Overview
IEC TR 63114:2018 - Electrical steel: Reverse bend test method for electrical steel strip and sheet describes the principles and technical details of the reverse bend test used to evaluate the ductility of electrical steel. The Technical Report is targeted at testing Epstein test strips from both non‑oriented and grain‑oriented electrical steel (test specimens shall not be annealed). It clarifies two commonly used modes of the test (Mode A and Mode B), differences in apparatus, and how to interpret results.
Key topics and requirements
- Scope: Applies to Epstein strip specimens for electrical steel of any grade; specimens must not be annealed.
- Test principle: Repeated alternate bending (reverse bends) over cylindrical mandrels until the first visible crack or fracture; the number of bends is used to quantify ductility.
- Specimen dimensions: Width = 30 mm ± 0.2 mm; length = 280–320 mm (Epstein strip per IEC 60404-2).
- Mandrel geometry: Cylindrical cambered surface with radius r = 5.0 mm ± 0.1 mm; mandrel surface must be wider than specimen.
- Two modes:
- Mode A - based on ISO 7799 (commonly used in Europe). ISO 7799 specifies a smaller specimen width (20–25 mm), hence IEC TR 63114 explains adaptation for 30 mm Epstein strips.
- Mode B - follows ASTM A720 / JIS C2550 (commonly used in America and Asia).
- Tensile force / test conditions: A tensile force (e.g., about 70 N) may be applied to maintain contact and localize bending; ambient test temperature (23 ± 5) °C.
- Result expression: Count alternate bends until the first crack visible to the naked eye or sudden fracture - this count represents ductility.
Practical applications and users
- Quality control laboratories in electrical steel plants and rolling mills - for routine ductility assessment of production lots.
- Manufacturers of transformer cores, electrical machines, and motors - to ensure material forming performance and in‑service reliability.
- Material and metallurgical testing labs - for comparative studies between Mode A and Mode B or research into forming behavior.
- Standards and compliance engineers - to incorporate test results into product specifications and acceptance criteria.
Related standards
- IEC 60404-2 (Epstein frame specimen details)
- ISO 7799 (reverse bend test reference for Mode A)
- ASTM A720 and JIS C2550 (references for Mode B)
- IEC product standards referencing reverse bend tests (e.g., IEC 60404‑8‑4, 8‑7, 8‑8)
Keywords: reverse bend test, electrical steel, ductility, Epstein strip, Mode A, Mode B, IEC TR 63114:2018, mandrel radius, tensile force, material testing.