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Duplex stainless steel - Part 2VIDEO ON THE TOPIC: Stick Welding Stainless Steel with 308L-16 Electrodes
The previous Job Knowledge article, No. Austenitic stainless steels can be welded with all the commercially available welding processes. There are matching filler metals available for most of the austenitic range of alloys, the exceptions being that there is no type filler metal available this alloy is generally welded with type filler metal and no type filler due to the problems of transferring titanium across the arc.
Type steels are usually welded with a type filler. Also mentioned In Job Knowledge was that the austenitic stainless steels are metallurgically simple alloys and room temperature mechanical properties are not significantly affected by variations in the welding procedure.
Basic coated manual metal arc electrodes with a controlled short arc length and basic agglomerated submerged arc fluxes are required for best toughness if arc welding processes are used.
These improve the creep strength by increasing the titanium and niobium content of the weld metal, forming a greater concentration of grain strengthening carbides. TIG GTAW welding of the root pass must always be carried out with an inert gas back purge to prevent loss of chromium and hence of corrosion resistance , argon being the gas generally used for this purpose. Nitrogen may be used but there is a risk of the weld deposit absorbing nitrogen, thereby becoming fully austenitic and hot crack sensitive.
Two characteristics of austenitic stainless steels that differentiate them from ferritic steels are the coefficients of thermal conductivity and expansion.
Higher expansions in a narrower HAZ result in higher residual stresses and more distortion. This is a particular problem with thin sheet fabrications where the achievement of the desired dimensional tolerances can be extremely difficult and costly to achieve. The use of accelerated cooling techniques such as copper chills or a freezing gas the liquid CO 2 low stress-no distortion technique typifies this approach have been used to reduce distortion to acceptable levels.
One of the main reasons for using an austenitic stainless steel is its corrosion resistance. Whilst this is primarily a function of the chromium content of the steel, carbon also has a major but adverse effect resulting in a form of corrosion known as intergranular or intercrystalline corrosion ICC or weld decay, a localised effect confined to the HAZ. Carbides present in the HAZ of an austenitic stainless steel dissolve on heating and reform on cooling during the welding heat cycle.
Unfortunately, these new precipitates form preferentially as chromium carbides on the grain boundaries, depleting chromium from the region immediately adjacent to the boundary, resulting in a local loss of chromium and a reduction in corrosion resistance. If sufficient chromium carbides are formed this results in a network of steel along the grain boundaries sensitive to corrosion; the steel has been sensitised.
There are several methods that may be used to overcome this difficulty. Whilst this will eliminate the chromium depleted regions it is rarely practical to solution-treat complex welded structures. The most obvious alternative technique is to reduce the carbon content.
This has two beneficial effects:. One other method is the addition of alloying elements that will form carbides in preference to chromium; thus the stabilised type and grades containing titanium and niobium respectively were developed. Titanium and niobium are very strong carbide formers that precipitate carbides at higher temperatures than those at which chromium carbides will form so there is no carbon available to react with the chromium.
However, even these stabilised grades may corrode in a very narrow band close to the fusion line the so-called knife-line attack in the presence of hot acids. This is due to the higher and more restricted temperature range at which the niobium or titanium carbides dissolve. The solution, as above, is to limit the carbon to 0. Welding consumables must also be selected with low carbon content if best corrosion resistance is required.
Most arc welding consumables contain less than 0. The other major service problem encountered with the austenitic stainless steels is that of stress corrosion cracking. This may be caused by strong alkali solutions but it is the halides chlorides, fluorides and bromides that are primarily responsible. Cracking takes place in areas of high stress, as the name suggests, and is not therefore confined solely to welds, but it is at and adjacent to welds that stresses approaching the yield point of the metal are found and these present a particular problem.
The cracking is transgranular and propagation rates can be extremely rapid given the ideal conditions. In hot concentrated chloride solutions, for example, penetration can occur in thin, sheet components within a few minutes. Austenitic stainless steels are therefore not generally used where halides are present. Even here, stress corrosion cracking SCC may occur due to contamination, either of the product in the pipe or vessel or externally from sea water, particularly where the liquid is able to concentrate in crevices.
It should be remembered that:. Local stress relief should be approached with caution as the temperature gradients may result in stresses developing outside the heated band; wider heated bands and more stringent control of temperature gradients than required by specifications or codes may therefore be necessary.
The alternative is to select a steel that is more resistant; the molybdenum bearing grade type is better than or Support for SMEs. Software Products.
Go to Technical knowledge Search. Login Login. Members' Portal. Welding of austenitic stainless steel. Part 2. Job Knowledge This has two beneficial effects: The lower the carbon content, the longer the time required to form the carbides. The lower the carbon content then the fewer carbides there are to form a continuous chromium depleted network.
Hence the 'L' grades, type L, or L, are preferred where best corrosion resistance is required. It should be remembered that: this may sensitise the steel so only low carbon grades should be used and the steel may embrittle due to sigma phase formation see Job Knowledge at the lower heat treatment temperatures. This article was written by Gene Mathers. For more information please email: contactus twi.
Published on December 17, December 1, SMAW or stick electrodes are consumable, meaning they become part of the weld, while TIG electrodes are non-consumable as they do not melt and become part of the weld, requiring the use of a welding rod. Electrode selection is critical to ease of cleanup, weld strength, bead quality and for minimizing any spatter. Electrodes need to be stored in a moisture-free environment and carefully removed from any package follow the directions to avoid damage. When molten metal is exposed to air, it absorbs oxygen and nitrogen, and becomes brittle or is otherwise adversely affected.
Stainless Steel Electrodes: “H” Versus “L” and Coating Types
This page is all about stick welding and it is broken down into three sections:. The simplest explanation of how stick welding works. Stick welding equipment is the simplest of all the electrical arc welding processes. A Stick Welder has four parts:. Stick welders can be both AC and DC power depending on the electrode type used. For most heavy industrial jobs or hobbyists a DC power supply can do just about anything.
Account Options Sign in. Selected pages Page 7. Page 8. Title Page. Table of Contents. Common terms and phrases AC-DC acid addition alloy annealed applications austenitic stainless steel base metal beam brazing carbon steel castings cause chromium cladding completely composition condition cooling corrosion covered cracking cutting defects deposited determine developer diameter effect electrode employed equipment fabrication ferritic Figure filler metal finished gives grades hardening heat heat treatment inch incl indications inspection joint layer length less Lime liquid listed low alloy steel machine magnetic manufacturers material maximum method mill nickel obtained operation pass penetrant performed pipe plate practice pressure procedure produce Radiographic range recommended removed resistance result rolling sensitivity shown shows solution specification specimens speed stainless steel stainless steel weld standard Step strength stress suitable surface Table technique temperature thickness tube tube sheet Type ultrasonic unit usually vessels weld metal x-ray. Bibliographic information.
No eBook available CengageBrain. Account Options Sign in. My library Help Advanced Book Search. Get print book. Shop for Books on Google Play Browse the world's largest eBookstore and start reading today on the web, tablet, phone, or ereader. Metal Fabrication Technology for Agriculture. Larry Jeffus.
Shielded metal arc welding
Shielded metal arc welding SMAW , also known as manual metal arc welding MMA or MMAW , flux shielded arc welding  or informally as stick welding , is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld. An electric current , in the form of either alternating current or direct current from a welding power supply , is used to form an electric arc between the electrode and the metals to be joined. The workpiece and the electrode melts forming a pool of molten metal weld pool that cools to form a joint. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag , both of which protect the weld area from atmospheric contamination.
Q: I have a new fabrication project for furnace racks made with H stainless steel and the specifications say to weld it with an EH electrode. What is the difference between , L and H? What do those mean? Therefore, this article will only address this type. While Austenitic stainless steels are very common, there are also Ferritic, Martensitic, Duplex and Precipitation Hardening types of stainless steels. You do need to use an EH electrode. The reason why will be explained shortly. It is typically used to make welding electrodes and used to join common types of austenitic stainless steels, such as , , and
Welding of austenitic stainless steel. Part 2
No eBook available CengageBrain. Great welding book for student motivation, because almost every thing they are practicing to weld on becomes a take home project, such as a birdhouse, candlestick, coin belt buckle, bookend, C-clamp and lots more. Even the first welding activity of striking an arc and running a short bead becomes a useful project Larry Jeffus is a welder with over 55 years of experience, and he maintains his own well-equipped welding shop. In his career he has passed many welding certification tests in a wide variety of processes, positions, and material types and thicknesses. Jeffus has provided welding and professional consulting services locally, nationally, and internationally to major corporations, small businesses, government agencies, schools, colleges, and individuals.
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