Related Research Articles
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.
Martensitic stainless steel is a type of stainless steel alloy that has a martensite crystal structure. It can be hardened and tempered through aging and heat treatment. The other main types of stainless steel are austenitic, ferritic, duplex, and precipitation hardened.
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.
Marine grade stainless alloys typically contain molybdenum to resist the corrosive effects of NaCl or salt in seawater. Concentrations of salt in seawater can vary, and splash zones can cause concentrations to increase dramatically from the spray and evaporation.
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.
Michael A. Streicher was an American metallurgist and engineer who became internationally recognized for his work on the testing and development of corrosion-resistant stainless steel alloys. He published widely in technical journals and textbooks and received numerous patents for his inventions.
A tube, or tubing, is a long hollow cylinder used for moving fluids or to protect electrical or optical cables and wires.
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.
Incoloy refers to a range of superalloys now produced by the Special Metals Corporation (SMC) group of companies and created with a trademark by the Inco company in 1952. Originally Inco protected these alloys by patent. In 2000, the SMC published a 61-page document entitled "High-Performance Alloys for Resistance to Aqueous Corrosion" highlighting Incoloy, as well as Monel and Inconel products, and their use in fluid environments such as sulfuric acid, hydrochloric acid, hydrofluoric acid, phosphoric acid, nitric acid, other acids as well as freshwater environments.
SAF 2507, also known as Sandvik SAF 2507, is a Sandvik-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 Type 630 stainless steel is a grade of martensitic precipitation hardened stainless steel. It contains approximately 15–17.5% chromium and 3–5% nickel, as well as 3–5% copper. The name comes from the chemical makeup which is approximately 17% chromium and 4% nickel. SUS630 is the same as 17-4PH, and they both refer to the same grade.
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 not harder than 316L, but 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. There is no difference between 316L and 904L steel in strength and hardness. Both have similar Rockwell hardness (HRB) which is less than 95 and their tensile strength are both about 490MPa. 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.
Duplex stainless steels are a family of alloys with a two-phase microstructure consisting of both austenitic and ferritic phases. They offer excellent mechanical properties, corrosion resistance, and toughness compared to other types of stainless steel. However, duplex stainless steel can be susceptible to a phenomenon known as 475 °C embrittlement or duplex stainless steel age hardening, which is a type of aging process that causes loss of plasticity in duplex stainless steel when it is heated in the range of 250 °C (480 °F) to 550 °C (1,020 °F). At this temperature range, spontaneous phase separation of the ferrite phase into iron-rich and chromium-rich nanophases occurs, with no change in the mechanical properties of the austenite phase. This type of embrittlement is due to precipitation hardening, which makes the material become brittle and prone to cracking.
References
- ↑ , Material datasheet for SAF 2205 (seamless tube and pipe) issued by Sandvik 2011-01-21
- ↑ , engineeringtalk.com article Jun 20, 2008
- ↑ , matweb.com Sandvik SAF 2205 Seamless tube and pipe
- ↑ "Stainless Steel - Grade 2205 Duplex (UNS S32205)". AZoM.com. 2001-10-19. Retrieved 2017-06-02.