More than 70% of the world's supply of nickel is used to make stainless steel, a cost-effective, strong, corrosion resistant alloy widely used for construction, transportation, development of medical devices and more. However, fluctuations in global nickel supply over the past two decades have posed significant challenges to maintaining stable production, according to a team of researchers at Tohoku University and Tsinghua University.
"Balancing the reduction of nickel usage with the need to preserve material strength has become a critical objective to ensure both sustainability and structural integrity," said Run-Zi Wang, an assistant professor at Tohoku University's Advanced Institute for Materials Research (WPI-AIMR).
To meet this need, Wang led the team to develop a new stainless-steel alloy that maintains strength without needing to incorporate nickel. They published their results on December 27 in Additive Manufacturing.
"Given that stainless steel production consumes a significant portion of the global nickel supply, this research proposes an innovative solution: fabricating bimetallic stainless-steel structures using additive manufacturing," Wang said, "This approach offers a sustainable alternative to stabilize costs and ensure long-term resource availability."
The 300 series or austenitic stainless steel -- which has the highest nickel content of all stainless steels -- is the most widely produced stainless-steel grade, responsible for 54% of total stainless-steel production. To achieve the same properties of the 300 series, the researchers turned to a type of nickel-free stainless steel classed as "ferritic," meaning it is magnetic and resistant to cracking caused by stress and corrosion.
Nickel-free ferritic stainless steel has gained renewed interest as a cost-effective alternative to stainless steels containing nickel, but its lower fracture strength and hardening rate compared to austenitic stainless steel limits its industrial applications. Hybrid bimetallic structures made of the two stainless steels offer a promising solution, balancing material performance and nickel consumption. Therefore, the main challenge of this study was to preserve stainless steel's strength while reducing dependence on nickel.
Using additive manufacturing, a type of 3D printing, the researchers fabricated a composite structure from nickel-free ferritic stainless steel and austenitic stainless steel. They specifically employed a technique called wire-arc directed energy deposition, which involves depositing metal layers via welding.
Once fabricated, the researchers analyzed the bimetallic structure's elemental distribution and mechanical properties. They found that the microstructure where the two metals interface revealed features associated with increased hardness and strength compared to either of the individual components alone.
This research contributes to lower-cost, high-performance manufacturing of stainless steel with preserved material strength that could benefit industries and consumers by reducing material costs, improving product durability and promoting sustainable metal manufacturing practices for the future.