Abstract
The effects of V on the disbonding characteristics of the 2 1/4Cr-1Mo steels overlayed by austenitic stainless steel were metallurgically studied. The addition of V to the 2 1/4Cr-1Mo steels significantly increases the resistance to disbonding. The scanning transmission electron microscope and energy-dispersive X-ray spectrometer observation showed that the V-modified and ordinary 2 1/4Cr-1Mo steels had different fine precipitates in terms of morphology, distribution and composition. The analyses of hydrogen diffusion and hydrogen evolution indicate that the fine precipitates in the V-modified steels trap hydrogen to increase the solubility of hydrogen and also decrease the diffusion of hydrogen. A theoretical calculation of hydrogen distribution during cooling from the atmosphere of elevated temperature and high pressure hydrogen indicates that both diffusion and solubility of hydrogen in the base metal affect the concentration of hydrogen at the interface between the base metal and the stainless steel overlay. It is concluded that the fine precipitates in the V-modified 2 1/4Cr-1Mo steel increase the resistance to disbonding by reducing the concentration of hydrogen at the interface during cooling.
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