ISO 4491-2:2023

Overview

ISO 4491-2:2023 - Metallic powders - Determination of oxygen content by reduction methods - Part 2: Loss of mass on hydrogen reduction (hydrogen loss) defines a standardized laboratory test to evaluate the relative loss of mass a metallic powder exhibits when heated in a stream of pure, dry hydrogen. The method is intended as a chemical characteristic important to the powder metallurgy industry and complements other oxygen-determination methods (see ISO 4491-1 and Annex A). It is not a direct measure of specific elemental contents and is not applicable to lubricated powders or mixtures of metal powders.

Key topics and technical requirements

• Scope and applicability: Applies to unalloyed, partially alloyed and fully alloyed metal powders listed in Table 1 (examples include tin, tin bronze, silver, copper, iron/steel, cobalt, nickel, tungsten, molybdenum, rhenium).
• Gas quality: Hydrogen and purge gases (nitrogen or argon) must have maximum oxygen 0.005% mass fraction and dew point ≤ −45 °C.
• Apparatus: Electrically heated tubular furnace with controlled temperature zone, gas-tight quartz or refractory tube (25–40 mm ID), enclosed thermocouple (±5 °C), laboratory balance (±0.1 mg), ceramic boat (powder depth ≤ 3 mm) and gas supply with flow meters.
• Sampling and sample size: Test as-received powder; two determinations per sample; typical test portion ≈ 5 g (smaller for low apparent density powders).
• Test procedure: Purge with N2/Ar, replace with H2 at specified flow (≥ 25 mm/s gas speed), maintain prescribed reduction temperature and time from Table 1, re-purge and cool under inert gas, weigh before and after.
• Result calculation: Hydrogen loss = (mass loss ÷ initial powder mass) × 100 (%). Report mean of two determinations with specified expression and permitted differences.
• Precision statement: Includes inter-laboratory repeatability and reproducibility data for representative powders (e.g., iron, copper, tungsten).

Applications and users

• Quality control laboratories in metal powder production and powder metallurgy
• Materials characterization for sintering, pressing and consolidation processes
• R&D groups assessing powder chemical state and oxygen-related behavior
• Suppliers verifying batch-to-batch consistency of alloy powders

This standard helps ensure comparable, reproducible hydrogen loss testing across labs, supporting product specifications, process control, and material selection.

Related standards

• ISO 4491-1 (related reduction methods and interpretation; consult for element-specific determinations)
• Other ISO/CEN powder metallurgy testing standards (see ISO catalogue)

Keywords: ISO 4491-2:2023, metallic powders, hydrogen loss, oxygen content determination, powder metallurgy, reduction methods, loss of mass on hydrogen reduction, test method, precision.