How do you read a hardness number? Brinell, Rockwell, Vickers

What do Brinell, Rockwell and Vickers numbers mean, and why can't one factor convert them?

A hardness number records how a hard point marks a surface under a stated load, so it means nothing until you know the test; the glossary names the three.

Our profiles show the details are part of the number. Nickel annealed rod and bar reads 90 to 120 HB at a 3000 kg load, and the profile notes Rockwell B 45 to 70 for it. Aluminium bronze C95400 continuous-cast bar reads 170 BHN as cast and 195 BHN heat treated at 3000 kg, while another supplier prints 177 heat treated at a 500 kg load, so the two are not like for like.

You cannot convert between scales with one factor, because Brinell and Vickers divide a load by a dent area, Rockwell reads a depth, and metals that work-harden behave differently under each indenter. Standards publish tables for material families, such as ASTM E140 and ISO 18265 for steel. They give estimates and suit neither work-hardened nor non-ferrous metals.

The steel pairs in our profiles agree with a steel table to within a point or two of HRC, but each is a single-source point: 17-4 PH stainless steel prints 352 HB beside 36 HRC in condition A and 420 HB beside 44 HRC in H900, and 1.2738 plastic mould steel 300 HB with 32 HRC.

How hard are tool steels and hardened steels in HRC?

Hardened tool steels read from the 40s to the low 60s HRC in our data, following the temper. AISI D2 cold-work tool steel reads 63 to 65 HRC after hardening at 990 to 1080 °C and before tempering. A tempering table from a thesis gives 63 HRC at 100 °C, 61 at 200 °C, 58 at 300 and 400 °C, 59 at 500 °C, 56 at 550 °C, 51 at 600 °C and 35 at 700 °C, without the hardening temperature or hold time. The small rise at 500 °C is secondary hardening, not a typo (general engineering knowledge, not in our data). AISI H13 hot-work tool steel (Uddeholm Orvar Supreme) reads 53 to 54 HRC before tempering and 45 HRC after 2 + 2 h at 610 °C.

Mould steels are supplied softer so that blocks can be machined. P20 plastic mould steel is pre-hardened at about 30 to 34 HRC; re-hardened it reads 51 HRC, then 42, 36 and 28 HRC after tempering at 500, 600 and 700 °C. 1.2738 plastic mould steel is supplied at 30 to 35 HRC (32 typical) and follows 51, 42, 39 and 28 HRC through the same steps. 1.2316 stainless plastic mould steel, the stainless mould grade, is about 30 HRC as delivered and printed as up to 48 HRC with no heat treatment attached.

Hardened stainless steels use the same scale. 17-4 PH stainless steel bar reads 44 HRC at H900, 38 at H1025 and 33 at H1150 as typical values; the ASTM A564 minimums for those three conditions are 40, 35 and 28 HRC. Stainless steel 420 reads 48 HRC tempered at 440 °F and 36 HRC tempered at 1000 °F.

Quenched and tempered Alloy steel AISI 4340 bars are a typical 24 to 38 HRC with the temper not stated. Soft steels such as Alloy steel AISI 4130 as supplied (18 to 22 HRC) sit at the low edge of the usable HRC range, where HB or HRB is the usual choice (general engineering knowledge, not in our data).

HRC is the wrong scale for a nitrided surface. The AISI D2 cold-work tool steel profile holds about 1250 HV1 after nitriding at 525 °C, with a case 0.3 mm deep after 30 h, and AISI H13 hot-work tool steel about 1100 HV0.2 with cases 0.12 to 0.2 mm deep. A cone that sinks through a case this thin measures the core, so use HV at a stated low load.

What Brinell values do carbon and alloy steels hold?

Plain carbon steels are quoted in HB for the form they are sold in. Carbon steel 1010 reads 95 to 105 HB with the form not stated, Carbon steel 1045 170 to 210 HB hot rolled, Carbon steel 1070 192 to 212 HB as a supplier range with the condition not specified, and Carbon steel 1215 167 HB as cold-drawn round bar.

Heat-treated alloy steels move with the ruling section. Alloy steel AISI 4140 reads 269 to 331 HB quenched and tempered at 10 to 100 mm, 275 HB typical at 50 mm, and 302 HB normalised at 870 °C in a 25 mm round.

Alloy steel AISI 4340 runs from 248 to 302 HB in condition T at 150 mm up to 363 to 429 HB in condition Y at 30 mm, with condition Z a minimum of 444 HB at 30 mm; annealed it reads 217 HB. The datasheet does not cite the standard that defines the letters T to Z, so ask which one applies. On a steel table 444 HB is about 47 HRC. The 24 to 38 HRC bar in the HRC chart is a separate, narrower typical range; conditions X to Z in the same profile (341 to 444 HB) go higher.

The scale follows the state of the steel. AISI H13 hot-work tool steel reads about 180 HB soft annealed and P20 plastic mould steel 280 to 325 HB as delivered; as the short answer shows for D2, a Brinell number for a supplied tool steel says nothing about the hardened tool.

How hard is stainless steel, and which scale does each grade use?

Annealed austenitic stainless steel is quoted as a maximum in Rockwell B or Brinell. Stainless steel 304L is 92 HRB maximum (ATI plate, sheet and strip) and 201 HB maximum (ICAST, ASTM A240); the profile also holds an approximate 150 HB annealed typical from CarTech. Stainless steel 304 is 201 HB and 92 HRB maximum under ASTM A240. AISI 321 stainless steel is 217 HB maximum for bar, with the temper not stated, and AISI 302 stainless steel 230 HB maximum under EN ISO 6931-1 (grade 1.4310, solution-annealed bar up to 40 mm), a European bar standard that is not comparable with the ASTM A240 plate limits.

Cold work moves a grade across scales. Stainless steel 301 reads a typical 85 HRB annealed, then 25, 32, 37 and 41 HRC in the quarter-hard, half-hard, three-quarter-hard and full-hard tempers. Duplex grades print both scales: Duplex stainless steel 2205 plate reads 293 HB maximum (ICAST) and 31 HRC maximum (ATI), both ASTM A240, and Super duplex stainless steel 2507 seamless tube 32 HRC maximum and bar 28 HRC maximum.

Martensitic grades depend on heat treatment, and their sources mix standards. AISI 416 stainless steel reads 220 HB maximum annealed for EN 1.4005 (X12CrS13), the European grade the profile lists, and 385 HB tempered at 900 °F from a Rolled Alloys bulletin. The same bulletin gives 26 to 32 RC after hardening with no temper. A 385 HB tempered product and a 26 to 32 RC product cannot be the same state, because 385 HB is well above 32 HRC on a steel table. Stainless steel 420 is 241 HB maximum annealed, and Stainless steel 431 260 HB annealed. Stainless steel 440C reads 60 HRC after a 300 °F temper (hardened at 1900 °F, oil quenched, 1 in round), 59 HRC at 400 °F and 56 HRC at 600 to 800 °F.

How hard are aluminium, cast iron, zinc and other soft metals?

Temper sets the number for aluminium, so quote it. Aluminium alloy 5083 sheet reads 75 and 89 HB in O/H111 and H32 (AZoM); H116 is 81 HB from a dealer datasheet with no product form. Aluminium alloy 5754 (AlMg3) sheet reads 52 HB in H114 and 70 HB in H24 (BS EN 485-2). Magnesium alloy AZ31B reads 73 HB as rolled, with no temper named. Zinc alloys carry vendor-sheet minimums citing ASTM B86, 82 HB for Zamak 3 and 91 HB for Zamak 5, and a ZA-8 range of 85 to 103 HB.

Cast irons are quoted by grade. Gray cast iron G1800 reads 120 to 187 HB and G4000 217 to 269 HB, with the test bar not stated; the five SAE J431 grades are summarised on Wikipedia, not taken from the standard. Ductile iron EN-GJS-400-15 reads 135 to 180 HB on one page and a typical 120 to 180 HB on another. Aluminium bronze C95400 has an ASTM B148 sand-casting minimum of 150 BHN, on a vendor sheet that disclaims it.

Some alloys are quoted in Rockwell B. Free-cutting brass C36000 half-hard H02 bar of 12.7 mm and under reads 60 to 80 HRB. Hastelloy C-276 solution-annealed sheet reads 88 HRBW and bar 86 HRBW.

When is Vickers used, and what about coatings, ceramics and polymers?

Vickers suits small, thin or brittle things. Palladium (Pd) annealed reads 40 HV, the N42H grade of NdFeB 620 HV, Aluminium alloy 3003 in the O temper 29 HV and TZM molybdenum alloy 200 to 250 HV as a reference value, all with the load not stated. Alumina (Al2O3) (Kyocera AO479O) reads 15.2 GPa to JIS R 1610 at 9.807 N, printed in gigapascals. Tungsten carbide (WC) grades are quoted at HV30: 1,300 to 1,605 HV30 for 94 percent WC grades and 1,200 HV30 for a 90 percent WC grade, as typical values.

A converted number is an estimate. Anodized aluminium Type III hard-coat reads 350 to 360 HV in one measurement on 7075-T6, while a second source gives 520 to 700 HV, converted from 50 to 60 HRC.

Polymers use durometer Shore scales in our data. Polyvinylidene fluoride reads 77 to 82 Shore D at 23 °C. Rigid Polyvinyl chloride (PVC) grades read 80 to 84 Shore D, Ethylene-chlorotrifluoroethylene 75 Shore D, and Fluoroelastomer FKM (Viton) 79 to 91 Shore A for its 75 and 90 Shore A grades.

Terms used

How to read this page

explanations of how the tests work are general engineering knowledge, not from our profiles. Every figure with a unit comes from a profile.

Brinell (HB, HBW, BHN)

a test that presses a ball into the surface under a stated load and reports hardness from the dent.

Rockwell scales (HRC, HRB, HRA)

tests that read how deep a point sinks under a stated load. C is for hard steels, B for softer metals, A for carbides. HRBW means Rockwell B with a tungsten indenter.

Vickers (HV, HV30)

a test that presses in a diamond pyramid and measures the dent. A number after HV, such as 30, names the test load.

Shore A and Shore D

durometer scales for rubbers and plastics. They are separate scales and cannot be compared with each other or with metal scales.

Tempering

reheating hardened steel to trade hardness for toughness. A higher tempering temperature usually gives lower hardness.

Annealed

heated and cooled slowly so the metal is soft. Soft-annealed is a delivery state of tool steels.

Pre-hardened

supplied already quenched and tempered to a working hardness, so a mould block is machined without a further heat treatment.

Ruling section

the bar thickness a datasheet value applies to. Thicker sections cool more slowly in the quench and harden less.

What to check before you order

1. Ask for the scale and test conditions together: HB with ball and load (for example HBW, a carbide ball, at 3000 kg), HRC or HRB with the letter, HV with its test load.
2. Ask for the condition beside the number: annealed, pre-hardened, tempered at a stated temperature with the hardening temperature, aged to H900 or H1150, and the temper for aluminium.
3. Say whether the number is a minimum, a maximum or a typical value, and for which section thickness. A datasheet typical is not an acceptance limit.
4. Write the test on the order: the standard (ASTM E10 for Brinell, E18 for Rockwell, E92 for Vickers, or the matching ISO standard), the test location and surface preparation, and for thin or case-hardened parts the load and sample thickness.
5. Paste-ready example: "17-4 PH bar, H1025, 35 HRC minimum (ASTM A564), tested to ASTM E18 on a ground surface."

What do we not know yet?

• Aluminium alloy 6061 and Aluminium alloy 7075-T6 hold no hardness value. The Aluminium alloy 5052 profile notes a Brinell figure of 60 for H32 on its datasheet but did not store it as a property.
• No hardness value is stored for Polyetheretherketone (PEEK) or PC, and no polymer profile that meets our bar holds Rockwell R, M or L, Brinell or Vickers. The Ethylene-chlorotrifluoroethylene profile notes a Rockwell R93 sheet value that was not entered.
• Among the profiles in this article only nickel and bronze C954 state a Brinell load, and Vickers loads are not stated for palladium, the N42H magnet, TZM or the aluminium alloys. Alloy steel AISI 4130 is left out of the Brinell chart because one of its stored annealed-bar values looks wrong and needs checking against its source.
• Pairs of two scales are printed for several grades (for example 17-4 PH, 1.2738, 5083 and 440C), some from different sources and none with test loads, so our data can neither confirm nor replace a conversion table.
• 1045 has no quenched-and-tempered hardness, and 1215 stores one cold-drawn value.

Questions people ask