From composition to form, a range of factors impact the characteristics of stainless steel products. One of the most important considerations is which grade of steel to use.
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This will determine a range of characteristics and, ultimately, both the cost and lifespan of your stainless steel products.
So how do you know where to start?
While every application is unique, these 7 questions highlight critical considerations to help you narrow down your options and find the grades best suited to your needs or application.
When you think of stainless steel, the first things that come to mind are probably resistance to acids and chlorides--such as those found in industrial applications or marine environments. However, temperature resistance is an important consideration as well.
If you need corrosion resistance, you’ll want to avoid ferritic and martensitic steels. Ideal stainless steel grades for corrosive environments include austenitic or duplex alloys such as grades 304, 304L, 316, 316L, , and 904L.
For high-temperature environments, austenitic grades are often best. Finding a grade with high chromium, silicon, nitrogen, and rare earth elements will further alter the steel’s ability to withstand high temperatures. Common grades for high-temperature environments include 310, S, and 446.
Austenitic steel grades are also ideal for low-temperature or cryogenic environments. For added resistance, you can look at low carbon or high nitrogen grades. Common grades for low-temperature environments include 304, 304LN, 310, 316, and 904L.
A steel with poor formability will become brittle if overworked and offer lower performance. In most cases, martensitic steels are not recommended. Furthermore, steel with low formability might not hold its shape when complex or intricate forming is required.
When choosing a steel grade, you’ll want to consider the form in which you’d like it delivered. Whether you want rods, slabs, bars or sheets will limit your options. For example, ferritic steels are often sold in sheets, martensitic steels are often sold in bars or slabs, and austenitic steels are available in the widest range of forms. Other steel grades available in a variety of forms include 304, 316, 430, , and 3CR12.
Machining isn’t typically a problem. However, work hardening can produce unintended results. The addition of sulfur can improve machinability but reduces formability, weldability and corrosion resistance.
This makes finding a balance between machinability and corrosion resistance a critical consideration for most multistage stainless steel fabrication processes. Depending on your needs, grades 303, 416, 430, and 3CR12 offer a good balance from which to narrow options further.
Welding stainless steel can lead to trouble—including hot cracking, stress corrosion cracking, and intergranular corrosion—depending on the grade of steel used. If you plan to weld your stainless steel, austenitic alloys are ideal.
Low carbon grades can further help with weldability while additives, such as niobium, can stabilize alloys to avoid corrosion concerns. Popular grades of stainless steel for welding include 304L, 316, 347, 430, 439 and 3CR12.
If your application requires heat treatment, you must consider how the various grades of steel respond. The final characteristics of certain steels are drastically different before and after heat treatment.
In most cases, martensitic and precipitation hardening steels, such as 440C or 17-4 PH, offer the best performance when heat treated. Many austenitic and ferritic stainless steels are non-hardenable once heat treated and therefore are not ideal options.
Steel strength is an essential factor to consider to maximize safety. Yet, overcompensating can lead to unneeded cost, weight, and other wasteful factors. Strength characteristics are loosely set by the family of steel with further variations available in different grades.
For example:
All of the previous considerations feed into the most important question in choosing a stainless steel grade—lifetime cost. Matching the stainless steel grades to your intended environment, usage and requirements, you can ensure long-lasting performance and exceptional value.
Take care to analyze how the steel will perform over the intended period of use and what costs might be involved in maintenance or replacement before deciding. Limiting costs upfront might result in far more spending over the life of your project, product, structure, or other application.
Of course, if the initial price is too great, you might need to make compromises. Finding a balance is essential to both short-term and long-term success. But by considering these seven points, you’re eliminating potential hazards and setting the foundation for choosing the optimal solution for your needs.
All steel is iron-based, but stainless steel contains chromium at 10% or more by weight. Chromium, provides corrosion resistance and a polished appearance, making it highly resistant to rust and staining, while ordinary steel does not have these properties, making it susceptible to corrosion and staining. Ordinary steel is used in a wide range of applications, from construction to manufacturing, where corrosion resistance is not a primary concern.
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Explore the Performance Diversity Across Various Stainless Steel Types
Stainless steel’s non-corrosive characteristic gives it a long lifespan. With the addition of nickel, the material survives even longer and in several types of environments. By adding molybdenum and nitrogen, stainless gains improved pitting and crevice corrosion resistance. Stainless steel has a high strength-to-weight ratio even at high temperatures. Adding alloys to stainless steel helps it resist heat and scaling. Stainless steel is easy to clean because the surface is non-porous. It is well suited for medical and food-grade applications because it prevents the absorption of bacteria and germs. Stainless steel does not stain and can be polished to create an aesthetic appearance.
Read Stainless Steel Characteristics for more information.
Stainless steels are classified according to their metallurgical structure: austenitic, ferritic, martensitic, precipitation hardening, and duplex. Austenitic stainless steels contain chromium and nickel. They are hardened only through cold working and are non-magnetic although some may become magnetic by cold working. Austenitic stainless steels are identified as T300 series stainless steels (typical alloys T304, T316). Alloys containing chromium, nickel, and manganese are identified as T200 series (T201, T202). Ferritic stainless steels are straight chromium. They are magnetic, have good ductility, and resist corrosion and oxidation. Ferritic stainless steels cannot be hardened by heat treatment and are identified as T400 series (T409, T430). Martensitic stainless steels are also straight chromium but can be hardened by heat treatment. They are magnetic and resist corrosion in mild environments. They have fairly good ductility and some can be heat treated to tensile strengths in excess of 200,000 psi. Martensitic stainless steels are identified as T400 series (T410, T416). Precipitation-hardening stainless steels are chromium-nickel types identified as alloys T17-4 or T17-7 PH. They can be hardened by solution treating and aging. Duplex stainless steels have an annealed structure which is typically equal parts of austenite and ferrite. The duplex grades are highly resistant to corrosion and pitting. They have about twice the yield strength of conventional grades. T is the standard alloy for duplex grade.
Learn More About Stainless Steel Types
Stainless steel finds diverse applications, including cookware, cutlery, sinks, aerospace components, medical instruments, oil and gas pipelines, beverage containers, and laboratory equipment. It is chosen for its resistance to corrosion and heat. Specifically, austenitic stainless steels excel in heat exchangers, medical devices,food and beverage machinery, chemical equipment, marine equipment and nuclear power. These applications showcase the versatility of austenitic stainless steels, which can meet the demands of industries requiring corrosion resistance, hygiene, strength, and high-temperature performance. Ferritic stainless steels serve in automotive, appliances, and cooking utensils. Ferritic stainless steels are favored in applications that require corrosion resistance in less aggressive environments and where their magnetic properties do not pose a problem. They are often chosen for their cost-effectiveness and resistance to staining and discoloration. Martensitic stainless steels are employed for industrial blades, fasteners, bearings and pump shafts. Martensitic stainless steels are known for their high strength, hardness, and wear resistance. These properties make them suitable for a variety of applications, particularly in situations where mechanical performance and durability are crucial. Precipitation hardening stainless steels find roles in valves, fittings, gears, marine components, and petrochemical equipment. Precipitation hardening stainless steels are well-suited for industries and situations that demand materials with a unique balance of high strength, toughness, and corrosion resistance. Duplex stainless steels are utilized in scenarios resembling those of austenitic and ferritic types, such as Water and wastewater treatment, storage vessels, processing equipment and more. Duplex stainless steels are a group of corrosion-resistant alloys with a combination of both austenitic and ferritic microstructures.
Learn Common Applications for Stainless Steel Tubes.
Grades 304 and 316 stainless steel are the most commonly used in marine settings, with 316 particularly renowned for its high corrosion resistance in aggressive marine environments. Stainless steel forms a protective oxide layer on its surface, which acts as a barrier against corrosion, even when exposed to salt water. This oxide layer is self-repairing and continues to protect the material over time. When properly maintained, stainless steel tubing can have a long lifespan in marine environments, often exceeding the lifespan of alternative materials.
Learn more about 304 vs. 316 Stainless Steel
Stainless steel can be either magnetic or non-magnetic, depending on its composition.
Austenitic Stainless Steel: This group, which includes grades like 304 and 316, is non-magnetic. Ferritic Stainless Steel: Ferritic stainless steels, such as 430, are typically magnetic.
Martensitic Stainless Steel: Martensitic stainless steels, like 410 and 420, are also typically magnetic.
It’s important to note that there are exceptions and variations within each of these groups, and some stainless steel grades may have slightly different magnetic properties based on their specific alloying elements and heat treatment
The “gauge” of stainless steel refers to the thickness. Gauge is represented numerically. For stainless steel, as the gauge number increases the material thickness decreases. This means 14 gauge is thicker than 16 gauge. The gauge is used to determine the thickness of the tube wall, which is a critical factor in its strength, durability, and suitability for specific uses.
Gain Insight intoStainless Steel Tubing Dimensions
The “L” indicates a low-carbon or “L-grade” stainless steel. Low-carbon stainless steels are designated by adding an “L” after the alloy grade number. For example, you might encounter designations like 304L or 316L stainless steel tubing.
The “L” signifies that the stainless steel alloy contains a reduced carbon content compared to the standard grades. Low-carbon stainless steels offer several advantages: improved weldability, reduced corrosion sensitivity, and maintained corrosion resistance.
While the L-grade stainless steels offer enhanced corrosion resistance and weldability, they may come at a slightly higher cost compared to their non-L counterparts.
In some instances the terms may be used interchangeably; however, there are some differences is in how the material is ordered and toleranced. Tubing is typically ordered to outside diameter and wall thickness; however, it may also be ordered as OD & ID or ID and Wall Thickness. Although tubing has three dimensions (O.D., I.D. and wall thickness) only two may be specified with tolerances and the third is theoretical. Pipe is typically ordered using the Nominal Pipe Size (NPS) standard and by specifying a nominal diameter (pipe size) and schedule number (wall thickness). Also tubing is usually ordered and held to tighter and more stringent tolerances and specifications than pipe.
Determine if Custom Tubing is Right for Your Application
Annealing is a heat treatment process used to modify the physical and mechanical properties of stainless steel tubing, making it more workable, softer, and less brittle. The annealed condition for stainless steel tubing involves heating the material to a specific temperature and then cooling it slowly. The exact annealing process can vary depending on the specific stainless steel alloy and the desired properties. This process makes it more workable, easier to bend, weld, and fabricate, and improves its machinability.
Cold working or work hardening is the process of strengthening a metal by deformation at temperatures below the recrystallization temperature. Any mechanical operation that creates permanent formation, such as bending, rolling, drawing performed at room temperature that increases the hardness strength of stainless steel.
Cold working decreases mechanical properties of metal like elongation, reduction of area and impact values. Cold working can be a cost-effective and efficient way to achieve the desired characteristics for stainless steel tubing.
Iron particles or other substances can become embedded in the stainless surface during fabrication or polishing operations. These particles must be removed or else they will cause discoloration, rusting, or even pitting. Oxidizing chemicals are used to form a passive layer along the surface of stainless steel to enhance resistance to corrosion. This process is the final preparation for stainless steel parts. It consists of immersing the parts in a nitric acid solution, rinsing with clear running water, and drying.
Explore our Surface Finish Guide for Further Insights Into Enhancing the Surface Finish of Stainless Steel and Ensuring Its Optimal Performance.
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