WIDTH OF HEAT AFFECTED ZONE

For this calculation the outer extremity of the HAZ must be clearly identified with a specific peak temperature. For example for most carbon or alloy steels, there is a distinct etching boundary (as observed on polished and etched weld cross-section), corresponding to a peak temperature of 730°C.

Now the problem reduces to the determination of the distance YZ at which Tp _ 730°C. 1 _ 4.13(0.0044)5 YZ 1

730 - 25 _ 720 + 1510 - 25

Yz _ 5.9 mm

Thus a region 5.9 mm wide, adjacent to the fusion boundary will be structurally changed,

i. e., it may be affected by the heat of welding.

If the steel plate is preheated to 200°C, its effect will be to widen the HAZ width. This plate was tempered at 430°C. Any temp. above this 430°C will modify its property. Now TP becomes 430°

1 _ 4.13 (0.0044) (5) YZ 1

430 - 200 _ 720 1510 - 200

Yz _ 28.4 mm.

Without preheat this width would be

1 _ 4.13 (0.0044) (5) YZ 1

(430 - 25) _ 720 + 1510 - 25 _ 14-2 mm Ans

Thus preheating has doubled the width of HAZ.

Finally if the net energy input is increased 50% to x 1.5 x 720 _ 1080 J/mm 1 _ 4.13 (0.0044) (5) YZ 1

430 - 25 _ 1080 1510 - 25

YZ _ 21.3 mm. Ans.

The weld width is also increased by 50%.