How to avoid stellite 6 crackings american welding society. Failure investigations of failed valve plug of ss 410 steels due to cracking, failure investigations of elbow applied at bhel power plant. Today, the hardening of sealing surfaces is performed by welding a material harder than the valve body material. Preheat and interpass temperature the combination of alloy content, carbon content, massive size and part rigidity creates a necessity to preheat in many buildup and hardfacing. Fisrtly, we had a 3mm thickness of 309mol overlay with fcaw. Metallurgical and wear behaviour of stellite 6 reinforced. 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.
Cobalt alloy 6b stellite 6b ams 5894 aircraft materials. 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. It may also contain tungsten or molybdenum and a small but important amount ofcarbon. Solidification cracks can appear in several locations, and orientations, but most commonly are. Joints must be carefully designed and properly constructed if uncontrolled cracking of concrete flatwork is to be avoided. 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. Influence of yttrium additive on wear behavior of stellite 6 at elevated temperatures 25 54. Apart from economics, other factors that determine the weld process include access, weld position and the alloy applied. Nace formerly the national association of corrosion engineers has published two specifications that provide guidance on reducing the risk of inservice cracking, these also being iso standards. 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. Due to the high cost of stellite when i got to the end of a. Aug 04, 2017 laser welding stellite blade support by amada miyachi america duration. Stellite is a range of cobaltchromium alloys designed for wear resistance. Kennametal, velan and carleton university formed a research team to evaluate new hardfacing alloys and application processes for advanced ultrasupercritical applications.
The chemical composition of stellite 6 is given in table 3. A comparative study for wear resistant of stellite 6 coatings. 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. This paper deals with the investigation of the microstructure and wear behavior of the stellite 6 cladding on precipitation hardening martensitic stainless steel 174ph using gas tungsten arc welding. It looks like most of the sections can be remade for the same or less money as itd cost to attempt the stellite overlay and attendant machining. Stellite 6 welds pretty clean unless it gets oxidized and then the puddle gets sluggish. In practice, however, an automated process is a much more efficient way to weldoverlay a complex. Concrete expands and shrinks with changes in moisture and temperature. Also we can apply other materials such as stellite 6 or 12 or nickel ni 100%. 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. 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.
The cocrw system alloy retains its hardness at elevated temperatures and is especially effective for wear. Hard facing hf and corrosionresistancealloy cra with hot wire, materials. Aug 15, 20 the carbides present in the cocrwbased stellite alloys are of chromiumrich m 7 c 3 type. Microstructure and wear behavior of stellite 6 cladding on. Stellite is a family of completely nonmagnetic and corrosionresistant cobalt alloys of various compositions that have been optimised for different uses. Stellite alloys chemical composition, mechanical properties. Can duplex stainless steels be hardfaced without adversely affecting the base material properties. We clearly mention that it is not possible to perform a stellite 6 completely free of hair cracks. Dilution, laser cladding, inconel 718, stellite 6 coating. Both solidification cracking and hot cracking refer to the formation of shrinkage cracks during the solidification of weld metal, although hot cracking can also refer to liquation cracking.
Both solidification cracking and hot cracking refer to the formation of shrinkage cracks during the solidification of weld metal, although hot cracking can also refer to liquation cracking solidification. Recharge by welding a carbon steel valve with inconel625 825 overlay, cladding. This article provides an overview of work done to evaluate suitable alternatives to stellite 6. 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. Hightemperature hardness and wear resistance of stellite. 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. 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. I have seen many valves refurbished in the field with stellite 21 being replaced with stellite 6. 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. The torch manipulation is generally automated and hence can achieve uniform overlays on complex parts. Carbon steels in service in the offshore and oil refinery industries are susceptible to a cracking mechanism known as sulfide stress cracking ssc or hydrogen stress cracking hsc when.
Stellite alloy is a range of cobaltchromium alloys designed for wear resistance. Stellite 6 steel chemical composition, metal properties. The issue of whether hardfacing adversely affects the properties of duplex stainlesssteel base. The different process steps are coupled in order to transfer the residual conditions from preceding processes to the ones following. Co and cr, fe 7 c 3 stellite overlay on monel castingm35 a we are trying to make overlay of stellite on monel castings. However, when parts become larger or more complex, alloy 6 will crack unless the preheat temperature is increased. Weld overlay coating, also known as hardfacing, is a method which involves application of hard and wear resistant. Seat overlay made of stellite 6 is possible but not recommended by us. This article is based on what that research team has discovered. C were investigated by plasma arc surfacing processes on q235 steel. Alternate stellite process material selection and properties.
Then we have to get 5mm thickness of cocra alloy overlay. Dry sliding wear map for stellite 6 against a wcco 9010 disc 12 49 figure 214. Tensile strength is 758 mpa, yield stress is 655 mpa, youngs. Aug 16, 2011 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. Introduction 1stellite 6 is a very versatile material that is used for hardfacing various component parts for applications requiring wear. 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. The maximum joint spacing should be 24 to 36 times the thickness of the slab. Recently i have been working with a gate made out of 316 ss, and i need to build up over 18. 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. Stellite is a trademarked name of deloro stellite company supplying stellite alloys like stellite3, stellite 6, stellite 12 and stellite 21. Plasma transferred arc welding of stellite 6 alloy on. I work with valves gates, stems etc and i do a lot of overlay including 316,410 and stellite 6.
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. Components are often hardfaced with stellite through a welding process. 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. Metallurgical aspects of welding stellite 12 to type 316l. Wear characteristic of stellite 6 alloy hardfacing layer by. Stellite 6 on super duplex welding processes in theory, the welding processes used can be manual.
Although the cracking is described as stress cracking, the main problem is the hardness of the parent metal, weld metal and heataffected zone haz. Hardfacing alloys and processes for advanced ultrasupercritical. If thick deposits are needed, use the appropriate buildup materials before hardfacing. Never attempt without pwht on a welded low alloy steel with stellite 6 application. Cip 6 joints in concrete slabs on grade what are joints. We took the method of smaw with the stick electrode of stellite 6. Aug 16, 2011 seat overlay made of stellite 6 is possible but not recommended by us.
Introduction 1 stellite 6 is a very versatile material that is used for hardfacing of various component parts for applications requiring wear resistance cobaltbase rods 1982. What is the best gas to use when doing a stellite overlay on 316ss. Try using inconel as a butter layer and deposited stellite 6 on top of this butter layer to reduce susceptibility to cracking, during and after hardfacing. For small, simple parts, cracking is not a usually a problem. 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. Stellite definition of stellite by the free dictionary.
Trying to find stellite 6 sleeves home practical machinist. It is easily deposited by a number of methods but you do have to be careful about contamination from sulphur or phosphorus. It is very easy to apply as an overlay, compared with the traditional cobaltbase wear alloys. This alloy also has higher hot hardness and resists galling like all stellite alloys when mated with another stellite alloy. Stellite failure on a p91 hp valve failure investigation. 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.
Since the thickness is 5mm, we have to do 2 layers. Deloro stellite company also supplies other products like casting, machinery, welding, coating, knives and many others. The alloys may also contain tungsten or molybdenum and a small but important amount of carbon. 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. The pta process is typically used to apply relatively thick i. Hightemperature hardness and wear resistance of stellite alloys. Tribological test was conducted to characterize the wear property. 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. Argon gas was used as the shielding gas as well as the medium for generation of plasma in pta process. The microstructure of stellite 6 contains hard m 7 c. Recharge by welding a carbon steel valve with inconel625 825overlay, cladding.
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. Metallurgical and wear behaviour of stellite 6 reinforced stainless steel 316 joints by ndyag laser welding process 2019280147 laser welding process is a most effective and predominant. Pdf stellite alloy mixture hardfacing via laser cladding. Stellite is a nonmagnetic alloy which contains a variety of different metal components with the main elements being cobalt and chromium. Bonding stellite 6 to alloy steel asme mechanical code. The stainless steel exterior surface provides corrosionresistance, high luster, and abrasionand dent resistance, and the aluminum on the inside providessacrificialprotectionfor the paintedauto body steeland for the stainless steel. Laser cladding, hvof, plasma spraying, stellite 6 coating, friction and wear, nickel alloy. Product forms ultimet alloy is available in most common wrought product forms. Slightly increased preheat, and tight stringer beads to deposit stellite 6 directly on top of low alloy steel. For example, in a 4inch 100 mm thick slab the joint spacing should be about saw. Stellite 21 will work harden to develop full hardness. Introduction 1 stellite 6 is a very versatile material that is used for hardfacing of various component. Stellite 6 can be supplied as steel plate sheet, round steel bar, steel tubepipe, steel stripe, steel billet, steel ingot, steel wire rods. Most of the time, this material is stellite, a cobaltbase.
Pwht is also required to reduce tensile stresses as much as possible for a hard facing stellite 6 application. Erosion test curves of stellite alloys 7 51 figure 215. If that temperature is increased to the point that cracking is alleviated, the interpass temperature required to avoid adverse effects in the duplex stainlesssteel base metal will be exceeded. With ultimet alloy, cracking of the overlay is not a consideration, and multiple layers may be applied, with little or no preheat. In practice, however, an automated process is a much more efficient way to weld overlay a complex surface. Bonding stellite 6 to alloy steel metengr materials 21 aug 08 17.
Dilution and wear properties of laser cladding stellite 6. A comparative study for wear resistant of stellite 6. 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. Stellite 6 is a cobase wear resistant alloy containing 1% c, 27% cr, 4. The following recommended practices should be observed. Two layers of stellite 6 were coated for a maximum thickness of 6 mm or higher. Stellite 6 will also have a good resistance to impact and cavitation erosion. Depending on how long the weld is and how its layed out, some cracking is usually inevitable with stellite 6 its normal.
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