ASTM A370 — Standard Test Methods and Definitions for Mechanical Testing of Steel Products

ASTM A370 — Standard Test Methods and Definitions for Mechanical Testing of Steel Products

Record: materials-std-002 (Materials, flagship standard). Issuing body: ASTM International.

1. What it is, who issues and enforces it

ASTM A370 is the umbrella standard governing mechanical testing of steel products — tension tests, bend tests, hardness tests, and Charpy impact tests — including specimen geometry, test procedure, and reporting. It is one of the most-cited standards in materials engineering: mill test reports (MTRs) certifying a heat of steel to a specification (A36, A516, A106, etc.) derive their mechanical-property values from tests performed per A370. Issuer: ASTM International Committee A01 on Steel. Enforcement is contractual and jurisdictional — invoked by material specifications, owner specs, and codes (ASME BPVC Section II/UG requirements reference A370 methods).

2. Scope

Covers tension testing (yield strength, tensile strength, elongation, reduction of area), bend tests, hardness testing (Brinell, Rockwell, portable), and Charpy V-notch impact testing of steel products — plate, sheet, strip, bar, forgings, castings, tubular products, and fasteners. It defines:

• Specimen types and dimensions (plate-type, round, tubular specimens; subsize Charpy specimens where material thickness is limited).
• Test apparatus and calibration requirements (grips, extensometers, testing-machine verification per ASTM E4).
• Test speed / strain-rate control — particularly the distinction between the rate used to determine yield (controlled strain rate through yield) and the rate for tensile strength.
• Definitions — the standard's other half: precise definitions of yield point vs. yield strength (offset method), elongation measurement (gauge marks, 2-in. vs. 8-in. gauge lengths), and reduction of area.

3. Key requirements in plain technical language

1. Yield determination discipline. A370 prescribes how yield is measured — halt-of-the-gauge (yield point by drop of beam/autographic diagram) or 0.2% offset — and the strain rate through the yield region. Testing too fast inflates apparent yield; MTR values are only comparable when the method matches.
2. Specimen orientation and location. Transverse vs. longitudinal specimens give different values (anisotropy from rolling); specifications dictate which, and A370 dictates how to prepare them (machining tolerances, surface finish — a rough specimen fails early).
3. Charpy impact testing. Specimen notch geometry (V-notch, 10×10 mm standard), test temperature control (±1°C discipline), and reporting of absorbed energy, lateral expansion, and percent shear — the toughness acceptance data behind low-temperature service qualification (cf. ASME B31.3 Table 323.2.2 and BPVC UCS-66).
4. Bend tests. Mandrel diameters as multiples of specimen thickness; acceptance is freedom from cracking on the tension face.
5. Hardness–tensile correlations. A370 includes the informative hardness conversion tables (commonly cited for approximate tensile strength from Brinell/Rockwell readings) — with explicit warnings that conversions are approximate and material-dependent.
6. Retest and rounding rules. Defined retest provisions and the rounding method for reported values (ASTM E29 practice) — disputes over a heat's acceptance often turn on these clauses.

4. Penalties and consequences

A370 is not law; consequences are commercial and professional: rejection of heats (a failed Charpy set at the specified temperature rejects the lot), project delays, and — where MTRs are falsified or tests misperformed — the fraud and liability exposure that follows a failure (pressure-vessel and structural failures have traced to substandard material accepted on bad test data). For licensed engineers, accepting non-conforming material data is a professional-conduct issue.

5. Version and live changes (checked 2026-09-30)

• A370 is revised on ASTM's cycle (revisions/reaffirmations roughly every few years; recent editions include A370-24). Changes are typically refinements to specimen figures, strain-rate language, and Charpy reporting — evolutionary, not revolutionary.
• Flag: always cite the edition year invoked by the governing material specification or contract; test-lab accreditation (ISO/IEC 17025) scopes reference specific editions.

6. Related certifications

• PE Metallurgical and Materials (Materials flagship) — the license whose exam and practice center on exactly this mechanical-testing knowledge.
• AWS CWI (Materials flagship) — bend tests per A370-adjacent methods are part of welder/welding-procedure qualification evidence.
• ASNT NDT Level II/III — hardness testing and the mechanical-test/NDT interface in failure analysis.
• AMPP programs — less direct; mechanical properties underpin fitness-for-service assessments that coatings/CP protect.

7. Honest flags

• A370's hardness conversion tables are approximate — quoting a converted tensile strength as a certified value is a misuse the standard itself warns against.
• Subsize Charpy specimens require correlation to full-size values; acceptance criteria must be adjusted — a frequent source of erroneous rejections/acceptances.

Record: materials-std-002.

Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.