The model is now a trend with model metal and hard, like the theme of stainless steel and subtlety, as in this modelMartensitic stainless steels are considered to be the most difficult of the stainless steel alloys to weld. Higher carbon contents will produce greater hardness and, therefore, an increased susceptibility to cracking.In addition to the problems that result from localized stresses associated with the volume change upon martensitic transformation, the risk of cracking will increase when hydrogen from various sources is present in the weld metal. A complete and appropriate welding process is needed to prevent cracking and produce a sound weld.Martensitic stainless steels are essentially alloys of chromium and carbon that possess a body-centered cubic (bcc) or body-centered tetragonal (bct) crystal structure (martensitic) in the hardened condition. They are ferromagnetic and hardenable by heat treatments. Their general resistance to corrosion is adequate for some corrosive environments, but not as good as other stainless steels.The chromium content of these materials generally ranges from 11.5 to 18 weight percent, and their carbon content can be as high as 1.2 weight percent. The chromium and carbon contents are balanced to ensure a martensitic structure after hardening. Martensitic stainless steels are chosen for their good tensile strength, creep, and fatigue strength properties, in combination with moderate corrosion resistance and heat resistance.The most commonly used alloy within this stainless steel family is type 410, which contains about 12 weight percent chromium and 0.1 weight percent carbon to provide strength. Molybdenum can be added to improve mechanical properties or corrosion resistance. Nickel can be added for the same reasons. When higher chromium levels are used to improve corrosion resistance, nickel also serves to maintain the desired microstructure and to prevent excessive free ferrite. The limitations on the alloy content required to maintain the desired fully martensitic structure restrict the obtainable corrosion resistance to moderate levels.Duplex stainless steels are two phase alloys based on the iron-chromium-nickel system. Duplex stainless steels usually comprise approximately equal proportions of the body-centered cubic (bcc) ferrite and face-centered cubic (fcc) austenite phases in their microstructure and generally have a low carbon content as well as, additions of molybdenum, nitrogen, tungsten, and copper. Typical chromium contents are 20 to 30 weight percent and nickel contents are 5 to 10 weight percent. The specific advantages offered by duplex stainless steels over conventional 300 series stainless steels are strength, chloride stress-corrosion cracking resistance, and pitting corrosion resistance.Duplex stainless steels are used in the intermediate temperature ranges from ambient to several hundred degrees Fahrenheit (depending on environment), where resistance to acids and aqueous chlorides is required. The weldability and welding characteristics of duplex stainless steels are better than those of ferritic stainless steels, but generally not as good as austenitic materials.
Current commercial grades of duplex stainless steels contain between 22 and 26 weight percent chromium, 4 to 7 weight percent nickel, up to 4.5 weight percent molybdenum, as well as some copper, tungsten, and nitrogen. Modifications to the alloy compositions have been made to improve corrosion resistance, workability, and weldability. In particular, nitrogen additions have been effective in improving pitting corrosion resistance and weldability.The properties of duplex stainless steels can be appreciably affected by welding. Due to the importance of maintaining a balanced microstructure and avoiding the formation of undesirable metallurgical phases, the welding procedures must be properly specified and controlled. If the welding procedure is improper and disrupts the appropriate microstructure, loss of material properties can occur.Because these steels derive properties from both austenitic and ferritic portions of the structure, many of the single-phase base material characteristics are also evident in duplex materials. Austenitic stainless steels have good weldability and low-temperature toughness, whereas their chloride SCC resistance and strength are comparatively poor. Ferritic stainless steels have good resistance to chloride SCC but have poor toughness, especially in the welded condition. A duplex microstructure with high ferrite content can therefore have poor low-temperature notch toughness, whereas a structure with high austenite content can possess low strength and reduced resistance to chloride SCC.The high alloy content of duplex stainless steels also makes them susceptible to the formation of intermetallic phases from extended exposure to high temperatures. Significant intermetallic precipitation may lead to a loss of corrosion resistance and sometimes to a loss of toughness.Duplex stainless steels have roughly equal proportions of austenite and ferrite, with ferrite being the matrix. The duplex stainless steels alloying additions are either austenite or ferrite formers. This is occurs by extending the temperature range over which the phase is stable. Among the major alloying elements in duplex stainless steels chromium and molybdenum are ferrite formers, whereas nickel, carbon, nitrogen, and copper are austenite formers.Composition also plays a major role in the corrosion resistance of duplex stainless steels. Pitting corrosion resistance can be adversely affected. To determine the extent of pitting corrosion resistance offered by the material, a pitting resistance equivalent is commonly used.Precipitation-hardening (PH) stainless steels are iron-chromium-nickel alloys. They generally have better corrosion resistance than martensitic stainless steels. The high tensile strengths of the PH stainless steels is due to precipitation hardening of a martensitic or austenitic matrix. Copper, aluminum, titanium, niobium (columbium), and molybdenum are the primary elements added to these stainless steels to promote precipitation hardening.Precipitation-hardening stainless steels are commonly categorized into three types martensitic, semiaustenitic, and austenitic based on their martensite start and finish (Ms and Mf) temperatures and the resulting microstructures. The issues involved in welding PH steels are different for each group.
Current commercial grades of duplex stainless steels contain between 22 and 26 weight percent chromium, 4 to 7 weight percent nickel, up to 4.5 weight percent molybdenum, as well as some copper, tungsten, and nitrogen. Modifications to the alloy compositions have been made to improve corrosion resistance, workability, and weldability. In particular, nitrogen additions have been effective in improving pitting corrosion resistance and weldability.The properties of duplex stainless steels can be appreciably affected by welding. Due to the importance of maintaining a balanced microstructure and avoiding the formation of undesirable metallurgical phases, the welding procedures must be properly specified and controlled. If the welding procedure is improper and disrupts the appropriate microstructure, loss of material properties can occur.Because these steels derive properties from both austenitic and ferritic portions of the structure, many of the single-phase base material characteristics are also evident in duplex materials. Austenitic stainless steels have good weldability and low-temperature toughness, whereas their chloride SCC resistance and strength are comparatively poor. Ferritic stainless steels have good resistance to chloride SCC but have poor toughness, especially in the welded condition. A duplex microstructure with high ferrite content can therefore have poor low-temperature notch toughness, whereas a structure with high austenite content can possess low strength and reduced resistance to chloride SCC.The high alloy content of duplex stainless steels also makes them susceptible to the formation of intermetallic phases from extended exposure to high temperatures. Significant intermetallic precipitation may lead to a loss of corrosion resistance and sometimes to a loss of toughness.Duplex stainless steels have roughly equal proportions of austenite and ferrite, with ferrite being the matrix. The duplex stainless steels alloying additions are either austenite or ferrite formers. This is occurs by extending the temperature range over which the phase is stable. Among the major alloying elements in duplex stainless steels chromium and molybdenum are ferrite formers, whereas nickel, carbon, nitrogen, and copper are austenite formers.Composition also plays a major role in the corrosion resistance of duplex stainless steels. Pitting corrosion resistance can be adversely affected. To determine the extent of pitting corrosion resistance offered by the material, a pitting resistance equivalent is commonly used.Precipitation-hardening (PH) stainless steels are iron-chromium-nickel alloys. They generally have better corrosion resistance than martensitic stainless steels. The high tensile strengths of the PH stainless steels is due to precipitation hardening of a martensitic or austenitic matrix. Copper, aluminum, titanium, niobium (columbium), and molybdenum are the primary elements added to these stainless steels to promote precipitation hardening.Precipitation-hardening stainless steels are commonly categorized into three types martensitic, semiaustenitic, and austenitic based on their martensite start and finish (Ms and Mf) temperatures and the resulting microstructures. The issues involved in welding PH steels are different for each group.
