The steel with good oxidation resistance and heat toughness under high temperature condition is called heat-resistant steel, which is typically utilized in producing boilers, vapor generators, power equipment, industrial furnaces as well as parts for air travel, petrochemical and also other heat fields. Today we are mosting likely to learn what makes heat-resistant steel so unique?
warm roll steel
High temperature oxidation resistance
The high temperature oxidation resistance of metal describes the resistance of steel to oxidation under heat. Oxidation is a typical chemical corrosion, steel and also oxygen call chain reaction is oxidation rust, deterioration products (oxidation film) comply with the surface area of the metal in high temperature air, burning gas as well as other oxidizing environment. With the advancement of oxidation, the thickness of the oxide movie remains to increase. Whether the metal remains to oxidize after oxidation reaches a particular level directly relies on the performance of the oxide film on the steel surface. If a thick and also steady oxide film is formed with a high binding force and also a high toughness of the oxide movie with the matrix steel, it can protect against the diffusion of oxygen atoms right into the steel and also reduce the oxidation speed. Otherwise, it will certainly speed up the oxidation as well as make the metal surface peel and fall off, leading to the early failing of WLDSTEEL components.
The structure of oxide layer on steel surface is associated with temperature level. Oxide layer is made up of thick Fe2O3+ Fe3O4, which can effectively prevent oxygen diffusion below 570 ℃. When warmed more than 570 ℃, the oxide movie is composed of FeO+ Fe2O3+ Fe3O4 (from the inside out). FeO is loose and porous, which accounts for around 90% of the thickness of the whole oxide movie. Steel atoms and oxygen atoms are very easy to spread out through the FeO layer to speed up oxidation. Heat FeO greatly decreases the oxidation resistance of steel. The greater the temperature, the faster the atom diffusion and oxidation speed.
The primary method to boost the oxidation resistance of steel is the enhancement of alloy components, such as Cr, Si and Al, to ensure that when the steel is in contact with oxygen at heat, it creates dense high-melting oxidation movies Cr2O3, SiO2 as well as Al2O3 initially, which cover the surface of the steel very closely and also avoid its more oxidation.
The high temperature toughness of metal refers to the resistance of steel materials to mechanical loading at heat, that is the resistance of metal materials to plastic deformation and also damages at heat. The mechanical homes of metal at high temperature are substantially different from that at space temperature. When the functioning temperature is more than the recrystallization temperature, the metal produces plastic contortion and job hardening. Besides being influenced by external forces, produced recrystallization as well as softening.
The mechanical homes of metals at high temperature relate to temperature, time and also microstructure. Creep typically happens at high temperature, that is, when the functioning temperature level is higher than the recrystallization temperature level, the working stress and anxiety exceeds the elastic limitation at that temperature level, and also the steel slowly deforms together with time. The greater the resistance of steel to slip, the higher its heat stamina.
The heat stamina of metals is usually shared by creep limitation and endurance toughness. Creep restriction is the anxiety worth when the residual deformation of metal reaches a specific value after a period of time at a specific temperature. Sturdy toughness refers to the stress and anxiety value of a steel material at a continuous temperature for a specific period of time. At high temperature, the grain boundary stamina of metal materials is lower than that of the within grain, so including alloy elements to raise the recrystallization temperature level, developing stable unique carbide, and also using crude crystal products to reduce grain border can properly boost the high temperature toughness of steel.
Mo is a crucial alloy element in creep resistant ferrite steel with an operating temperature level of as much as 530 ° C.Molybdenum in solid option can minimize creep rate of steel extremely successfully. Molybdenum can slow down the pile and coarsening of carbide at high temperature. Vanadium, titanium and niobium are strong carbide developing elements, which can develop fine spread carbide and improve the high-temperature stamina of steel. Titanium, niobium as well as carbon substances can likewise prevent intercrystalline deterioration of austenitic steel at high temperature or after welding.