Hardness Conversion Chart: HV, HRC, HB & HRB

The required hardness of a workpiece could be defined by its functionality. If a harder or softer hardness on the workpiece is required, heat treatment will be helpful for modifying it specification. Typically, we are using some kinds of differnt heat treatment below to meet the requirements:

Quenching: Increasing Surface and Core Hardness

The way to increase the hardness of workpiece made of carbon steel or alloy steel is general performed by quenching which is to heat the workpiece above its critical temperature and hold for a period of time. After that, the workpiece have to be rapidly cooling in the water, oil or air to complete the quenching process. In that way, quenching could increase the hardness but decrease the ductile of the workpiece.

Tempering: Balancing Hardness and Toughness

Tempering is used to increase the toughness of the tooling or spring made of carbon steel or alloy steel. For parts featuring with excess hardness or becoming too hard/brittle after quenching, a consequently tempering process could reduce the hardness and increase the ductile by heating the workpiece to a temperature below its critical point and then steadily cooling to a lower termperature

Annealing: Reducing Hardness for Machining

annealing is similar to tempering which is also capable of altering the properties of a workpiece to reduce its hardness and increase its ductile. Under a proper heating temperature, the freedom moving atoms of the metal workpiece could achieve a more equilibrium state. After the heating stage, the workpiece is usually left in the oven for steadily cooling while recrystallization and grain growth are happening. For parts made of carbon steel or alloy steel, if it is a terminal or connector spare part for crimping, a annealing heat treatment might be required.

Case Hardening: Hard Wear Surface, Tough Core

There are a lots of heat treatment methods to partially harden the workpiece. Case hardening is capable of increasing the stiffness of the outer case of a carbon steel of alloy steel, and keep its core area soft as before for better ductile property. The hardened outer case of the workpiece can be much more durable and wear resistant. However, the hardened surface will be no longer suitable for machining. Therefore, case hardening is generally applied once the workpiece has been completed from CNC machining process.

Tensile Strength Rm 820-2180 [MPa]

Vickers: F ≥ 98 N, diamond pyramid (HV)
Brinell: F = 29.421 N, ball ø 10 mm (HB)
Rockwell: F = 1,471 N, diamond cone (HRC)

Tensile Strength Rm 255-930 [MPa]

1 MPa = 1 N/mm²

Vickers: F ≥ 98 N, diamond pyramid (HV)
Brinell: F = 29.421 N, ball ø 10 mm (HB)
Rockwell: F = 980 N, ball 1/16″ (HRB)

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Vickers Hardness Test (HV)

On metallic materials from very low to very high hardness, the Vickers hardness test is applicable. This hardness test is particularly suitable for very small and very hard samples.

Rockwell Hardness Test (HRC / HRB)

If the hardness of the metallic materials is within the following ranges, the Rockwell hardness test is applicable:

HRB: 20 bis 100HRB
HRF: 60 bis 100HRF
HRC: 20 bis 70HRC
HRA: 20 bis 88HRA
HRD: 40 bis 77HRD
HR15N: 70 bis 94HR15N
HR20N: 42 bis 86HR30N
HR45N: 20 bis 77HR45N

Brinell Hardness Test (HB)

The hardness test according to Brinell is for metallic materials with the steel ball is determined as indenter only up to 450HB, the overlying hardness values were determined with the hard metal ball.

HV,HB,HRC Hardness comparison table, How to modify the hardness on a workpiece?

How to Use a Hardness Conversion Table

Start with the hardness scale specified on the drawing. If the supplier’s test report uses another scale, use the conversion table only as a reference and confirm the acceptable range with the engineering team. For precision CNC parts, the test location, surface preparation, part thickness and heat treatment condition can all affect the result.

When conversion is acceptable

Conversion is useful during early quotation, material selection and supplier communication. It can also help compare older drawings that use HB or HRB with newer requirements that specify HV or HRC.

When direct testing is required

For final inspection, aerospace, automotive, medical, tooling and safety-related parts should follow the exact standard on the drawing. A converted value should not replace the specified hardness test unless the customer approves it.

Hardness Selection Tips for CNC Machined Parts

Higher hardness can improve wear resistance, but it may also increase brittleness, machining cost, grinding time and the risk of distortion after heat treatment. A good hardness requirement should balance strength, wear life, dimensional stability and the final application environment.

• Shafts, pins and wear parts: often require controlled hardening or case hardening for surface durability.
• Aluminum housings and brackets: usually rely more on alloy selection and anodizing than high hardness values.
• Stainless steel parts: hardness depends strongly on alloy grade, cold working and heat treatment route.
• Precision components: specify both hardness range and measurement position when function is critical.