Cooling Rates in Stainless Steel Welds

Abstract

A study has been made of the effects of manual weld heat input and plate thickness on the cooling rates at the bond of various weld beads which were deposited on a chromium-nickel stainless steel type 304 with a E347 stainless steel covered electrode of 4 mm diameter.
Cooling rate was determined from weld thermal curves which were measured at the weld bond with specimens either of uniform thichkness or of tapered thickness along the weld line.
The result is summarized as follows;
1) With regards to the two kinds of conventional parameters of weld heat input, I/V and I/√V where I is welding current and V is welding speed, the parameter I/V proved to be more useful for correlation of cooling rates, while I/√V more favourable for cross sectional area of weld bead.
2) The cooling rate in bead welding on stainless steel increased rapidly as the bead length became shorter than about 30 mm.
3) The effects of temperature concerned (T), preheating temperatute (T₀), welding current (I), welding speed (V) and plate thickness (t) on the cooling rate at the bond of a bead weld were found to be satisfactorily correlated by an empirical parameter P,
P=( T-T₀/ I/V )^1.6(1+ 2/π arctan t-t₀/α), (t₀ and a are constant) and the cooling rate CR (°C/sec)=0.20×P^0.85, which may be approximated by a simpler relation, CR=0.067P.
4) The cooling rate in the first layer deposited in a double-Vee groove weld was found to be practically identical to that in a long bead which was welded on the same thickness with the same welding condition. However, the cooling rate in a single Vee groove weld was smaller.
5) As the plate thickness was increased, the cooling rate was saturated to a constant value. The plate thickness of saturation is about 17mm in stainless steel for welding current 90 to 140 A, arc voltage 20 to 22V and welding speed 6 to 8 ipm, although it is about 24mm in carbon steel for a standard welding condition of welding current 170A, arc voltage 24V and welding speed 6ipm.