An important parameter that needs to be calculated is the peak temperature reached at any point in the material during welding. The cooling rate from this peak temperature will deter­mine the metallurgical transformations likely to take place in the HAZ.

is given by equation (1) where

Tp = the peak or max. temp. °C, at a distance Ymm from the weld fusion boundary (this eq. doesnot apply for temps. within the weld metal) t = plate thickness T0 = initial plate temperature °C Tm = melting temperature of base metal pc = 0.0044 Uses of this equation

1. Determining peak temperature in specific locations in HAZ.

2. Estimating width of HAZ.

3. Effect of preheat on width of HAZ.

Example 1. A single full penetration weld pass is made on steel using the following parameters:

E = 20 V, I = 200 A, v = 5 mm/s, T0 = 25°C, Tm = 1510°C

pC = 0.0044 J/mm3.°C, t = 5 mm, f1 = 0.9 Hnet = 720 J/mm.

Calculate the peak temperatures at distances of 1.5 and 3.0 mm from the weld fusion boundary.

(i) At Y _ 1.5 mm.

1 _ 4.13 (0.0044) 5(1.5) 1

Tp - 25 _ 720 1510 - 25

Tp _ 1184°C. Note that at Y _ 0, Tp = Tm.

(ii) At Y_ 3.0 mm

1 _ 4.13 (.0044) 5(3) 1

Tp - 25 _ 720 1510 - 25

TP _ 976°C.