Periodic Reporting for period 1 - ROAD-SiM (Recycling-oriented alloy design for next-generation of sustainable metallic materials)
Okres sprawozdawczy: 2022-09-01 do 2024-08-31
European industry increasingly focuses on recycling to reach carbon neutrality by 2050. Recycling offers enormous energy savings and CO2 reductions; namely 58%, 92% and 65% for steel, aluminium and copper, respectively, compared to primary metals production. However, there are several problems hindering metals recycling such as the progressive accumulation of metallurgical impurities in alloys produced from scrap metal. An effective solution to counter these problems is the development of new alloys, recycling-friendly by design for transition to circular economy supported by European green deal, EuRIC Circular Metals Strategy and other initiatives.
Concentrated solid solution alloys, including some of the established alloys, have considerable potential for enhanced tolerance to said compositional deviations. This entails that the alloys’ properties do not significantly change by deviating from the chosen average composition, due to the extended compositional space with desired microstructures. Additionally, they show tolerance to higher impurity levels due to their intrinsically high ductility. These attributes are essential for the next generation of robust, recycling-friendly alloys designed for production from metal scrap as raw material, as compared to older alloys designed for production from metallic ores.
The objective of the project is the in-depth evaluation of the consequences of the compositional alterations on the changes induced to the basic mechanical properties and damage tolerance of highly alloyed systems. For such evaluation, new experimental alloys will be prepared. The ultimate goal is the preparation of scrap-compatible metallic materials for sustainable metallurgy. The partitioning effects of alloying and impurity elements will be studied with a special focus on their interactions with the lattice and microstructural defects. The high alloys stainless steel base material will be used due to its promising properties for the purposes of ROAD-SiM and its similarity to other systems. Thus, the obtained knowledge will be generally applicable for a large scale of similar materials
Concentrated solid solution alloys, including some of the established alloys, have considerable potential for enhanced tolerance to said compositional deviations. This entails that the alloys’ properties do not significantly change by deviating from the chosen average composition, due to the extended compositional space with desired microstructures. Additionally, they show tolerance to higher impurity levels due to their intrinsically high ductility. These attributes are essential for the next generation of robust, recycling-friendly alloys designed for production from metal scrap as raw material, as compared to older alloys designed for production from metallic ores.
The objective of the project is the in-depth evaluation of the consequences of the compositional alterations on the changes induced to the basic mechanical properties and damage tolerance of highly alloyed systems. For such evaluation, new experimental alloys will be prepared. The ultimate goal is the preparation of scrap-compatible metallic materials for sustainable metallurgy. The partitioning effects of alloying and impurity elements will be studied with a special focus on their interactions with the lattice and microstructural defects. The high alloys stainless steel base material will be used due to its promising properties for the purposes of ROAD-SiM and its similarity to other systems. Thus, the obtained knowledge will be generally applicable for a large scale of similar materials
In the main part of the project, the fracture resistance and microstructures of a model material, (X1CrNiMoN25-22-2) prepared from re-melted foundry scrap contaminated with systematically varying Sb-concentrations of 250-520 ppm and 0.14 wt. % of S and were investigated. The combination of state-of-the-art microstructural characterization techniques including SEM-EBSD-ECCI, EPMA and APT were used, together with quasi-standard fracture toughness measurement using compact tension specimens. The deliberately contaminated alloys were also compared a conventional high-purity, vacuum-refined steel with identical composition. The materials were tested in standard in standard solution annealed condition. All contaminated steels having considerable fraction of oxides and sulphide inclusions combined with microstructural heterogeneity still retained unexpectedly high fracture toughness. Importantly, the tensile properties were not altered by the contamination. The contamination by tramp Sb decreased the only very slightly by 9-15%. The exceptionally high values of fracture toughness were enabled by considerable plasticity and strain hardening capacity of the austenitic alloy. While the S contamination resulted in formation of suphide inclusions, the Sb tramp element was found to be completely dissolved in the austenitic matrix phase and it did not segregate to the grain boundaries. The investigation showed, that highly ductile austenitic alloys and probably also similar FCC systems with large plasticity show an exceptionally high tolerance to various types of contamination and are an ideal candidate for future damage-tolerant materials. It has also proven that the investigation of local partitioning of elements with very low concentrations (impurities) is considerably difficult by standard metallurgical methods and new work-flow had to be developed.
A part of the project activities was also focused on study of CoCrNi complex concentrated alloy doped with nitrogen as contaminant that may originate from air melting. The alloy underwent high pressure torsion (HPT) and subsequent annealing treatments. A micro-cantilever bending tests were used here to evaluate mechanical properties of the materials produced in small volumes. The introduction of N results in a reduction of grain size and increased hardness and bending strength. The alloy with nitrogen showed also more extensive anneal hardening at intermediate temperatures of 300-500 °C. It showed that nitrogen presence in low concentrations in the CoCrNi system increases the mechanical response.
A part of the project activities was also focused on study of CoCrNi complex concentrated alloy doped with nitrogen as contaminant that may originate from air melting. The alloy underwent high pressure torsion (HPT) and subsequent annealing treatments. A micro-cantilever bending tests were used here to evaluate mechanical properties of the materials produced in small volumes. The introduction of N results in a reduction of grain size and increased hardness and bending strength. The alloy with nitrogen showed also more extensive anneal hardening at intermediate temperatures of 300-500 °C. It showed that nitrogen presence in low concentrations in the CoCrNi system increases the mechanical response.
Obtained findings provides an extension of knowledge in area of recyclability of high-alloy steels and other complex systems and the influence of metallurgical and tramp impurities on their properties, together with work-flow for the measurement of low-concentration elements. These results will contribute to the advancement of industry towards a circular economy in an area of highly alloyed stainless steel that are to be masively applied in future European hydrogen economy. The interdisciplinary results also enrich the basic understanding of property-microstructure-defects interplay.