Effect of Welding Peak Temperature on Microstructure and Impact Toughness of Heat-Affected Zone of Q690 High Strength Bridge Steel

The effect of peak temperature (TP) on the microstructure and impact toughness of the welding heat-affected zone (HAZ) of Q690 high-strength bridge steel was studied using a Gleeble-3500 thermal simulation testing machine. The results show that the microstructure of the inter critical heat-affected zone (ICHAZ) was ferrite and bainite. The microstructure of fine grain heat-affected zone (FGHAZ) and coarse grain heat-affected zone (CGHAZ) was lath bainite (LB) LB, lath martensite (LM), and granular bainite (GB), but the microstructure of FGHAZ was finer. With the increase in peak temperature, the content of LB and GB decreased, the content of LM increased, and the lath bundles of LM and LB gradually became coarser. With the increase in peak temperature, the grain size of the original austenite increased significantly, and the impact toughness decreased significantly. When the peak temperature was 800 °C, the toughness was the best. For CGHAZ, the peak temperature should be less than 1200 °C to avoid excessive growth of grain and reduction of mechanical property.

Mechanical Properties of Bridge Steel from the Late 19th Century

This article presents the results of testing of the strength of structural steel taken from a railway bridge. It was built within the borders of today’s Poland during the late 19th century and was in use for over 100 years, until the early 21st century. The main mechanical parameters of the bridge steel, such as its static and impact strength were determined. The results of the analysis of fracture surfaces with the aim of the identification of the material’s macrostructure are also presented. This article discusses the findings and analyses the values of material parameters in the context of requirements resulting from existing standards, and compares the results with those obtained during the testing of bridge steels of a similar age and operational period.