Analysis of Carbon Equivalents in Steel Components

Significance of the Topic

Carbon content and its equivalent in steel critically influence weldability, susceptibility to cold cracking and overall structural integrity. By quantifying the combined effect of carbon and alloying elements (Mn, Cr, Mo, V, Cu, Ni, Si), carbon equivalence (CE) offers a unified metric for predicting hardenability and hydrogen-induced cracking risk in welded components, especially in scrap-based electric arc furnace steels.

Objectives and Study Overview

This application note evaluates the Thermo Scientific Niton Apollo handheld LIBS analyzer for rapid, on-site determination of carbon equivalence in steel. The study focuses on repeatability of CE calculations using IIW and AWS formulas across multiple X65 steel samples and demonstrates the instrument’s suitability for field weldability assessment.

Methodology and Instrumentation Used

Sample Preparation and Analysis

• Surface cleaning to remove contaminants
• Argon purge to minimize ambient interference
• Laser-Induced Breakdown Spectroscopy capturing emission lines of C and alloying elements

Instrumentation

• Thermo Scientific Niton Apollo handheld LIBS analyzer
• High-purity argon purge system
• Integrated laser source and detection optics
• Pseudo-element programming for automatic CE calculation

Main Results and Discussion

CE Classification

• CE ≤ 0.35: Excellent weldability
• 0.36–0.40: Very good
• 0.41–0.45: Good
• 0.46–0.50: Fair
• > 0.50: Poor

Repeatability

• Average CE-IIW: 0.290 (RSD 3.1 %)
• Average CE-AWS: 0.337 (RSD 2.4 %)
• Elemental precision: RSD < 5 % for C, Mn, Cu, Si, Ni, Cr; higher RSD observed for Mo, V, Ti, Al due to lower concentrations

The results confirm consistent, lab-quality performance in under 10 seconds per reading, suitable for field conditions.

Benefits and Practical Applications of the Method

• Rapid, reliable CE measurement on site without bulky OES equipment
• Enhanced safety when working at heights or in confined spaces
• Immediate weldability feedback for repair, maintenance and QA/QC
• Automated CE calculation reduces operator error

Future Trends and Applications

Handheld LIBS is poised for integration with digital quality-management systems and cloud data platforms, enabling real-time monitoring and traceability. Advanced chemometric models may further refine alloy characterization, while extending applications to non-ferrous alloys, coatings and corrosion studies.

Conclusion

The Niton Apollo handheld LIBS analyzer delivers fast, precise carbon and CE measurements with strong repeatability, offering a powerful tool for on-site weldability assessment across petrochemical, offshore, pipeline and general steel fabrication industries.

Reference

• Wilson B. Analysis of Carbon Equivalents in Steel Components Using the Niton Apollo Handheld LIBS Analyzer. Thermo Fisher Scientific Application Note; 2019.