Prevention of delayed cracking of iron based hardfacing. Stellite 3 is superior and this improved resistance increases as loads are increased or speeds are increased to 10 times to 25 times that of stellite alloy 6 or 12. Typical applications include saw teeth, hardfacing, and acidresistant machine parts. In certain condition eg amines in water etc which attacks the stellite these are not used. Stellite is usually better but not alll stellite is a family and not under all circumstances.
Not familiar with your rod so i dont know the hardness rating there are many factors involved when hard facing according to the nature of the part but as a general rule its not good practice in the type of things i do to use 600 or over hardness without buttering the base metal with say 400 first this is when cracking seems to be a problem if your stuck in the field with only. When the stellite 6 is coated over steels by hardfacing directly, there is admixture of stellite 6 alloy and base metal, resulting in a higher iron content in the overlay. Stellite definition of stellite by the free dictionary. Impact wear resistance of stellite 6 hardfaced valve seats. Because of the presence of the carbide network, the overlay is somewhat prone to cracking, although resistance to cracking is very good for an alloy of this hardness level. Pdf solidification structure of stellite overlayer. Most of the time, this material is stellite, a cobaltbase. Is it true that stellite 6 hf will leave hairline cracks on the surfece. Aug 15, 20 the carbides present in the cocrwbased stellite alloys are of chromiumrich m 7 c 3 type. We took the method of smaw with the stick electrode of stellite 6. Erosion test curves of stellite alloys 7 51 figure 215.
For small, simple parts, cracking is not a usually a problem. The prequlualified procedure has worked well in the past however, current production tests are showing intergranular cracking in the monel inconel haz, but only after application of the stellite. Influence of yttrium additive on wear behavior of stellite 6 at elevated temperatures 25 54. Grade 22, wc9 or creep strength enhanced ferritic steel i. Stellite 6 is a cobalt based alloy but is very tolerant of dilution from other materials and is often used on stainless to give a wear resistant area, e. This alloy is very popular since it can retain hardness even at elevated temperature.
If the service media calls for wear resistance they the technique to be adopted is hardfacing, if for corrosion resistance then weld overlay. Ultimet alloy is an ideal welding material with exceptional ductility and resistance to weld cracking. The laserclad layers, which consisted of refined solidification structures, were characterized by increased hardness and. The solidification structures of the overlayers of stellite 1, 6 and 21 cobalt base alloys after overlaid on spheroidal graphite cast iron by plasma transferred arc process were studied in this. Check availability with our sales department by submitting your inquiry below to see if a metal source, llc can provide your stellite alloy metal requir. Stellite alloys also tend to have extremely high melting points due to the cobalt and chromium content. The full stellite baffle stack contained in every surge 762 helps to extend the life of your suppressor by negating the effects of erosion wear when compared to inconel or stainless steel baffles. These coatings are applied to a thickness of about 0. Checkcracking, or checking as its sometimes called, occurs in the metal carbide families and can be seen as cracks that are perpendicular to the bead length see figure 2. A comparative study for wear resistant of stellite 6 coatings on nickel alloy. Stellite article about stellite by the free dictionary.
This alloy also has higher hot hardness and resists galling like all stellite alloys when mated with another stellite alloy. The issue of whether hardfacing adversely affects the properties of duplex stainlesssteel base materials depends on several factors. Massive sections joining, tyres, gears, dissimilar metal. Today, the hardening of sealing surfaces is performed by welding a material harder than the valve body material.
Stellite the general name for a group of cobaltbase hard facing alloys containing chromium, tungsten, silicon, and other. All the valves had cracks in the seat area hardface going back into the base material. This is not the same as your specification ss the applications will decide what is required. Stellite12 alloy due to its higher content of w which makes it the hardest one of them 2. Cracking has been observed in valve components at the stellite steel interface and in the weld dilution zone formed between the steel and clad. Stellite alloys chemical composition, mechanical properties. The distinctive difference between cobalt 6k proprietary name stellite 6k and cobalt 6b the alloy used in talonite is that 6k contains about 50% more carbon than 6b, making. The top diameter of the cone is mm,while the other is 300mm,and the thickness of the cone is 12mm duplex steel,that is sa516 gr. Pdf delamination failures of stellite hardfacing in.
For comparison with conventional hardfacing techniques, a plasma transferred arc pta method was chosen for parallel experiments in this study. All valves had cracks in the seatarea hardfacing going back into the base material. Oct 24, 2002 stellite 6 is a cobalt based alloy but is very tolerant of dilution from other materials and is often used on stainless to give a wear resistant area, e. Dry sliding wear map for stellite 6 against a wcco 9010 disc 12 49 figure 214. In some cases the stellite had become disbonded from the base material and had moved downstream. The chemical composition of stellite 6 is given in table 3. Can duplex stainless steels be hardfaced without adversely affecting the base material properties. Then we have to get 5mm thickness of cocra alloy overlay. Pdf solidification structure of stellite overlayer formed. This required removal of the remaining stellite and undercutting of the base material. Stellite alloy is a range of cobaltchromium alloys designed for wear resistance. Welding and hard facing consumables electrodes wires.
The trademark owners of stellite claim that stellite 6 is the most widely used of their range of stellite alloys, offering a proven industry standard for generalpurpose wear resistance, and high mechanical and chemical perfromance in hostile environments. A cobaltbased alloy, stellite 6, was deposited on the seat face of control valves using a coaxial laser cladding process. The stellite surface overlay becomes very hard, corrosive resistant, wear resistant and has high resistance to galling. The phase and carbide distribution, and misorientation has been studied by ebsd. It alters the microstructure of coated stellite 6 and base metal and affects its mechanical properties at high temperature. The wear resistance of alloy 6b is due to the chemical composition and is not a product of heat treatment or other hardening mechanisms. Without a heat treat oven, slow cool generally means completely burying the part in a big cat box filled with vermiculite and leaving it alone at least overnight. Stellite 6k is one of a series of cobaltchromium alloys, which are basically a combination of cobalt 50%plus, chromium between 2530%, and several other elements. The material itself has been around since the 1900s and was originally seen as a substitute for traditional metal cutlery which suffered from general wear and tear and was also prone to staining. Failure analysis of stellite overlay on the surface of wedge gate valve disc of. Users might consider investing time to learn about stellite and welding procedures for hardfacing. Mar 28, 2017 typically, a stellite part is precisely cast so that only minimal machining is necessary.
Probably after final machining the surface will show hair cracks which is normal in case of using stellite 6 and this do not affect the sealing functiont we. Norem, a cobaltfree alloy, is used as the hardfacing cladding on the valves for nuclear applications in place of stellite to lower the activation level. Cocrw meets or exceeds ams 5894, pwa 1196, mcs 1012 and uns r30016. Welding tips and tricks view topic kennametal stellite. Cracking has been observed in valve components at the stellitesteel.
A stellite baffle will be glowing red and taking abuse long after baffles constructed of other materials yield and collapse. Without a heat treat oven, slow cool generally means completely burying the part in a big cat box filled. It has good galling wear resistance, which is equivalent to that of stellite,, as a result of welding contraction, the ductility of hardfacing welds decreases and cracking occurs. Hpa cobalt 6b is a wear resistant alloy used for stems, balls, rails and bushings.
In line weld repairs of valve defects valve magazine. Pdf delamination failures of stellite hardfacing in power. Stellite alloy distributor in the usa a metal source, llc inventory consists of various stellite alloy grades in any size or form as indicated below. Anytime you have an adhesive, abrasive or erosive atmosphere, we recommend that you use stellite coatings on your machine parts to increase productivity. Tensile strength is 758 mpa, yield stress is 655 mpa, youngs. Stellite 6 and this do not affect the sealing functiont we normally do. Stellite overlay of carbon steel is often the standard material offered as an overlay of a cobalt based alloy over carbon steel gives you the best of both worlds. This required removal of the remaining stellite and undercutting of. Concerning stellites, all obtained coatings have a dendritic microstructure and no cracks or. In stellite alloys this generally has the following effects. These hardfacing layers are applied as an overlay onto a steel. Stellite 6 welds pretty clean unless it gets oxidized and then the puddle gets sluggish. Delamination failures of stellite hardfacing in power. The torch manipulation is generally automated and hence can achieve uniform overlays on complex parts.
Developing the ductility and thermal fatigue cracking property of. I have seen many valves refurbished in the field with stellite 21 being replaced with stellite 6. Delayed cracking of norem weld has been identified. Laser cladding, hvof, plasma spraying, stellite 6 coating, friction and wear, nickel alloy. Thermal fatigue cracking is one of the main lifelimiting factors for the brake discs of trains. Stellite was a major improvement in the production of poppet valves and valve seats for the valves, particularly exhaust valves, of internal combustion. The stellite will be typically overlaide over the base a105. Instead of using stellite 6 overlay on smaller sizes 22cr duplex components e. It is very easy to apply as an overlay, compared with the traditional. We clearly mention that it is not possible to perform a stellite 6 completely free of hair cracks. However, when we finished the second layer and let it cool gradually wrapping the cone with insulate material, we could see some crackings on the second. In metal on metal wear stellite 3 is superior and this improved resistance increases as loads are increased or speeds are increased to. Stellite failure on a p91 hp valve failure investigation. Stellite hardfacing test hey friends, i had a problem in my company, where i just joined for training, there are some components clad with pta process, but ndt showed that there are cracks and some defects in the components, please if anyone can suggest a solution or just guide me to a link whre i can get one.
Sprayfuse coatings, also referred to as selffluxing overlay coatings, are first applied to the component surface using a flame spraying process and then subsequently. Hightemperature hardness and wear resistance of stellite. Typical hardfacing materials deposited by thermal spraying include cermets such as wcco and aluminabased ceramics. Introduction 1 stellite 6 is a very versatile material that is used for. Defects were the same as those found on the section i valves. Stellite 6 is a well know overlay in the pump and valve industry. Seat overlay made of stellite 6 is possible but not recommended by us. When field welding, stellite 21 is preferred as only modest preheat is required and because stellite 21 is more ductile, as deposited, than stellite 6. Delamination failures of stellite hardfacing in power plants. Stellite alloy is designed for wear resistance, and thats why we use it. Since the thickness is 5mm, we have to do 2 layers. Recharge by welding a carbon steel valve with inconel625 825overlay, cladding.
Prevention of delayed cracking of iron based hardfacing welds. The pta process is typically used to apply relatively thick i. Seawater applications are not suitable for stellite 6, as it is at high risk of cracking in that environment. Fisrtly, we had a 3mm thickness of 309mol overlay with fcaw. The photograph showed both transverse and longitudinal cracks in the overlay. Failure analysis of surface stellite alloy overlayer on disc of wedge. Hardfacing a standard term for a wearresistant weld overlay is commonly used for seat and guide surfaces on valve trim of all styles. There are a large number of stellite alloys composed of various amounts of cobalt, nickel, iron, aluminium, boron, carbon, chromium, manganese, molybdenum, phosphorus, sulfur, silicon, and. Also we can apply other materials such as stellite 6 or 12 or nickel ni 100%. Comparative study of cobased alloys in repairing low cr. Essentially for hardfacing overlay versus corrosion resistant overlay the difference is the service and application media. Valve industry needs both type of alloys depending on the service. Welding and hard facing consumables electrodes wires rods. Stainless steel verlays ladding and weld a stainlesssteelcladmetal or alloy is a compositeproductconsistingof athin layer of stainless steel in the form of a veneer integrally bonded to one or both surfaces of the substrate.
A comparative study for wear resistant of stellite 6. Most crackings are perpendicular to the welding seam. Overlay repair of dissimilar metal alloy 82182 welds with. Alloy 6b uns r30016 ams 5894 description alloy 6b is a cobaltbased alloy with great wear, erosion and abrasion resistance. These hardfacing layers are applied as an overlay onto a steel substrate, such as crmo steel i. The sequence of the primary welding process and the following secondary processes of machining, and heat treatment has been modelled to predict the residual conditions in a stellite 6 overlay weld on a p91 steam turbine valve. Implementation of stainless steel buffer layer for reducing crack. Microstructure evolution and failure behavior of stellite 6. Aug 16, 2011 seat overlay made of stellite 6 is possible but not recommended by us.
Hard facing hf and corrosionresistancealloy cra with hot wire, materials. Cracking has been observed in valve components at the stellitesteel interface and in the weld dilution zone formed between the steel and clad. A metal source, llc stellite alloysstellite alloys. Hightemperature hardness and wear resistance of stellite alloys. Your resource for protection, repair and joining solutions welding electrodes continuation steel welding electrodes product applications features mechanical properties xhd 2222 principal applications. It may also contain tungsten or molybdenum and a small but important amount of carbon composition. Preliminary inspection showed that there were three cracks in the two. When they are applied to steels by hardfacing, there is intermixing of the stellite alloy and the steel, resulting in a higher iron content in the overlay, especially in the first layer.
Depending on how long the weld is and how its layed out, some cracking is usually inevitable with stellite 6 its normal. They generally occur from 38 to 2 inches apart and are the result of high stresses induced by the contraction of weld metal as it cools. Stellite alloy, commonly known as cobaltbased alloy, is a kind of cemented carbide. The netlike m23c6 eutectic carbides in the stellite 6 coating transformed to. In some cases, the stellite had become disbonded from the base material and had moved downstream.
Stellite 6b hpa cobalt 6b uns r30016 high performance. This requires removal of the stellite and undercutting the base material. It is easily deposited by a number of methods but you do have to be careful about contamination from sulphur or phosphorus. Also, ultimet alloy possesses high tensile strength comparable to many duplex stainless steels combined with excellent impact toughness and ductility. I am currently applying stellite 6 onto cast monel 400 astm a494m351 using pta and normally use an inconel 625 buttering layer. Mar 08, 2005 the brittle nature of the metal carbides leads to check cracking, and as multiple layers are applied, stress continues to build, concentrating at the root of the check cracks, until separation or spalling occurs between the parent metal or buffer and the hardfacing deposit. Recharge by welding a carbon steel valve with inconel625 825 overlay, cladding. Steam valves sidebar welcome to combined cycle journal. However, when we finished the second layer and let it cool gradually wrapping the cone with. Stellite 6 hard facing onto monel welding, bonding.
The efficacy of the peening process to prevent weld from cracking is demonstrated. A stellitelined barrel has a service life of 18,000 rounds whereas a chromedplated barrel has a. What is the best gas to use when doing a stellite overlay on 316ss. This is a lower hardness version of stellite 6 and is more forgiving. Stellite 21 will work harden to develop full hardness. When we finished the first stellite 6 layer, there is no cracking found.
Stellite is a nonmagnetic alloy which contains a variety of different metal components with the main elements being cobalt and chromium. Plasma transferred arc welding of stellite 6 alloy on. Alternate stellite process material selection and properties. The principal object of such a product is to com bine, at low cost, the desirable properties of the. The different process steps are coupled in order to transfer the residual conditions from preceding processes to the ones following.
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