Most stainless steels are considered to be weldable and may be welded in a variety of processes including arc welding. resistance welding process electron beam and laser beam welding friction welding and synchronized sailing for all of these welding processes The joint surface and any fill metal must be clean. The coefficient of thermal expansion of austenitic stainless steels is 50% greater than that of carbon steels and this must be considered for minimal twisting. Low electrical and thermal conductivity Usually useful Welding requires low welding current. Because heat is not removed from the joint like carbon steel. In resistance welding, a lower current can be used because of its higher resistance characteristics. Stainless steels which require special welding processes will be discussed in the next section.
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- Ferritic stainless steel
Ferritic stainless steels with additions of 11.5 to 30% chromium and up to 0.20% carbon and a small amount of ferrite stabilizers, aluminum, columbian, titanium and molybdenum. They are all room temperature ferrites. So it doesn’t transform into Austenite. and cannot be hardened by means of knowledge. This group includes the more common types 405, 409, 430, 442 and 446. Welding of ferritic stainless steels requires the selection of a fill metal used that meets or exceeds the chromium level of the base metal. Type 409 is a flux cored wire. It can be used to weld types 402,410,414 and 420. Generally, when the carbon must match the carbon in 420 steel, type 420 fill metal is required, which can be found as solid core wire and flux cored wire. Alternatively, austenitic fillers types 308, 309 and 310 can be used to weld martensitic steels themselves. or to other steels that require toughness as added
- Austenitic stainless steel
Austenitic steels are alloyed with 16-26% chromium, manganese plus 10-24% nickel and carbon up to 0.40%, and a few other trace elements such as molybdenum, titanium, columbia and tantalum. The balance between chromium and nickel + manganese is achieved. Commonly tuned to provide 90-100% austenite microstructures. These alloys are characterized by good strength and high toughness. This group includes the types 302, 30+310, 316, 321 and 3+7.
Welding of austenitic stainless steels requires the selection of fill metal to match most alloys, aligning the microstructure with some ferrite. to avoid hot cracking As will be discussed below, to obtain this, type 308 filler is used for type 302, 304 and 321 stainless steels. The other stainless steel must be welded to match the fill metal that meets the properties. and able to weld type 347 stainless with type 308L filler
*Type 308L, these fillers can be supplied. It is a flux covered electrode. solid core wire and flux filament wire
*Type 321 can be supplied on a limited basis as solid core wire and flux cored wire.
- There are 3 types of stainless steel hardened by crystallization:
3.1 Martensitic crystallization hardened stainless steels – They can be hardened by quenching from an austenite heating temperature [approximately 19000F (10380C)] and aging between 900. to 11500F (482 to 6210C), as these steels contain less than 0.07% carbon, since martensite is not very hard and hardening after curing (precipitation) reactions. An example of this group is 17.4. PH, 15.5PH and PH 13 Mo
3.2 Stainless steels are hardened by semi-austenitic crystallization. It does not convert to martensite when cooled from austenite because the martensite transformation temperature is lower than room temperature. These steels must be treated as force conditions. This consists of heating in the range of 1350 to 17500F (732 to 9540C) to precipitate carbon and/or alloyed elements into carbide or intermetallic compounds. This eliminates the alloy from melting, thereby reducing the formation of austenite stabilization. which increases the martensite deformation temperature. Therefore, a martensite structure is obtained by cooling to room temperature. Curing steel between 850 and 11000F (454 to 5930C) reduces stress and martensite to increase toughness. Flexibility, hardness and corrosion resistance Examples of this group are 17.7 PH, PH 15.7 Mo, and AM 350.
3.3 Stainless steels are hardened by austenitic crystallization after annealing of austenitic annealing temperatures. Although after the actual number of evening jobs They are hardened by annealing reactions including melting operations between 1800 and 20500F (982 to 11210C), water or oil quenching and annealing at 1300 to 13500F (704 to 7320C) up to 24 hours. Examples of these steels include A286 and 17-10P
4.Duplex stainless steel
Duplex stainless steels are the group of stainless steels most developed today and have approximately the same microstructure of ferrite and austenite. Useful over steel Plain ferritic and austenitic stainless steel They provide higher yield strength and greater resistance to stress corrosion cracking. duplex microstructure It is obtained in steel with the addition of 21.25 % Chromium and 5.7% Nickel by heating to 1832 to 19220F (1000 to 10500C) followed by water quenching. The weld metal of this mixture tends to be mostly ferrite because the filler hardens to ferrite and partially deforms to austenite. No hot working or heat treatment Because hot work or annealing of most weld fillers is impractical. Generally, the fill metal mixture is modified by adding 8.10% nickel, so the microstructure as welded will contain more austenite.