Approach
In an effort to reduce the carbon footprint of steelmaking, there is and will be an increased usage of scrap for the production of steel. The recycling of scrap metals inevitably leads to the ‘unintentional’ alloying of the steel produced with “residual” elements. The amount of the residual elements will depend on various factors, including the quality of scrap, the prior application from which the scrap steel originates and the efficiency of scrap sorting. The residual elements can affect the processing conditions of the steel and its final mechanical properties depending on the nature of their presence in steel.
MOWSES will be the first systematic study on the effect of many residual elements in larger concentrations expected from the future green steels produced by the Electric Arc Furnace (EAF) route, particularly in the welding HAZ of heavy plates in a wide range of strength levels and delivery conditions. MOWSES will not only investigate individual effects, but also synergetic effects between different residual elements.
WP1: Material selection and finalisation of test matrix, DILLINGER
Work package 1 focusses on the selection of chemical compositions and steel grades for the project and the development of scenarios for the impact of residual elements such as Cu, Ni, Cr, Mo, Sn, As, Pb… These elements’ effects, including potential synergies, will inform a composition matrix of approximately 50 variants. The team will employ CALPHAD modelling to explore the influence of residual elements on metallurgical phase transformations, such as austenite to ferrite, and other possible phase formations. This modelling covers temperature ranges applicable to steel processing, welding, and heat treatments. Preliminary investigations will guide the refinement of compositions, narrowing down the most promising options for detailed analysis in subsequent stages. Early identification of reference compositions ensures timely material preparation for experimental work.
WP2: Laboratory production of material, COMTES
Comptes FHT AS and OCAS will produce the selected test materials, hot roll them into plates and deliver them to the relevant partners. The plates will serve as base materials for characterisation, welding thermal cycling, and weldability studies. The mechanical properties of the plates will be tested through tensile tests, hardness measurements, and Charpy impact tests at various temperatures, including extremely low ones like –100°C and –40°C. The ductile-to-brittle transition temperature is identified, and digital image correlation (DIC) is used in tensile tests to provide detailed insights into deformation behaviour. The results contribute to refining the material selection process of work package 1 and informing other project tasks.
WP3: Thermomechanical welding simulations, TU Delft
In work package 3, TU Delft will carry out welding simulations. The steel samples will undergo thermal cycles using Gleeble simulators, to replicate critical heat-affected zone (HAZ) conditions during welding. The focus is on two areas: coarse-grained HAZ (CGHAZ) and intercritical reheated CGHAZ (IRCGHAZ). In the latter, repeated heating creates brittle zones and martensite/austenite structures. A large number of samples will be tested, with simulations representing both low and high welding heat inputs. Treated samples will then be analysed for microstructural and mechanical properties using etching, optical microscopy, hardness testing, and impact testing at a single temperature. Promising steel compositions and welding conditions will be selected for further testing on over 1,000 samples, evaluating tensile strength, impact resistance, and fracture toughness under different conditions. Fracture surfaces are analysed using advanced methods to understand weak points in the microstructure, crack initiation, and the role of residual elements. Findings will guide material improvement and inform project outcomes.
WP4: Specific weldability investigations, RWTH Aachen
In work package 4, welding procedures will be developed, considering two welding processes—GMAW and SAW. Here, the simulated and actual thermal cycles in the heat-affected zone (HAZ) will be compared. Numerical simulations will be used to identify critical stress areas in the HAZ, validated through residual stress measurements. In a next step, the welded materials will be tested thoroughly using a variety of methods. The sensitivity of welded materials to hydrogen-induced cold cracking (HICC), which occurs when hydrogen interacts with a hardened microstructure during welding, will be examined. Digital imaging and acoustic emission techniques will monitor cracking, and hydrogen content in the weld will be measured. A heat treatment process will be developed to prevent embrittlement during welding. The maximum number of thermal cycles that welded materials can endure will be tested.
WP5: Advanced microstructure and micromechanical characterisation, UGent
In work package 5 the team under the lead of the University of Gent will carry out detailed micro-structural analysis of the plates and HAZ samples to identify crystallographic phases, inclusions, and the effects of residual elements on mechanical properties. Welded samples will be examined to ensure they match the simulated HAZ samples in terms of precipitates, grain size, and packet orientations. Micromechanical testing will focus on different microstructure features in the HAZ, like ferrite and martensite, which have varying mechanical properties. This testing will help understand brittle failure mechanisms and the effects of residual elements. Additionally, machine learning models will be trained to analyse local brittle zones in the HAZ.
WP6: Prediction of the early failure in the HAZ of welded structure made of green steels, TU Delft
In a first step, the existing fracture models to simulate both ductile and brittle fracture at TUDelft will be updated, using data from WP5 and simulations from previous tasks for calibration. Then a parametric study using the DelftBlue supercomputer will be carried out, to explore combinations of residual elements and optimise material recommendations. An AI surrogate model for predicting HAZ toughness will be developed and, validated against simulation data, to accelerate materials development. Then predictions will be compared to the results of the experimental tests from WP7. The goal is to develop recommendations, based on the outcomes of the different work packages, experiments and simulations, for the maximum allowable residual element content for welded steels.
WP7: Heavy gauge demonstration welding trials, OCAS
This work package aims to demonstrate the applicability of materials produced in small quantities and limited plate thicknesses for thicker materials from (semi-)industrial casts. Based on findings from WP3 and WP4, the chemical composition for demonstration trials will be specified. Then, full-thickness, multipass welding trials will be conducted using gas metal arc welding (GMAW) (low heat input) and submerged arc welding (SAW) (high heat input). Welded samples will undergo mechanical properties testing of the heat-affected zone (HAZ).
WP8: Project coordination, OCAS
Throughout the whole project duration, OCAS and Eurice GmbH will be responsible for project management, to ensure the efficient collaboration between the partners.
WP9: Dissemination, Communication & Exploitation of results, Eurice
To ensure maximum impact of the project, its findings will be communicated to relevant audiences throughout the whole project. Additionally, Eurice GmbH will develop an exploitation strategy and support the partners with intellectual property management.