ISO 15349-2:2021

Overview

ISO 15349-2:2021 specifies an infrared absorption method after combustion in an induction furnace (with preheating) for determining very low carbon contents in unalloyed steel. The method covers carbon mass fractions from 0.0003 % to 0.009 % and defines the principle, reagents, apparatus, sampling, calibration and reporting requirements for accurate low-carbon analysis.

Key topics and technical requirements

• Principle: pre‑heating a test portion followed by high‑temperature combustion in an induction furnace under a pure oxygen flow; carbon is converted to CO2 and/or CO and measured by infrared absorption.
• Applicable range: 0.0003 % to 0.009 % carbon (mass fraction).
• Calibration: performed using sucrose standard solutions or calcium carbonate to establish the calibration curve for IR response.
• Reagents & gases:
  • Water of analytical grade (ISO 3696, Grade 2) and CO2‑free water preparation.
  • Oxygen minimum purity 99.95 % (volume fraction); provisions for oxygen purification if organic contaminants are suspected.
  • Drying/purifying agents such as magnesium perchlorate or phosphorus pentoxide, and attapulgus clay impregnated with sodium hydroxide for oxygen purification.
• Apparatus: commercially available combustion/IR analyser systems; specific items include ceramic crucibles (high‑temperature ignition), tin capsules, glass‑fibre filters, microbalance (0.1 µg resolution) and micropipettes. Crucibles and consumables require prescribed pre‑treatment (e.g., ignition, acid cleaning) to minimize background carbon.
• Sampling & sample preparation: follow ISO 14284 or national equivalents; recommended sample particle size between 0.75 mm and 2.0 mm.
• Procedure & quality control: blank tests, instrument stabilization, oxygen flow control, dust collection and filter maintenance; instrument zeroing and adjustments using certified reference materials where applicable.
• Safety: precautions for handling oxygen cylinders, hot crucibles and combustion by‑products are emphasized.

Applications and users

ISO 15349-2:2021 is intended for:

• Metallurgical and chemical analysis laboratories performing low carbon analysis of unalloyed steels.
• Steel manufacturers and quality‑control (QC) teams monitoring carbon levels in products for mechanical properties and compliance.
• Third‑party testing laboratories and certification bodies verifying material composition for specification conformance.
• Instrument manufacturers and users of induction furnace carbon analysers and infrared carbon analysers implementing standardized methods.

Practical benefits include traceable, repeatable low‑carbon measurement, compatibility with commercial analyser systems, and guidance on calibration and sample handling to reduce analytical bias.

Related standards

• ISO 15349 series (other parts)
• ISO 14284 - Sampling and preparation of samples for chemical composition
• ISO 3696 - Water for analytical laboratory use
• ISO 648 / ISO 1042 - Laboratory glassware (pipettes, volumetric flasks)

Keywords: ISO 15349-2:2021, unalloyed steel, low carbon determination, infrared absorption, induction furnace, carbon analysis, sucrose calibration, calcium carbonate.