Universal Goniometer for Steel Analysis

This article describes the analytical performance of Thermo Scientific^™ ARL^™ X900 Series for steel analysis with Moiré fringe goniometer.

Ferrous base materials are very important products worldwide since they serve as the foundation for various applications, such as construction, automotive, and manufacturing.

Accurately analyzing these materials ensures compliance with their chemical specifications and allows for high-quality, efficient production.

Irons

There are various types of irons, 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 the form of laminae or nodules.

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

ARL X900 Simultaneous/Sequential X-Ray Fluorescence Spectrometer. Image Credit: Thermo Fisher Scientific - Elemental and Phase Analysis

Low Alloy Steels

This category includes steels used in various applications such as:

• Castings, rails, axels, boiler and ship plates, and automobile bodywork.
• Girders for various bridge and structural components.
• Wires, nuts, bolts, forgings, springs, cutting steels.

From a compositional point of view, these steels can be recognized by the fact that the alloying elements generally total less than 5 to 7 %. Typically, the primary alloying elements are included at less than the following concentrations:

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

High Alloy Steels

High alloy steels contain, in addition to iron and carbon, considerable concentrations of one or more of the following elements: nickel, chromium, manganese, silicon, cobalt, tungsten, molybdenum and vanadium.

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

Instrument Parameters and Conditions

The 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.

With the two detectors (flow proportional and scintillation counters), exact elemental analysis from boron to californium is achievable.

The spectrometer can also handle up to 24 fixed monochromator channels in addition to the goniometer, or up to 32 fixed monochromator channels in the absence of a goniometer.

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

It should be noted that an XRF spectrometer is a very accurate comparator, but the accuracy of the final analysis is entirely dependent on the quality of the standards used for calibration and on the care and reproducibility of sample preparation which must be identical for CRMs and for routine samples as well.

Typical Performance in Low Alloy Steel Samples Using the Goniometer

Table 1 summarizes the normal limits of detection. Calibration was performed using a set of international steel standards with approved goniometer settings for crystal, detector, and collimator, as well as the maximum power of 4200 W. 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. Limits of detection (LoD) are computed using the calibration curve for 10 seconds and 100 seconds of counting time per element, respectively.

Because 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 10 s and 100 s counting time. Source: Thermo Fisher Scientific - Elemental and Phase Analysis

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 2500 W.

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 twice that of a single hour. This is due to the ARL X900 WDXRF Spectrometer's remarkable 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 - Elemental and Phase Analysis

Table 2b. Sample 2—short-term precision test over one hour using the goniometer at 2500 W—low alloy steel. Source: Thermo Fisher Scientific - Elemental and Phase Analysis

Table 3. Long-term repeatability over 60 hours using the goniometer at 2500 W—carbon steel. Source: Thermo Fisher Scientific - Elemental and Phase Analysis

Conclusion

The ARL X900 Simultaneous-Sequential XRF Spectrometer enables straightforward steel analysis. The Moiré fringe goniometer can analyze any element that is 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 in the event that any of the fixed channels fail.

Thermo Fisher Scientific offers complete calibrations for steel alloys. In this situation, the spectrometer's commissioning time is kept to a minimum.

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

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

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental and Phase Analysis.

For more information on this source, please visit Thermo Fisher Scientific - Elemental and Phase Analysis.