Another reflective cracking treatment strategy was to place a crack relief layer, usually an opengraded asphalt base, followed by an asphalt overlay. The alloys may also contain tungsten or molybdenum and a small but important amount of carbon. 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 operations. 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. Welding modifications, such as weld overlay wol and. 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. It has good galling wear resistance, which is equivalent to that of stellite.
Another approach is to apply a nickel based buffer layer as a first weld layer with little or no preheat and a very low interpass temperature. Still another option was sawing joints in the asphalt overlay to match the existing joints in the old pcc pavement and sealing with silicone or hotpoured rubber sealant also known as sawcut. Dont ignore cracks and joints underneath decorative overlays. Cra weld overlay dilution and corrosion resistance twi. Treatments for reduction of reflective cracking of asphalt overlays on jointedconcrete pavements in georgia wouter gulden and danny brown for the past 6 years, the georgia department of transportation has placed. Failure analysis of surface stellite alloy overlayer on disc of wedge.
Can duplex stainless steels be hardfaced without adversely affecting the base material properties. 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. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Reflection cracks can also occur over existing hma pavement cracks, cement or lime stabilized base, etc. 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.
Diffraction signal from the upper tip, and reflection signal from the corner trap of the crack. Instead of using stellite 6 overlay on smaller sizes 22cr duplex components e. We built several new housings from scratch and before the stellite went on wed clad with stainless. Ni alloy 625 weld overlays onto pump, valve or sealing surfaces exposed to brackish water, sea water or sour gas service. They occur directly over the underlying rigid pavement joints. Research engineer texas transportation institute report 045173 project 04517 project title. Crack sealfill the cracks to prevent further deterioration or remove and reconstruct to full depth fixing any support issues. 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. Mueller1, luis carney1, sun tai ngin1, john l yadon1 1navair, issc code 4341, building 793, nas jax, jacksonville, fl 322120016 keywords. 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. Tribological test was conducted to characterize the wear property. 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. Stellite 6 is a well know overlay in the pump and valve industry. Overlay repair of dissimilar metal alloy 82182 welds with. A pipe or pipe fitting for use in harsh environment such as in petroleum refinery processes for cracking petroleum feedstocks, the pipe or pipe fitting comprising a 0. Tribaloy t800 alloy is one of the highsilicon, intermetallic wear alloys. Seawater applications are not suitable for stellite 6, as it is at high risk of cracking in that environment. Cracking the case of cracks in overlays and toppings.
Cracking resistance of stellite 6 clad austenitic stainless steel components can be greatly enhanced by providing smooth composition gradient across substrateclad interface. Expansion joints in the underlying slab that are not honored will telegraph through an overlay. Failure analysis of weldrepaired b1900 turbine blade shrouds. Stellite alloy, commonly known as cobaltbased alloy, is a kind of. Weld cracking of re strained joints has been observed and other work has indicated that microfissures frequently form during. This is personal experience from the my time in the electric power industry stellite 6 typically is applied only in shop and not in the field. It was caused largely by brittle fracture that had propagated through the alloy 21 buffer layer. When we finished the first stellite 6 layer, there is no cracking found. The cracks occur directly over the underlying cracks or joints.
Solidification cracking of austenitic stainless steel overlays is a common problem in cladding ring grooves and other carbon steel features. This article looks at a special type of cladding, weld overlay cladding. Stellite alloys 1, 6, and 12 are the most popular materials within this group. Tig welding variant also could produce weld overlay with very low dilution overlay exhibited a marked drop in corrosion resistance at dilution levels 36%fe, in the selected test environment of 10wv% nacl at ph3. Stellite is a registered trade mark of deloro stellite. How to control check cracking and use to your advantage. In opposition to thermal spraying, which provides a mechanical bond with the substrate, the hardfaced weld overlay forms a metallurgical bond with the substrate. As a result of welding contraction, the ductility of hardfacing welds decreases and cracking occurs. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. They are destined for parts lap or overlay weld stelliting. Weld overlay coating, also known as hardfacing, is a method which involves application of hard. Overlays either structural or nonstructural make up a large portion of the roadway paving done today. Controlling reflection cracking in hma overlays of pcc.
Failure analysis of weldrepaired b1900 turbine blade shrouds erik m. Hightemperature hardness and wear resistance of stellite. Kentuckys experience with rehabilitating pcc pavements. Failure analysis, welding, hardface, turbine blade abstract. Generally, the existing pavement should be structurally sound, level, clean and capable of bonding to the overlay.
But, more often than not, its movement in the substrate that will produce cracks in the overlay. Develop statewide recommendations for application of pcc joint reflective. The highly versatile weld overlay process provides the practical combination of readily available base materials, coated with a. Stellite 6 welds pretty clean unless it gets oxidized and then the puddle gets sluggish. Prevention of delayed cracking of iron based hardfacing welds. Prior to that it was owned by union carbide, stellite division.
If thick deposits are needed, use the appropriate buildup materials before hardfacing. Stellite 6 is a cobase wear resistant alloy containing 1% c, 27% cr, 4. Time technique or pet peak echo technique and spot satellite pulse. In stellite alloys this generally has the following effects. Never attempt without pwht on a welded low alloy steel with stellite 6 application. We would like to show you a description here but the site wont allow us. Bonding stellite 6 to alloy steel asme mechanical code. Type of pavement cracks and how to repair engineering. In firearms history, stellite was first used starting around world war ii to line the first 12 inches of barrel in the m2hb in order to help mitigate barrel throat erosion. Harden stellite cutters slices along the inside edge of concrete and masonry expansion joints without having to go back with a wire brush to clean a straight edge. Because we face some problems during after overlaying stellite gr.
Stellites are very resistant to wear, corrosion in acidic environment and hot oxidation. Had to keep heat on it til it was completely welded. Co and cr, fe 7 c 3 stellite 21 were the elements mo and cr. Stellite exhibits unparalleled hardness and toughness as well as an extremely high melting point due to its cobalt and chromium content. Solidification cracks can appear in several locations, and orientations, but most commonly are.
Failure analysis of stellite overlay on the surface of wedge gate valve disc of a nuclear power plantj. 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. How to avoid stellite 6 crackings american welding society. Any of the following treatments may be employed in an effort to control reflection cracking in an hma overlay of jpcp. Kennametal, velan and carleton university formed a research team to evaluate new hardfacing alloys and application processes for advanced ultrasupercritical applications. Dissimilar metal weld joints and their performance in nuclear. Stainless steel cladding and weld overlays 109 clapding metal. 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. Stainless steel cladding and weld overlays asm international. Jointing and crack control in decorative concrete applications. Most of the time in our production job, we face crackslack of fusion while hardfacing stellite on inconel 825 monel. The appropriate uns number has been given wherever possible. Welding and hard facing consumables electrodes wires rods. 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.
Apr 24, 2009 dont ignore cracks and joints underneath decorative overlays fix these imperfections before applying a decorative concrete overlay to avoid future surface problems. 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. The susceptibility of this alloy to hot cracking during welding is not well documented. But these alloys are expensive, so the need for cladding as a means to reduce alloy use is bound to intensify. Grade 22, wc9 or creep strength enhanced ferritic steel i. Hardfacing hardfacing welding weld overlays hfw industries. 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.
A stellite alloy mixture hardfacing consisting of 70% stellite 3 and 30% stellite 21, is created via laser cladding for control valve seat sealing surfaces, aiming at enhancing hardness and wear. Pdf fracture behavior of laserclad joint of stellite 21 on aisi 316l. Fracture behavior of laserclad joint of stellite 21 on aisi 316l stainless steel author links open overlay panel p. Hardfacing a standard term for a wearresistant weld overlay is commonly used for seat and guide surfaces on valve trim of all styles. Weld overlay coating, also known as hardfacing, is a method which involves application of hard and wear resistant. This article presents development of graded overlay of stellite 6 on aisi 304 stainless steel substrate using 2. Issues such as cracking along the weld line, hydrogeninduced cracking, and porosity, among others, have been reported. In this application the stellite always had cracks in it but it didnt matter. Stellite alloys chemical composition, mechanical properties. The w containing stellite alloys have better corrosion resistance in oxidizing acid.
Aug 16, 2011 seat overlay made of stellite 6 is possible but not recommended by us. Clad interface in contrast to initiationcontrolled brittle crack propagation across the interface. Joint sealant removal blade slices through expansion. Hardfacing alloys and processes for advanced ultrasupercritical. Reflection cracking by far, the biggest problem in hma overlays of pcc pavement caused by movement at pcc joints and cracks pcc loadinduced movement joint closes hma slabs contract joint. Forged or cast base materials of group 1, carbon steels. Fracture behavior of laserclad joint of stellite 21 on. Implementation of stainless steel buffer layer for reducing crack. 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. Due to the high cost of stellite when i got to the end of a rod id let the rod stay in the puddle then fuse my next rod onto the last and keep on trucking. Laser assisted deposition of graded overlay of stellite 6. For small, simple parts, cracking is not a usually a problem.
This alloy also has higher hot hardness and resists galling like all stellite alloys when mated with another stellite alloy. It is possible to avoid these problems by selecting the right alloy process and parameters to minimize dilution and keep the resultant crni equivalency ratio above 1. Existing surface preparation for overlays pavement. Seat overlay made of stellite 6 is possible but not recommended by us. The degree of surface preparation for an overlay is dependent on the condition and type of the existing pavement. Weld cladding overlay the process and equipment needed. Metallurgical aspects of welding stellite 12 to type 316l. Astm a182 f310s slip on ring type joint flange 112 cl600. Hard facing hf and corrosionresistancealloy cra with hot wire, materials. Effect of welding variables on cracking in cobaltbased sma. Specialist, stronger joints need specialist fusion technology, and castolin eutectic uses specialized welding, brazing and coating processes to achieve this. Slightly increased preheat, and tight stringer beads to deposit stellite 6 directly on top of low alloy steel. C photographic stellite alloy mixture hardfacing showing no cracking.
Cracking has been observed in valve components at the stellite steel interface and in the weld dilution zone formed between the steel and clad. Fracture behavior of laserclad joint of stellite 21 on aisi 316l stainless steel. Hightemperature hardness and wear resistance of stellite alloys. C were investigated by plasma arc surfacing processes on q235 steel. 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. Pdf stellite alloy mixture hardfacing via laser cladding for control. Alternate stellite process material selection and properties. Pdf delamination failures of stellite hardfacing in. Aug 16, 2011 stellite is a registered trade mark of deloro stellite. Cracking has been observed in valve components at the. Hardfacing materials generally consist of carbide, nickel, cobalt or ironbased alloys supplied in a rod, wire or powder form to suit the process being used.
Preheating of substrate could reduce thistendency of cracking. Our systems and products are designed both for oems and end users, and they range from simple userfriendly manual applications to major automated high volume systems. In this chapter, the hardfacing of gate valves, and measurement of bead geometry and residual stresses induced are detailed. Cracking that contributed to the disbonding of the hardfacing from the base metal developed near the interface between the valve seat and the stellite. 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. Treatments for reduction of reflective cracking of asphalt. The stellite trademark, which was applied to the first cobalt wear alloys, is still in use. Since the thickness is 5mm, we have to do 2 layers. It is easily deposited by a number of methods but you do have to be careful about contamination from sulphur or phosphorus. The methodology, which is used to inspect the weld overlay clad joint, is illustrated in figure 2. Aug 15, 20 the carbides present in the cocrwbased stellite alloys are of chromiumrich m 7 c 3 type.
Despite all efforts to prevent random cracking in decorative concrete slabs or overlays, some such cracking may still occur. Joint reflection cracking specifically refers to reflection cracks arising from underlying pcc pavement joint movement. Appropriate preheat treatments or buttering layers are the mitigation measures often applied to prevent the cracking occurrence of hardfacing. Graded overlay of three layers was formed by cladding with sile test. We clearly mention that it is not possible to perform a stellite 6 completely free of hair cracks. The wrought co35ni20cr10mo alloy is used for making permanent fixation devices and joint replacement components e. What is the best gas to use when doing a stellite overlay on 316ss. Preheating of substrate could reduce thistendency of cracking but did not completely remove its formation. Delamination failures of stellite hardfacing in power. 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. Other difficulties are en countered in the welding of 718. Microstructure evolution and failure behavior of stellite 6.
Local cracking occurred mainly in surfacing layer, and shedding. This article is based on what that research team has discovered. I always preheated a minimum of 300 degrees f up to 600 degrees f and wrap the piece in cerwool so it would cool slowly. 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. As the blade slices along the joint s inside edge, the sealant is completely scraped clean with one pass of the blade. Most overlay experts agree that the most common crack inducing culprit is the substrate, and there can be multiple factors involved. Weld overlay provides the assurance of a heavyduty metallurgicallybonded protective layer that will not be undermined or dislodged in service. Materials are type 304l stainless steel and mediumcarbonsteel. Wear characteristic of stellite 6 alloy hardfacing layer by. Stellite delamination in hp, hrh steam valves posted on may 22, 20 by team ccj stellite liberated from a large block valve was. Stellite is a very versatile material for hardfacing of various component parts for applications requiring.