ASTM A370 - Test Methods and Definitions for Mechanical Testing of Steel Products
ASTM A370 Standard: Understanding Its Significance in the Mechanical Testing of Steel Products
Introduction
The ASTM A370 standard is a critical benchmark in the realm of steel product testing, catering especially to steel, stainless steel, and related alloys. This comprehensive standard not only encompasses a variety of tests and definitions but also ensures that the tested mechanical properties align with the stipulated product specifications, maintaining a uniform testing method to generate reproducible and comparable outcomes.
Below, we explain the range of mechanical tests covered by this standard.
In-Depth into ASTM A370
Issued under a fixed designation, ASTM A370, this standard is continually revised and updated to ensure it meets the evolving demands and technological advancements in the field of steel product testing. Notably, it is sanctioned for use by agencies of the U.S. Department of Defense, underscoring its credibility and applicability.
Scope and Application
ASTM A370 is expansive, covering tests like Tension, Bend, Hardness, Brinell, Rockwell, Portable, and Impact, each catering to distinct aspects of mechanical property assessment. Moreover, it accommodates annexes for specific product types, including Bar Products, Tubular Products, Fasteners, Round Wire Products, and more, ensuring a holistic approach to testing.
Flexibility and Adaptability
One of the standout features of ASTM A370 is its adaptability to both inch-pound units and SI units, facilitating seamless international application. The meticulous conversion processes and attention to detail ensure that the integrity of data and testing outcomes remains uncompromised, regardless of the unit system employed.
Tension
Bend Test
The bend test is a crucial evaluative procedure used primarily to assess a material's ductility, offering insights into its ability to deform under bending stresses without failure. Although it’s not a direct indicator of service performance, the bend test plays a significant role in determining a material's flexibility and strength.
Key Elements of the Test
The test’s intensity is influenced by the bend angle and the material’s cross-section. Factors such as chemical composition, tensile properties, hardness, and the type and quality of steel are integral in this evaluation. Detailed protocols for conducting this test are provided in Test Methods E190 and E290, ensuring consistency and accuracy in the results.
Hardness
The hardness test is a prevalent technique used for gauging a material's resistance to penetration, serving as an indirect method to estimate its tensile strength. It involves applying a fixed load to the surface of the material being tested and measuring the depth or size of the impression. Results from this test can often be converted from one hardness scale to another, such as from the Rockwell to the Brinell scale, or even to an estimated tensile strength using established tables and conversion values. However, it's essential to remember that all converted hardness values should be treated as approximations, ensuring that they’re used with caution in material evaluation and selection processes.
Hardness testing finds its utility in various applications where a quick, non-destructive method is needed to approximate material strength and durability. In specific contexts, product specifications allow for alternative hardness testing to confirm adherence to given hardness requirements. In such cases, the hardness values obtained, and their respective scales are recorded in a defined format. For instance, a recording of "353 HBW (38 HRC)" signifies that the tested material exhibited a hardness value of 38 on the Rockwell C scale, which converts to a Brinell hardness of 353. This multifaceted approach ensures that hardness testing remains adaptable and comprehensive in assessing material quality and performance.
Brinell
The Brinell hardness test is a standard procedure for measuring the hardness of a material, particularly beneficial for metals with a coarse or uneven grain structure. The process entails applying a specific load to the flat surface of a test specimen through a tungsten carbide ball of a known diameter. The resulting indentation’s average diameter forms the basis for calculating the Brinell Hardness Number (HBW). The formula for determining HBW considers the applied load and the indentation's size, offering a quantifiable metric that reflects the material's hardness. Standard tables are often used to simplify this calculation, providing HBW values corresponding to various indentation diameters.
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In a typical Brinell test, a 10-mm tungsten carbide ball is used with a 3000-kgf load for hard materials. However, for softer materials or thin sections, lighter loads of 1500 or 500-kgf are employed. The test's flexibility allows the use of other loads and indentor sizes as needed, ensuring the method's adaptability across a range of materials and conditions. When reporting the Brinell hardness values, it is essential to state the diameter of the ball and the applied load, except when standard conditions are used. The Brinell test's utility extends to different material conditions, but it’s often specifically tailored for materials that have undergone quenching and tempering or normalizing and tempering. It provides invaluable data that aids in the comprehensive assessment of material quality, durability, and suitability for various applications, ensuring that materials meet the stringent standards required for their intended use.
Rockwell
The Rockwell hardness test provides a measure of the hardness of materials through assessing the depth of penetration of a penetrator under specific conditions. Initially, a minor load of 10 kgf is applied to achieve an initial penetration and set the penetrator in position on the test specimen. Subsequently, a major load, whose value depends on the chosen scale, is applied, leading to an increased depth of penetration. Upon removal of the major load, while the minor load is still in effect, the Rockwell hardness number is determined. This number, usually displayed by a machine, is arbitrary and is proportional to the difference in depth of penetration caused by the major and minor loads; it increases with increasing hardness.
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Various scales are available for different testing requirements, with the B and C scales being the most common. The B scale utilizes a 1/16-inch tungsten carbide ball and a major load of 100 kgf, while the C scale employs a diamond brale with a 150 kgf major load, both alongside a consistent minor load of 10 kgf. For testing very thin steel or surface layers, Rockwell superficial hardness machines are employed, utilizing lighter loads of 15, 30, or 45 kgf with different penetrators to encompass a broad range of hardness values. Such versatility ensures the Rockwell test’s adaptability to diverse material types and conditions, offering precise, rapid, and repeatable hardness measurements essential in quality control, material selection, and research applications.
Charpy Impact
The Charpy V-notch impact test is a dynamic procedure where a notched specimen is struck and fractured by a single blow in a specialized testing machine. This test measures the energy absorbed during fracture, percentage shear fracture, and lateral expansion, offering insights into the material's ductile versus brittle behavior. Alloys can exhibit transitions in behavior when tested at various temperatures. Above the transition temperature, materials demonstrate ductile fracture, absorbing significant energy. Below this temperature, brittle fracture occurs, absorbing less energy. Specifications may require minimum absorbed energy or fracture appearance at specified temperatures or the determination of transition temperatures.
Portable Hardness Test
The portable hardness test is employed when traditional fixed-location Brinell or Rockwell tests are impractical due to the size, location, or other logistical challenges associated with the test specimen. Various standardized methods like A956, A1038, and E110 guide the use of portable equipment. Test results are reported strictly according to the chosen standard. For instance, A956 uses the Leeb impact device and the hardness number is appended with HLD, indicating the method used. A1038 uses the UCI method under a specific force and is noted accordingly. E110 results are appended with /P, signifying a portable hardness tester's use. Each method ensures accurate, reliable results, even when testing in situ or on large, installed, or complex components.