The,role,alloying,elements,and business, insurance The role of alloying elements and rare earth elements in hea
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Niobiumis also a strong carbide forming elements, niobium carbide is very stable athigh temperature, and only slightly less than the titanium carbide. Due to theniobium with good heat-resistance, so it has a wide range of applications in low-alloyheat-resistant steel and high-alloy heat-resistant steel. Multicomponent alloysniobium pearlitic low-alloy heat-resistant steel use in the steam generator,the temperature can up to 550 ° C. Niobium applied to heat-resisting steel whichcontaining 12% chromium, improve the hot strength of steel. in high-alloyheat-resistant steel, niobium carbide precipitation occupies an importantposition in its thermal, therefore there is a certain ratio between the carboncontent and niobium content in the steel. Low carbon (0.04% to 0.07%) heat-resistantaustenitic steel, the niobium content should be 10x% C. Therefore, the niobiumcontent in the heat-resistant high-alloy steel is generally 1% to 2%.Tantalum and niobium in the periodic table isin the same family, the role of tantalum in heat-resistant steel is similarwith niobium. Tantalum is expensive, in the ordinary heat-resistant steel isnot add tantalum substantially, but usually brought into with the addition ofniobium in the steel. Usually add tantalum only in casting high temperaturealloys.Boron and nitrogen have a strong affinitywith oxygen. The trace boron powder (0.001%) in steelcan increase its hardenability member. Boron adsorption on the austenite grainboundaries, reducing the intergranular energy, impede the nuclei of ferriteformation, thus prolonging the incubation period of proeutectoid ferrite andbainite transformation, boron only in solid soluble form present in the steelin order to play an effective role. When boron react with residual nitrogen andoxygen in the steel and form a stable inclusions, will have an adverse effecton the performance of the steel. In pearlitic heat resistant steel, trace boroncan improve the high temperature strength of the steel; added 0.025% boron inthe austenitic heat resistant steel can be improved its creep resistance, butthe boron content is higher, contrary to its role. Add boron to strengthen grainboundary and endurance strength is very important for enhancing theheat-resistant steel. The boron atom is mainly distributed in the grainboundary, and therefore boron plays an important role on the grain boundarystrengthening.Rare earth elements to improve theoxidation resistance of the heat-resistant system have obvious role. An oxideof the rare earth elements can increase the adhesion between the matrix metaland the oxide film, because of rare earth oxides on the base metal have the"pinning" effect. According to metal powder supplier, rare earth metallanthanum and cerium can reduce the volatility of Cr 2 O 3 , improve the composition of the oxide,becomes more stable (Cr La), 2 O 3 oxide film, lanthanum within the range of 1100 ~ 1200 is easily to decompose NiO film. REE is also a gooddesulfurization degassing agent in steel, can clear the state of the shape anddistribution of the inclusions and other harmful impurities (such as arsenic,antimony, bismuth, etc.) can be improved, so as to improve and enhance thequality of steel and heat properties. Rare earth elements have a certain rolein refining the grain size of the steel. The rare-earth elements have verystrong affinity with oxygen, sulfur, phosphorus, nitrogen, hydrogen and thelike, with arsenic, antimony, lead, bismuth, tin and so on also can form a highmelting point compound. So it is a good deoxidation, get rid of sulfur andadditive to remove other unwanted impurities and gases. REE can improve thecreep resistance of the heat-resistant steel. Added mixed rare earth in Cr 25 Ni 20 heat-resistantsteel to can 25% improve its lasting strength at 650 ;in Cr 13 Ni 16 Nb and N,36CrTiAl steel added 0.01% Ce, for its creep strength have varying degreesimproving.Source:http://www.mhcmp.com
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