The advanced manufacturing characteristics of the forging industry come from many sources and suppliers. This article – the fourth in our series – concentrates on advanced raw materials, which add shape and value to materials ranging from specialty and microalloyed steels to metal-matrix composites.
As we move forward with this installment on forging alloys, we can look back at Part 1 of our series (Feb. 2015), which defined advanced manufacturing. You may recall that from a process perspective, attributes of advanced manufacturing include:
- Sophisticated design and development process
- High-performance computing
- Precision measurement systems
- Integrated information technologies
- Advanced robotics
- Control systems with real-time process monitoring and feedback loops
- Low-rate and high-rate production capabilities
- Elaborate, complex and expensive equipment
Forgings are used in critical applications in aerospace, automotive, energy and defense, to name but a few. In these competitive fields, original equipment manufacturers (OEMs) are constantly pushing the envelope to achieve a commercial advantage. Attaining increases in strength, toughness, fatigue resistance and weight reduction results in constant pressure to produce ever-increasing higher-performance parts. This requires sophisticated developments to forge and heat treat metals to higher levels of performance. Developing an optimum microstructure, while forming a metal component at temperatures in excess of 1600°F, is one of the most formidable tasks faced by any manufacturer, truly demonstrating that forging isadvanced manufacturing.
From a forging-alloy perspective, metal suppliers manufacture high-quality alloys in accordance with these attributes. Upon further examination, these cutting-edge suppliers depend on nearly all of these attributes, with the possible exception of advanced robotics. But as quickly as technology advances, robotics are likely to appear on melt-shop floors in the near future imparting more quality to alloys, especially those used in demanding applications.
This installment will illustrate that advanced-alloy manufacturing is integral to the manufacture of high-performance forgings. Working with TimkenSteel, Electralloy and Triton Systems, we have illustrated that alloy manufacture is within the realm of advanced manufacturing.
At Forge Fair 2015, TimkenSteel’s Patrick Anderson revealed how this “100-year-old start-up” imparts quality in its alloys. The company’s emphasis on advanced steel technology integrates its applications metallurgical laboratory, advanced computational modeling, advanced product and process engineering, and development labs at its new Technology Center to focus on the design and manufacture of high-quality steels in terms of cleanliness and soundness, especially “center soundness.” A closer look inside TimkenSteel reveals the company’s use of advanced manufacturing techniques, tools and technology from steel production to inspection.
TimkenSteel, especially with its strong understanding of initial flaw size, strives to eliminate any potential stress riser, be it porosity, inclusions, segregation, etc. Focusing on soundness, the microporosity of the cast ingot is modeled and minimized through solidification modeling via Magmasoft. Recognizing that porosity could still remain within a cast ingot, hot working the steel compresses and greatly minimizes porosity. To attain the highest grades possible, TimkenSteel combines forging deformation with rolling deformation in their forge-rolled process path. Validation is accomplished through the company’s heavy investment in ultrasonic testing to model and verify the soundness of their product, which results from a combination of forging and rolling operations. Through steady, focused investments, TimkenSteel has leveraged advanced manufacturing techniques to be a leader in large-diameter bar that meets strict ultrasonic and dimensional specifications.
Electralloy has developed proprietary forging practices to push the strength levels of their product higher than previously considered practical and to extend the higher strengths to larger and larger diameters. The company optimized the chemistry and homogeneity of the alloy to aid in achieving higher strength levels and has established a more robust product and process capability. The results are an as-forged bar product that can be machined directly into high-strength, corrosion-resistant shafts (including large-diameter ship shafts) or nonmagnetic drill string components that are capable of outperforming less-expensive material alternatives or substituting for more-costly alloys.
An example of Electralloy’s efforts is Nitronic®50, which is a high-nitrogen-bearing austenitic stainless steel that provides a combination of corrosion resistance, strength and low magnetic permeability unique among stainless steels. Nitronic 50 remains essentially nonmagnetic even after cold work or cooling to subzero temperatures. These properties make the alloy attractive in marine applications for hardware and shafts, and down-hole applications for nonmagnetic drill string components including “measure while drilling” (MWD) or “logging while drilling” (LWD) chassis, particularly in its high-strength form. Nitronic 50 is not generally hardenable by heat treating but does work-harden rapidly during cold or “warm” working. To achieve this combination of enabling properties, Electralloy has developed and deployed a suite of processing tools and technologies that are truly advanced, yet proprietary.
An exciting new metal-matrix composite (MMC) that lends itself to forging is being developed by Triton Systems in Chelmsford, Mass. The product is a high-strength aluminum alloy randomly reinforced with chopped ceramic (alumina-silicate) fibers. Called FRA™, its ideal applications are those that capitalize on its excellent wear resistance, light weight and elevated-temperature strength properties. Compared to steel and cast iron, tests have proven that this material has equivalent or better resistance to various forms of wear (abrasive, fretting, metal-to-metal sliding) while having only one-third the density of ferrous alloys. Furthermore, compared to conventional high-strength aluminum alloys, the product has greater than three times the elevated-temperature strength.
Figure 3 is an overview of FRA applications and markets. Note that there are various defense applications for the product (e.g., bearing liners, reinforcement lugs for aluminum castings) that are on track for platform qualification. Recently, some potentially high-volume commercial opportunities have emerged. The Triton Systems team believes efforts to reduce the cost of FRA components will be critical to successfully penetrating these emerging markets. To penetrate these markets, forging of net shapes makes FRA possible. Under the Defense Logistics Agency’s PRO-FAST Program, the Forging Defense Manufacturing Consortium and Triton Systems are exploring various product forms enabled by forging. Figure 3 illustrates the combination of advanced-alloy process technology coupled with forging to yield a high-performance shape.
There are many other alloy systems and forging feedstock producers around the world. In order to be competitive, however, they all have to be advanced manufacturers to meet the demands of their customers and their customers’ applications, which require guaranteed strength, fatigue resistance and toughness. In many cases, the raw material requires well-designed and controlled processes in the forge shop to meet the requirements of the end users. Two examples of this are microalloyed steel and nickel-based superalloys.
Microalloyed steels are iron-based alloys with small additions of vanadium, niobium or columbium. While typical alloy-steel forgings are heat treated to achieve mechanical properties, microalloys can be control-cooled after forging to meet mechanical properties at a lower cost and energy input. Microalloyed steels can be produced with higher strength and toughness than low-alloyed steels with the same microstructure and are therefore very attractive to automotive drivetrain forgers.
The process window required to achieve an optimum microstructure requires a strong metallurgical background. Microalloy steel forging relies on a precipitation process within a temperature range that produces a specific microstructure. The optimum temperature range and cooling rate vary with part, size, forging equipment and alloy composition.
Preparing this article was a team effort between SCRA Applied R&D, Scientific Forming Technologies Corporation (SFTC), TimkenSteel, Electralloy and Triton Systems. Jon Tirpak and John Walters appreciate the support received from the Defense Logistics Agency (DLA) through its Manufacturing Technology Program –
PRO-FAST. DLA clearly understands the need to partner with industry in investigating, developing and deploying technical and enterprise solutions within the U.S. forging industry to support many small and medium businesses and also support the military, which needs forgings for critical applications.
Co-author John Walters is vice president of Scientific Forming Technologies Corporation, Columbus, Ohio. He may be reached at 614-451-8330 or firstname.lastname@example.org. Co-author Jon D. Tirpak is the executive director of FDMC and FAST program manager. He is also president of ASM International. He may be reached at 843-760-4346, or email@example.com
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