1.What are the core testing methodology standards?
Charpy impact test: Most commonly used.
ISO 148-1:2016 (International Standard): Metallic materials-Charpy impact test-Part 1: Test method.
ASTM E23:2023 (American Standard): Metallic materials-Standard impact test method with notched specimens.
GB/T 229-2020 (Chinese Standard): Metallic materials-Charpy impact test method. This standard is a modification of ISO 148-1 and is the most authoritative reference in China.
Ackerch impact test: Historically used, now rarely used for evaluating cold-rolled steel sheets/coils, but may be encountered in some older standards or for specific materials.
2.What are the key testing elements and sample requirements?
Specimen Type: Standard Charpy V-notch impact specimens are most commonly used.
Sampling Location: Sampling is typically done at 1/4 of the width of the steel coil/plate or within a certain distance from the edge to avoid edge effects and center segregation zones. Specific locations are specified in the product standard.
Sampling Direction: This is crucial. Due to grain elongation along the rolling direction caused by cold rolling, the material exhibits anisotropy.
Longitudinal Specimen: The notch direction is perpendicular to the rolling face, and the impact direction is parallel to the rolling direction. Typically, this type exhibits the highest impact toughness.
Transverse Specimen: The notch direction is perpendicular to the rolling face, and the impact direction is perpendicular to the rolling direction. Typically, this type exhibits lower impact toughness than the longitudinal type.
The sampling direction must be clearly specified in the standard, usually indicated in the product standard (e.g., "transverse specimen"). Comparative data must be taken in the same direction.
3.What are the specific provisions in the product standards?
General Structural Steel:
GB/T 5213-2019 Cold-rolled Low-carbon Steel Sheet and Strip: Specifies impact toughness requirements at room temperature or -20°C for some grades.
EN 10130:2006 (European Standard) Cold-rolled Low-carbon Steel Sheet and Strip for Cold Forming.
JIS G 3141:2017 (Japanese Standard) Cold-rolled Steel Sheet and Strip.
ASTM A1008/A1008M (American Standard) Cold-rolled Carbon Structural Steel Sheet.
High-strength Steel and Advanced High-strength Steel:
GB/T 20564.1~.7 Series High-strength Cold-rolled Steel Sheet and Strip for Automotive Use: May specify impact toughness for various high-strength steels (such as duplex steel (DP), transformation-induced plasticity steel (TRIP), etc.).
EN 10346:2015 "Continuously hot-dip coated steel sheet and strip – Technical delivery conditions" (Many cold-rolled coils are galvanized substrates and follow this standard).
Automotive industry standards: Company standards from OEMs such as Volkswagen, General Motors, and Toyota impose very stringent impact toughness requirements on cold-rolled high-strength steel used in safety structural components (such as A/B pillars and crash beams), often including testing at a series of temperatures.
4.What do typical test contents and reports include?
Impact energy absorbed at a specified temperature: e.g., KV₂ (impact energy of a V-notch specimen at a specified temperature, measured in Joules (J)).
Ductile-brittle transition temperature: By conducting tests at a series of temperatures (e.g., +20°C, 0°C, -20°C, -40°C, -60°C) and plotting an impact energy-temperature curve, the temperature range in which a material transitions from ductile to brittle fracture is determined. This is crucial for low-temperature applications.
Fiber fraction: Measured as the percentage of ductile fracture on the fracture surface of a specimen, aiding in the assessment of toughness.
5.What are the summary and operational steps?
Determine the material standard: First, check the quality certificate of the cold-rolled coil to clarify the product standard number and grade it follows (e.g., GB/T 5213 DC01, or Volkswagen standard VW50075, etc.).
Refer to the product standard: In the product standard, look for the "Mechanical Properties" or "Technical Requirements" section to see if impact testing requirements are specified.
If so, the standard will specify: the test method standard (e.g., GB/T 229), the specimen orientation (transverse/longitudinal), the test temperature (e.g., room temperature, -20℃), and the minimum impact energy requirement.
Perform the test: Prepare the specimen and conduct the test according to the test method standard referenced in the product standard.
Result judgment: Compare the measured impact absorbed energy with the minimum value specified in the standard to determine whether it is qualified.
Key point: There is no single "universal standard" for the impact toughness of cold-rolled coils; it is a combination system of "specific requirements specified in the product standard + operational details specified in the method standard." The material grade and application are the keys to finding the specific test standard.