ISO 4491-3:2025

Overview

ISO 4491-3:2025 - "Metallic powders - Determination of oxygen content by reduction methods - Part 3: Hydrogen-reducible oxygen" - specifies a laboratory method to determine the hydrogen-reducible oxygen content in metallic powders containing 0.05 % to 3 % oxygen (mass percentage). The method applies to unalloyed, partially or fully alloyed metal powders and to carbide + binder mixtures. It excludes powders that contain lubricants or organic binders, and is intended to be used together with ISO 760 (Karl Fischer method) and ISO 4491-1 (general guidelines).

Key topics and technical requirements

• Principle: Dry a weighed test portion, reduce metal oxides in a stream of dry hydrogen, absorb the water produced in anhydrous methanol and quantify by Karl Fischer titration (visual or electrometric end‑point).
• Applicability: Unalloyed, alloyed and hardmetal/binder mixtures; can be extended to carbon-containing powders using a nickel catalytic converter that converts CO/CO2 to methane + water at 380 °C.
• Test portion masses (guidance):
  • 0.05–0.5 % O → 5 g sample
  • 0.5–2.0 % O → 2 g sample
  • 2.0–3.0 % O → 1 g sample
• Reduction temperatures: Specified per metal (examples from the standard):
  • Copper: 850 ±15 °C
  • Iron and steel: 1 100 ±20 °C
  • Nickel, cobalt, tungsten: 1 000 ±20 °C
  • Tin: 425 ±10 °C
  • Hardmetal mixtures: 1 000 ±20 °C
• Apparatus: Hydrogen and N2/Ar supply with purifiers, gas selection and drying units, gas‑tight quartz/refractory reduction tube with furnaces, boats, titration flask with electrodes, burette, and optional nickel catalytic converter. Typical gas flows and conditioning steps are defined in the procedure.
• Reagents & safety: Use analytical‑grade reagents. Karl Fischer reagent contains iodine, SO2, pyridine and methanol - handle with care and follow safety instructions. Do not stop hydrogen flow while the hot tube remains hot.

Practical applications and users

• Quality control and R&D laboratories in powder metallurgy, hardmetal and additive manufacturing powder supply chains.
• Producers of metal powders (unalloyed or alloyed) and carbide + binder systems who need reliable oxygen measurement for process control and specification compliance.
• Test houses and material certification labs that require standardized, repeatable oxygen determinations for acceptance testing, troubleshooting or material development.

Related standards

• ISO 760 - Determination of water - Karl Fischer method (general method)
• ISO 4491-1:2023 - Metallic powders - Determination of oxygen content by reduction methods - Part 1: General guidelines
• Other parts of the ISO 4491 series (see ISO website for the full list)

Keywords: ISO 4491-3:2025, metallic powders, oxygen determination, hydrogen-reducible oxygen, Karl Fischer titration, powder metallurgy, catalytic converter, reduction method, laboratory standard.