In this chapter, the hardfacing of gate valves, and measurement of bead geometry and residual stresses induced are detailed. I know that stellite can be a bit difficult to deposit and the method of deposition can have a significant influence on the overlay cracking. The cocrw system alloy retains its hardness at elevated temperatures and is especially effective for wear applications at high temperatures or in a corrosive environment, and are widely used as a wear, corrosion, and heatresistant material 43. 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. Also we can apply other materials such as stellite 6 or 12 or nickel ni 100%. Stellite 6 is a cobase wear resistant alloy containing 1% c, 27% cr, 4. Introduction 1 stellite 6 is a very versatile material that is used for. Came in next morning and as i continued to overlay next set of flats i heard some tings. Developing the ductility and thermal fatigue cracking property of.
It is a trademarked name of the deloro stellite company and was invented by elwood haynes 1 in the. Stellite was a major improvement in the production of poppet valves and valve seats for the valves, particularly exhaust valves, of internal combustion engines. It may also contain tungsten or molybdenum and a small but important amount ofcarbon. The laserclad layers, which consisted of refined solidification structures, were characterized by increased hardness and. For this purpose, stellite6 coating materials and two different types of cutting tool materials ceramics and tungsten carbide were used. Understanding some of the basics about hardfacing can go a long way toward instilling confidence in your hardfacing product selection. Developing the ductility and thermal fatigue cracking. How to control check cracking and use to your advantage. Author links open overlay panelyingwuyanliu huichen yongchenhongyuli xinyucao.
However, in larger and more complex parts, cracking can occur from the buildup. Can duplex stainless steels be hardfaced without adversely affecting the base material properties. We have been hardfacing on 1 thick carbon with 532 stellite 6 cobalt alloy. Impact wear resistance of stellite 6 hardfaced valve seats with laser cladding article in materials and manufacturing processes 237. Two materials were compared in terms of surface roughness in different cutting speeds and. Hpa cobalt 6b is a wear resistant alloy used for stems, balls, rails and bushings. Stellite 21 is much less prone to cracking in our experience when we. Stellite alloy is a range of cobaltchromium alloys designed for wear resistance. By reducing their erosion from hot gases, the interval between maintenance and regrinding of their seats was dramatically lengthened.
The different process steps are coupled in order to transfer the residual conditions from preceding processes to the ones following. Hardfacing a standard term for a wearresistant weld overlay is commonly. In single layer applications you probably will have small cracks. What is the best gas to use when doing a stellite overlay on 316ss. Your resource for protection, repair and joining solutions. In further studies, the mechanism of thermal cracking of stellite 6 coating was revealed. 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.
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. Usually, on a cracked or worn out valve disc with low alloy steel material grades, it is preferable to give a buttressing layer of inconel 625 or equivalent. These hardfacing layers are applied as an overlay onto a steel. The results showed less cracking and pore development for stellite 6 coatings applied to. 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. Implementation of stainless steel buffer layer for reducing crack. This article presents development of graded overlay of stellite 6 on aisi 304 stainless steel substrate using 2. Recharge by welding a carbon steel valve with inconel625 825overlay, cladding. Since the thickness is 5mm, we have to do 2 layers.
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. Author links open overlay panelyingwuyanliu huichen yongchenhongyulixinyucao. Materials are type 304l stainless steel and mediumcarbonsteel. Depending on how long the weld is and how its layed out, some cracking is usually inevitable with stellite 6 its normal. They are resistant to corrosion, erosion, abrasion and sliding wear. Hard facing hf and corrosionresistancealloy cra with hot wire, materials. Hi, we are doing stellite 6 hvof coating on valve plug for plug valves. Longwear certified air melt ingots alloy cross reference index cobalt based alloys. Then we have to get 5mm thickness of cocra alloy overlay.
However, when we finished the second layer and let it cool gradually wrapping the cone with. Laser assisted deposition of graded overlay of stellite 6. Impact wear resistance of stellite 6 hardfaced valve seats. I am not aware of another method to protect the bores of the balls. A comparative study for wear resistant of stellite 6. Case study of stellite 6 hardfacing through laser overlay laser cladding offers many advantages compared to traditional welded overlay, including less overall heat input, a smaller heataffected zone, reduced thermal distortion, better bonding, more uniform layers of overlay and a lower rate of iron from the substrate diluting the stellite. In addition to the above specifications we can offer manufacturing to customer individual requirements and specifications including toll melting and remelting. Cobalt alloy 6b stellite 6b ams 5894 aircraft materials. The netlike m23c6 eutectic carbides in the stellite 6 coating transformed to.
We took the method of smaw with the stick electrode of stellite 6. A cobaltbased alloy, stellite 6, was deposited on the seat face of control valves using a coaxial laser cladding process. Stellite definition of stellite by the free dictionary. Stellite 6 welds pretty clean unless it gets oxidized and then the puddle gets sluggish. Hightemperature hardness and wear resistance of stellite alloys by samit kapoor a thesis submitted to the faculty of graduate and postdoctoral affairs in partial fulfillment of the requirements for the degree of master of applied science in mechanical engineering carleton university ottawa, ontario 2012, samit kapoor.
Hardfacing a standard term for a wearresistant weld overlay is commonly used for seat and guide surfaces on valve trim of all styles. Pdf delamination failures of stellite hardfacing in power plants. Hightemperature hardness and wear resistance of stellite. For comparison with conventional hardfacing techniques, a plasma transferred arc pta method was chosen for parallel experiments in this study. 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. Microstructure evolution and failure behavior of stellite 6. Alternate stellite process material selection and properties. This is a better and more fool proof approach even for buttressed inconel 625 layer welding done before application of stellite 6. Fixturing which would chill the weld rapidly should not be. Pdf delamination failures of stellite hardfacing in. Ti addition made the m 23 c 6 eutectic carbide change to the tic carbide. Laser cladding, hvof, plasma spraying, stellite 6 coating, friction and wear, nickel alloy. 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. The term cladding includes not only weld overlays but also solidstate processes such as explosive cladding, mechanical cladding or rollbonding.
A strategy is given to improve the ductility and thermal fatigue cracking feature of stellite 6 coating by adding ti and ni. Once cooled back to room temperature, it recovers its full original hardness. Pdf microstructure evolution and failure behavior of stellite 6. It is easily deposited by a number of methods but you do have to be careful about contamination from sulphur or phosphorus.
Cobalt chrome also maintains tough erosion and impact resistance qualities. Bonding stellite 6 to alloy steel asme mechanical code. Users requiring more precise data for scientific or engineering calculations can click on the property value to see. This was overlayed with stellite 6 at a location that one would expect to be overlayed. I have to tell you, this is an awesome alloy i just sharpened it, about 5 light strokes on the white sharpmaker stones, and it was sharper than when i purchased it. The performance of the tool materials in the turning operation was analyzed. When we finished the first stellite 6 layer, there is no cracking found.
Most crackings are perpendicular to the welding seam. The alloy stellite 6 has less tendency to crack than for example stellite 12, but only when multilayer technique is used. In this study, the machinability of stellite6 coating material was examined. Stellite overlay on duplex stainless welding, bonding. Stellite 6 overlay on the disk contact surfaces of a dual plate check valve. How to avoid stellite 6 crackings american welding society. Stainless steel cladding and weld overlays 109 clapding metal. I received a contract job to help out a company hardface their ss316 parts with stellite 6 filler so they can be machined back down to a certain height. Stellite 6b is supplied in the solution treated condition to ams 5894 and its wear resistant. The following 19 answers to frequently asked questions may help you select hardfacing products that are most appropriate for your application.
Massive sections joining, tyres, gears, dissimilar metal. Cracking resistance of stellite 6 clad austenitic stainless steel components can be greatly enhanced by providing smooth composition gradient across substrateclad interface. Never attempt without pwht on a welded low alloy steel with stellite 6 application. The workhorse hardfacing alloy in the valve industry is generically known as alloy 6, although it is often called stellite 6. Welding and hard facing consumables electrodes wires rods. Stellite 6 is a well know overlay in the pump and valve industry.
Plasma transferred arc welding of stellite 6 alloy on stainless steel for wear resistance. Pwht is also required to reduce tensile stresses as much as possible for a hard facing stellite 6 application. Delamination failures of stellite hardfacing in power plants. I bought a george young stellite 6k kitchen knife about a year ago. These hardfacing layers are applied as an overlay onto a steel substrate, such as crmo steel i. Kennametal stellite, former deloro stellite inc category notes none some of the values displayed above may have been converted from their original units andor rounded in order to display the information in a consistent format. Cocrw meets or exceeds ams 5894, pwa 1196, mcs 1012 and uns r30016. Initial looks at the overlay suggests that the stellite hadnt bonded with parent at all. Welding and hard facing consumables electrodes wires. The issue of whether hardfacing adversely affects the properties of duplex stainlesssteel base materials depends on several factors.
Pdf in recent years, several incidents of cracking and failures have been observed in stellite. A buttressed layer to be on the safeside is given usual preheat to 250 deg cent and then also pwht for additional application of stellite 6 alloy by gtaw process. A comparative study for wear resistant of stellite 6 coatings on nickel alloy. Stellite 21 overlay we have issues with stellite 6 our parts were not very rigid and so we stayed with the. Grade 91 substrate, stellite 21 butter layer and stellite 6 hardfacing alloys. 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. I was wondering if any one could offer any tips on how i go about this. Overlay repair of dissimilar metal alloy 82182 welds with. Overview of deloro stellite group the company dates back to 1907 with the invention of a family. Cracking has been observed in valve components at the stellitesteel.
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