Laser beam (LB) welding is increasingly being used in welding of structural steels. The thermal cycles associated with laser beam welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone that usually exhibits a high hardness for C-Mn structural steels due to the formation of martensite. It is rather difficult to determine the tensile properties of a laser weld joint area due to the small size of the fusion zone. Complete information on the tensile and fracture toughness properties of the fusion zone is essential for prequalification and a complete understanding of the joint performance in service, as well as for conducting the defect assessment procedure for such weld joints. Therefore, an experimental investigation on the mechanical properties of laser welded joints using flat microtensile specimens (0.5 mm thick, 2 mm wide was carried out to establish a testing procedure to determine the tensile properties of the weld metal and heat-affected zone (HAZ) of the laser beam welds. In the present work, two similar joints, namely, ferritic-ferritic and austenitic-austenitic and one dissimilar ferritic-austenitic joint were produced with a CO 2 laser using 6-mm-thick steel plates. In addition to the testing of flat microtensile specimens, the mechanical properties were examined by microhardness survey and conventional transverse and round tensile specimens. The results of the microtensile specimens were compared with standard round tensile specimens, and this clearly showed the suitability of the microtensile specimen technique for such joints. The crack tip opening displacement (CTOD) tests were also performed to determine the fracture toughness of the LB welds using three-point bend specimens. The effect of strength heterogeneity (mismatchingj across the weld joint and at the vicinity of the crack tip on the CTOD fracture toughness values was also discussed.

Determination of mechanical and fracture properties of laser beam welded steel joints

A continuum damage model for ductile fracture of weld heat affected zone

https://rosap.ntl.bts.gov/view/dot/34533/dot_34533_DS1.pdf

Second Generation Models for Strain-Based Design

Interfacial crack-tip constraints and J-integrals in plastically mismatched bi-materials

Strength mis-matching between the base and weld metals exerts a marked influence on the deformation behavior as well as on the fracture resistance of the weld HAZ. HAZ-notched CTOD test results for high strength steel welds were discussed with attention to mis-matching effect. Stress fields in the HAZ were addressed by 3D FEM with a model having a notch at the HAZ/weld metal boundary. Strength overmatching of the weld metal brings about different effects depending on the toughness level of the HAZ. In the case of the HAZ with moderate toughness, strength overmatching results in crack path deviation toward a softer material due to asymmetrical plastic deformation. On the other hand, for the embrittled HAZ, the overmatch condition lowers the critical CTOD value of the HAZ. This is attributed to elevation of the local stress in the HAZ by constraint effect of the overmatched weld metal. The geometry of the test specimen also affects the degree of crack tip constraint. The deep notch bend specimen produces the largest geometrical constraint. The fracture resistance of the weld HAZ is controlled by the combined effects of strength mis-matching and the specimen geometry. The geometrical constraint in the deep notch bend specimen was more significant than the constraint by 25% strength overmatching in the tension specimen.

Effect of Strength Mis-Match on Fracture Mechanical Behavior of HAZ-Notched Weld Joint

The effects of the microstructural features of the coarse grained heat affected zone (CGHAZ) on fracture behaviour and toughness properties were investigated in under- and overmatched weld metals. CTOD (with various notch orientations) and Charpy-V impact tests were carried out on CGHAZ of bead-on-plate submerged arc welds with weld metal yield strengths of 248, 620 and 964 MPa on a StE 460 C-Mn Steel with a yield strength of 458 MPa. The microstructural features of the CGHAZ's of three mismatched weldments were determined in terms of microhardness surveys, martensite amount and grain size measurements of the CGHAZ's. Additionally, chemical composition gradient of CGHAZ was analysed, using the SEM-EDX system. Some possible mechanisms leading to the different amount of martensite formation in CGHAZ of the mismatching welds are also discussed.

Microstructure and weld metal matching effects on heat affected zone toughness

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Microstructure and weld metal matching effects on heat affected zone toughness