Research On Weldability Of Dissimilar Joint Of Austenitic Stainless Steel And Low Alloy Steel

With the development of science and technology, dissimilar material welding iswidely used in the modern industry. In the coal-fired power plant thermal system, as theincreasing of the power generation’s unit capacity and parameters, power station boilerheating surface parts where working temperature above580℃mostly used chromiumnickel austenite stainless steel with great oxidation resistance and creep resistance. And thecomponents where working temperature below580℃still use chrome-molybdenum lowalloy heat resistant steel for economic reason. Because the different between austenitestainless steel and low alloy heat resistant steel in chemical composition, structure,physical properties and mechanical properties. The mechanical performance and servicelife of dissimilar joint will be reduced under the long-term and high temperature service.Carbon diffuses from low alloy steel to stainless steel which called “uphill diffusion”isone of the most important reasons for high temperature failure of dissimilar joint.The experimentation use12Cr1MoV low alloy heat resistant steel as base metal, useA102austenitic stainless steel electrode as welding material for overlaying. In order toresearch how the different high temperature aging time affect the carbon diffusion andmicrostructure of dissimilar joint. Simulate the working environment of dissimilar joint.After high temperature aging treatment of dissimilar joint at welding state,500℃/5h,500℃/50h,500℃/100h and observing the changes of carbon diffusion, microstructure andmicrohardness on dissimilar joint. And with A102electrode for standard, adding suitableamount of carbon and silicon to the Stainless steel weld joint, aging at similar time,measuring the carbon content distribution of dissimilar joint. Observe the influence oncarbon diffusion of dissimilar joint by carbon and silicon.The results of experiment show that: on welding state, recrystallization zone of basemetal forming block ferrite and acicular ferrite structure with high stability. Hightemperature aging did not have affect on these structures. The coarse grained HAZ formingupper bainite and granular bainite structure with carbon supersaturated, and thesestructures degraded after High temperature aging. Transforming tempered sorbite with strip cementite that distributed irregularity. Along with the increasing time of hightemperature aging, the amount of carbon diffused from low alloy steel to stainless steelincreased, the microhardness of the stainless steel where near the fusion line increased, butthe microhardness of Low alloy steel reduced. Adding carbon element to weld joint caninhibit carbon diffusion of dissimilar joint. But the effect is unconspicuously, and the widthof recarburization zone increasing. Adding silicon element to weld joint can inhibit carbondiffusion effectively, and did not appeared recarburization zone after500℃/100h hightemperature aging treatment.