(Second in a three-part series)
- Our previous column, which appeared in the July issue, defined U.S. standards, international standards and industry-specific standards. From the ASTM and the SAE in the United States to Europe’s Euronorm, Japan’s JIS, the international ISO, China’s GB and Russia’s GOST, there are many classification and specification systems used worldwide. Each standards development organization has subtle differences in how it defines metal properties. An increase in international trade has made it more difficult for companies to pull standards and thoroughly understand them--which can result in inefficiencies along the supply chain.
Achieving a common vocabulary with regard to mechanical properties, physical properties and the ability to convert from one material is the primary goal of any standard. Specifications assist in all phases of a product’s life cycle--from concept to design, engineering and recycling. However, standards are not universally equivalent and interchangeable, and deciphering their meanings is an arduous process, requiring metallurgists to search from book to book, paper to paper and document to document.
Finding common ground
The main factors for researching equivalency include chemical composition, manufacturing method, product shape, and mechanical and physical properties. Additional factors such as deoxidation method, hardenability, corrosion and heat resistance, and other properties have an influence on interchangeability.
The considerations for steel alone are complex, yet metallurgists work with numerous materials. Steel equivalents usually are grouped based on chemical composition and, to some extent, mechanical properties. The cross-reference tables of equivalent steels often come from recommendations of standards development organizations. Steels can be classified by a large variety of criteria: composition (carbon, low-alloy or stainless); method of manufacturing (open hearth, basic oxygen process or electric furnace methods); product form (bar, wire, plate, sheet, strip, tubing or structural shapes); finishing method (hot rolling, cold rolling, surface or plating techniques); deoxidation practice (killed, semi-killed, capped or rimmed steel); microstructure (ferritic, pearlitic and martensitic); and heat treatment (annealing, quenching or tempering).
These groupings mean it is necessary to consider physical properties carefully: Steels classified as equivalent may not have precisely the same chemistry or precisely the same tensile and yield strength, and they typically will require further evaluation before determining interchangeability. Making a decision on the equivalency of two steels can be an error-prone process. The number of possible criteria for comparison and the associated combinations are very high. Consequently, defining steel equivalents requires a careful study of the specifications by qualified professionals. Most of the specifications are complex documents that cannot be condensed into a few lines of text.
For instance, ASTM A108, a specification that covers cold-finished carbon and alloy steel bars for heat treatment, machining into components or for as-finished conditions, such as shafting in construction applications, is seven pages long. Multiply that by a wide variety of materials used on a project and add international cross-referencing, and the potential for a costly mistake increases.
Although metals are used in a variety of applications around the world, including 80 to 90 percent of structural applications, there is much less emphasis placed on metals and metallurgy as a science. Despite these challenges, one of the primary uses for standards is to communicate with manufacturers in other countries. The ability to determine metal equivalencies successfully allows a U.S. company, referring to ASTM standards, to consult with its manufacturer in India and find a comparable material with its overseas suppliers. MM
The Key to Metals database brings together global metal properties and standards into one integrated and searchable database. Quick and easy access to mechanical properties, chemical composition, cross reference tables and more gives users useful information for more than 150,000 alloys.