Andrei Filatov

The quality of heavy plates produced from low-carbon steel is directly linked to the structural characteristics inherited from the initial continuously cast thick slabs. This study explores how different casting technologies affect the morphology and distribution of allotriomorphic ferrite along prior austenite grain boundaries (PAGBs) within these slabs. Using quantitative microstructural analysis based on advanced computer vision techniques (OpenCV), the research identifies significant variations in ferrite boundary thickness and volume fraction associated with different casting methods. These microstructural differences strongly correlate with variations in Charpy V-notch impact energy (KVZ20) and susceptibility to microcrack formation during subsequent rolling processes. The results obtained allow us to evaluate the influence of the cast structure on the formation of the initial structural characteristics of the material, especially on the formation of microcracks of the slab microstructure and their propagation during further processing.

Large‐scale steel storage tanks for liquid CO ₂ are critical elements in Carbon Capture and Storage infrastructure. This study investigated the weldability and mechanical performance of 34 mm thick joints made from cold‐resistant microalloyed steel grade P460NL1. The main welded joints are produced using automatic submerged arc welding (SAW 121‐2) with a V‐groove and heat input of 1.5 ± 0.1 kJ mm ⁻¹ . Microstructural analysis revealed stable zoning with bainitic structures, maximum hardness of 222 HV ₅ , and microhardness values not greater than 323 HV _0.3 in the heat‐affected zone (HAZ). In the as‐welded condition, Charpy impact energy exceeded 186 J at −40 °C and remained above 88 J at −50 °C. Post‐weld heat treatment increased yield strength from 452–453 MPa to 465–468 MPa, while slightly reducing tensile strength and impact energy in the fusion line. Additional weldability tests included controlled thermal severity and bead‐on‐plate welding tests, both confirming the absence of cracking and acceptable HAZ hardness. Strain aging tests showed retention of ductile behavior down to −60 °C. High‐temperature tensile testing up to 450 °C confirmed structural stability over a wide operating range. These findings support the use of P460NL1 steel for high‐integrity welded structures in demanding CO ₂ storage conditions.

Using the results from testing industrial batches of 23 mm steel heavy plates after thermomechanical rolling and subsequent post-weld heat treatment, the patterns of fatigue crack formation in the fracture specimens during CTOD (Crack Tip Opening Displacement) testing for fracture toughness are investigated. Visual, microstructural, and fractographic studies of the nature of fracture formation and the surface of the secondary separations have been conducted. The probable causes of the manifestation of the potential “pop-in” effect on the load–displacement diagrams of the notch opening displacement are described, as well as its potentially negative impact on the interpretation of test results.