This study is concerned with a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds. The influence of the LBZ on toughness was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests. Micromechanical processes involved in microvoid and cleavage microcrack formation were also identified using notched round tensile tests and subsequent scanning electron microscopy (SEM) analyses. The LBZ in the HAZ of a mUltipass welded joint is the intercritically reheated coarse-grained HAZ whose properties are strongly influenced by metallurgical factors such as an effective grain size and high-carbon martensitic islands: The experimental results indicated that Charpy energy was found to decrease monotonically with increasing the amount of martensitic islands, confirming that the martensitic island is the major microstructural factor controlling the HAZ toughness. In addition, microvoids and microcracks were found to initiate at the interface between the martensitic island and the ferrite matrix, thereby causing the reduction in toughness. These findings suggest that the LBZ phenomena in the coarse-grained HAZ can be explained by the morphology and the amount of martensitic islands.

Microstructure and Local Brittle Zone Phenomena in High-Strength Low-Alloy Steel Welds

Advanced Heat Resistant Steels for Power Generation

The trend in welding on a world basis is discussed and the close cooperation between science and industry to develop new welding processes and solve existing problems is emphasised. Possible future development in welding is outlined, and some of the newer welding processes are briefly discussed.

Welding in the world

Investigation of residual stress distribution of dissimilar Al-7075-T6 and Al-6061-T6 in the friction stir welding process strengthened with SiO2 nanoparticles

Solute-dislocation interactions and creep-enhanced Cu precipitation in a novel ferritic-martensitic steel

Super304H, which is an austenitic heat-resistant steel, was aged at 650 °C for up to 5000 h. Its microstructural evolution during aging was observed by scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD). The precipitate evolution in the aged specimens was analyzed by both X-ray diffraction (XRD) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED). In addition, the precipitation kinetics of M23C6 carbide was established. Hardness and impact tests were performed on the aged specimens. Finally, the relationship between the mechanical properties and microstructural evolution was revealed. After aging, Super304H steel exhibited the same fine grains as in the as-received condition with a Cu-rich phase, secondary Nb(C,N) precipitates inside the grains, and M23C6 carbides mainly at grain boundaries. The Cu-rich phase and the secondary Nb(C,N) precipitated in specimens aged for 500 h; this leads to a marked increase in hardness. Precipitation of the Z phase also occurred in the aged Super304H steel. M23C6 carbides precipitated rapidly during aging, with content approaching 90% of the saturated content in specimens aged for 5000 h. The reduction in impact toughness in Super304H steel was found to be associated with the precipitation of the M23C6 carbide, which is similar to that in the HR3C steel. However, the deterioration was much less significant as compared to HR3C steel because of the discontinuous distribution of carbides at grain boundaries due to the fine grain size.

Xue Wang

Papers

Precipitate evolution during the aging of Super304H steel and its influence on impact toughness

Laves-phase evolution during aging in 9Cr-1.8W-0.5Mo-VNb steel for USC power plants

Laves-phase evolution during aging in fine grained heat-affected zone of a tungsten-strengthened 9% Cr steel weldment

Correlation between microstructure and mechanical properties of 6061-T6 double-side FSW joint

Damage assessment in structural steel subjected to tensile load using nonlinear and linear ultrasonic techniques