Research on 830MPa high strength steel welding material for marine engineering

1. Overview

High-strength steel plays a vital role in the construction of self-elevating offshore platforms due to its lightweight and durability. Among these, 690MPa grade steel has been widely adopted in marine engineering. To further reduce the structural weight of such platforms, ArcelorMittal's INDUSTEEL steel mill introduced SUPERELSO830, a 830MPa-grade high-strength steel. This material is produced through hot rolling, quenching, and tempering, ensuring consistent toughness across the entire plate thickness. It meets a minimum toughness of 50J at -60°C, with a yield strength of at least 830MPa. The steel is available in two thicknesses: 89mm and 160mm. To address the welding challenges associated with SUPERELSO830, INDUSTEEL collaborated with the French Air Liquide Welding Group. Together, they developed both electrode arc welding and flux-cored wire submerged arc welding processes. The test results demonstrated that the welding procedure fully satisfies the required performance standards, making it suitable for use in demanding offshore environments.

2. Submerged Arc Welding Solution

The Air Liquide Welding Group developed a specialized flux-cored wire for welding SUPERELSO830. Similar to the materials used for 690MPa-grade steels, this wire contains alloying elements like nickel, chromium, and molybdenum, which enhance the mechanical properties of the weld. However, these elements can also affect the toughness, so careful optimization of the chemical composition is essential to maintain a balance between toughness and yield strength. To ensure excellent weld toughness, special measures were taken, such as using high-alkalinity fluxes to minimize oxygen and diffusion hydrogen levels in the weld metal. The flux-cored wire, designated as FLUXOCORD83, was tested with the flux OP121TT/W on 1000mm × 350mm × 160mm test plates. The welding parameters are detailed in Table 1.

Table 1: Welding Parameters

Table 2 presents the chemical composition of the base metal and the weld metal. Compared to 690MPa-grade steel, this material has a higher nickel content (4.26%), contributing to increased yield strength. Table 3 provides an overview of the mechanical properties of the weld metal and joints, showing that the yield strength exceeds the 830MPa minimum specified for the base metal, while the tensile strength surpasses 870MPa. The impact value also exceeds the 47J at -60°C requirement.

Table 2: Chemical Composition of SUPERELSO 830 and All Weld Metal (FLUXOCORD 83/OP121TTW)

Table 3: Mechanical Properties of All Weld Metal and Welded Joints (FLUXOCORD 83/OP121TTW)

Notably, the root toughness of the 830MPa base material is higher than that of the 690MPa version. This difference is primarily due to the distinct chemical compositions of the two base metals. The higher nickel content (4.26%) in the 830MPa steel helps maintain a stable Ni level in the weld metal after dilution, along with lower vanadium content (0.031% vs. 0.053%) and reduced impurities. This collaboration between INDUSTEEL and Air Liquide demonstrates how advanced welding technologies can meet the demands of high-strength steel applications in marine structures. (Created by CTAS Laboratory, Air Liquide, AE.Traizet, E.Galand, C.Chovet, B.Leduey, translated by Gao Pengcheng and Mo Qingshan) For more detailed information, please refer to the attached documents.

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