Photograph courtesy of Charter Steel, Inc.
Advances in Springmaking Materials By C. Richard Gordon
(Editor’s note: Rick Gordon’s article was developed as part of the overall theme of “Advances in Springmaking.” With so many developments to discuss, this is the first of several articles to come in future issues of Springs. Gordon will also discuss these advances as a part of his presentations during the 2021 SMI Metal Engineering eXpo.)
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dvances in the production of springmaking materials over time have resulted in improvements in spring performance. Since the majority of springs are produced from carbon and alloy steels, production methods of these materials will be described here. Production improvements have occurred in the areas of steelmaking, continuous casting, rod rolling, wire drawing and wire processing. Improvements in springmaking machine technology will be treated separately.
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One important performance characteristic for springs subjected to cyclic loading is fatigue life. As the SMI technical committee looked at available spring fatigue data, it was discovered that spring fatigue data available from ASM International was developed prior to the publication of their “Metals Handbook, 8th edition” in 1961. More recent data was published by the Society of Automotive Engineers (SAE) in their 1997 publication, “Manual on Design and Application of Helical and Spiral Springs (HS-795).” The SAE manual data is included in the Advanced Spring Design software (ASD7). These advances in springmaking materials motivated the SMI technical committee to explore the potential impact/improvements to historical fatigue life, assumptions that were based on decades-old wire production practices. This project is currently underway. The improvements in steelmaking, rod rolling, wire drawing and wire processing technology will be briefly described below and are planned to be presented in detail in two technical sessions at the the 2021 SMI Metal Engineering eXpo in September.
Steelmaking and Continuous Casting
Improvements in steel manufacturing processes have yielded advancements in the purity of steel for higher-quality
end-use products such as springs. Clean steel is produced by judiciously controlling parameters in melting, refining, degassing and casting operations. As we look at the steel production process, there are two primary production methods used today: the integrated steelmaking process and the minimill process. In the integrated steelmaking process, molten iron produced in a blast furnace is refined in an oxygen steel making furnace to produce steel. A typical furnace charge is 85 percent blast furnace iron and 15 percent scrap. The quality of the scrap is an important factor in the quality level of the steel being produced. Steel produced using the integrated steelmaking process can have very low levels of residual elements, which is desirable for high quality materials used to produce springs. In the minimill process, steel is produced in an electric arc furnace where 100 percent steel scrap and scrap substitutes, such as direct reduced iron (DRI) pellets or briquettes, hot briquette iron (HBI), or pig iron, are melted. Scrap used in both processes is available in different quality levels, where residual elements such as copper, nickel, chromium and molybdenum vary by scrap type. Historically, steel produced using the integrated process was preferred for high quality grades due to the low residual element composition (copper,
