Steel Analysis & Testing with XRF Spectrometry and Goniometry

Ferrous base materials are essential products worldwide as they are the foundation for various applications, including construction, automotive, and manufacturing. It is important to correctly evaluate these materials to ensure compliance with their chemical standards and enable high-quality, efficient manufacturing.

Irons

Various types of irons exist, each defined by its composition and application. They fall into two primary categories:

• Hot metal, commonly known as pig iron, is the primary raw material used in steel production
• Cast irons are used to make semi-manufactured items

Metallographically, white cast iron with a cementite structure differs from grey cast iron, which contains free graphite in laminae or nodules.

These make gray cast iron inhomogeneous and difficult to examine. Alloy cast irons contain alloying elements such as nickel, chromium, manganese, copper, etc., which improve hardness, corrosion resistance, and engineering qualities.

ARL X900 Simultaneous/Sequential X-ray Fluorescence Spectrometer. Image Credit: Thermo Fisher Scientific – Production Process & Analytics

Low Alloy Steels

This category includes steels used in various applications, including:

• Steel castings, rails, axels, boiler and ship plates, automobile bodies
• Girders, all kinds of bridge and structural sections
• Wires, nuts, bolts, and forgings of any description
• Springs, cutting steel

From a compositional standpoint, these steels are differentiated because the alloying elements often amount to <5–7%. The major alloying elements are typically present at less than the following concentrations:

Mn 2%; Cr 3%; Ni 5%; Cu 1.5%; Mo 1.5%; and V 1%

High Alloy Steels

Aside from iron and carbon, high alloy steels contain significant amounts of nickel, chromium, manganese, silicon, cobalt, tungsten, molybdenum, and vanadium.

This category includes stainless steels such as 18/8, austenitic, maraging, and martensitic, and forms of special stainless steels, tool steels, high-speed steels, and high-manganese steels.

Instrumental Parameters and Conditions

The Thermo Scientific™ ARL™ X900 XRF Spectrometer features a patented Moiré fringe goniometer. The unique friction-free positioning system ensures analytical speed, versatility, and reliability.

Up to nine crystals and four collimators can be installed. The two detectors (flow proportional and scintillation counters) allow for exact elemental analysis ranging from boron to californium.

The spectrometer can also handle up to 24 fixed monochromator channels in addition to the goniometer or up to 32 channels without a goniometer.

The ARL X900 XRF Spectrometer can be calibrated with commercially supplied certified reference material (CRM) standards or user-provided, well-analyzed samples.

While an XRF spectrometer is an accurate comparator, the accuracy of the final analysis depends on the quality of the calibration standards used and the care and reproducibility of sample preparation, which must be the same for CRMs and routine samples.

Typical Performance in Low Alloy Steel Samples Using the Goniometer

Table 1 summarizes the normal limits of detection (LoD). Calibration was performed using a set of international steel standards, approved goniometer settings for crystal, detector, and collimator, and a maximum power of 4200W.

Phosphorus was measured using two distinct crystals to compare their performance. If necessary, all elements from B to Cf can be studied. However, Table 1 only covers a subset of the most common elements tested in steels.

LoD is computed using the calibration curve for 10 and 100 seconds of counting time per element, respectively. As the goniometer measures one element after the other, it is generally advantageous to employ shorter counting durations to achieve a final result in a few minutes.

Table 1. Typical limits of detection in ferrous matrix for the goniometer at 10s and 100s counting time. Source: Thermo Fisher Scientific – Production Process & Analytics

Typical Precision Tests

The stability of an instrument represents the precision that may be achieved. Over one hour, two low alloy steel samples were subjected to a short-term repeatability test consisting of 11 runs.

At each run, all items were counted throughout a 10-second period. This test employed a power level of 2500W.

A long-term repeatability test of 18 measurements of a carbon steel sample over 60 hours was undertaken (Table 3). All elements were counted using a 10-second interval. The power level was set to 2500 W for this test.

The standard deviation over 60 hours is less than double that of a single hour. This is attributed to the ARL X900 WDXRF Spectrometer’s exceptional stability.

Table 2a. Sample 1—short term precision test over one hour using the goniometer at 2500 W—low alloy steel. Source: Thermo Fisher Scientific – Production Process & Analytics

Table 2b. Sample 2—short term precision test over one hour using the goniometer at 2500 W—low alloy steel. Source: Thermo Fisher Scientific – Production Process & Analytics

Table 3. Long term repeatability over 60 hours using the goniometer at 2500 W—carbon steel. Source: Thermo Fisher Scientific – Production Process & Analytics

Conclusion

The ARL X900 Simultaneous-Sequential XRF Spectrometer allows for easy steel analysis. The Moiré fringe goniometer can analyze any element not fitted as fixed channels.

The goniometer analysis is performed concurrently with the measurement of the fixed channels. It can also serve as a backup if any of the fixed channels fail. Thermo Fisher Scientific offers complete calibrations for steel alloys, keeping the spectrometer’s commissioning time to a minimum.

These matrix types provide great precision for regular or R&D analysis, particularly when an innovative, high-counting fixed channel monochromator is utilized for elements such as Ni, Co, or Mo.

Thermo Fisher Scientific^™ OXSAS^™ Software, which runs on the latest Microsoft Windows^®, simplifies operation.

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This information has been sourced, reviewed, and adapted from materials provided by Thermo Fisher Scientific – Production Process & Analytics.

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