High Performance Stainless Steels as Enablers of a More Sustainable Future

To talk about sustainability in the steel industry is not an easy task, as the perception of value can change quite a lot depending on which side of the supply chain one is on. The three main pillars of sustainability are society, environment, and economy; and the impact generated by the steel making process affects all of them. This is why the industry has been under scrutiny over the last few years, and technological developments will be needed to increase the quality of steel making processes, therefore increasing quality of life in the world for future generations.

By Caio Pisano, Technical Market Development Manager, CBMM | Niobium

According to a report published in April 2022, by the Global Efficiency Intelli­gence, the iron and steel industry ac­counts for around 7% of global green­house gas (GHG) emissions and 11% of global carbon dioxide (CO2) emissions. These numbers are indeed concerning, nevertheless, the solution to a more circular and sustainable economy can come from within this very industry. This article is intended to bring some insights on how to get there; a small spoiler – stainless steel will play a major role in this strategy.

The industry has been adapting itself quite fast on the consolidation of fun­damental concepts of sustainability and this adaptation process will be crucial for the proper evaluation of the supply chain as a whole, considering the TCO (Total Cost of Ownership) of solutions versus a short-term cost analysis will also be a crucial paradigm shift, that will enable the usage of more adequate ma­terials to already consolidate solutions.

Longevity of Solutions

Following this cost perspective, one could give many examples and consider many different aspects, but this article will focus on two: longevity of solutions, and technical performance of materi­als. On longevity of solutions, there are many studies conducted by public and independent agencies showing that the global cost of corrosion in the world is between 2% and 4% of the global GDP, representing trillions of USD losses among the supply chain over the years.

The development of higher corrosion resistance stainless steels is an inter­esting alternative to that, materials such as duplex stainless steels, super austenitic stainless steels, and super fer­ritic stainless steels are solutions that require less, or no maintenance when compared to coated carbon steels or other grades in many applications. Even within these stainless steel families, it is worth noting that many solutions are still relying on the usage of ‘status-quo’ grades, such as AISI 304 or AISI 316L, however ferritic stainless steels, such as AISI 444 and AISI 445, are interest­ing alternatives with lower costs. Being in a World Cup year, one example where ferritic stainless steels are successfully being used in architecture is the Allianz Stadium in Brazil, where the facade was produced with AISI 444.

Technical Performance of Materials

The other concept is the technical per­formance of materials, and the metallur­gical development of stainless steel. This direction will be the core target of this ar­ticle. Once the industry manages to com­bine the development of higher strength, higher corrosion resistance, and higher temperature performance grades with cost efficiency, the TCO of solutions will become more and more positive. That is why the consideration of ferritic stainless steel can be one of the ways to achieve this. Another important strategy is to in­vite the end users to be part of the de­velopment process and projects, as they can give the guidelines and targets of de­velopment, mitigating risks and reducing time to market.

Diving deeper on this topic, an interesting approach to improve the technical per­formance of stainless steels is the com­bination of proper alloying strategy with the best practices in the steel shop. One example is the usage of stabilizing ele­ments, such as Niobium (Nb), as an alter­native to the classical production routes with Batch Annealing’s (BAF). As it is well known, the production of non-stabilized ferritic grades can lead to the generation of martensite in the hot rolling process, which later will require long anneal­ing processes, consuming a substantial amount of energy, time, and money, and generating a lot of emissions. Once Ni­obium (Nb) is added, or other stabilizing elements, to these ferritic grades (AISI 430, for example), martensite will no lon­ger be formed in the hot rolling process, and therefore it is possible to optimize the production route, reducing annealing time and the carbon footprint per ton of steel. This is an interesting way of look­ing at technical developments, with sus­tainability as a target!

From the Application Perspective

On the application perspective there are also many different directions to explore. It is important to emphasize the devel­opment of solutions for the production and consumption of green hydrogen. Within the many technologies available, one with the highest yield is solid oxide electrochemical cells, electrolyzers, or fuel cells that operate in very high tem­peratures, in the range between 600°C and 1,000°C. The development of ferritic grades with the proper performance for this application, proper cost competitiv­ity, and most importantly proper carbon footprint, will be an important enabler of this technology. Once again, combining the strategy of alloy design with produc­tion process development is crucial.

Considering the structural components segment, an important milestone for the stainless steel industry is to succeed on the development of higher strength and cost-effective grades, as alternatives to the classic coated carbon steels. This challenge can be met once again with the combination of alloying strategy and process optimization, where the us­age of some alloying elements, such as Niobium (Nb), can promote the develop­ment of strengthening mechanisms (i.e grain refinement and precipitation). To­gether with a more appropriate homo­geneity of the microstructure, this leads to a better toughness, and therefore a better applicability of these materials as alternatives to the status-quo materials.

From the sustainability perspective, the development of these alternatives with stainless steels bring benefits from the beginning. Right away it will be possible to promote a better corrosion perfor­mance, and less stress and costs relat­ed to maintenance. Additionally, it will be possible to promote better circular­ity of the solution, as stainless steel is 100% recyclable, and in the end of the lifetime of these components, they can be remelted without losing any perfor­mance in the manufacturing process.

Conclusion

All things considered, the discussion about sustainability in the steel business is quite extensive and unfortunately it cannot be restrained to a single article; the main players in the supply chain are working hard to achieve targets, howev­er there are no magic solutions available for short-term results. The development of high-performance stainless steels will be one of the many enablers of a more sustainable and healthy future. One can be sure of only one thing – whatever di­rection the industry goes, stainless steel will be there!