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class rules to ensure the suitability of the welding
consumables for the extra-high notch toughness steels
classified as E-grade of mild steel and EH-grade of high
strength steel (EH32, EH36). E- and EH-grade steels are
used for the more important parts of a ship's hull, such
as stress-concentrating corners, to ensure the resistance
of the hull against brittle fracture during a voyage.
The Use of Proper Amperage and Voltage is Essential With CO2 gas shielding, DW-55E offers glossy bead appearance with fine ripples, negligible spatter losses and self-peeling slag removal in uses over a broad range of welding currents as shown in Fig. 3 in all-position welding with single pass and multiple passes.
Heat Input is a Key Factor in Quality Control of Welds Heat input (HI = A x V x 60/S where A is for welding current; V is for arc voltage; and S is for travel speed) is a predominant factor particularly in control of impact toughness of welds. Table 2 shows recommended heat input for DW-55E in all-position welding. The minimum heat input is to control hardness (Hv: 280 max) of the weld metal, while the maximum heat input is to ensure impact notch toughness of the weld metal.
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Travel Speeds Determine Fillet Leg Lengths In quality control of fillet welds, control of leg length is essential, provided the fillet weld has no excessive concavity. Figure 4 shows how travel speed determines leg length of fillet welds in use of DW-55E.
Low Ambient Temperatures and Thick Base Metals Require Preheating Mild steel and 490N/mm2-class high strength steel have quite good weldability and DW-55E weld metals contain diffusible hydrogen as low as Grade H10 01 the ship-class requirement (0.10ml/g max). However cold cracking can occur in the welds when the ambien temperature is low and the base metal is thick Therefore, preheating the base metal by 30-150°C (an exact temperature depends on the metal temperature and plate thickness) is recommended in order to prevent cold cracking in the welds. Where the surrounding temperature exceeds 5°C and plate thickness is 25mm or less, no preheating is needed. |