Material analysis of American standard double-ended studs bolt

In critical industrial sectors such as petrochemicals, power energy, pressure vessels and cryogenic equipment, and pressure pipelines, the performance, suitability, and service life of fasteners directly affect the safety and stability of the entire system. As a crucial basic fastener, the correct selection of the appropriate material for studded bolts is extremely important. The American Society for Testing and Materials (ASTM) standard, with its stringent grading and globally recognized authority, has become an important guideline for fastener selection in the industrial field. This article will delve into the two core standards, ASTM A193 and A320, explaining the performance characteristics of key material grades such as B7, B8, B8M, B16, and L7, providing a professional guide for selecting high-performance studded bolts.

　　I. ASTM A193 Studded Bolt Material Standard

　　The full name of the ASTM A193 standard is "Materials for Alloy Steel and Stainless Steel Bolts for High Temperature and High Pressure Equipment." This standard specifies the chemical composition, mechanical properties, and heat treatment requirements for threaded fasteners such as alloy steel and stainless steel bolts and studs suitable for high-temperature or high-pressure service. This standard is the core basis for connection systems in power plant boilers, hydrogenation reactors, high-temperature valves, and other equipment. B7/B7M Chromium-Molybdenum Alloy Steel Bolted Stud

　　ASTM A193 B7: This is the most widely used high-strength alloy steel stud material. It is typically made of chromium-molybdenum alloy steel, and undergoes a quenching and tempering heat treatment process to achieve a minimum tensile strength of 125 ksi (approximately 860 MPa) and a minimum yield strength of 105 ksi (approximately 725 MPa). B7 material maintains good resistance to relaxation and creep at temperatures up to 450°C, making it an essential fastener for high-temperature, high-pressure carbon steel and alloy steel flange connections.

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　　ASTM A193 B7M: As an "improved version" of B7, B7M maintains the same strength level while specifically limiting the hardness range (235 max) and increasing the impact toughness requirements. This characteristic gives it excellent resistance to sulfide stress corrosion cracking (SSC) and makes it specifically designed for acidic environments rich in wet hydrogen sulfide (H₂S) (such as oil and gas extraction and refining plants), making it a safe choice for harsh corrosive conditions.

　　Chemical Composition


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