HEAT FLOW EQUATIONS—A PRACTICAL APPLICATION

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.

л/2ne pcty

1

1

...(1)

(Tp T0) - t-‘net

where e = base of natural logarithm = 2.71828128

Thus 42кЄ = V2 x 3.14 x 2.71821828 = 4.13.

pc = 0.0044.

Peak Temperature (Tp)

Peak temperature equation. For a single pass full penetration butt weld in sheet or plate. Peak temperature in the base metal adjacent to the weld Tp in HAZ region

Tm T0

4.13 p CtY

Htief

1

1

...(2)

Tp - T0

Tm T0

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.

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