The index of martensitic steels with moderated carbon content is AISI 420 steel, which contains 13% chromium and 0.35% carbon in weight. The increase in carbon content and the temperature of the austenite leads to the formation of a M23C6 carbide in grain boundaries . These steels are used in cutting tools, surgery and dentistry, axes, valves, pumps, blades, and steam turbine parts and plastic injection molds.

 

 

The high carbon martensitic steels index is AISI 440 steel. High levels of chromium make them used in marine or seawater environments. High level of carbon Stabilizing austenite and lead to increase toughness, mechanical strength and abrasion. These steels are usually not welded. Common uses of these steels are: bearings, valleys and spray nozzles.

 

Duplex stainless steels have 18-29% chromium, 2.5-8.5% nickel and 1-4% molybdenum, up to 2.5% manganese, up to 2% silicon and up to 0.35% nitrogen. These steels have a ferritic-austenitic structure. The volume percent of ferrite and austenite vary between 0.3 and 0.7 in the two-phase structures of different steels. The ratio of ferrite to austenite determines the mechanical properties of duplex steels. The steel Yield strength increases with increasing ferrite volume. The maximum strength is related to the structure with a maximum of 80% ferrite. Compared to austenitic steels, these steels have a much higher yield strength (about 2 or 3 times higher) and have higher cracking resistance due to corrosion stress, but their deep drawing properties are less than austenitic steels. Compared to ferritic steels, they have higher toughness, ductility and weldability. Duplex steels are not suitable for Working temperatures from 300 to 950 Celsius.

 

The corrosion resistance of stainless steels increases with increasing chromium content, the corrosion resistance agent is because of the presence of a thin chromium hydroxide layer on their surface. The quality of this surface layer depends on the chemical composition and processes applied to stainless steels. The protective layer should be continuous and non-porous, free from contamination and not corrosive. Stainless Steel 316 with 2.5% molybdenum and 18% chromium has the highest rupture strength among the 3XX group and is used in a variety of industries such as oil and gas and petrochemicals, food industry, pharmaceuticals, and etc. It should be noted that these steels are not resistant to all corrosive environments. In chlorine-containing environments Under tension have less corrosion resistance than building steels.

 

 

Austenitic steels offer an excellent combination of corrosion resistance, flexibility, toughness and weldability. However, their yield strength is relatively low in the annealed state and is in a ranges of 200 to 250 MPa. The 3XX series has a higher nickel content than the 2XX series and cantain manganese up to 2% .

 

precipitation hardening steels are high-strength alloys with good flexibility and toughness and high corrosion resistance. PH steels can have austenitic or martensitic background. PH steels contain less than 0.1% carbon weight percent with nickel and molybdenum. Molybdenum is usually added to increase mechanical properties and corrosion resistance.

 

Creep is a limiting factor in the life of parts or structures at high temperatures. Experience has shown that many methods of metals hardening at temperatures above the half of melting point (Kelvin), lose their effects. Oxidation resistance for temperatures above 600 ° C is an important factor in determining the properties of matters. For this purpose at least 8% of chromium in steel is essential. several steels with 5 to 12 percent chromium and some molybdenum are available to improve creep resistance.