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Guest Editorial

Testing and identifying materials

By Peter Schlafly & Viktor Pocajt

(Third in a three-part series)

December 2010

- Within the last decade, the development of next-generation spectrometers has increased the speed and versatility of the chemical analysis of a wide variety of metals. Using modern X-ray Fluorescence (XRF) and Optical Emission Spectrometers (OES), including portable models, the chemical analysis of a metal can be completed in seconds. These tools are highly effective for performing tasks such as controlling, sorting and positively identifying materials.

Companies increasingly are using fast and accurate composition analysis to control materials and processes in the iron- and steel-making industry, foundries, scrap sorting, metal processing and machining, laboratories, reverse engineering and forensics.

Challenges ahead
Although obtaining chemical analysis is simple with modern spectrometry, the identification of material still has many pitfalls. Often, operators and engineers cannot identify the material precisely or its designation, origin or detailed properties. However, for proper identification, they should be able to answer the following questions: What is this grade? What is its designation? Where is it from? What are its other properties? How can I replace it?

Books, classic searchable grade libraries and search engines cannot efficiently answer these questions for several reasons:

  • When interpreting analysis data, search engines cannot distinguish between the attributes defined by the standard specifications and the commonly present trap elements and impurities that an expert would ignore otherwise.
  • There is measurement error and nonhomogeneity in the material, which tends to bias the operator or a classic software engine.
  • Operators, engineers and classic software packages are usually not able to rank elements quickly and reliably by relevance for the analyzed metal grade.
  • Books can be an inefficient search resource and lack comprehensiveness and universal character. Because there are hundreds of thousands of metal grades worldwide, books often only cover one group of materials or one group of standards.

 

Using these types of methods for material identification can incur large costs and decreased revenue through thousands of working hours spent in research, costs of communication, costs acquiring specifications and standards, and the inevitable cost of rework and scrap due to inadequate material selection.

Expert material identification
Top experts in material identification follow a detailed process, first identifying material by rough classification, discovering the metals category to which the unknown alloy belongs, for example, stainless steel, low-carbon, low-alloy steel, aluminum alloy or titanium alloy. Then, an expert focuses on the most-important alloying elements for this category, for example, carbon, chrome, nickel and manganese for conventional stainless steel. Based on the most-important alloying elements, the next step is to find similar alloys from available data sources. Finally, the expert selectively narrows the list of results by evaluating and comparing less-important alloying elements and mechanical properties.

Once the expert identifies the specific grade, determining which metals are interchangeable requires careful consideration. The main factors to consider include composition, product shape and mechanical and physical properties.

Additional factors such as manufacturing method, finishing method, deoxidation method, hardenability, corrosion and heat resistance also may have significant influence on metal equivalency and its potential interchangeability. Therefore, it is important to recognize that a judgement on the equivalency of two metals is highly dependent on circumstances in each particular case.

Searchable material databases provide great assistance in completing identification. In addition, they can save time when searching for equivalent materials and their properties and provide a common platform for engineering, purchasing and manufacturing, which can create new opportunities for increased effectiveness and efficiency throughout a company and its corresponding supply chain. 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.

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