The wide application and importance of stainless steel bolts are self-evident. They account for a large proportion in the bolt market, so the formulation and strict compliance of stainless steel bolt standards are crucial. This article will detail the relevant standards, specifications and standard sizes of stainless steel bolts to provide reference for practical applications.
I. Standards for Stainless Steel Bolts
Standards for stainless steel bolts can refer to those for carbon steel bolts, and specifically need to comply with relevant national standards and international standards. Among them, according to national standards (such as GB/T 6170-2015 "Hexagon Nuts, Style 1" and GB/T 5782-2016 "Hexagon Head Bolts, Full Thread"), the mechanical property grade codes for stainless steel bolts and nuts are mainly: A2-70 (corresponding to material 0Cr18Ni9) and A4-70 (corresponding to material 0Cr17Ni12Mo2).
Note: The previous versions GB/T 6170-2000 and GB/T 5782-2000 in the original text have been updated to the latest versions, which are corrected here to ensure the timeliness of the standards; "0r18Ni9" is a typo and corrected to "0Cr18Ni9".
II. Standard Sizes and Relevant Specifications of Stainless Steel Bolts
(I) Specifications of High-Strength Stainless Steel Bolts for Steel Structures
High-strength bolts used for steel structure joints cover two types of quenched and tempered alloy steels, which are suitable for large hexagon bolts for structural use, with a tensile strength of 1040-1210 megapascals (MPa).
The American Institute of Steel Construction (approved by the Research Committee) stipulates that ASTM A325 and ASTM A490 series large hexagon structural bolts can be used for steel structure connections. Such bolts are specially used for steel structure connection scenarios, with a bolt diameter specification range of M12-M36. Their types and chemical composition are specified as follows: Type 1 is medium carbon alloy steel, and this specification applies to ASTM A325 and ASTM A490 large hexagon structural bolts adopted by the Research Committee in its published steel structure specifications.
It should be noted that this standard uses imperial/pound as the only unit of measurement and does not include other units of measurement; this standard is not intended to address all issues related to potential safety hazards (if any). Users are responsible for determining the applicability and limitations of this standard in establishing appropriate safety and health practices before use.
(II) Relevant ASTM Standard Specifications
1. ASTM A325 Standard: Heat-treated high-strength bolts for steel structures, with a minimum tensile strength of 120/105 kilopounds per square inch (ksi).
2. ASTM A490 Standard: High-strength bolts corresponding to strength grade 10.9, suitable for steel structure joint connections.
3. ASTM A563M Standard: "Carbon and Alloy Steel Nuts (Metric)". Nuts that meet this specification need to be used with the ASTM A490M large hexagon bolt specification. The different grade requirements for nut surface finish shall ultimately determine the applicable nut grade and surface treatment specification according to the bolt type and surface treatment method.
(III) Material and Performance Test Specifications
Alloy steels certified by the American Iron and Steel Institute are classified as structural alloy steels if their alloy element content exceeds any of the following ranges or contains specified elements with a specific minimum content: manganese ≤ 1.65%, copper ≤ 0.60%, silicon ≤ 0.60%; or aluminum, chromium ≤ 3.99%, as well as other alloy elements such as cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium added to achieve the required alloying effect.
For bolts with a diameter less than M24, their length range is 21.4D to 2D (D is the bolt diameter). Such bolts need to undergo a wedge load axial tensile test, and the test results shall meet the minimum tensile load, proof load or alternative proof load requirements specified in Table 4.
Bolts with a diameter less than M24 and a length shorter than 2D shall undergo axial tensile testing based on hardness. After completing the hardness test and tensile test of the bolts as required, record the first occurrence of the minimum hardness reading. The purpose of this test is to optimize the bolt production process and improve the quality and service performance of stainless steel bolts by detecting the decarburization near the surface (complete decarburization and incomplete decarburization) and core hardness.
III. Summary
In summary, the formulation and strict compliance of stainless steel bolt standards are the key to ensuring the quality and performance of stainless steel bolts, and also an important prerequisite for ensuring the safety of use and the stable operation of industrial infrastructure. Therefore, researching, mastering and strictly implementing these standards and specifications is an important task for industrial manufacturers and relevant institutions, aiming to provide users with higher quality and more reliable stainless steel bolt products.
