How to Determine Soluble and Insoluble Aluminum in Low Alloy Steels

There is an increasing demand for cleaner steels. Aluminum plays a central role in the cleanliness of steel. Therefore, detailed aluminum analysis can offer additional information relative to the steelmaking process and the purity of manufactured steel.

Aluminum can form non-metallic inclusions (insoluble oxides) throughout the deoxidation step and in the secondary metallurgy. Particularly low alloy, Al-killed steels, where aluminum employed during the deoxidation process during steelmaking demonstrates high tendency for inclusion formation.

As a consequence of deoxidization, steel displays some insoluble aluminum content, which reveals itself in the form of aluminum oxide inclusions with greater hardness.

These inclusions can cause defects in the final steel product, thereby compromising the quality of the steel and leading to additional costs. Therefore, it is crucial to acquire as much information as possible about the aluminum content in the steel.

The Q8 MAGELLAN combined with new evaluation features in ELEMENTAL.SUITE v2.0 software facilitates analysis of not only the total aluminum but can also “separate” the total aluminum into fractions Al-soluble (in the metal lattice) and Al-insoluble (in the form of aluminum oxides).

The Q8 MAGELLAN offers rapid analysis with no additional production costs, using standard sample preparation.

Steel quality control for every production step.

Figure 1. Steel quality control for every production step. Image Credit: Bruker AXS Inc.

Q8 MAGELLAN with operator.

Figure 2. Q8 MAGELLAN with operator. Image Credit: Bruker AXS Inc.

Symmetric Al-channel single spark distribution of clean, inclusion-free steel.

Figure 3. Symmetric Al-channel single spark distribution of clean, inclusion-free steel. Image Credit: Bruker AXS Inc.

The Principle – Single Spark Evaluation (SSE) Al-Soluble & Al-Insoluble

While the sample is being analyzed, the spark (one of thousands during the analysis) is drawn towards the grain boundaries in the metal lattice. This is the prefered location of Al-oxides, and since the Al-concentration in these oxides is much higher compared to the bulk metal, an increased Al-signal is generated.

These high Al-signals produce an asymmetric single spark distribution (see Figure 4) which is processed by utilizing a statistical filter. As a result of this assessment, the various fractions of total and soluble aluminum can be distinguished.

Asymmetric tail (at higher Al concentrations) on the single-spark distribution indicates inclusions that effect steel cleanliness.

Figure 4. Asymmetric tail (at higher Al concentrations) on the single-spark distribution indicates inclusions that affect steel cleanliness. Image Credit: Bruker AXS Inc.

This result for the total and the soluble aluminum enables the calculation of the insoluble Al fraction. The unparallelled SSE capabilities of the Q8 MAGELLAN enable a detailed data treatment that offers invaluable, additional information.

Sampling and Sample Preparation

The chemical composition of the various stages of the steel refining process and casting are monitored by accurately establishing the composition of the steel samples extracted from the liquid steel.

The sample surface is prepared via grinding or milling to produce a flat and homogeneous surface. All samples used for the data collection were prepared following standard sample preparation procedure using silicon-carbide paper with grinding machine, BS118 P60.

Certified Reference Material (CRM)

CRM is reference material chracterized by a metrological valid procedure for one or more specified properties, alongside a certificate that provides the value of the specified property, its associated uncertainty and a statement of metrological traceability.

Instrument Description

Optical System

  • Paschen-Runge mount: 750 mm
  • Photomultiplier Detectors
  • Single-vacuum optic Source
  • Wavelength range: 110 nm – 800 nm  

Source 

  • Current curve by programmable logic modules
  • Digital generation of any discharge curve
  • Discharge time 10 μs to 2 ms
  • Maintenance-free, inductive ignition, integrated emergency stop
  • Maintenance-free, inductive ignition
  • max. 200 A peak current
  • max. 1000 Hz spark sequence 

Software 

  • Analysis software with integrated single spark evaluation (SSE)
  • Comprehensive statistic evaluation, SPC charts (option)
  • Efficient Service @ short term
  • Email-supported reporting system
  • Integrated analysis management using SQL database
  • Integrated systems for diagnosis and maintenance via the internet or telephone provided
  • Material quality monitoring with dynamic internal and external limit check
  • Material identification of unknown samples 

Weight & Dimensions 

  • 970 x 1050 x 1350 mm / 38 x 41 x 53“ (W x H x D)
  • Weight 300 kg / ~ 660 lbs. 

Evaluation Sequence  

  • Excitation of non-metallic aluminum fractions (insoluble) and bulk material
  • Analysis of the single spark signals
  • Application of a statistical algorithm to determine and quantify the “asymmetric” single spark distribution 

Performance Evaluation  

Measurements were performed using low alloy steel certified reference materials on the Q8 MAGELLAN. The certified element concentrations for the reference material and the measured element concentrations are displayed in Table 1.

Table 1. Comparison of certified with measured values. Source: Bruker AXS Inc.

CRM Altot [%]
(certified)
Altot [%]
(measured)
Alsol [%]
(certified)
Alsol [%]
(measured)
181A 0.016 0.015 0.014 0.013
184A 0.022 0.020 0.016 0.019
187B 0.027 0.023 0.025 0.021
189A 0.041 0.038 0.039 0.036
186B 0.042 0.040 0.038 0.037
185A 0.060 0.060 0.054 0.056
188A 0.093 0.085 0.083 0.080
183A 0.150 0.150 0.141 0.141

 

Plots of the certified vs. measured values for Al-total and Al-soluble soluble (see Figures 5 and 6) displays a clear linear correlation (> 99%), with each measured value falling within the scope of specified uncertainties of the CRM.

Linear fit between certified and measured values for Al-total.

Figure 5. Linear fit between certified and measured values for Al-total. Image Credit: Bruker AXS Inc.

Linear fit between certified and measured values for Al-soluble.

Figure 6. Linear fit between certified and measured values for Al-soluble. Image Credit: Bruker AXS Inc.

ELEMENTAL.SUITE.

Figure 7. ELEMENTAL.SUITE. Image Credit: Bruker AXS Inc.

Spark stand of the Q8 MAGELLAN.

Figure 8. Spark stand of the Q8 MAGELLAN. Image Credit: Bruker AXS Inc. 

ELEMENTAL.SUITE supports daily tasks and work. Automated average and limit checks guarantee safe operation. Just one click is all it takes to print, save and report analyses. Designed for optimal usability and flexibility, ELEMENTAL.SUITE offers a plug-in-based architecture to meet all analytical requirements. 

Conclusion 

The Q8 MAGELLAN, combined with the latest aluminum soluble option in ELEMENTAL.SUITE for low alloy steels, offers the correct answers, fast, using the most up-to-date, advanced technologies. 

It facilitates the determination of the aluminum soluble and insoluble concentration levels into the normal analysis process with no additional time or special conditioning. 

The rapid analysis demonstrates high accuracy and is well-suited for routine daily analysis where steel cleanliness is a crucial quality criterion.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Bruker AXS Inc.. (2022, February 21). How to Determine Soluble and Insoluble Aluminum in Low Alloy Steels. AZoM. Retrieved on August 30, 2022 from https://www.azom.com/article.aspx?ArticleID=21282.

  • MLA

    Bruker AXS Inc.. "How to Determine Soluble and Insoluble Aluminum in Low Alloy Steels". AZoM. 30 August 2022. <https://www.azom.com/article.aspx?ArticleID=21282>.

  • Chicago

    Bruker AXS Inc.. "How to Determine Soluble and Insoluble Aluminum in Low Alloy Steels". AZoM. https://www.azom.com/article.aspx?ArticleID=21282. (accessed August 30, 2022).

  • Harvard

    Bruker AXS Inc.. 2022. How to Determine Soluble and Insoluble Aluminum in Low Alloy Steels. AZoM, viewed 30 August 2022, https://www.azom.com/article.aspx?ArticleID=21282.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type
Submit