ISO 21988:2006

Overview

ISO 21988:2006 - Abrasion-resistant cast irons - Classification defines grades of abrasion-resistant white cast irons by chemical composition and Brinell hardness. The standard covers three main types: unalloyed or low-alloy cast irons, specific nickel‑chromium cast irons (4% Ni/2% Cr and 9% Cr/5% Ni), and high‑chromium cast irons with chromium content ranges from >11% up to 40%. ISO 21988:2006 sets designation rules, order information, manufacturing and heat‑treatment guidance, sampling and testing procedures, and requirements for microstructure and retesting.

Key topics and technical requirements

• Classification and designation: Materials are designated using symbols that indicate Brinell hardness and chemical composition (including chromium ranges). Designations follow guidance in ISO/TR 15931.
• Chemical composition: Grades are specified by elemental ranges (tables for unalloyed/low alloy, Ni‑Cr, and multiple high‑Cr ranges are provided).
• Hardness: Brinell hardness is the reference property and shall be tested per ISO 6506‑1. Tables in the standard link hardness classes to composition.
• Microstructure: Typical structures (eutectic carbides, martensitic matrices, etc.) are described; microstructure examination is performed when agreed between purchaser and manufacturer.
• Manufacture & heat treatment: The manufacturer decides manufacturing routes unless specified. Options (as‑cast, hardened, tempered, soft‑annealed, etc.) are listed; Annex A gives heat‑treatment guidance. Special machining considerations for high‑Cr grades (soft‑anneal vs machining hardened/as‑cast with CBN tools) are noted.
• Sampling & testing: Chemical analysis methods (spectrographic, X‑ray, wet chemical) and Brinell hardness testing requirements, locations (castings or cast‑on test blocks), and acceptance criteria are covered. Portable hardness devices may be used if validated.
• Retests & validity: Rules for invalid tests, retesting procedures and the manufacturer’s options when results are nonconforming are specified.

Applications

ISO 21988:2006 is targeted at materials and components that require high resistance to abrasive wear, commonly used in:

• Mining and mineral processing equipment (liners, crusher parts)
• Earth‑moving machinery
• Milling and grinding equipment
• Wear parts in manufacturing and heavy industry

Using this standard helps ensure consistent abrasion resistance, predictable service life, and clearer purchasing specifications for wear‑resistant castings.

Who uses this standard

• Foundries and cast iron manufacturers
• Materials and quality engineers specifying wear‑resistant components
• Purchasing agents ordering abrasion‑resistant castings
• Design engineers in mining, quarrying, and heavy machinery industries
• Test laboratories performing chemical and hardness analysis

Related standards

• ISO/TR 15931 - Designation system for cast irons and pig irons
• ISO 6506‑1 - Brinell hardness test - Test method

Annexes in ISO 21988:2006 provide guidance on heat treatment, hardness conversions (Brinell/Vickers/Rockwell C), microstructures, and composition vs. casting thickness - useful for implementation and supplier‑buyer agreements.