| Pearlite heat-resistant steel is often used to manufacture boiler and steam turbine in 350℃to 550℃high temperature of the equipment, but many exterior pipes is made by austenitic stainless steel. So it inevitably involve in welding problems about the two different kinds of steel. Practice shows that, when the two kinds of steel welding joint in process of welding and after service in high temperature, carbon element can thread fusion welding area to diffuse from heat resistant steel to stainless steel and form carbon migration. Because of decarburization layer and carburet layer, in heat resistant steel side form softening area but in stainless steel side form sclerosis area. In high temperature hot fatigue load can cause joint fracture and can be influenced the safety in production.The paper in allusion to fusion area will form carbon migration layer have obvious difference because of weld seam on both sides of the metal and alloy composition. According to electronic microscope we analysis the real elements in the welding fusion and find out the specific position relations between carburet layer to decarburization layer. It explained the changes of microscopic structure perpendicular to bond line. According to the measuring of the carbon and alloy element chemical composition, we calculated original chemical a gradient from the weld bead and make quantitative analysis stainless steel and heat-resistant steel dissimilar steel welding carbon migration process in theory. The experiment used thermodynamics fick's law that converted actual carbon concentration to effective carbon concentration and calculated the diffusion process. It deduces carbon diffusion theory formula for stainless steel and heat resistant steel heterogeneous steel welding. The experiment made new electrode and analysis component perpendicular to bond line. According to the carbon diffusion theory formula we draw the theory curve and contrast to the actual carbon diffusion curve. It further proves the influence of the four elements C, Cr, Mo, Ni for carbon diffusion of stainless steel and heat resistant steel dissimilar welding. We try to quantitative explain the carbon diffusion phenomenon and according to results used for welding materials development and formulate welding procedure.The conclusion show that austenitic stainless steel and pearlite heat-resisting steel in heterogeneous steel welding is the presence of carbon migration layer (carburet layer and decarburization layer). The decarburization layer located close to heat-resistant steel and close to carburet layer. According to the effective carbon concentration deduced, theoretical curve and measured curve is basically same. It can be more accurate simulation out the biggest carbon content and minimum carbon content of carbon migration. The new heat resistant steel electrode and stainless steel electrode further proves that the accuracy of the theoretical formula. Cr is the most important influence factors for stainless steel and heat-resisting steel in heterogeneous steel carbon diffusion. C, Ni and Mo are weaker. |
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