Choosing the right technology for stainless steel analysis

As a leading supplier of handheld LIBS (laser induced breakdown spectroscopy) technology, we have been asked recently whether LIBS will replace OES (optical emission spectroscopy) in the near future. Though LIBS is a fairly new analytical technology with plenty of potential, it isn’t quite ready to replace OES for accurate material identification requirements. Mikko Jarvikivi, Product Manager at Hitachi High-Tech, explains why there’s a place for both technologies.

The arrival of portable instruments capable of accurately analysing the chemical make-up of materials has been a real benefit for companies across a range of industries. With the right portable analyser, material sorting, positive material identification (PMI) and quality assurance or control tasks can be carried out quickly and efficiently. 

LIBS-based handheld analysers like the Vulcan by Hitachi High-Tech provide a fast and cost-effective solution. When you need to sort alloys or carry out PMI testing, LIBS instruments offer excellent performance with stainless steels and aluminium-based metals, and provide good performance where titanium and low alloy steels are involved. The Vulcan leaves a smaller mark on the sample, is robust, little user training is required, and it has a low cost of ownership.

While great advances have been made with LIBS technology in recent years, OES analysers still have much lower limits of detection for 100% accuracy, which is critical for reliable separation of L-grade stainless steels.  Both technologies have a place; which you choose will depend on the job at hand.



Analysing steels

In some alloys, elements that affect the hardness, melting point, strength and workability of the metal are present at well below 100ppm, and laser-based analysers can’t currently give accurate readings at these low levels. In most instances – including carbon steel - an OES-based analyser such as Hitachi High-Tech’s PMI-MASTER is the better, reliable alternative.

Carbon

Carbon is not only important when it comes to separating L- from high grades in stainless steel, but it’s also the most important element for iron and steel grades enabling the separation of low and unalloyed steels. For decades, mobile and stationary OES has been a well-established and recognised method for these applications.

Though there’s been a focus on measuring carbon in steels, it’s important to note that carbon isn’t the only element of interest in steels. Measurements for nickel, chromium, manganese, silicon and titanium content can all be obtained with an OES analyser, in contexts where you need to calculate carbon equivalency accurately. In contrast, LIBS devices simply cannot measure sulphur and phosphorous. Where refractory elements with high hardness and melting points including molybdenum, niobium, tantalum, tungsten and hafnium are present, many of the current LIBS analysers will struggle to measure them accurately.

Duplex steels

In the fast-growing area of duplex steels, the easy identification and separation of duplex grades via nitrogen content is an important application.

Other important trace elements

Meanwhile, there’s growing interest in low concentrations of boron – down to lower than 5ppm. Boron as an alloying element improves the hardness and hardenability of steel alloys through heat treatment. It’s particularly useful in construction, tools and for objects like screws.

But boron is undesirable in unalloyed steels as it has a bad influence on welding properties. The limit for boron to be classified as alloyed steel is just 0,0008ppm. Many customs offices around the world need to verify incoming imported steel for this very low limit.

As with a range of all technical relevant elements including carbon, OES analysers provide better accuracy and more reliable results for nitrogen, boron and all other relevant main and trace elements.

A trusted method

While handheld LIBS devices are faster, smaller and less expensive, the technology inside is still being developed. OES has been around for decades and is a trusted method of achieving accurate readings even for very low levels of detection. The bottom line is: can you afford to get small shifts in the amount of carbon and other elements wrong?

Even very small shifts in the amount of carbon- and other elements – in a sample will affect the material’s strength, brittleness and how it is worked in terms of methods, tools and temperatures. And, if an incorrectly graded alloy ends up in a part, tool or machine that ultimately fails, it could result in catastrophic accidents, costly product recalls, lawsuits and loss of reputation. With OES, precision and repeatability are guaranteed.

At Hitachi High-Tech, we’ve been supporting different industries with analysis technology for over 40 years. We recognise that a range of different technologies must coexist to give you the best solution for your application and analysis needs. That’s why our experts get to know your needs before recommending the best product for the job.

Our LIBS-based Vulcan handheld analyser is excellent for stainless steel and aluminium sorting, and some PMI quality control tasks. For fast, non-destructive analysis, the X-MET8000 range of handheld XRF analysers leads the market. To accurately determine the chemical composition of a full range of alloys, our OES range of stationary and mobile analysers promise uncompromised performance.

To find out more, contact us to book a demonstration today.


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Date: 6 March 2018

Author: Mikko Jarvikivi, LIBS Product Manager

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