Industrial Surface Chemistry

5 Factors to Consider When Selecting a Grade of Stainless Steel

How do you know which grade of stainless steel to choose? Consider this analysis.

According to Thomas Net:

“Stainless steel is a commonly used material in applications ranging from medical instruments or chemical storage to transport or power generation because of its high corrosion resistance, hygiene, and strength. While there are more than 3,500 grades of steel, not all grades are created equally.

“With so many options, how can you ensure you’re selecting the appropriate grade for your specific needs?

1. Choose the Right Metal for Your Operating Environment

“To determine which grade of steel will uphold best in a given environment, think about the conditions your final product will face. Extremely low pH, high stresses and high temperatures, and crevice corrosion negatively impact stainless steel performance. Steels in the austenitic T3XX series, like the common types 316 and 304 alloys, retain their strength, toughness, and corrosion-resistant properties over the broadest temperature range.

“Corrosion resistance is the main reason for choosing austenitic stainless grades. Type 316, with its molybdenum addition, even resists chloride ions found in marine and chemical processing applications. With any steel grade, high-quality structural design is the best defense against corrosion.

2. Prioritize Strength, Ductility, and Toughness

“Next, consider these three top mechanical qualities:

Strength: The stress a metal can withstand before it fractures or deforms
Ductility: The ability of a material to have its shape changed, such as being drawn out into a wire or thread, without losing strength or breaking
Toughness: The metal’s ability to deform and absorb energy before fracture

“Stainless steel contains 10–30% chromium as its alloying element, which is what helps it resist corrosion. The nickel addition in austenitic grades provides the highest toughness and ductility among stainless grades. Grades high in chromium, molybedenum, and nickel are the most resistant to corrosion.

“Alloy content is not the only aspect to consider when choosing a grade of stainless steel; the material’s processing also affects is mechanical response. The duration of time steel is held at different temperatures as part of its cooling process, as well as the total speed at which it is cooled, can affect its overall quality.

“While the hardness of carbon steels can be increased by heat treatment, austenitic stainless is hardened by cold working operations like rolling, bending, swaging, or drawing at temperatures below the recrystallization temperature. Be aware that increasing hardness by cold working operations decreases other properties like elongation and impact resistance.

3. Factor in Form and Process

“Austenitic stainless steel is widely available in bar, wire, tube, pipe, sheet, and plate forms; Most products require additional forming or machining before they can be used for their specific application.

“Stainless steel tubing, for instance, may need bending or coiling, re-drawing, machining, welding, or end forming. If your stainless steel will see machining processes like CNC machining, drilling, reaming, bevel cutting, chamfering, knurling, or threading, choose a machining rate that mitigates the risk of work hardening or select a “free machining” grade containing sulfur.

“When welding any stainless steel parts, embrittlement in the weld area is a top concern. Choose a lower carbon grade like 304, 304L, or 316L to reduce carbide formation.

4. Consider Your Customers’ Preferences

“Many designers choose stainless steel for its aesthetic appearance, whether that appearance is a shiny, electropolished “bright” finish, a dull “pickled” finish, a matte surface polished to a specific RMS, or a light-absorbing black oxide coating. Austenitic stainless steel can take any of these finishes plus the common addition of passivation.

“Customers may also need certification for application-specific specifications. For instance, ASTM A213 and A249 should be used for boiler, superheater, and heat-exchanger tubes, while ASTM A908 should be used for hard-drawn austenitic stainless steel industrial needle tubing. There are more than 12,000 ASTM standards, and each addresses a specification so customers know the technical standards tested for chemical composition, heat treatment or temper, and other physical and mechanical attributes.

5. Manage Material Cost and Availability

“Although high-performing austenitic stainless steels are the most expensive stainless steels up front, they are well worth the investment. Choosing a corrosion-resistant material well-suited to its application reduces maintenance, downtime, and replacement costs. Life-cycle costing methods can quantify current and future costs and create an “apples-to-apples“ comparison of different materials.”

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