Oxygen and Nitrogen in Solid Iron, Steel, Nickel-Base, and Cobalt-Base Alloys

Importance of the Topic

Accurate determination of oxygen and nitrogen concentrations in iron, steel, and nickel- or cobalt-based alloys is essential for process control and ensuring consistent mechanical properties. Oxygen removal controls carbon monoxide formation and inclusion levels, influencing porosity and material integrity. Nitrogen content directly affects strength, corrosion and wear resistance, but excessive nitrogen can cause embrittlement and formability issues.

Objectives and Study Overview

This application note evaluates the LECO ON736 analyzer for simultaneous measurement of oxygen and nitrogen in solid and powdered metal samples. It outlines required hardware, optimal settings, calibration procedures, and demonstrates expected performance metrics, enabling laboratories to adopt a reliable, cost-effective analytical workflow.

Used Instrumentation

• LECO ON736 Oxygen/Nitrogen Determinator
• Graphite crucibles (LECO 776-247)
• Lower electrode tips (611-351-182 non-automated, 611-351-181 automated)
• Nickel capsules (502-822) for chip/powder samples
• Reference materials: LECO Certified Reference Materials (LCRM®), LECO Reference Materials (LRM®), NIST standards

Methodology

• Sample Preparation: Remove surface contamination by filing or light grinding; rinse with acetone and dry; analyze immediately per ASTM E1806 and ISO 14284 guidelines.
• Analysis Protocol: Follow ASTM E1019. Determine instrument blank with three replicates. Perform instrument calibration/drift correction using at least three replicates of reference materials (~1 g each). Log samples with appropriate identifiers.
• Atmospheres: Two gas methods—helium and argon—employ automated sample drop introduction. Key parameters include analysis delays (20 s He, 35 s Ar), vacuum on time (7 s), and element-specific integration times (30 s O, 55 s N in He; 35 s O, 85 s N in Ar).
• Furnace Settings: Pre-outgas with two cycles at 5500 W (He) or 4000 W (Ar) for 12 s, cool 5 s. Analysis step at constant power (4800 W He, 3500 W Ar) for approximately 2.75 min (He) or 3.75 min (Ar).
• Replicates: Perform at least three measurements per sample or standard to ensure statistical reliability.

Main Results and Discussion

Testing of reference steel pins and iron granules demonstrated excellent accuracy and precision under both gas atmospheres:

• Oxygen determinations ranged from 0.0011 % to 0.0620 % with RSD typically below 5 %.
• Nitrogen results spanned 0.0004 % to 0.0681 %, also yielding low RSD values.
• Helium and argon methods produced comparable averages and standard deviations, confirming methodological robustness.

Benefits and Practical Applications

• Simultaneous O/N measurement accelerates throughput in QA/QC and research laboratories.
• Minimal sample preparation reduces handling errors and turnaround time.
• Compliance with ASTM and ISO standards ensures global acceptance.
• Versatile for solids, chips, and powders in steel, nickel-base, and cobalt-base alloys.

Future Trends and Potential Applications

Advancements may include fully automated sample loading systems, enhanced detection limits via optimized furnace control, integration with laboratory information management systems (LIMS), and AI-driven data analysis for predictive process control. Expanding to novel alloy systems and alternative inert gases will broaden the method’s applicability.

Conclusion

The LECO ON736 determinator offers a reliable, efficient, and precise approach for concurrent oxygen and nitrogen analysis in ferrous and non-ferrous alloys. Its performance meets or exceeds standard requirements, supporting quality control and research needs.

References

• ASTM E1019: Standard Test Methods for Determination of Carbon, Sulfur, Nitrogen, and Oxygen in Steel and Iron by Combustion Infrared Absorption
• ASTM E1806: Standard Practice for Sampling Steel and Iron for Determination of Nitrogen
• ISO 14284: Iron and Steel — Determination of Total Nitrogen — Modérée Combustion Method
• LECO ON736 Operator’s Instruction Manual