ISO 3738-2:1988

Overview

ISO 3738-2:1988 defines the preparation and calibration of standard test blocks for the Rockwell hardness test (scale A) specifically for hardmetals (cemented carbides). It specifies primary, secondary and working standard test blocks calibrated from master standards to be used for the verification of Rockwell hardness testing machines and indenters. This Part 2 is intended to be read in conjunction with ISO 3738‑1 (test method details).

Key topics and technical requirements

• Block materials and series: Blocks are hardmetals based on tungsten carbide and cobalt (no free carbon or eta phase). Nominal hardness series: 93, 92, 91, 88.5 and 85.5 HRA (groups of five blocks per series).
• Dimensions and surface finish:
  • Nominal diameter: 45 mm, nominal thickness: 8 mm.
  • Chamfer: 45° on 0.8 mm edge.
  • Test face flatness: max 0.010 mm; parallelism: max 0.020 mm/50 mm.
  • Surface roughness: Ra < 0.2 μm; test surface may be polished.
• Preparation steps:
  • Remove at least 0.35 mm of the test face before final calibration.
  • Marking conventions: primary blocks marked with CCPA and series identifiers; secondary blocks marked S; working blocks marked W.
• Calibration and statistical control:
  • Hardness determinations carried out per ISO 3738‑1 procedures; readings recorded to 0.01 HRA and rounded to 0.02 HRA for reporting.
  • Primary block acceptance: mean and standard‑deviation calculations across sets of impressions (e.g., 20 impressions distributed on the surface); if mean standard deviation sp > 0.07 HRA the block is rejected.
  • Secondary blocks: similar calibration against primaries; reject if s > 0.10 HRA.
  • Correction limits: if machine+indenter correction > 0.20 HRA (primary) or > 0.30 HRA (secondary), inspect equipment and repeat calibration.

Applications and users

ISO 3738‑2 is used to establish traceable, uniform Rockwell hardness standards for hardmetals and to:

• Verify and calibrate Rockwell hardness testing machines and indenters.
• Support quality control in cemented carbide and powder metallurgy manufacturing.
• Provide reference blocks for metrology laboratories, calibration service providers, tooling and cutting‑tool manufacturers, and testing laboratories.
• Reduce wear of master standards by using a tiered system (primary → secondary → working blocks).

Related standards

• ISO 3738-1 - Hardmetals - Rockwell hardness test (scale A) - Part 1: Test method (see for measurement and indenter specifications).
• Calibration and laboratory accreditation standards and local national metrology guidance may be used in conjunction for traceability and reporting.

Keywords: ISO 3738-2, Rockwell hardness, hardmetals, standard test blocks, calibration, primary standard blocks, secondary standard blocks, working standard blocks, Rockwell A scale, verification.