A comparative study on microstructure and mechanical properties near interface for dissimilar materials during conventional V-groove and narrow gap welding

The aim of the paper is to evaluate the local tensile and fracture toughness properties of the dissimilar metal weld joints between SA508Gr.3 Cl.1 and SA312 Type 304LN pipe. Weld joints have been prepared by manual gas tungsten arc welding (GTAW) process with conventional V-groove and automatic hot wire gas tungsten arc welding with narrow gap using different filler wires/electrode such as Inconel 82/Inconel 182 and ER309L/ER308L. The tensile and fracture toughness test specimens have been machined from different regions of dissimilar metal weld such as heat affected zones, fusion lines, buttering layer, weld metal and both base metals. Tensile and fracture toughness tests have been carried out as per the ASTM standard E8 and E1820 respectively. Tensile and fracture toughness results of all the regions of dissimilar metal weld joints have been discussed in this paper. Metallurgical and fracture surface examinations have also been reported to substantiate the tensile and fracture toughness results. Need for the local properties for integrity assessment of the dissimilar metal weld joints has also been brought out.

Experimental investigation of local tensile and fracture resistance behaviour of dissimilar metal weld joint: SA508 Gr.3 Cl.1 and SA312 Type 304LN

Two types of welded joints were prepared using low alloy carbon steel and austenitic stainless steel as base materials In one variety, buttering material and weld metal were Inconel 82 In another type, buttering material and weld metal were Inconel 182 In case of Inconel 82, method of welding was GTAW For Inconel 182, welding was done by SMAW technique For one set of each joints after buttering, stress relief annealing was done at ~923 K (650 °C) for 90 minutes before further joining with weld metal Microstructural investigation and sub-size in situ tensile testing in scanning electron microscope were carried out for buttered–welded and buttered–stress relieved–welded specimens Adjacent to fusion boundary, heat-affected zone of low alloy steel consisted of ferrite–pearlite phase combination Immediately after fusion boundary in low alloy steel side, there was increase in matrix grain size Same trend was observed in the region of austenitic stainless steel that was close to fusion boundary between weld metal-stainless steel Close to interface between low alloy steel-buttering material, the region contained martensite, Type-I boundary and Type-II boundary Peak hardness was obtained close to fusion boundary between low alloy steel and buttering material In this respect, a minimum hardness was observed within buttering material The peak hardness was shifted toward buttering material after stress relief annealing During tensile testing no deformation occurred within low alloy steel and failure was completely through buttering material Crack initiated near fusion boundary between low alloy steel-buttering material for welded specimens and the same shifted away from fusion boundary for stress relieved annealed specimens This observation was at par with the characteristics of microhardness profile In as welded condition, joints fabricated with Inconel 82 exhibited superior bond strength than the weld produced with Inconel 182 Stress relief annealing reduced the strength of transition joints and the reduction was maximum for specimen welded with Inconel 82

Effect of Stress Relief Annealing on Microstructure & Mechanical Properties of Welded Joints Between Low Alloy Carbon Steel and Stainless Steel

AbstractCracking, or disbonding, along the fusion boundary in dissimilar metal welds has been a persistent problem, particularly in applications where austenitic alloys are clad on to structural steels for corrosion protection. Many failures in dissimilar metal welds occur as a result of cracking along a boundary that runs parallel to the fusion boundary in the adjacent weld metal. A preliminary investigation was undertaken to determine the nature and evolution of boundaries and structure in dissimilar metal welds using a simple ternary system composed of a pure iron substrate and a 70Ni–30Cu (Monel) filler metal. Changes in base metal dilution were found to alter the evolution of boundaries and structures near the fusion boundary dramatically. Optical metallography and electron microanalysis reveal that the resulting weld microstructures and boundaries are similar to those observed in engineering materials used for cladding and corrosion resistant overlay. Transmission electron diffraction analysis revea...

A fundamental investigation of boundaries and structures in dissimilar metal welds

The progress of tensile deformation of cold rolled interstitial-free high-strength (IFHS) steel in the as-received and 10 pct tensile pre-strained conditions has been studied through testing of miniature sized specimens in scanning electron microscope. Strength and ductility of the steel obtained through insitu tests have been compared with the macro tensile test results. The insitu test results show that the yield strength and tensile strength of miniature sized specimens are less as compared to that of macro tensile test results. But, uniform strain in case of insitu tests is higher than that obtained in case of macro tensile specimens. The insitu tests reveal that intergranular cracking of surface grains and formation of both intergranular and transgranular voids precede the final ductile fracture. The areal density of voids is found to increase with increase of Von Mises equivalent plastic strain. Under pre-strained condition void nucleation strain of the steel is found to be lower as compared to the as-received condition.

Insitu investigation of tensile deformation behaviour of cold-rolled interstitial-free high-strength steel in scanning electron microscope

Low-alloy steel and 304LN austenitic stainless steel were welded using two types of buttering material, namely 309L stainless steel and IN 182. Weld metals were 308L stainless steel and IN 182, respectively, for two different joints. Cross-sectional microstructure of welded assemblies was investigated. Microhardness profile was determined perpendicular to fusion boundary. In situ tensile test was performed in scanning electron microscope keeping low-alloy steel-buttering material interface at the center of gage length. Adjacent to fusion boundary, low-alloy steel exhibited carbon-depleted region and coarsening of matrix grains. Between coarse grain and base material structure, low-alloy steel contained fine grain ferrite-pearlite aggregate. Adjacent to fusion boundary, buttering material consisted of Type-I and Type-II boundaries. Within buttering material close to fusion boundary, thin cluster of martensite was formed. Fusion boundary between buttering material-weld metal and weld metal-304LN stainless steel revealed unmixed zone. All joints failed within buttering material during in situ tensile testing. The fracture location was different for various joints with respect to fusion boundary, depending on variation in local microstructure. Highest bond strength with adequate ductility was obtained for the joint produced with 309L stainless steel-buttering material. High strength of this weld might be attributed to better extent of solid solution strengthening by alloying elements, diffused from low-alloy steel to buttering material.

Effect of Structural Heterogeneity on In Situ Deformation of Dissimilar Weld Between Ferritic and Austenitic Steel

Dissimilar material weld joints, consisting of low-alloy steel and 304LN austenitic stainless steel (SS), have critical application in boiling water reactors in the nuclear industry. It was predicted that phase transformation adjacent to the fusion boundary and stress distribution across the transition joint play a key role in the structural degeneration of these welds. Quantitatively, to evaluate their contribution, two different joints were considered. One was fabricated with buttering material 309L SS (M/S Mishra Dhatu Nigam Limited, Hyderabad, India), and the other was produced with buttering material IN182 (M/S Mishra Dhatu Nigam Limited, Hyderabad, India). Base materials remained the same for both. Thermomechanical simulation on dissimilar material welds was performed using finite-element modeling to predict the thermal effect and stress prone area. Temperature-dependent thermal and structural properties were considered for simulation. Simulation results were compared with microstructural characteristics, and data were obtained from the in-situ tensile test. Simulation results exhibited that stress was at maximum in the buttering material and made the zone weaker with respect to adjacent areas. During the validation of results, it was observed that failure occurred through buttering material and endorsed the inference. The variation in mechanical properties of the two welds was explained considering the effect of thermal state and stress distribution.

Three-Dimensional Thermomechanical Simulation and Experimental Validation on Failure of Dissimilar Material Welds

In scanning electron microscope tensile testing was carried out to assess the mechanical properties and consequent failure characteristics of dissimilar weld consisting of low alloy steel and low nitrogen austenitic stainless steel. These transition joints find wide spread application in pressurized heavy water reactors. A number of premature failures have been reported in recent past during service exploitation of same joints. Thus, it becomes essential to identify the governing criteria resulting in such type of de-generation. In present endeavour, two types of joints were considered; one weld was fabricated by buttering with 309L stainless steel and the other one was made by buttering with IN82 Ni base alloys. From experimentation, weld strength was evaluated along with uncertainty analysis. Effect of various contributing factors over uncertainty was discussed. It was quantitatively shown that microstructural characteristics influenced more dominantly than physical parameters to the uncertainty of joint efficiency.

J Korody

Papers

Effect of Structural Heterogeneity on In Situ Deformation of Dissimilar Weld Between Ferritic and Austenitic Steel

Three-Dimensional Thermomechanical Simulation and Experimental Validation on Failure of Dissimilar Material Welds

Effect of different parameters on uncertainty during evaluation of strength of dissimilar metal weld