A small washer plays a crucial role in bolted connections. It increases the contact area, protects connected surfaces, distributes pressure, and prevents bolt loosening. The quality of washers largely depends on their raw material—stainless steel sheets. The ASTM A240 standard provides essential guidance for selecting high-quality stainless steel materials for washer production.

ASTM A240 is a critical specification for stainless steel plates, sheets, and strips used in pressure vessels and general applications. This standard comprehensively defines the chemical composition and mechanical properties of various stainless steel alloys, including ferritic, austenitic, martensitic, duplex, super duplex, and high-molybdenum grades.

Manufacturers producing metal washers for bolted assemblies commonly use ASTM A240-compliant materials such as 304, 304L, 316, 316L, 321, 347, 309, 310, 316Ti, 317L, Xm-19, 904L, 409, 410, 430, duplex S31803, S32205, super duplex S32750, S32760, S32550, high-molybdenum UNS S31254, and alloy 20.

ASTM A240 covers numerous stainless steel grades, each with unique chemical compositions and mechanical properties suited for different applications:

• 304 Stainless Steel: A classic 18-8 chromium-nickel austenitic stainless steel with excellent corrosion resistance, heat resistance, and workability. Its balanced properties make it a popular choice for general-purpose washers.
• 316L Stainless Steel: A low-carbon chromium-nickel-molybdenum austenitic grade offering superior corrosion resistance, particularly in chloride environments. Ideal for marine or chemical industry applications.
• 321 Stainless Steel: A titanium-stabilized 18-8 chromium-nickel austenitic grade that resists intergranular corrosion during welding. Suitable for washers requiring welding.
• 410 Stainless Steel: A 12% chromium martensitic grade offering moderate corrosion resistance and strength that can be enhanced through heat treatment. A cost-effective option for washers needing strength more than corrosion resistance.
• 904L Stainless Steel: A high-nickel-molybdenum super austenitic grade with exceptional corrosion resistance, especially in acidic environments. Used for washers in extreme corrosive conditions.
• UNS S31803: A ferritic-austenitic duplex stainless steel combining high strength with good toughness and corrosion resistance. Suitable for washers needing both strength and corrosion resistance.
• UNS S32750: A super duplex grade offering higher strength and corrosion resistance than S31803, particularly in chloride environments. Used for washers in extreme conditions.
• UNS S31254: A high-molybdenum austenitic grade with exceptional pitting and crevice corrosion resistance, especially in seawater. Ideal for marine engineering applications.

The standard strictly defines chemical composition percentages for each grade to ensure proper performance characteristics:

The standard also specifies mechanical properties including tensile strength, yield strength, elongation, and hardness:

Choosing the appropriate stainless steel sheet for washer manufacturing requires careful consideration of the operating environment, load requirements, and budget constraints. Corrosive environments demand grades like 316L, 904L, or super austenitic stainless steels, while high-strength applications benefit from duplex or super duplex grades.

By understanding ASTM A240 standards and selecting appropriate stainless steel grades, manufacturers can produce high-quality washers that ensure reliable and safe bolted connections. This approach significantly contributes to engineering quality and equipment safety.