Hardness ↔ Tensile Strength Reference Converter

Estimate Brinell hardness and ultimate tensile strength from a Rockwell C (HRC) reading for quenched & tempered low-alloy steel such as 4130/4140, using interpolation between published reference points (20–50 HRC).

METALLURGY REFERENCE · APPROXIMATE SAE J417 / ASTM E140 CONVERSION RANGE

Hardness ↔ Tensile Strength Reference Converter

Interpolates between published approximate HRC–HB–tensile reference points for quenched & tempered low-alloy steel (e.g. 4130/4140). Not a substitute for the current edition of ASTM E140.

Input Rockwell Hardness (HRC)
[20 to 50 HRC]

SYZ 4130/4140 normalized & tempered rod end body standard: HRC 32–38. Range capped at 50 HRC — the linear approximation breaks down above this and ASTM E140 requires the full published table.

HRC	≈ HB	≈ R_m (MPa)
20	225	772
25	253	862
30	286	1000
35	327	1145
40	371	1289
45	421	1451
50	481	1636

Estimated Ultimate Tensile Strength (Rm)

≈1,116 MPa

✔
≈161,900 PSI · Brinell ~319 HB · Standard 4130/4140 quenched & tempered range

Reference-Table Interpolation (not a single ASTM formula)

Standard Reference
ASTM E140 (“Standard Hardness Conversion Tables for Metals”) publishes conversion tables for non-austenitic steels — it does not publish a single linear equation across the full hardness range.

Calculation Method
Piecewise-linear interpolation between the reference points shown in the table, approximating commonly published SAE J417 / ASTM E140 conversion ranges for quenched & tempered alloy steel.

SYZ Quality Note
Rod end body (4130/4140 forged, Q&T): controlled to HRC 32–38. Bearing ball (52100/GCr15): through-hardened to HRC 58–62 — outside the reliable range of this linear-region converter; consult the full ASTM E140 table for hardness above 50 HRC.

Assumptions & Limitations

Reference points are approximate published values for quenched & tempered alloy steel — actual conversion is material- and process-dependent.
Not valid for austenitic stainless steel, cast iron, or non-ferrous alloys.
Conversions are approximations, never a replacement for direct mechanical (tensile) testing on safety-critical parts.

STATIC REFERENCE DATA

Reference Table (also shown in the calculator above)

Precomputed values from the exact formula used above — useful as a quick lookup without re-entering inputs.

HRC	≈ HB	≈ Rm (MPa)	≈ Rm (PSI)
20	225	772	111,970
25	253	862	125,043
30	286	1000	145,038
35	327	1145	166,069
40	371	1289	186,954
45	421	1451	210,470
50	481	1636	237,282

WORKED EXAMPLE

Checking SYZ Rod End Body Hardness Spec

SYZ’s 4130/4140 forged, quenched & tempered rod end body is controlled to HRC 32–38. What tensile strength range does that correspond to?

HRC 32 interpolates between the 30 HRC (1,000 MPa) and 35 HRC (1,145 MPa) table rows → ≈ 1,058 MPa (≈153,450 PSI).
HRC 38 interpolates between the 35 HRC (1,145 MPa) and 40 HRC (1,289 MPa) table rows → ≈ 1,231 MPa (≈178,600 PSI).
So the HRC 32–38 spec band corresponds to an estimated ultimate tensile strength range of roughly 1,058–1,231 MPa (153–179 ksi) — consistent with typical 4130/4140 quenched & tempered chromoly performance.
This is an approximation for quick reference only; certified mechanical properties come from the mill test report, not from this converter.

Related reading: Metallurgy & Quality Control →

Hardness ↔ Tensile Strength Reference Converter

Hardness ↔ Tensile Strength Reference Converter

Reference Table (also shown in the calculator above)

Checking SYZ Rod End Body Hardness Spec

Need this verified for final design?