Material Hardness and Heat Treatment for CNC Parts

Defining a hardness requirement

A grade name alone does not define acceptance hardness. State the grade and specification, delivery condition, required treatment, measurement location and acceptance range on the drawing. CNC-Turkey reviews new-part manufacturing against these requirements; general table values are not a production guarantee.

Review by material family

• ✓16MnCr5 / 20MnCr5: separate surface, core and case requirements in the case-hardening specification.
• ✓C45 / 42CrMo4: state supply condition and target properties; a grade does not have one fixed hardness.
• ✓Aluminium 6061 / 7075: specify alloy and temper, such as T6; do not report HBW/HV results under an HRC heading.
• ✓Bronze, brass, cast iron and plastics: select a method suited to the grade and product specification; do not automatically apply steel conversion tables.

An important distinction for stainless steel

Austenitic stainless steels such as 304 and 316L cannot be hardened by quenching and tempering like martensitic steels. Cold working can increase hardness. Martensitic grades such as 420 and precipitation-hardening grades require separate assessment; one hardness row cannot represent all stainless steels. Technical reference: Atlas Steels stainless steel handbook.

HRC, HBW and HV measurements

HRC, HBW and HV identify different test methods; equal numbers do not mean equal hardness. A thin surface layer and the core may require different test methods. Retain the scale, test conditions and measurement location in the report. ISO 18265 limits conversions to applicable materials; a conversion table does not automatically replace direct testing.

What to include in your RFQ

For a pin order, surface hardness requirements and core toughness needs are reviewed together. Specify surface/core acceptance values, effective case depth where required, dimensions after finishing and reporting needs on the drawing. CNC-Turkey confirms material, quantity, process sequence, final inspection and delivery scope during quotation.

About the historical hardness table

This guide updates the fixed-value approach in the historical Doğa Makina table. The original file remains archived; mixed scales and general equivalence labels should not be used as order acceptance criteria. An actual test report and a target specification are separate documents.