Selecting Stainless Steel Grades - 5 Things to Consider

Selecting Stainless Steel Grades - 5 Things to Consider

Stainless steel is widely utilized in a variety of industries, from medical instruments and chemical storage to transportation and power generation, due to its superior corrosion resistance, hygiene, and strength. Despite the availability of over 3,500 types of steel, not all stainless steel grades offer the same benefits.

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Given the multitude of options, how can you be certain you’re selecting the right grade for your particular needs?

1. Select Based on Operating Environment

To determine the best steel grade for your environment, consider the conditions your final product will face. Low pH levels, high stresses, high temperatures, and crevice corrosion can all negatively impact stainless steel's performance. Steels in the austenitic T3XX series, such as the widely used 316 and 304 alloys, maintain their strength, toughness, and resistance to corrosion across a wide range of temperatures.

Corrosion resistance is the primary reason austenitic stainless grades are chosen. The addition of molybdenum in Type 316 helps resist chloride ions found in marine and chemical processing settings. Regardless of the steel grade, a well-designed structure is the best defense against corrosion.

2. Emphasize Strength, Ductility, and Toughness

Next, focus on three key mechanical properties:

• Strength: The stress a metal can endure before it deforms or fractures
• Ductility: The ability to be reshaped, such as being drawn into wire or thread, without losing strength
• Toughness: The ability to absorb energy and deform before breaking

Stainless steel's chromium content (10--30%) provides corrosion resistance. In austenitic grades, the addition of nickel enhances toughness and ductility. Grades high in chromium, molybdenum, and nickel offer the greatest resistance to corrosion.

However, alloy content is not the only factor to consider. Processing also affects mechanical properties. The duration steel is held at certain temperatures during cooling, as well as the cooling speed, impacts its overall quality.

While carbon steels can be hardened by heat treatment, austenitic stainless steels are hardened through cold working operations like rolling, bending, and drawing at temperatures below the recrystallization threshold. Note that increasing hardness through cold working can reduce properties such as elongation and impact resistance.

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3. Consider Form and Processing

Austenitic stainless steel is commonly available in various forms, including bar, wire, tube, pipe, sheet, and plate. Most products require additional forming or machining to suit specific applications.

For example, stainless steel tubing may need bending, coiling, re-drawing, machining, welding, or end forming. If your stainless steel will undergo machining processes like CNC machining, drilling, reaming, or threading, select a machining rate to minimize work hardening or choose a "free-machining" grade that contains sulfur.

When welding stainless steel, embrittlement of the weld area is a concern. Opt for lower carbon grades like 304, 304L, or 316L to reduce carbide formation.

4. Meet Customer Preferences

Many designers select stainless steel for its visual appeal, whether it’s 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 grades can achieve these finishes and may also undergo passivation.

Customers might also require specific certifications. For example, ASTM A213 and A249 are recommended for boiler, superheater, and heat-exchanger tubes, while ASTM A908 is suitable for hard-drawn austenitic stainless steel industrial needle tubing. With more than 12,000 ASTM standards, each one addresses specifications to ensure that technical standards are met.

5. Manage Costs and Availability

Though austenitic stainless steels are expensive, their long-term value justifies the cost. Opting for a corrosion-resistant material suitable for its application minimizes maintenance, downtime, and replacement expenses. Life-cycle costing methods can help in making direct comparisons between different materials.

Selecting a Stainless Steel Supplier

At Eagle Stainless, we're here to help you prioritize your material requirements and assist you in choosing the ideal stainless steel grades for your application. Our quality management certifications signify our dedication to quality and ensure you receive the best guidance for selecting stainless steel.

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