Wear Part Hardness Testing: Choosing Between Brinell, Rockwell and Leeb

Hardness is a core acceptance indicator for wear parts, yet the two most common field errors are using the wrong hardness scale (measuring an inhomogeneous casting with Rockwell) and treating a converted value as an equivalent value. More than 40 years of wear casting and testing experience since the 1980s at Grand Heavy shows that hardness testing looks simple but the wrong method is more dangerous than no test — it produces a wrong conclusion that appears well founded. This guide explains how to choose between the three methods and how to control their errors.

图：大美智造耐磨件实物——每批随附材质成分单与热处理过程记录，支持硬度复检

I. Principles and Scope of the Three Methods

1. Brinell (HBW) — first choice for inhomogeneous material

• Principle: a hardmetal ball is pressed into the surface under a specified test force and the indentation diameter is measured;
• Character: high test force and a large indentation, so the reading reflects an average over a substantial area;
• Best for: cast materials with inhomogeneous microstructure — manganese steel, high chrome iron and other wear castings. The indentation spans many grains and microstructural regions, giving representative and repeatable results;
• Not for: thin sections (indentation depth may exceed available thickness) and finished machined surfaces (large visible indentation).

2. Rockwell (HRC) — fast testing of homogeneous material

• Principle: a diamond cone indenter is applied with a preliminary then a main test force, and indentation depth is measured and converted to a hardness value;
• Character: low test force, small indentation, fast and directly readable;
• Best for: relatively homogeneous material — quenched and tempered steel, hardened steel, forgings;
• Key limitation: a small indentation means the reading represents only a local point. In cast microstructure (coarse grains, uneven carbide distribution) different points on the same part can differ widely, giving a one-sided conclusion. Using Rockwell to assess cast wear parts is the most common field misuse.

3. Leeb (HL) — convenient field testing of large parts

• Principle: rebound method — an impact body strikes the surface and the ratio of rebound velocity to impact velocity is measured;
• Character: portable, non-destructive, usable on site, suitable for large parts, installed components and cases where sampling is impractical;
• Best for: field screening and multi-point surveys on large parts;
• Key limitation: the Leeb value is a rebound quantity, not hardness directly, and must be converted to Brinell or Rockwell. Conversion depends on the elastic modulus of the material, so using one conversion table across different materials introduces systematic error. It is also highly sensitive to surface roughness, specimen mass, thickness and curvature.

II. Error Control: Where Each Method Loses Accuracy

Warning: hardness conversion (the easiest trap)

• Conversion tables are built from specific materials and statistical relationships. Converted values are for reference only and must not be treated as equivalent for acceptance;
• Conversion relationships differ between carbon steel, alloy steel, cast iron and manganese steel; using the wrong table introduces systematic bias;
• Correct approach: acceptance must be judged on the measured value in the scale specified by the requirement. If the specification states HBW, measure HBW rather than submitting a converted Leeb value.

图：硬度检测实验室——布氏、洛氏与便携里氏仪器各有适用范围，选错方法比不测更危险

III. A Field Lesson: Hardness Passed, Wear Life Failed

A quarry received a batch of wear liners and sampled them with a portable Leeb hardness tester. The converted readings appeared to pass, so the batch was accepted. The liners then chipped well before expected life, and the quarry concluded the supplier had cut corners.

We re-tested, and the problem lay in the test method itself:

• Issue 1: test points not ground. The castings had as-cast surfaces, and the Leeb method is highly sensitive to surface roughness. Readings on the rough surface were clearly high and widely scattered — the pass itself was unreliable;
• Issue 2: wrong conversion table. The parts were manganese steel but a conversion relationship for ordinary steel was used, a systematic bias;
• Issue 3 (most fundamental): the wrong criterion. Manganese steel is characterised by modest as-delivered hardness but exceptional work hardening under impact. Judging its wear resistance by as-delivered hardness is using the wrong indicator entirely. The right things to examine are chemical composition, water toughening quality (metallography) and toughness for the duty.

The conclusion was not that the liners failed but that the test method and criterion were wrong. Brinell testing and metallographic analysis on samples confirmed the batch met composition and water toughening requirements. Fracture analysis of the failed parts later traced the chipping to tramp iron impact on the duty side, unrelated to material — exactly the pattern we documented in failure mode analysis.

Three rules were recorded: 1. castings use Brinell, homogeneous parts use Rockwell, field surveys use Leeb; 2. converted values are reference only, not acceptance criteria; 3. for manganese steel judge microstructure and work hardening, not as-delivered hardness.

IV. Method Selection Table (Save This)

Three-step selection: 1. Is the microstructure homogeneous? If not, use Brinell; 2. Can a sample go to a laboratory? If yes, use Brinell or Rockwell; 3. Field only and the part is large? Use Leeb, but grind the surface, use the correct conversion table and average multiple points.

V. Insider Gotchas

• Using Rockwell on cast wear parts: the small indentation represents a local point only, and inhomogeneous cast microstructure makes readings vary widely across one part. Castings should use Brinell;
• Treating converted values as equivalent: conversion tables are statistical relationships for specific materials and are reference only. If the requirement states HBW, measure HBW;
• Judging manganese steel by as-delivered hardness: as-delivered hardness is inherently modest (about HB 180 to 220); wear resistance comes from impact work hardening. Rejecting it on as-delivered hardness is using the wrong indicator;
• Taking Leeb readings on as-cast surfaces: roughness strongly affects the rebound method, giving high and scattered values. Grind the point flat first;
• Concluding from a single reading: all methods should use multiple points averaged, with maximum and minimum recorded. A single reading is not representative;
• Assuming higher hardness means better wear: hardness is necessary but not sufficient. With insufficient toughness, high hardness chips more readily — a pattern repeatedly confirmed in failure mode analysis.

VI. When NOT to Test It Yourself

• Tests serving as quality dispute or acceptance evidence: must be issued by an accredited third-party laboratory per the standard method; in-house data cannot be the criterion;
• Judging manganese steel water toughening quality: hardness cannot reveal grain boundary carbides; metallographic analysis is required — see the water toughening standard explained;
• Thin-wall parts or finished machined surfaces: Brinell damages the surface and Rockwell may be limited by thickness; use non-destructive methods or agree a sampling method with the supplier;
• Only a Leeb tester and no reference blocks: data from an uncalibrated instrument without verification is not trustworthy; resolve metrology first.

Three actions: 1. Choose the scale by microstructure homogeneity (castings to Brinell); 2. Grind the test point, verify the conversion relationship and average multiple points; 3. Read hardness together with the composition certificate and metallographic report for a complete material assessment.

FAQ

• Q: Which hardness tester should be used for wear castings? A: Prefer Brinell (HBW). Cast microstructure is inhomogeneous and the large Brinell indentation reflects an area average with better representativeness and repeatability. The small Rockwell indentation can give different conclusions depending on test point location.
• Q: Can a Leeb reading be used directly as Brinell hardness? A: No. Leeb values must be converted, and the conversion depends on the elastic modulus of the material, so one table across different materials gives systematic error. Converted values are reference only; acceptance uses the scale specified in the requirement.
• Q: Is low as-delivered hardness in manganese steel a defect? A: No. As-delivered (water toughened) hardness is inherently modest at about HB 180 to 220; wear resistance comes from work hardening under service impact. Judge manganese steel by chemical composition and microstructure after water toughening, not as-delivered hardness.
• Q: Does higher hardness mean better wear resistance? A: Hardness is a necessary but not sufficient condition. High hardness with insufficient toughness chips readily under impact. Selection must consider hardness and toughness together with the actual duty.
• Q: What should be watched when using a Leeb tester on site? A: Three things matter most: 1. Grind the test point flat (as-cast surfaces read high and unstable); 2. Use the correct conversion relationship for the material; 3. Average multiple readings. The instrument also needs periodic verification with reference blocks.
• Q: Does Grand Heavy support hardness testing and material analysis? A: Grand Heavy wear parts ship with material certificates and heat treatment records, and we assist customers with hardness re-testing, metallographic analysis and joint failure analysis. See also GB/T 5680 water toughening explained and the purchase and acceptance checklist.

VII. Final Verdict

Three rules for hardness testing: 1. castings use Brinell, homogeneous parts use Rockwell, field surveys use Leeb; 2. converted values are reference only, not acceptance criteria; 3. for manganese steel judge microstructure and work hardening, not as-delivered hardness. The wrong method is more dangerous than no test, because it yields a wrong conclusion that looks well founded. Foshan Grand Heavy Trading Co., Ltd. has built mining equipment and wear casting expertise for 40+ years, holds 20+ patents, partners with Central South University and Guangdong University of Technology, and is certified as a National High-Tech Enterprise [To be added: certificate number]. We serve CNBM, Conch Cement and clients across 6 overseas markets with 24-hour response from Guangzhou, Foshan and Changsha.

Grand Heavy — Castings use Brinell, converted values are reference only!