FeCrAl resistance heating element- Scaling resistance

FeCrAl heating element is used as catalytic substrate that is a metallic substrate providing different advantages as compare to ceramic substrates. A metallic substrate provides higher resistance to shock and vibration, it provides greater conductance to heat instead ceramic. Additionally, it can be fabricated easily in thin foil and provides honeycomb structure to deliver wide surface area and is lightweight.

Different FeCrAl resistance heating elements consists of Yttrium that offers considerable oxidation resistance characteristics and conserve oxide layer, however Yttrium has some drawbacks. It is expensive and reduces weight while melting and pouring of iron alloys. Because of high reactivity of yttrium, it reacts with various elements such as oxygen and loses to slag and furnace refractory materials. Because of high reactivity of Yttrium, a costly vacuum induction melting is used for development of FeCrAl Cr25Al5 that have Yttrium as a compositional element. Additionally, while vacuum melting and casting, receiving Yttrium in alloy is below 49.9% of that was added in the molten metal. Unfortunate delays, or problems that prevent the quick pouring of melt, efficiency % decreases significantly.

Additionally, vacuum induction heating method is not adequate to attain considerable magnitude of Yttrium by remelting the scrap of FeCrAl alloys.

The catalytic system that comprises of aluminum bearing ferrite steel that treats as substrate, particularly a FeCrAl alloy has Yttrium. FeCrAl heating element is subjected to keep the characteristic of development of stable alumina layer while the substrate surface heating that the alumina film secures the material from oxidation to make it corrosion resistant.

To adjust the drawbacks of Yttrium, various cheap elements are excluded. FeCrAl alloy is a heating element that consists of silicon, titanium and various rare earth metals. FeCrAl alloys consist of 10-15% chromium, 1-3.5% aluminum, 0.8-3% silicon, 0.01-0.5% calcium, cerium and other rare earth metals have scale adherence. The patent also requires aluminum and silicon concentration from 2-5%, titanium reduction about 0.2% and combination of oxygen and nitrogen concentration below 0.05%.

The high temperature oxidation resistance alloys have nominal concentration of cerium states that a FeCrAl alloy with significant magnitude of cerium provide prolong oxide coating. These alloys comprise cerium magnitudes from 0.01- 0.37%. FeCrAl alloy nominal content of cerium of 0.01% receives spaling whereas FeCrAl alloy with cerium by .04% - 0.37% describe no signs of spalling. Cerium is available in the latter alloys in the development of cerium-iron intermetallic compounds that is precipitated at the grain levels.

FeCrAl heating element has cerium about 5% cerium and also has 0.5% carbon and 0.5% nitrogen.

The key reason of developing FeCrAl alloys is to improve the oxidation resistance, scaling resistance and hardness at the elevated temperatures above 2102oF – 1150oC.

FeCrAl heating element

FeCrAl has good heat absorption and radiation characteristics for combustion units. It is also featured for use in combustion units and is also used in glass sealing by an inclusion of 2% rare earth metals in its main chemistry.

Although, industry still needs an alloy that is cheap to fabricate by small cost alloying composition that can be made by cheap melting methods and that provides resistance to heat cyclic oxidation from very low to high temperature of 1600oF, in the internal combustion exhaust conditions and offers good hot workability. Additionally, the heating element should be fit to provide an improved aluminum oxide surface that lasts on the metallic surface in the heat cyclic conditions. It then needs heating element that is fit for additional processing to provide an improved aluminum oxide layer to offer wide surface area and strengthen more catalytic materials to be used on the alloy by aluminum oxide layer.

The FeCrAl alloy must be fit to get stabilized in the high temperatures with wide creeping strength characteristics. A hot processing iron stainless steel alloy is offered to provide outstanding resistance to heat cyclic oxidation and scaling at the high temperatures. It is then fit for fabrication on the retainable aluminum oxide layer. The alloy consisting of up to 25% chromium, 8% aluminum and various 0.002- 0.05% rare earth elements like cerium, lanthanum, neodymium and praseodymium with the whole content of rare earth metals about 0.06% silicon, 1% manganese and general steel contaminants.

The FeCrAl heating element is also stabilized by inclusion zirconium or niobium that stabilizes and offers high temperature creeping resistance. An oxidation resistance catalytic substrate that offers consistent aluminum oxide layer also offers catalytic system with substrate. The production of hot working ferrite steel is also delivered that comprises of steps of development of alloy melt and hence producing an aluminum bearing ferrite steel. It is also then processed to develop a reliable aluminum oxide layer.

Normally, a FeCrAl alloy is developed with an addition of rare earth metals particularly cerium or lanthanum that provides hot processing alloy and prevents heat cyclic oxidation and has scaling resistance at the high temperatures. It is then fit for the development reliable aluminum oxide.

Chromium content offers needed characteristics such as oxidation and corrosion resistance. The chromium concentration is limited to avoid unnecessary hardness and strength that prevent formability of FeCrAl heating element. The concentration of chromium below 8% offers inadequate resistance to heat cyclic oxidation. The key role of chromium is to provide outstanding corrosion resistance, oxidation resistance and there is a link between number of heat cycles to fail and enhanced content of chromium.

Concentration of chromium above 25% enhances the service of FeCrAl heating element and also creates problem in the development of alloy.