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The effect of using a higher niobium content on the CGHAZ Charpy Toughness at different test temperatures and different cooling rates.
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The data confirms the significantly greater flexibility and tolerance to increased heat input of the higher niobium steel over the full range of practically relevant cooling rates. A heat input of 10 kJ/cm, as might be encountered in Gas Metal Arc Girth Welding (GMAW), of thick-walled pipe >20mm wall thickness would result in a t (800-500) of <5 secs whilst pipe mill multi arc submerged arc welding on the same material might have a heat input in the range 40 to 50 kJ/cm resulting in a t (800-500) in the range 50 to 90 secs.
Example 1: 1,219 mm diameter, 23.7 mm thick pipes, produced with ArcelorMittal X70 steel using niobium content above 0.08%.
Both welds SAWH and GMAW presented excellent properties.