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F436 Washer Hardness Testing - Rockwell C Procedure (38-45 HRC)
ASTM F436/F436M Section 4 specifies a hardness band of 38 to 45 HRC (Rockwell C scale) for hardened steel washers in both Type 1 carbon steel and Type 3 weathering steel. The hardness test follows ASTM E18 with a diamond cone (Brale) indenter under 150 kgf major load, performed on the bearing face of the finished washer. This page documents the test procedure, sample preparation, conversion to Vickers (HV) and Brinell (HBW), and the failure modes when the band is missed.
F436 hardness band and conversions
| Property | F436 spec | Notes |
|---|---|---|
| Rockwell C min | 38 HRC | Below this, soft washer creeps under HSFG preload |
| Rockwell C max | 45 HRC | Above this, brittle fracture risk under impact |
| Vickers equivalent | ~372 to 434 HV | Per ASTM E140 conversion table for steel |
| Brinell equivalent | ~352 to 415 HBW | Per ASTM E140 conversion table for steel |
| Test method ref | ASTM E18 | Rockwell C is the F436-specified primary method |
| Indenter | Diamond cone (Brale) | 120 deg included angle, 0.2 mm spherical tip |
| Major load | 150 kgf | Standard for HRC scale |
| Preliminary (minor) load | 10 kgf | Sets the reference depth |
F436 sample preparation per E18
The washer bearing face must be ground or polished before testing to remove any scale, mill finish, or coating that would corrupt the indenter depth measurement. F436 commercial washers ship with a phosphate-and-oil or HDG finish that interferes with HRC; the test face must be locally ground flat to 32 microinch Ra or better. Three readings are taken at the bearing face on locations spaced 120 degrees apart, averaged for the reported hardness. The thickness of the washer at the test location must be at least 10 times the indent depth — for F436 standard-thickness 0.097 to 0.177 inch washers this is satisfied without issue.
Three readings per F436 lot — sampling table
| Lot size | Sample washers per lot | Readings per washer | Total readings |
|---|---|---|---|
| Up to 800 pieces | 5 | 3 | 15 |
| 801 to 8,000 pieces | 13 | 3 | 39 |
| 8,001 to 22,000 pieces | 20 | 3 | 60 |
| 22,001 to 110,000 pieces | 32 | 3 | 96 |
| Over 110,000 pieces | 50 | 3 | 150 |
Sampling above follows the F1470 attribute-acceptance-sampling reference cited by F436. Every reading must fall within the 38-45 HRC band; a single out-of-band reading flags the lot for 100-percent inspection. TorqBolt's QA-QC team applies the 5/13/20 sample sizes from this table on every F436 production order and lists the per-piece readings on the EN 10204 mill cert.
What failure modes the band catches
| Out-of-band condition | Failure mode in service |
|---|---|
| Below 38 HRC (under-hardened) | Washer creeps under HSFG bolt preload, brinelling indentation forms, installed clamp load decays 5 to 25 percent |
| Above 45 HRC (over-hardened) | Brittle fracture risk under impact loading or shock; potential hydrogen embrittlement sensitivity in HDG application |
| Bearing face decarburised | Surface reads soft (below 38 HRC) even if core is in-band; F436 requires testing on ground bearing face to bypass |
| Mixed-heat lot | Some pieces in-band, some out; 100-percent inspection required on flagged lots |
Cross-references
For the full F436 material and mechanical specification including chemistry, dimensional tolerance and surface-finish requirements, see F436 washer specifications. The torque values that depend on the hardness band being preserved are tabulated on F436 tightening torque chart. For Type-3 weathering chemistry that uses the same hardness band but different alloy envelope, see F436 Type 3 washers.
Frequently asked questions
What is the F436 hardness range?
ASTM F436/F436M Section 4 specifies the hardness band as 38 to 45 HRC (Rockwell C scale), applicable to both Type 1 carbon steel and Type 3 weathering steel washers. The corresponding Vickers range is approximately 372 to 434 HV, and the Brinell range is approximately 352 to 415 HBW per ASTM E140 conversion tables. The lower bound prevents creep under high-strength bolt preload; the upper bound prevents brittle fracture under shock loading.
How do I test F436 hardness in-house?
Use a Rockwell C hardness tester per ASTM E18 with a diamond Brale indenter and 150 kgf major load. Grind the washer bearing face flat to 32 microinch Ra or better to remove any coating or scale. Apply three readings per washer at locations 120 degrees apart; the average must fall in the 38 to 45 HRC band. Sample 5 washers per 800-piece lot (or per F436 / F1470 sampling table for larger lots). Document every reading on the mill cert for traceability.
Can I use Vickers (HV) or Brinell (HBW) instead of Rockwell C?
F436 cites Rockwell C as the primary method. Vickers HV is permitted as a referee or supplementary test when the washer thickness is below the HRC limit (about 1 mm equivalent for the F436 hardness band). Brinell HBW is rarely used because the indent diameter exceeds practical washer geometry. ASTM E140 conversion tables are the bridge between scales; project specifications occasionally cite HV directly for European projects, in which case 372 to 434 HV is the equivalent F436 band.
What happens if a single reading falls outside 38 to 45 HRC?
A single out-of-band reading flags the lot for 100-percent inspection per F436 / F1470 sampling protocol. If the out-of-band reading is below 38 HRC, the lot likely has incomplete heat treatment (quench or temper); if above 45 HRC, the lot may be over-quenched or the temper temperature was too low. Both cases require the lot to be re-heat-treated and re-tested before release. TorqBolt's QA flow rejects any lot with even a single out-of-band reading without further investigation.
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