R. M. Huizenga

Stress relaxation due to ultrasonic impact treatment on multi-pass welds

Abstract Ultrasonic impact treatment (UIT) is a relatively novel technique applied to the toe of welded joints to improve the fatigue life by changing the weld geometry and the residual stress state. In this study, the stress relaxation due to ultrasonic impact treatment is investigated on a six pass welded high strength quenched and tempered steel section. Stress measurements in two orthogonal directions were conducted by energy dispersive synchrotron X-ray diffraction. Results show that the application of only ultrasound to a welded component re-distributes the residual stresses more uniformly, while mechanical impacts in combination with ultrasound is an effective way to release the residual stresses. After welding, diffraction peak broadening due to the lattice distortion, characterised by the full width at half maximum (FWHM), is observed in the region of the weld toes. Ultrasonic impact treatment reduces the FWHM at these locations.

Pass-by-pass stress evolution in multipass welds

Abstract In multipass welding, each successive thermal cycle will introduce local melting, solid state phase transformations, grain growth, grain refinement, recrystallisation and recovery, all of which lead to a complicated stress state. Most stress measurements performed on multipass welded components represent the final residual stress state. Information concerning stress evolution on a pass-by-pass basis is difficult to find. In this investigation, six pass welds were made on high strength quenched and tempered steel sections, and depth resolved strain measurements in two orthogonal directions were carried out after each weld pass using energy dispersive synchrotron X-ray diffraction. The residual stresses were calculated using biaxial Hooke’s law. A thermal–metallurgical–mechanical welding model was constructed and validated with temperature and pass-by-pass stress measurements, which improves the reliability of the model. Cross-sectional stress distributions are presented after each pass, revealing the weld stress development in multipass welds.

In Situ Phase Transformation Studies on a Transformation Induced Plasticity Steel Under Simulated Weld Thermal Cycles Using Synchrotron Diffraction

In situ phase transformation behaviour of aluminium-containing transformation induced plasticity steels, while subjecting them to heat affected zone weld thermal cycles have been studied. Experiments were carried out at ID11 of the European Synchrotron Radiation Facility, Grenoble, France. A specially designed oven was used to simulate the weld thermal cycles. Time–temperature resolved 2D synchrotron diffraction patterns were recorded and used to calculate volume fractions and lattice parameters of the phases. Results show that during heating, the retained austenite starts to decompose to ferrite and iron carbides once the temperature reaches 290°C. The lattice parameter of austenite increases linearly up to 290°C, followed by an increase in slope due to the formation of iron carbides. The combined effect of carbon concentration and thermal expansion causes scatter in the lattice parameter of austenite once the temperature reaches the inter-critical (α + γ) region. It is also observed that a significant amount of austenite (6–7%) was found to be retained at room temperature despite a high cooling rate (>20°C s−1). Even after cooling the samples to room temperature, austenite was found to continue decomposing upon further holding and the volume fraction of retained austenite decreased continuously with time at room temperature.

Residual Stress Measurements in Multi-Pass Welded High Strength Steel Using Energy Dispersive Synchrotron X-Ray Diffraction

Six pass welds were made on a 16 mm thick high strength quenched and tempered structural steel plate (S690QL1, Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt.%)). Depth resolved measurements in two orthogonal directions were carried out using energy dispersive synchrotron X-ray diffraction at the ID15 beamline of the European Synchrotron Radiation Facility. The strains were calculated from the shift in the local d-spacing for four bcc planes ({200}, {211}, {220}, {310}). The planar stresses were calculated from the biaxial Hooke’s law, using the diffraction elastic constants of the individual planes. A two dimensional cross-sectional residual stress map with a depth resolution of 2 mm was obtained. Transverse compressive stresses were found at the weld toes and root. Transverse tensile stresses were present in the middle of the plate. Longitudinal tensile stresses concentrated along the fusion line. This work describes the procedures to obtain the depth resolved residual stress map and the generated results provide necessary information to validate thermal mechanical finite element model of multi-pass welding.

Transformation-Induced Diffraction Peak Broadening During Bainitic and Martensitic Transformations Under Small External Loads in a Quenched and Tempered High Strength Steel

Insitu phase transformation behavior of a high strength S690QL1 steel during continuous cooling under different mechanical loading conditions has been used to investigate the effect of small external loads on the transformation-induced plasticity during bainitic and martensitic transformations. The results show that during phase transformations, the untransformed austenite undergoes plastic deformation, thereby retarding further transformation to bainite/martensite. This occurs independent of external load.

Anisotropy in Thermal Expansion of Bainitic Ferrite

The evolution of local d-spacings between lattice planes of bainitic ferrite in a high strength quenched and tempered structural steel, S690QL1 (Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt pct)), has been determined to calculate the thermal expansion behavior. For this purpose, in-situ continuous cooling tests have been carried out in a high-energy synchrotron X-ray diffractometer. The results indicate thermal anisotropy in the bainitic ferrite planes.

Synchrotron diffraction analysis of retained austenite in welded transformation induced plasticity (TRIP) steels

Abstract A quantitative analysis of the retained austenite (RA) fractions in gas tungsten arc welded silicon and aluminium containing transformation induced plasticity steels was carried out by synchrotron X-ray diffraction measurements. The variation in RA transverse to the weld line was measured to study the effect of weld thermal cycles on the stabilisation of austenite in the heat affected zone (HAZ) and the fusion zone (FZ). The results showed that the FZ of silicon based steels contained a higher amount of RA (∼7%) than aluminium based steels, which contained only ∼4%. During the solidification of the weld pool, aluminium was found to partition to solidifying δ-ferrite and to stabilise the soft δ-ferrite grains at the fusion boundaries. Owing to this partitioning, the HAZ was enriched in carbon and the RA content was found to increase with distance from the fusion boundaries. In contrast, this partitioning behaviour was not present in silicon based transformation induced plasticity steels and a lesser amount of RA was found in the coarse grained HAZ than in the FZ.

Correction to: In-Situ Synchrotron X-ray Diffraction Studies on Effects of Plastic and Elastic Loading on bcc Phase Transformations of a 3rd Generation 1 GPa Advanced High Strength Steel

In the original article there is an error in the first sentence of the abstract. bcc-to-bcc should be fcc to bcc. The corrected sentence is as follows:In this paper, we describe the effects of mechanical loading on fcc to bcc phase transformations of an Advanced High Strength Steel during cooling.

In Situ Synchrotron Diffraction Studies on Peak Broadening During Bainitic Transformation in a High Strength Quenched and Tempered Steel

In situ synchrotron diffraction studies were carried out on a high strength (830 MPa yield stress) quench and tempered S690QL1 structural steel during continuous cooling under different mechanical loading conditions. The volume fraction and lattice parameters of co-existing phases were calculated from the time resolved 2D diffraction patterns. The effect of applied stress on the kinetics of austenite to bainite phase transformation and the transformation plasticity were analysed from the diffraction analysis. The results show that small tensile stresses applied at the transformation temperature do not change the kinetics of the phase. The absence of peak broadening in the bainitic ferrite reflections during phase transformation demonstrated that the plasticity was accommodated in austenite grains.

In Situ Synchrotron Diffraction Studies on the Formation, Decomposition and Stabilisation of Austenite in TRIP Steels During Simulated Weld Thermal Cycles

In situ phase transformation behaviour of silicon and aluminium containing TRIP steels, while subjecting them to heat affected zone weld thermal cycles, have been studied. Time-temperature resolved 2D synchrotron diffraction patterns were recorded and used to calculate volume fractions and lattice parameters of the co-existing phases. Results show that during heating, the retained austenite starts to decompose once the temperature reaches 290 °C. The variation in the lattice parameters of austenite and ferrite reflect the nature of phase transformations that occur during cooling from austenitisation temperatures. The lattice parameter of austenite increases linearly up to 290 °C, followed by an increase in slope due to the formation of iron carbides. The combined effect of carbon concentration and thermal expansion causes scatter in the lattice parameter of austenite once the temperature reaches the inter-critical (α + γ) region. It is also observed that a significant amount of austenite (6–7 %) was found to be retained at room temperature despite a high cooling rate (>20 °C s−1). Even after cooling the samples to room temperature, the volume fraction of retained austenite decreased with time at room temperature.