Introduction to Stainless Steel
Stainless steel refers to a group of alloy steels that typically contain 10 to 30% chromium. Chromium has a high resistance to corrosion and heat, thanks to its low carbon content. Other elements, such as nickel, molybdenum, titanium, aluminum, niobium, copper, nitrogen, sulfur, phosphorus, or selenium, may be added to improve corrosion resistance, boost oxidation resistance, or impart particular properties. Most stainless steels are melted first in electric-arc or basic oxygen furnaces, then refined in another steelmaking vessel, mostly to reduce carbon content.
A mixture of oxygen and argon gas is pumped into liquid steel during the argon-oxygen decarburization process. It is feasible to remove carbon to regulated amounts by oxidizing it to carbon monoxide without simultaneously oxidizing and losing valuable chromium by changing the ratio of oxygen and argon. As a result, lower-cost raw materials like high-carbon ferrochromium might be employed in the first melting process.
Stainless steel comes in over a hundred different grades. The majority of stainless steel is divided into five categories: austenitic, ferritic, martensitic, duplex, and precipitation-hardening. The highest corrosion resistance is usually found in austenitic steels, which contain 16 to 26 percent chromium and up to 35 percent nickel. They are nonmagnetic and cannot be hardened by heat treatment. They are used in cutlery, surgical instruments, wrenches, and turbines because they can be hardened by heat treatment and have moderate corrosion resistance.
The strength of precipitation-hardening stainless steel is due to the addition of aluminum, copper, and niobium to the alloy in amounts of less than 0.5 percent of the total mass. It has a corrosion resistance comparable to austenitic stainless steel, and it contains 15 to 17.5 percent chromium, 3 to 5 percent nickel, and 3 to 5 percent copper. The construction of long shafts is done with precipitation-hardening stainless steel.
Types of Stainless Steel Grades
- Type 102 is austenitic stainless steel that is commonly used in furniture.
- The 200 Series is an austenitic chromium-nickel-manganese alloy used in general metalworking.
- The austenitic chromium-nickel alloy 300 Series is a series of austenitic chromium-nickel alloys. Grade 304 stainless steel is the most common stainless steel grade. Food utensils, surgical scrub sinks, and instruments are made of this stainless steel series.
- Ferritic and martensitic chromium alloys in the 400 Series. This series includes the cheapest stainless steel, which is used in car exhausts, as well as higher-grade cutlery steel and the hardest stainless steel, which is used in replica swords and blades.
- The 500 Series is a series of heat-resistant chromium alloys.
- Precipitation hardening produces the martensitic alloy series 600.
- Type 2205 is a duplex alloy with exceptional strength and corrosion resistance (both ferritic and austenitic).
- Type 2304 is a similar alloy to type 2205 in every way except for the lower molybdenum concentration, which results in lesser pitting corrosion resistance.
Five Factors to consider when choosing the right Stainless Steel Grade
Take into account the operating environment
It’s crucial to evaluate the working environment before selecting the proper stainless-steel grade, as environmental factors can have an impact on the final product. Stainless steel is affected by temperature, low pH, stresses, and crevice corrosion. As a result, it’s recommended to choose 316 or 304 metals, which have the best strength, hardness, and corrosion resistance over a wide temperature range. The molybdenum in Type 316 resists the chloride ions seen in marine and chemical applications. Corrosion is best resisted by high-quality structural design.
Formability and Weldability are two terms that are often used interchangeably.
Weldability and formability are also critical. An austenitic grade of stainless steel, such as 304, or a ferritic grade, such as 430, is required for applications that demand good formability. Martensitic grades, such as 410, are brittle and weak, making them a poor choice. Weldability is another important characteristic of a material. Under welding, poor stainless-steel grades can split, intergranular corrode, or stress corrode. Austenitic grades, like formability, are the most weldable. Lower carbon in 304L and niobium stabilizers in 347 both help to prevent these problems. Stainless steel grades 430 and 439 are also suitable for welding. Even though martensitic stainless steel has a reduced carbon content, it is not normally appropriate for welding.
Corrosion Resistance Level
Fabricators frequently require a steel grade with good corrosion resistance, as previously noted. Varied grades, of course, provide different amounts of resistance. Due to the presence of chromium alloys, austenitic stainless steel has the greatest level. In this scenario, grade 316 is also a viable option. Due to their lack of nickel and chromium, martensitic and ferritic stainless steels are less corrosive than other stainless steels. The ability of a material to endure heat treatment is another aspect of corrosion resistance. Depending on the grade of stainless steel, heat-treating may have a distinct effect.
Everything Narrows Down to Toughness, Ductility, and Strength
When it comes to stainless-steel grades, tensile strength, ductility, and toughness are all important considerations. The amount of stress applied to the steel before it deforms is known as its strength. Ductility refers to a material’s ability to change shape without losing its strength. The capacity of the steel to deform without fracture is referred to as toughness. Given all of this, stainless steel alloyed with chromium and nickel alloys improves these properties and provides the best corrosion resistance. Each grade, however, reacts differently to timing, temperature, and cooling speed.
Cost and Availability of Materials
The most expensive grade is high-performance austenitic stainless steel. It is, nevertheless, the most deserving. When it comes to stainless steel grades, you want the best value for your money. The frequency with which you change the steel may end up costing you more in the long run than acquiring a grade with higher overhead. As a result, choose a more corrosive-resistant grade to save money on maintenance, replacement, and downtime. Experiment with different grades until you discover the one that provides the best value and the longest service life before needing to be replaced.
Selecting a Stainless Steel Supplier
Newzel Industries, a seasoned stainless steel supplier, will assist you in prioritizing your material requirements and guiding you toward the best stainless steel grade for your application. Newzel Industry’s commitment to quality is obvious at every step of the process, with quality management certifications in place to assist you in making the optimal steel option for your industrial application.