Stainless steel, also known as inox, corrosion-resistant steel (CRES), or Rustless steel, is an alloy of iron that is resistant to rusting and corrosion. It contains at least 10.5% chromium and usually nickel, and may also contain other elements, such as carbon, to obtain the desired properties. Stainless steel's resistance to corrosion results from the chromium, which forms a passive film that can protect the material and self-heal in the presence of oxygen.
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
Surgical stainless steel is a grade of stainless steel used in biomedical applications. The most common "surgical steels" are austenitic SAE 316 stainless and martensitic SAE 440, SAE 420, and 17-4 stainless steels. There is no formal definition on what constitutes a "surgical stainless steel", so product manufacturers and distributors often apply the term to refer to any grade of corrosion resistant steel.
Terne plate is a form of tinplate: a thin steel sheet coated with an alloy of lead and tin. The terne alloy was in the ratio of 10-20% tin and the remainder lead. The low tin content made it cheaper than other tinplates.
Monel is a group of alloys of nickel and copper, with small amounts of iron, manganese, carbon, and silicon. Monel is not a cupronickel alloy because it has less than 60% copper.
AL-6XN is a type of weldable stainless steel that consist of an alloy of nickel (24%), chromium (22%) and molybdenum (6.3%) with other trace elements such as nitrogen.
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with a limited diffusion of ions.
Alloy 20 is an austenitic stainless steel containing less than 50% iron developed for applications involving sulfuric acid. Its corrosion resistance also finds other uses in the chemical, petrochemical, power generation, and plastics industries. Alloy 20 resists pitting and chloride ion corrosion, better than 304 stainless steel and on par with 316L stainless steel. Its copper content protects it from sulfuric acid. Alloy 20 is often chosen to solve stress corrosion cracking problems, which may occur with 316L stainless. Alloy of the same name with the designation "Cb-3" indicates niobium stabilized.
Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected and sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. The chemical environment that causes SCC for a given alloy is often one which is only mildly corrosive to the metal. Hence, metal parts with severe SCC can appear bright and shiny, while being filled with microscopic cracks. This factor makes it common for SCC to go undetected prior to failure. SCC often progresses rapidly, and is more common among alloys than pure metals. The specific environment is of crucial importance, and only very small concentrations of certain highly active chemicals are needed to produce catastrophic cracking, often leading to devastating and unexpected failure.
Austenitic stainless steel is one of the five classes of stainless steel by crystalline structure. Its primary crystalline structure is austenite and it prevents steels from being hardenable by heat treatment and makes them essentially non-magnetic. This structure is achieved by adding enough austenite-stabilizing elements such as nickel, manganese and nitrogen. The Incoloy family of alloys belong to the category of super austenitic stainless steels.
The SAE steel grades system is a standard alloy numbering system for steel grades maintained by SAE International.
Marinisation is design, redesign, or testing of products for use in a marine environment. Most commonly, it refers to use and long-term survival in harsh, highly corrosive salt water conditions. Marinisation is done by many manufacturing industries worldwide including many military organisations, especially navies.
Zeron 100 is a super duplex stainless steel developed by Rolled Alloys. The alloy has excellent corrosion resistance combined with high strength. It typically contains 25% chromium and 7% nickel and 3.6% molybdenum along with copper and tungsten additions. Zeron 100 has a 50–50 austenitic–ferritic structure. It also has greater resistance to chloride pitting, crevice corrosion and stress corrosion cracking than exhibited by the standard 300 series stainless steels.
SAF 2205, is a Alleima-owned trademark for a 22Cr duplex (ferritic-austenitic) stainless steel. SAF derives from Sandvik Austenite Ferrite. The nominal chemical composition of SAF 2205 is 22% chromium, 5% nickel, 3.2% molybdenum and other alloying elements such as nitrogen and manganese. The UNS designation for SAF 2205 is S31803/S32205 and the EN steel no. is 1.4462. SAF 2205 or Duplex 2205 is often used as an alternative to expensive 904L stainless steel owing to similar properties but cheaper ingredients. Duplex stainless steel is available in multiple forms like bars, billets, pipes, tubes, sheets, plates and even processed to fittings and flanges.
SAF 2507, is a Alleima-owned trademark for a 25Cr duplex (ferritic-austenitic) stainless steel. The nominal chemical composition of SAF 2507 is 25% chromium, 7% nickel, 4% molybdenum and other alloying elements such as nitrogen and manganese. The UNS designation for SAF 2507 is S32750 and the EN steel no. is 1.4410. SAF derives from Sandvik Austenite Ferrite.
Duplex stainless steels are a family of stainless steels. These are called duplex grades because their metallurgical structure consists of two phases, austenite and ferrite in roughly equal proportions. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as Type 304 or 316. The main differences in composition, when compared with an austenitic stainless steel is that the duplex steels have a higher chromium content, 20–28%; higher molybdenum, up to 5%; lower nickel, up to 9% and 0.05–0.50% nitrogen. Both the low nickel content and the high strength give significant cost benefits. They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc. and in the petrochemical industry in the form of pipelines and pressure vessels. In addition to the improved corrosion resistance compared with the 300 series duplex stainless steels also have higher strength. For example, a Type 304 stainless steel has a 0.2% proof strength in the region of 280 MPa (41 ksi), a 22%Cr duplex stainless steel a minimum 0.2% proof strength of some 450 MPa (65 ksi) and a superduplex grade a minimum of 550 MPa (80 ksi).
SAE 304 stainless steel is the most common stainless steel. The steel contains both chromium and nickel metals as the main non-iron constituents. It is an austenitic stainless steel. It is less electrically and thermally conductive than carbon steel. It is magnetic, but less magnetic than steel. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.
SAE 316L grade stainless steel, sometimes referred to as A4 stainless steel or marine grade stainless steel, is the second most common austenitic stainless steel after 304/A2 stainless steel. Its primary alloying constituents after iron, are chromium, nickel (10–12%) and molybdenum (2–3%), with small (<1%) quantities of silicon, phosphorus & sulfur also present. The addition of molybdenum provides greater corrosion resistance than 304, with respect to localized corrosive attack by chlorides and to general corrosion by reducing acids, such as sulfuric acid. 316L grade is the low carbon version of 316 stainless steel. When cold worked, 316 can produce high yield and tensile strengths similar to Duplex stainless grades.
904L is an austenitic stainless steel. It is harder than 316L, and its molybdenum addition gives it superior resistance to localized attack by chlorides and greater resistance reducing acids; in particular, its copper addition gives it useful corrosion resistance to all concentrations of sulphuric acid. Its high alloying content also gives it greater resistance to chloride stress corrosion cracking, but it is still susceptible. Its low carbon content makes it resistant to sensitization by welding and which prevents intergranular corrosion.
Ferritic stainless steel forms one of the five stainless steel families, the other four being austenitic, martensitic, duplex stainless steels, and precipitation hardened. For example, many of AISI 400-series of stainless steels are ferritic steels. By comparison with austenitic types, these are less hardenable by cold working, less weldable, and should not be used at cryogenic temperatures. Some types, like the 430, have excellent corrosion resistance and are very heat tolerant.
