Metals Testing Glossary: Key Terms and Acronyms

What are the essential mechanical test terms used in metals testing?#

The core metals mechanical test terms include ultimate tensile strength (UTS), yield strength (offset method), tensile elongation, and reduction of area, all governed by ASTM E8/E8M. Impact toughness is quantified by the Charpy V-notch test (ASTM E23), while fastener integrity uses proof load (ASTM F606). Engineering stress and true stress are distinct measures, critical for finite-element input and forming simulations.

Tensile strength and ductility terms#

Ultimate Tensile Strength (UTS)
The maximum engineering stress a material withstands before necking or fracture, calculated as the peak load divided by original cross-sectional area. Reported in ksi or MPa. Governed by ASTM E8/E8M for standard tension testing; fasteners may be tested per ASTM F606.

Yield Strength (Offset Method)
The stress at which a material exhibits a specified amount of plastic deformation, typically 0.2 % strain offset for metals without a sharp yield point. A line parallel to the elastic slope is drawn from 0.2 % strain; its intersection with the stress-strain curve defines yield. ASTM E8/E8M prescribes the 0.2 % offset when constant-rate-of-extension or strain-control is used.

Tensile Elongation
Percent increase in gauge length after fracture, a measure of ductility. A 2-inch (50 mm) gauge length is typical. ASTM E8/E8M defines two types: elongation after fracture (manual placement of broken halves) and percent elongation at break from an extensometer signal. Percent elongation depends on gauge length, so values are only comparable for identical specimen geometry. For a deeper walk-through of this data, see How to Read a Tensile Test Report (Step by Step).

Reduction of Area
Percent decrease in cross-sectional area at the fracture location, also a ductility indicator. It measures the material’s ability to flow plastically before rupture and is less sensitive to gauge length than elongation. Calculation and reporting follow ASTM E8/E8M.

Stress measures and conversions#

Engineering Stress vs. True Stress
Engineering stress uses original cross-sectional area throughout the test; true stress divides load by instantaneous area. Beyond yield, the two diverge, and true stress is essential for forming simulations. The distinction matters when converting tensile data to finite-element inputs. For selection guidance, see Engineering Stress vs True Stress: When to Use Each.

Impact and load tests#

Charpy V‑Notch Impact Test
A pendulum impact test measuring energy absorbed in fracturing a notched specimen at a given temperature. Results in joules or ft‑lbf, with notch geometry V or U. ASTM E23 standardizes specimen preparation, temperature conditioning, and verification. Useful for toughness screening, ductile-to-brittle transition curves, and weld qualification. For a practical overview, refer to Charpy V‑Notch Impact Testing: A Practical Explainer.

Proof Load
A static axial load applied to a fastener for a specified dwell time (typically 10 or 15 seconds) without causing permanent deformation. It is a pass/fail test rather than a measurement. Proof load values for various grades are listed in ASTM F606, ISO 898-1, and other product standards. The test confirms a fastener can sustain its rated preload without yielding. Additional context is in Fastener Testing: Proof Load, Wedge Tensile and Hydrogen Embrittlement.

What are the standard hardness tests for metals and how do they compare?#

The primary hardness tests are Brinell (HBW, ASTM E10), Rockwell (HRC/HRB, ASTM E18), Vickers (HV, ASTM E92/E384), and Knoop (HK, ASTM E384). Brinell integrates over a large area for heterogeneous microstructures, Rockwell provides rapid QC readings, Vickers spans macro to micro loads, and Knoop excels on thin layers. Hardness conversion via ASTM E140 is approximate because plastic response differs by alloy class.

Macroindentation tests: Brinell and Rockwell#

Brinell Hardness (HBW)
A hardened tungsten carbide ball (1, 2.5, 5 or 10 mm) is pressed into the surface under a defined force, and the diameter of the impression is measured optically. Reported as HBW, e.g., 200 HBW 10/3000 (10 mm ball, 3000 kgf). ASTM E10 specifies the method. Brinell testing integrates hardness over a large area, making it forgiving of coarse-grained or heterogeneous microstructures.

Rockwell Hardness (HRC, HRB, etc.)
The most common rapid-production hardness test. A diamond cone (HRC) or steel/tungsten carbide ball (HRB) indenter is loaded in two steps, and depth difference is directly read. ASTM E18 governs Rockwell testing and lists the many scales. Rockwell C (HRC) is typical for quenched and tempered steels; Rockwell B (HRB) for softer alloys. Because each scale is arbitrary, conversion to other scales is approximate.

Microindentation tests: Vickers, Knoop, and microhardness#

Vickers Hardness (HV)
A diamond pyramid indenter with a 136° angle applies a light to moderate load (typically 1 g to 50 kgf), leaving a square impression whose diagonal is measured. HV values are proportional to the load/diagonal² ratio, making HV nearly independent of load within a homogeneous material. ASTM E92 covers Vickers testing. Vickers is the basis for most hardness conversion tables up to ~1000 HV.

Knoop Hardness (HK) A rhombic-based diamond pyramid indenter produces an elongated impression ideal for very thin layers, brittle materials, or steep hardness gradients. ASTM E92 covers Knoop as well. Because the long diagonal is measured, Knoop tests at very low loads can resolve features Vickers cannot.

Microhardness A general term for Vickers or Knoop testing at loads ≤1000 g (1 kgf). Governed by ASTM E384, microhardness is critical for evaluating case depth, coatings, single phases, and gradient zones. For a dedicated explanation of case-depth mapping, see Microhardness Testing for Case Depth and Coatings.

Hardness test comparison table#

Hardness conversion caveats#

Hardness conversion charts (ASTM E140) provide approximate cross-reference. However, because plastic response differs by alloy class, converted values carry significant uncertainty. The reasons are explored in Hardness Conversion Charts: Why They Are Not Universal. For a side‑by-side comparison of test selection, see Rockwell vs Brinell vs Vickers: Hardness Test Comparison.

What metallography and microstructural terms are essential in metals testing?#

Metallographic evaluation relies on terms like macroetch (ASTM E381) for revealing weld solidification patterns, grain size number G (ASTM E112), case depth (ASTM E384/E1077), decarburization (ASTM E1077), and inclusion rating (ASTM E45). These terms connect processing to properties, exposing grain refinement, surface carbon loss, and non-metallic particle distribution in quality investigations and failure analyses.

Macroetch A deep chemical etch of a ground surface, often a weld cross-section or billet slice. Reveals solidification patterns, seams, segregation, excessive penetration, or cracking visible to the unaided eye. ASTM E381 specifies test methods for macroscopic evaluation of steel bars, billets, and forgings. For welds, macroetching is a crucial part of procedure qualification, detailed in Macro Etching for Weld Inspection: Procedure and Interpretation.

Grain Size Number (G) A dimensionless index where G = 1 corresponds to 15.5 grains/mm² at 100x magnification, and each increment doubles the areal grain count. ASTM E112 defines the comparison and planimetric methods. Fine grain size (high G) typically improves strength and toughness. For procedures, see Grain Size Measurement: ASTM E112 Comparison and Planimetric Methods.

Case Depth The distance from the surface to a defined hardness limit (e.g., 50 HRC or 550 HV) or to the point where carbon/nitrogen content matches the core. Measured with microhardness traverses per ASTM E384, or by optical interpretation of the etched case. ASTM E1077 provides guidance on decarburization and case depth measurement in steel.

Decarburization Loss of carbon from the steel surface during heat treatment in oxidizing atmospheres, producing a soft, low‑strength layer detectable by a drop in microhardness or a change in microstructure. ASTM E1077 defines evaluation procedures, including total and partial decarburization depth. Additional measurement detail is in Measuring Decarburization and Carburization Depth in Steel.

Inclusion Rating Non‑metallic particles (sulfides, alumina, silicates, globular oxides) are assessed by comparison with standard charts per ASTM E45. Ratings are reported by type, severity, and length. Acceptance limits for product forms are often specified in ASTM, SAE, or customer standards.

How is chemical composition analyzed in metals testing?#

Metal chemical analysis commonly uses optical emission spectroscopy (OES, ASTM E415/E1086) for rapid multi-element results, combustion analysis (ASTM E1019) for trace carbon and sulfur, and X-ray fluorescence (XRF, ASTM E572/E2465) for field alloy identification. Each method differs in speed, accuracy, and the elements it can quantify, making them complementary tools for grade verification and process control.

Optical Emission Spectroscopy (OES) An arc or spark ablates a small area of the sample, vaporizing atoms and exciting their outer electrons. As electrons return to ground state, they emit characteristic wavelengths that are dispersed by a grating and measured by photomultiplier tubes or CCD detectors. ASTM E415 covers carbon and low‑alloy steel; ASTM E1086 addresses stainless steel. OES delivers rapid, simultaneous multi‑element analysis in seconds, making it the workhorse of incoming inspection. Additional detail is in Optical Emission Spectroscopy (OES) for Metal Analysis.

Combustion Analysis (LECO) A sample is heated to ~3000 °C in an induction furnace under oxygen flow. Carbon and sulfur oxidize to CO₂ and SO₂, measured by infrared cells. Results are often reported as “Leco carbon” by analysts because of the dominant instrument manufacturer. ASTM E1019 covers carbon, sulfur, nitrogen, and oxygen. Combustion analysis generally surpasses OES for trace-level non‑metallics.

X-ray Fluorescence (XRF) Primary X-rays excite secondary (fluorescent) X-rays from the sample; each element emits at unique energies. Handheld and benchtop units are common for alloy identification (positive material identification, PMI). While standardless quantification is routine, certified reference materials improve accuracy. ASTM E572 and E2465 cover XRF for steel.

What certifications and reporting terms apply to metals testing?#

Quality assurance in metals testing uses terms such as Material Test Report (MTR), ISO/IEC 17025 accreditation, NIST traceability, Positive Material Identification (PMI), and Laboratory Scope of Accreditation. These terms define the documentation, calibration chains, and lab competence needed to ensure that reported properties meet purchase order requirements and are legally defensible.

Material Test Report (MTR) A summary of the chemical and mechanical test results for a specific heat or lot of material. Also called a mill test certificate. It lists UTS, yield, elongation, reduction of area, hardness, chemistry, and the standards referenced. ASTM A6, A20, and A1016 require MTRs for various steel products. Rounding of test data follows ASTM E29.

ISO/IEC 17025 The international standard for competence of testing and calibration laboratories. Accreditation by a recognized body (A2LA, ANAB, etc.) verifies that a lab has a documented quality management system, uses validated methods, maintains calibrated equipment, and participates in proficiency testing. It is the benchmark for credible test data.

NIST Traceability Measurement results are traceable to the International System of Units (SI) through an unbroken chain of calibrations linked to national metrology institutes (NIST in the U.S.). Hardness blocks, load cells, and thermocouples are all calibrated with traceable reference standards.

PMI (Positive Material Identification) PMI is field verification of alloy grade using handheld XRF or OES. PMI does not replace full OES analysis but confirms that the alloy has not been mixed or substituted.

Laboratory Scope of Accreditation The official list of test methods an ISO/IEC 17025‑accredited lab is approved to perform. Customers must verify that a particular method (e.g., ASTM E8, E18) appears on the scope before quoting work.

What process-specific testing terms relate to welding and forming in metals?#

Welding and forming testing employs terms like Weld Procedure Qualification Record (WPQR), guided-bend test (ASTM E190), Welder Performance Qualification (WPQ), hydrogen embrittlement (ASTM F519), and normalization. These terms cover joint integrity verification, ductility assessment, hydrogen-induced cracking risk, and heat treatment microstructural refinement.

Welding qualification terms#

Weld Procedure Qualification Record (WPQR) The document that records all essential and non‑essential variables used during the welding of a test coupon and the results of NDT and destructive tests (tensile, bends, impact, macro). It proves that a Weld Procedure Specification (WPS) can produce acceptable joints. For a complete list of required tests, see Weld Procedure and Welder Qualification: Test Checklist.

Bend Test A ductility assessment where a weld or base metal specimen is bent over a mandrel to a predetermined angle (90° or 180°). The tensile surface is examined for cracking. ASTM E190 covers guided‑bend tests; for comparisons with elongation, see Bend Testing vs Tensile Elongation for Ductility.

Guided‑Bend Test A bend test using a jig to ensure uniform radius and controlled strain, standard in weld qualification per ASME Sec. IX and AWS D1.1.

Welder Performance Qualification (WPQ) Testing to confirm that a welder can deposit a sound weld using a specific process and position. Macro‑etch, bend, and sometimes radiography are used for acceptance.

Hydrogen and heat treatment terms#

Hydrogen Embrittlement (HE) A time‑dependent loss of ductility in high‑strength steels due to absorption of atomic hydrogen during pickling, plating, or service. Testing by sustained‑load or step‑load methods per ASTM F519.

Normalization A heat treatment that refines grain structure and homogenizes composition by heating above the upper critical temperature and cooling in still air. Normalized microstructures are evaluated via grain size and hardness.

Key takeaways#

• Use ASTM E8 for tensile properties, ASTM E18/E10/E92 for macro hardness, and ASTM E384 for microhardness traverses.
• Proof load is a pass/fail no‑deformation test; it is not a tensile stress measurement.
• Hardness conversions (ASTM E140) are approximate because plastic flow differs among alloys; whenever possible, specify the primary scale.
• Macroetch and microhardness traverses reveal decarburization and case depth per ASTM E381 and E1077.
• OES (ASTM E415/E1086) gives rapid multi‑element analysis; trace C/S require combustion (ASTM E1019).
• An MTR is only reliable when the testing laboratory holds ISO/IEC 17025 accreditation for the relevant test standards.