This Small Business Innovation Research Phase I project will focus on the development a new family of nanoengineered low-alloy steels that surpass the state-of-the-art in coupling high strength (>2,000 MPa tensile strength) with high elongation (>20%). The outcome of this project will be the creation of a domestically-designed and produced, and lower cost advanced high strength steel (AHSS), based on a low alloy chemistry and lower energy intensity manufacturing process. The commercialization of a non-commodity fourth-generation AHSS family of structural materials with ultrahigh strength, and toughness without sacrificing elongation will provide significant value for the U.S. steel makers. These cost-effective low-alloy steels could displace current AHSSs and other exotic materials, such as aluminum, metal or ceramic matrix composites, and fiber reinforced composites to be used in a variety of applications in the Defense, Off-Highway, and Automotive industries. Furthermore, the proposed manufacturing technique can be easily retrofitted to current steel plate and sheet production lines with minimal new equipment. The U.S. market for AHSS is in excess of $5 billion and is expected to double within the next five years.
Current advanced high strength steels (AHSSs) employ high alloy content, increasing their cost, and feature trade-offs between strength and ductility. A new steel manufacturing process will be developed, combining a patented ultra-high strength steel austempering process with grain deformation, nanostructuring the steel to deliver high elongation. The nanoengineering deformation and heat treatment processes for the proposed fourth-generation steel have been proven in the laboratory and have greatly improved structural performance. Other industrial steel grain nanostructuring means have shown improvements in tensile strength, but have exhibited low elongation, and their manufacturing methods have not been easily translated to sheet production. It is anticipated that the proposed manufacturing process can be used to make plate, sheet, and net-shape steel products. Completion of this effort will result in a technical model to optimize steel properties, a series of prototype steels, and the design of a prototype manufacturing line which can be scaled in Phase II to penetrate the multi-billion dollar AHSS market.
Project Description & Objectives In July, 2014 Detroit Materials was awarded an NSF SBIR Phase I for the further development of our proprietary steel through means of a new thermomechanical deformation process. It was hypothesized that this new process would create a nanostructured steel with 2000 MPa tensile strength and 20% elongation by taking advantage of Hall-Petch strengthening through reduction in ferrite grain size. No known steel had been able to achieve these mechanical properties. The technical objectives for Phase I in order to achieve this goal were 1) to develop a nucleation model describing the effects of the thermomechanical processing of the steel in order to optimize properties, 2) to prototype the concept of the high-temperature deformation process and to characterize the material, and 3) to develop a conceptual prototype process design. Accomplishments Through the duration of this project the team has been able to overcome multiple challenges including the optimization of the base material and far from ideal experimental equipment. Yet, the team has been able to achieve multiple commercially viable material grades. While the team is focused on bulk steel products, such as castings, forgings and rolled bar materials, we have developed materials that could be further developed into sheet steel. Below are some of the outstanding mechanical properties achieved in Phase I: 4G Net-Shape Process 1432 MPa UTS and 9.5% elongation 1794 MPa UTS and 10.0% elongation 4G Rolled Bar & Plate 1169 MPa UTS and 25% elongation 1861 MPa UTS and 9.7% elongation These materials show meet and exceed the DOE 2025 goals for sheet steels and bulk materials. Technical Through this Phase I DM has developed a nucleation model that can be used to optimize three distinct and unique high-temperature deformation processes, and has shown that each process can improve the mechanical properties of our high strength steel beyond what is achievable through traditional austempering. The nucleation model offers optimization of not only the high-temperature deformation processes, but also of the traditional austempering process. With the results of the model and the optimization of the base material coupled with the high-temperature deformation processes, DM has achieved high strength steel with 25% elongation and over 1860 MPa of tensile strength. Microscopy has shown that these advanced steel have refined microstructures that cannot be produced by traditional heat treatment. At the end of Phase I, DM has produced a nucleation model that is an extremely useful tool to scale production, and a series of extreme-performance steels that have high commercial value. Further, DM has shown that our high strength steel has the unique property of castability into complex net-shape components, which cannot be cast by any other known high strength steels. Commercialization The results produced by this project and the base material have garnered significant interest from multiple companies in different industries. We have secured a very strong commercialization partner in Interpower Induction. They are the third largest heat-treating company in the world and will provide process expertise in addition to use of their facilities and prototyping equipment. Additionally we have started commercial discussions with American Axle Manufacturing (AAM), Grede Holdings and GS Engineering. With AAM we are discussing independent material testing and possible applications. We have identified 2 possible applications to manufacture with our 4G material. We are also in very initial conversations with GM Ventures, Tremec, Jatco, AGCO to identify possible applications and R&D budget sources. Conclusions and recommendations All three high-temperature deformation methods yielded steel specimens with increased strength and elongation compared to specimens produced with the standard austempering process. While no single sample met our scientific reach goal of Technical Objective II (2000 MPa tensile strength and 20% elongation) samples exceeded the elongation goal and samples also achieved 93% of the strength goal, Table 1. These results are seen as a success as there is no other known low-alloy cast steel that can meet these extreme mechanical properties, and it is expected that this high-temperature deformation process can be utilized to increase the performance of other alloys with similar composition. Discussions with potential customers and strategic partners within the automotive industry have indicated that this low-alloy high performance material offers great lightweighting capability in its current form. Still, each deformation method experiment was hindered by engineering problems associated with controlling the temperature of the steel sample. Dedicated equipment that can consistently and evenly heat the samples and maintain the temperature of the samples through deformation would greatly improve the properties of the steel. Detroit Materials will continue to improve our processes between Phase I and Phase II, with confidence that we can reach the goal of Technical Objective II of 2000 MPa tensile strength and 20% elongation. DM will also continue to characterize the 4G material for fracture toughness and impact resistance.
