fusion line by welding.
3. For the prediction of the microstructure and hardness in the heat-affected zone near fusion line from the C-C-T diagram, the use of cooling time from 800°C to 500°C is more reasonable than the use of cooling rate.
4. The cooling time is nearly equal on different portions in the neighbourhood of fusion line, and if the welding conditions are decided, the cooling time near fusion line can be estimated.
5. When the cooling time from 800°C to 500°C is presented as a function of the arc energy per unit bead length, namely, J= 60EI/v Joule/cm, the relation between the cooling time and J is not changed approximately by kinds of covered eledtrode.
6. The cooling time in case of use of direct current is slightly larger than that of alternate current, for the same value of J=60EI/v.
