Sulfur Determination in Ultra Low Sulfur Steel, Nickel, and Superalloys (CS844, CS844ES)

Importance of the Topic

Sulfur impurities at trace levels can compromise oxide scale formation and degrade mechanical properties of high temperature alloys used in aerospace and industrial applications.
Accurate quantification of ultra-low sulfur content is therefore critical for quality control and lifetime prediction of steels, nickel and superalloys.

Objectives and Article Overview

This application note describes the development and validation of a combustion-based method for determining sulfur at sub-ppm to low-ppm levels in steel, nickel and superalloy matrices using the LECO CS844 and enhanced sensitivity CS844ES analyzers.
Key goals include demonstrating detection limits, precision, repeatability and comparison between regular and enhanced sensitivity modes.

Methodology

Sample Preparation

• Abrasion or solvent cleaning (acetone) followed by warm air drying to remove surface contamination.
• Use of ceramic crucibles preheated to ≥1000 °C (1 h) or ≥1250 °C (15 min) to eliminate background sulfur.
• Addition of LECOCEL II HP accelerator (1.000 ± 0.005 g) to each sample.

Analytical Procedure

• Blank determination with at least three replicates to establish baseline signal.
• Calibration/drift correction using certified reference materials and linear regression across relevant concentration ranges.
• Sample analysis with 1.0 ± 0.2 g portions, with duplicate mode runs (regular and enhanced sensitivity) to compare performance.

Instrumentation

• LECO CS844/CS844ES sulfur analyzer with infrared detection.
• 528-018HP ceramic crucibles, 502-173 LECOCEL II HP accelerator, 773-579 metal scoop and 761-929 tongs.
• Optional autoloader for automated sample introduction.

Main Results and Discussion

Analyses of certified reference materials yielded the following average sulfur concentrations (ppm) and standard deviations:

• Steel chip LCRM (~1 ppm S): regular 1.06 ± 0.043, ES 1.06 ± 0.036
• Nickel wire (~0.5 ppm S): regular 0.52 ± 0.058, ES 0.56 ± 0.048
• Low alloy silicon steel (~3.7 ppm S): regular 3.66 ± 0.094, ES 3.83 ± 0.078
• Nickel superalloy (~2 ppm S): regular 2.03 ± 0.121, ES 2.01 ± 0.058
• Single crystal nickel alloy (~0.7 ppm S): regular 0.69 ± 0.13, ES 0.77 ± 0.09

Enhanced sensitivity mode achieved comparable accuracy with reduced variability, extending detection capability toward 0.1 µg absolute sulfur.

Benefits and Practical Applications

• High precision quantification of sulfur at ultra-low levels supports stringent quality standards in aerospace, power generation and petrochemical industries.
• Enhanced sensitivity mode allows detection previously achievable only by GD-MS, at lower cost and higher throughput.
• Robust sample preparation and calibration protocols ensure reliability for QA/QC laboratories.

Future Trends and Applications

• Integration of automated sample handling and data management to increase productivity and traceability.
• Further lowering detection limits through advanced furnace designs and detector technologies.
• Expansion to other heteroatom analyses (e.g. nitrogen, chlorine) in complex alloy matrices.

Conclusion

The LECO CS844/CS844ES combustion analyzer delivers accurate and reproducible sulfur determinations in ultra-low sulfur steels, nickel and superalloys. The enhanced sensitivity mode provides improved precision at trace levels, supporting critical material qualification and quality control in high temperature alloy manufacturing.

References

• ASTM E1806 Standard Practice for Preparation of Metallographic Specimens.
• LECO CS844/CS844ES Operator’s Manual.
• NIST SRM 861 Nickel-Based Superalloy Certificate.