Rockwell to Brinell Hardness Converter
Convert between Rockwell HRC, Brinell HB, and Vickers HV hardness scales for metals. Based on ASTM E140 conversion relationships.
Rockwell to Brinell Hardness Converter
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Formula: 30 HRC = 286 HB = 302 HV | 40 HRC = 371 HB = 392 HV | 50 HRC = 481 HB = 513 HV | 58 HRC = 615 HB = 653 HV | 60 HRC = 654 HB = 697 HV
Worked example โ 58 HRC = 615 HB = 653 HV (tensile roughly 2,122 MPa / 308 ksi)
Formula
30 HRC = 286 HB = 302 HV | 40 HRC = 371 HB = 392 HV | 50 HRC = 481 HB = 513 HV | 58 HRC = 615 HB = 653 HV | 60 HRC = 654 HB = 697 HV
There is no exact formula from Rockwell C to Brinell, because Rockwell reads the residual depth of a diamond cone while Brinell reads the surface area of a ball impression - two different physical measurements. ASTM E140 therefore publishes a table rather than an equation, and this converter interpolates that table for non-austenitic steels: 30 HRC is 286 HB, 50 HRC is 481 HB, and 60 HRC is 654 HB. Brinell values stop at 65 HRC (739 HB) because above that the ball indenter itself deforms. Tensile strength is a separate empirical rule of thumb, roughly 3.45 MPa per Brinell point, dependable only between about 120 and 450 HB.
Worked Examples
Example 1: Tool Steel Hardness Conversion
Problem:A tool steel is heat treated to 58 HRC. What are the equivalent Brinell and Vickers hardness values?
Solution:Read the 58 HRC row of ASTM E140 Table 1 directly - no algebra is involved: HB = 615 (HBW 10/3000 tungsten carbide ball) HV = 653 (Vickers) Tensile strength estimate: 615 x 3.45 = 2,122 MPa (308 ksi) That estimate is well outside the 120-450 HB band where the hardness-to-tensile rule is dependable, so treat it as indicative only.
Result:58 HRC = 615 HB = 653 HV (tensile roughly 2,122 MPa / 308 ksi)
Example 2: Casting Quality Verification
Problem:A steel casting tests at 250 HB. What is the approximate Rockwell C hardness?
Solution:250 HB falls between the 247 HB (24 HRC, 260 HV) and 253 HB (25 HRC, 266 HV) rows of ASTM E140 Table 1, so interpolate: Fraction = (250 - 247) / (253 - 247) = 0.5 HRC = 24 + 0.5 x 1 = 24.5 HV = 260 + 0.5 x 6 = 263 Approximate tensile: 250 x 3.45 = 862.5, so about 863 MPa (125 ksi) 24.5 HRC sits near the bottom of the Rockwell C range, where HRB on a 1/16 in ball is the more repeatable test.
Result:250 HB = 24.5 HRC = 263 HV (tensile roughly 863 MPa / 125 ksi)
Frequently Asked Questions
What is the Rockwell hardness scale and how is it measured?
The Rockwell hardness test measures the depth of penetration of an indenter under a large load compared to the penetration made by a preload. The Rockwell C scale (HRC) uses a diamond cone indenter with a 150 kg major load and is the most commonly used scale for testing hardened steels. The test involves applying a minor load of 10 kg to seat the indenter, then applying the major load of 150 kg, and measuring the additional depth of penetration. The hardness value is calculated from the depth measurement using a formula specific to each scale. Rockwell testing is fast, typically taking less than 15 seconds, and requires minimal surface preparation compared to other hardness test methods.
What is the Brinell hardness test and when should it be used?
The Brinell hardness test uses a hardened steel or tungsten carbide ball indenter pressed into the test material under a specified load, typically 3000 kgf for steels using a 10 mm ball. After the load is removed, the diameter of the resulting impression is measured using a microscope, and the Brinell hardness number (HB) is calculated by dividing the applied load by the surface area of the indentation. Brinell testing is particularly useful for materials with coarse or uneven microstructures such as castings, forgings, and rough surfaces where the larger indentation averages out local variations. The test is less suitable for very hard materials above approximately 650 HB because the ball indenter can deform and produce inaccurate results.
How accurate are hardness conversion calculations?
Hardness conversion calculations provide approximate equivalents because different tests measure fundamentally different material responses. Rockwell tests measure penetration depth while Brinell tests measure indentation diameter, and Vickers tests measure diagonal length of a square impression. The conversions in this tool are based on empirical relationships derived from ASTM E140 standard conversion tables for steel. Accuracy is typically within plus or minus 2 to 5 percent for carbon and alloy steels within the valid range. However, conversions become less reliable for non-ferrous metals, stainless steels, and materials with unusual work-hardening characteristics. For critical applications, always perform the actual hardness test in the required scale rather than relying solely on conversions.
What is the Vickers hardness scale and how does it relate to Rockwell and Brinell?
The Vickers hardness test uses a square-based diamond pyramid indenter with a 136-degree angle between opposite faces. The test can use any load from 1 gf to 120 kgf, making it versatile for both micro and macro hardness testing. Vickers hardness (HV) is calculated by dividing the applied force by the surface area of the indentation measured through the diagonals of the square impression. Unlike Rockwell and Brinell scales, the Vickers scale is continuous and does not require scale changes for different hardness ranges. Vickers numbers are roughly comparable to Brinell numbers below 300 HB, but the scales diverge at higher hardness values. Vickers testing is especially valuable for thin materials, surface hardness measurements, and weld heat-affected zone analysis.
What HRC range corresponds to commonly heat-treated steels?
Different steel applications target specific HRC ranges based on the required balance of hardness and toughness. Mild steel in its annealed condition typically measures below 20 HRC and is not usually tested on the C scale. Medium carbon steels quenched and tempered for general machinery parts usually fall between 28 and 38 HRC. Spring steels and higher-strength fasteners are tempered to 38 to 48 HRC. Tool steels for cutting applications range from 58 to 65 HRC, while high-speed steel cutting tools reach 62 to 67 HRC. Case-hardened surfaces on gears and bearings typically measure 58 to 63 HRC. Each application has an optimal hardness window where the steel provides adequate wear resistance without being too brittle for the service conditions.
Can I estimate tensile strength from hardness values?
Yes, there is a well-established empirical relationship between Brinell hardness and tensile strength for carbon and alloy steels. The approximate formula is Tensile Strength in MPa equals HB multiplied by 3.45, or in psi equals HB multiplied by 500. This relationship is reasonably accurate for steels with hardness between 120 and 450 HB. For example, a steel with 200 HB has an approximate tensile strength of 690 MPa (100 ksi). However, this correlation applies primarily to quenched and tempered carbon and alloy steels and should not be used for austenitic stainless steels, cast irons, non-ferrous metals, or precipitation-hardened alloys. For these materials, the relationship between hardness and tensile strength follows different correlations.
What factors affect hardness test results and conversions?
Multiple factors influence hardness test results beyond the inherent material hardness. Surface roughness affects indentation measurement accuracy, particularly for Brinell and Vickers tests where the impression dimensions are optically measured. Specimen thickness must be sufficient to prevent the indentation from being influenced by the support surface, generally requiring at least ten times the indentation depth. Test location matters because edges and previous indentations create stress fields that distort results. Temperature affects material behavior, with most standards requiring testing at room temperature. Internal residual stresses from machining, welding, or heat treatment can alter local hardness readings. Proper surface preparation, correct loading procedures, and appropriate indenter condition are all essential for reliable measurements.
Why are there different Rockwell scales (A, B, C) and when do I use each?
Different Rockwell scales exist because no single indenter and load combination works well across the full range of material hardness. The Rockwell C scale (HRC) uses a diamond cone with 150 kg load and is designed for hardened steels between 20 and 70 HRC. The Rockwell B scale (HRB) uses a 1/16 inch steel ball with 100 kg load and covers softer materials from 20 to 100 HRB, including annealed steels, copper alloys, and aluminum alloys. The Rockwell A scale (HRA) uses a diamond cone with 60 kg load and is suitable for extremely hard materials like cemented carbides and thin case-hardened surfaces. There are also superficial Rockwell scales (15N, 30N, 45N) that use lighter loads for testing thin materials, coatings, and small parts.
How do I choose the right hardness test for my material?
Selecting the appropriate hardness test depends on several factors including material type, specimen size, surface condition, and the purpose of testing. For hardened steels and tool steels, the Rockwell C scale is the standard choice due to its speed and simplicity. For softer metals like aluminum and brass, use Rockwell B or Brinell testing. For castings with coarse grain structures, Brinell is preferred because the larger indentation averages microstructural variations. For thin materials, coatings, or weld zones, Vickers microhardness or superficial Rockwell testing provides the necessary spatial resolution. For field testing of large components that cannot be moved to a laboratory, portable Rockwell or Leeb rebound hardness testers offer practical solutions with reasonable accuracy.
What is the ASTM E140 standard and why is it important for conversions?
ASTM E140 is the Standard Hardness Conversion Tables for Metals that provides internationally recognized conversion relationships between Rockwell, Brinell, Vickers, and other hardness scales. Published by ASTM International, this standard contains detailed tables based on extensive empirical testing of various steel types and other metals. The tables cover conversions for carbon steel, alloy steel, and tool steel in both hardened and annealed conditions. Engineers and quality control professionals rely on ASTM E140 when specifications require hardness values in a different scale than the test equipment available. The standard clearly states that conversions are approximate and should not be used as substitutes for actual measurements when precision is critical, particularly for acceptance testing and certification purposes.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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