ISO 439:2020

Overview

ISO 439:2020 - "Steel and cast iron - Determination of silicon content - Gravimetric method" specifies a laboratory gravimetric procedure for measuring silicon content in steel and cast iron. The method is applicable for silicon mass fractions between 0.10 % and 5.0 %. It describes the full workflow from sampling and reagents to ignition, weighing and result calculation. The standard updates precision data from earlier editions and includes safety notes for reagents such as perchloric and hydrofluoric acids.

Key topics and technical requirements

• Scope and applicability
  • Applicable for silicon contents 0.10–5.0 % (mass fraction) in steel and cast iron.
  • Results may be less accurate for samples containing Mo, Nb, Ta, Ti, W, Zr or high chromium levels.
• Analytical principle
  • Dissolution of the test portion with hydrochloric and nitric acid.
  • Conversion of acid-soluble silicon compounds to hydrated silicon dioxide using perchloric acid fumes.
  • Filtration, ignition to form impure SiO2, treatment with hydrofluoric and sulfuric acid, final ignition and gravimetric weighing.
• Reagents and apparatus
  • Key reagents: HCl, HNO3, HClO4, HF, H2SO4; use analytical-grade chemicals and grade 2 water (ISO 3696).
  • Required apparatus: platinum crucibles, muffle furnace (800–1 100 °C), medium-texture low-ash filter paper.
• Sampling and sample size
  • Sampling per ISO 14284; use millings/drillings ≤ 0.2 mm thick.
  • Test portion masses recommended by silicon range (≈5 g, 2.5 g, or 1 g).
• Precision
  • Interlaboratory precision (repeatability and reproducibility) is reported and re-evaluated in this edition; smoothed values for r and R are provided for common Si levels.
• Safety
  • Explicit warnings on perchloric acid (explosive vapors) and hydrofluoric acid (highly hazardous).

Applications and who uses it

• Metallurgical and chemical testing laboratories performing silicon analysis in steel and cast iron.
• Quality control and specification testing in steel mills, foundries, heat-treatment shops.
• Research laboratories and conformity assessment bodies requiring a standardized gravimetric method for reporting Si content.
• Useful where instrumental methods (ICP/OES) are unavailable or when a primary gravimetric determination is required.

Related standards

• ISO 14284 - Sampling and sample preparation for chemical composition determination.
• ISO 3696 - Water for analytical laboratory use - Specification and test methods.
• ISO 5725 series - Precision of measurement methods (used for interlaboratory precision analysis).

Keywords: ISO 439:2020, silicon determination, gravimetric method, steel and cast iron, silicon content, analytical method, perchloric acid, hydrofluoric acid, muffle furnace, ISO 14284, ISO 3696.