Overview
ISO/TS 7705:2017 - "Guidelines for specifying Charpy V‑notch impact prescriptions in steel specifications" provides practical guidance for including Charpy V‑notch impact requirements in steel product standards and delivery documents. The Technical Specification explains the role of Charpy testing as a reproducible, low‑cost delivery control and classification tool for notch toughness, describes the information obtainable from impact testing (energy vs temperature curves), and gives recommendations on specifying tests, sample selection and interpretation.
Key topics
- Purpose and scope: guidance for specifying Charpy V‑notch test prescriptions in steel specifications.
- Notch toughness vs fracture toughness: distinguishes small‑scale notch tests (Charpy, drop‑weight) from fracture‑mechanics tests (e.g., CTOD - ISO 12135) and focuses on notch tests suitable for delivery control.
- Charpy test fundamentals: description of the absorbed‑energy versus temperature curve with upper shelf, transition range and lower shelf, and emphasis that energy results are reported in joules (J).
- Historical and practical reference values: commonly used reference levels (27 J for many unalloyed steels; higher levels such as 40 J for certain fine‑grain or quenched‑and‑tempered steels) are discussed.
- Factors affecting impact results: material thickness, stress state, temperature, steel type, loading rate, surface condition, residual stresses, yield strength, specimen orientation, notch sharpness, specimen position and striker type.
- Subsize test pieces: standard specimen is 10 mm × 10 mm; standardized subsize specimens include 10 mm × 7.5 mm, 10 mm × 5 mm and 10 mm × 2.5 mm. The document cautions that subsize specimens shift the transition to lower temperatures and reduce upper‑shelf energy; empirical corrections exist but there is no simple mathematical conversion.
- Specification practice: recommendations cover selection and preparation of samples, cutting and machining, number and location of test pieces, and interpretation of results.
Applications
ISO/TS 7705:2017 is intended for people who prepare or apply steel product specifications and quality control procedures:
- Standards writers and product committees specifying mechanical delivery conditions
- Steel producers and mill QA teams establishing acceptance criteria
- Welding engineers and structural designers using impact requirements for fabrication and service temperature considerations
- Inspection and testing laboratories implementing Charpy V‑notch testing for delivery control
Related standards
- ISO 12135 (CTOD fracture toughness testing) - referenced as a complementary fracture‑mechanics approach for design rather than routine delivery testing.
Keywords: Charpy V‑notch, impact test, impact energy, transition temperature, subsize test pieces, ISO/TS 7705:2017, steel specifications, notch toughness.