The alloy stellite 6 has less tendency to crack than for example stellite 12, but only when multilayer technique is used. Since the thickness is 5mm, we have to do 2 layers. Stellite 6 hard facing onto monel welding, bonding. How to control check cracking and use to your advantage. Hardfacing is a metalworking process where harder material is applied to. Aug 15, 20 the carbides present in the cocrwbased stellite alloys are of chromiumrich m 7 c 3 type.
Hpa cobalt 6b is a wear resistant alloy used for stems, balls, rails and bushings. Stellite alloy is a range of cobaltchromium alloys designed for wear resistance. Stellite 21 is much less prone to cracking in our experience when we can talk the customer into it over 6 we do it every time. Number of bids and bid amounts may be slightly out of date. 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. If your valve orifice is narrow and the valve is throttled in service quite often, then stellite 6 would give a better long. Cobalt alloy 6b stellite 6b is a cobaltbased, chromiumtungsten alloy used extensively in wear environments where its low friction coefficient minimises the risk of seizing and galling, even in applications where lubrication is not practical.
For small, simple parts, cracking is not a usually a problem. These hardfacing layers are applied as an overlay onto a steel substrate. The material is also resistant to erosion and most. This alloy also has higher hot hardness and resists galling like all stellite alloys when mated with another stellite alloy. Most of the time, this material is stellite, a cobaltbase. There are a large number of stellite alloys composed of various amounts of cobalt, nickel, iron, aluminium, boron, carbon, chromium, manganese, molybdenum. It is easily deposited by a number of methods but you do have to be careful about contamination from sulphur or phosphorus. Hardfacing a standard term for a wearresistant weld overlay is. This type of polishing was used only for sem observation of stellite6 deposit before wear corrosion experiments. The chemical composition of stellite 6 is given in table 3. The hot hardness of stellite 6 weld overlays drops off sharply as iron content increases up to 10%fe, but at higher fe contents the drop is insignificant up to 20%fe. Implementation of stainless steel buffer layer for reducing crack.
The laserclad layers, which consisted of refined solidification structures, were characterized by. I have never heard of using stellite 21 as an interlayer before welding stellite 6. This article presents development of graded overlay of stellite 6 on aisi 304 stainless steel substrate using 2. It is a trademarked name of the deloro stellite company and was invented by elwood haynes 1 in the early 1900s as a substitute for cutlery that stained or that had to be constantly cleaned. 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. Product forms ultimet alloy is available in most common wrought product forms. A comparative study for wear resistant of stellite 6 coatings. The brittle nature of the metal carbides leads to checkcracking, 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. Hard facing hf and corrosionresistancealloy cra with hot wire, materials. Some of the main advantages that stellite 6b cobalt chromium alloy provides includes. Pdf delamination failures of stellite hardfacing in power. Delamination failures of stellite hardfacing in power plants.
With ultimet alloy, cracking of the overlay is not a consideration, and multiple layers may be applied, with little or no preheat. Table 1 gives the chemical composition and some physical properties of stellite 6 alloy. However, when we finished the second layer and let it cool gradually wrapping the cone with. Stellite definition of stellite by the free dictionary. The microstructure evolution, elements diffusion and fracture behavior of the stellite 6 weld overlay, deposited on 10cr9mo1vnbn f91 steel by the tungsten inert gas tig cladding process, were. Cracking has been observed in valve components at the stellitesteel interface and in the weld.
Fisrtly, we had a 3mm thickness of 309mol overlay with fcaw. Two layers of stellite 6 were coated for a maximum thickness of 6 mm or higher. Stellite is a family of completely nonmagnetic and corrosionresistant cobalt alloys of various compositions that have been optimised for different uses. Laser assisted deposition of graded overlay of stellite 6.
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. Erosion test curves of stellite alloys 7 51 figure 215. Developing the ductility and thermal fatigue cracking. Overlay repair of dissimilar metal alloy 82182 welds with. I am currently applying stellite 6 onto cast monel 400 astm a494m351 using pta and normally use an inconel 625 buttering layer. Argon gas was used as the shielding gas as well as the medium for generation of plasma in pta process. Stellite 6b cobalt alloy steel cobaltchromium alloy. Ti addition made the m 23 c 6 eutectic carbide change to the tic carbide. Dry sliding wear map for stellite 6 against a wcco 9010 disc 12 49 figure 214.
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. I have seen many valves refurbished in the field with stellite 21 being replaced with stellite 6. The modified stellite 6 coating with improved performance may play an important role in prolonging the service life of brake discs. Sprayfuse coatings, also referred to as selffluxing overlay coatings, are first applied to the component surface using a flame spraying process and then subsequently. Recharge by welding a carbon steel valve with inconel625 825 overlay, cladding. It may also contain tungsten or molybdenum and a small but important amount ofcarbon. These hardfacing layers are applied as an overlay onto a steel substrate, such as crmo steel i. Alloy of cobalt from 50 to 65 %, chromium from 25 to 35 %, tungsten from 4 to %, carbon from 1 to 2,5 % and other elements molybdenum, nickel, iron, titanium. Guidelines for stellite hardfacing onto steels page 2 of 7 march 22, 2007 carbon equivalent vs preheat temperature 0 50 100 150 200 250 300 350 0. Influence of yttrium additive on wear behavior of stellite 6 at elevated temperatures 25 54. Typical hardfacing materials deposited by thermal spraying include cermets such as wcco and aluminabased ceramics. Hightemperature hardness and wear resistance of stellite alloys. It is also possible to apply tungsten carbide containing nickel based overlay, although the high meltpool temperature places limitations on carbide size, volume fraction and binder alloy composition.
Stellite 6 welding rods hai stellite 6 rod is cobalt base rod. We took the method of smaw with the stick electrode of stellite 6. These coatings are applied to a thickness of about 0. A metal source, llc stellite alloysstellite alloys.
Laser assisted deposition of graded overlay of stellite 6 on. 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 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. Cracking resistance of stellite 6 clad austenitic stainless steel components can be greatly enhanced by providing smooth composition gradient across substrateclad interface. 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. Then we have to get 5mm thickness of cocra alloy overlay. Pta hardfacing of stellite 6 on stainless steel has been carried out in plasma transferred arc pta welding machine since it is a semiautomated process. If this is not a critical factor and you are using a rigid setup, i see no problems in using the 60 grit with a higher infeed. 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. 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. A comparative study for wear resistant of stellite 6. 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. Microstructure evolution and failure behavior of stellite 6. Aug 12, 2011 the alloy stellite 6 has less tendency to crack than for example stellite 12, but only when multilayer technique is used.
Alternate stellite process material selection and properties. Today, the hardening of sealing surfaces is performed by welding a material harder than the valve body material. 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. Tensile strength is 758 mpa, yield stress is 655 mpa, youngs. Can duplex stainless steels be hardfaced without adversely affecting the base material properties. Stellite 21 will work harden to develop full hardness. Plasma transferred arc welding of stellite 6 alloy on. Also we can apply other materials such as stellite 6 or 12 or nickel ni 100%. Stellite 6 is a well know overlay in the pump and valve industry. 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. So it is possible to apply the material without cracks but in cases where the hard facing also is used for corrosion resistance or for a perfect. It may also contain tungsten or molybdenum and a small but important amount of carbon composition. Co base stellite 6 hardfacing was deposited onto the stellite 21. Stellite 6b is supplied in the solution treated condition to ams 5894 and its wear resistant.
The netlike m23c6 eutectic carbides in the stellite 6 coating transformed to. For comparison with conventional hardfacing techniques, a plasma transferred arc pta method was chosen for parallel experiments in this study. 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. See each listing for international shipping options and costs. Pdf delamination failures of stellite hardfacing in. Hardfacing a standard term for a wearresistant weld overlay is commonly used for seat and guide surfaces on valve trim of all. 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. Find great deals on ebay for stellite and stellite tool bit. 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. Recharge by welding a carbon steel valve with inconel625 825overlay, cladding. 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.
The initial state of stellite6 surface before experiments was. The microstructure of stellite 6 contains hard m 7 c. Stellite 6b hpa cobalt 6b uns r30016 high performance. Depending on how long the weld is and how its layed out, some cracking is usually inevitable with stellite 6 its normal. Stellite failure on a p91 hp valve failure investigation. The alloy currently most suited for cutting tools, for example, is stellite 100, because this alloy is quite hard, maintains a good cutting edge at high temperature, and resists hardening and annealing.
Stellite 21 is a little softer hard facing alloy compared to stellite 6 and may stand the same duties same steam service without erosion corrosion of disc or failure of stems and comparatively easier than stellite 6. Stellite 6 welds pretty clean unless it gets oxidized and then the puddle gets sluggish. 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. Stellite alloys chemical composition, mechanical properties. Hightemperature hardness and wear resistance of stellite.
A hard carbide phase in the cocr alloy matrix makes this material highly resistant to corrosion and galling. Stellite 6b is a cobaltbased steel alloy that maintains a wide range of material benefits for industrial applications throughout the world. The issue of whether hardfacing adversely affects the properties of duplex stainlesssteel base materials depends on several factors. A cobaltbased alloy, stellite 6, was deposited on the seat face of control valves using a coaxial laser cladding process. Pdf delamination failures of stellite hardfacing in power plants. Stellite 6 overlay on the disk contact surfaces of a dual plate check valve photo courtesy of crane stockham valve table 1. Stellite 6 overlay on the disk contact surfaces of a dual plate check valve. The micrographs of the stellite6 on surface and cross section have been obtained after polishing till diamond grade 1 m. Plasma transferred arc welding of stellite 6 alloy on stainless steel for wear resistance. 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.
Stellite is a nonmagnetic alloy which contains a variety of different metal components with the main elements being cobalt and chromium. Cocrw meets or exceeds ams 5894, pwa 1196, mcs 1012 and uns r30016. The different process steps are coupled in order to transfer the residual conditions from preceding processes to the ones following. A strategy is given to improve the ductility and thermal fatigue cracking feature of stellite 6 coating by adding ti and ni. Cobalt alloy 6b stellite 6b ams 5894 aircraft materials. 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. However, limited reports can be found to study the thermal fatigue cracking property of a stellite 6 coating modified with both titanium and nickel. Most crackings are perpendicular to the welding seam. Cracking has been observed in valve components at the stellitesteel. In single layer applications you probably will have small cracks. Microstructure evolution and failure behavior of stellite.
Developing the ductility and thermal fatigue cracking property of. Author links open overlay panelyingwuyanliu huichen yongchenhongyuli xinyucao. It is very easy to apply as an overlay, compared with the traditional cobaltbase wear alloys. Thermal fatigue cracking is one of the main lifelimiting factors for the brake discs of trains. Because of the presence of the carbide network, the overlay is somewhat prone to cracking. Stellites are very resistant to wear, corrosion in acidic environment and hot oxidation.
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