Study On Microstructure And Properties Of Dissimilar Weld Joint Between TP310H And T22 Stainless Steel

With decreasing energy supply and increasing environmental awareness in recent years, higher requirements for power station technology have been made at home and abroad. Superheater is one of the most important parts of power station boiler. Because steam temperature is different in each section of heating surfaces, they shall be fabricated with various steels with different chemical composition and microstructure properties. In economic view, welding of TP310H/T22 dissimilar steels appears in outlet transition section of superheater and reheater for power station boiler at home and abroad, especially designed and manufactured according to ASME Code. Because TP310H and T22 have different physical properties and chemical composition, their welded joints would be subject to some complicated changes in microstructure and properties, which, however, is not much studied. Now we believe, Study on Microstructure and Properties of Dissimilar Weld Joint Between TP310H and T22 Stainless Steel under different filling materials is of great significance, because based on it, welding procedures can be reasonably made to provide critical basic data and theoretical basis for obtaining good welded joints with overall performance, besides it has practical significance to ensure safe operation of the boiler.As well as welding characteristics of T22 ferritic heat-resistant steel and TP310H austenitic stainless steel are concerned, dissimilar steels are GTAW welded hereby, with ER309L, ER309LMo and ER310 as austenitic stainless steel wire, and ERNiCr-3 and ERNiCrMo-3 as filler material. Welding parameters will be optimizated based on lots of welding simulation tests. After welding, what effects the different filling materials have on microstructure, composition analysis, phase structure and mechanical properties of TP310H/T22 dissimilar welded joint will be studied with comprehensive application of metallurgical microscope, scanning electron microscopy, energy spectroscopy and X-ray diffraction and test of mechanical properties at room temperature.Three kinds of austenitic filler materials each have a transition layer at T22-WM interface, among which, ER310 has a transition layer with the smallest width, yet nickel-based filler material has no layer. The ferrite content in weld metal is in direct proportion to equivalent of chromium-nickel in filler material and in inverse proportion to impact toughness. Austenite grain coarsening phenomenon is not very evident at TP310H-WM interface.Stretching and bending properties of welded joints can satisfy actual application. Tensile strength values of the joint are greater than minimum standard tensile strength of T22 steel, and the fracture is located in T22 raw material and tensile fracture is typically characteristized with ductile fracture. Meanwhile, face and back bending have no surface cracks at the weld and heat affected zone, and base metal is well fused at both sides, showing the joints with good plasticity. Shock values are nearly the same at both sides of heat-affected zone and their trends are similar to each other. However, impact toughness is different for different weld metals, whose order is:ER310>ER309L> ER309LMo>ERNiCr-3>ERNiCrMo-3. The result shows that impact fracture of the welding metal belongs to toughness fracture. By contrast, ER310 filler material has the best toughness. From fusion zone to the side of T22 raw material, overheated zone rises sharply, and the hardness near fusion line is rather high, the most up to 295HV. With the distance from fusion line increasing, the hardness decreases and gradually approaches to hardness of base metal. The microhardness of TP310-side heat-affected zone has a little change, close to that of base metal. The order of weld zone hardness in this 5 kinds of filling materials is ERNiCrMo-3>ER309LMo>ERNiCr-3> ER309L>ER310.Above all, according to the study on microstructure and properties of dissimilar weld joint between TP310H and T22 stainless steel under different filling materials, the comprehensive performances of ERNiCr-3 soldering wire is the best.