Stainless steel is the main element of Cr is higher than 12% increase, to make steel in the passive state, but also has characteristics of stainless steel. According to the microstructure of stainless steel into ferritic, martensitic, austenitic, austenitic + ferritic and precipitation hardening stainless steel. Austenitic stainless steel at room temperature, the organization is usually pure austenite, there are also some small amount of austenite + ferrite, this small amount of ferrite helps to prevent hot cracking.
First, the characteristics of austenitic stainless steels:
1, prone to hot cracking.
    Preventive measures: (1) as the weld metal showed a biphasic organization controlled ferrite content of 3-5% or less. Because a large number of ferrite dissolved harmful physical S, P impurities. (2) try to use high quality alkaline drug skin electrodes to limit the weld metal in the S, P, C and other content.
2, intergranular corrosion: According to the chromium depletion theory, weld and heat affected zone heated to 450-850 ℃ in the temperature-sensitive zone in the grain boundary precipitation of chromium carbide, chromium depleted grain boundary cause, not the degree of corrosion resistance .
   Preventive measures: (1) the use of low-carbon or low carbon Welding Wire China consumables, such as the A002, etc.; using titanium, niobium and other elements of the electrode stabilization, such as the A137, A132 and so on. (2) by wire or rod to weld into a certain amount of ferrite forming elements, the weld metal into austenite + ferrite phase organization, (general control of ferritic 4-12%) . (3) reduce the weld pool heat, use a smaller welding current and welding speed faster, speed up the cooling rate. (4) of the resistance to intergranular corrosion demanding welding conditions for stabilizing annealing after welding
3, stress corrosion cracking: stress corrosion cracking of welded joints in a particular corrosive environment by the tensile stress arising from the delayed cracking phenomenon. Welded joints of austenitic stainless steel to stress corrosion cracking of welded joints is more serious failure mode, showed no plastic deformation of brittle failure.
Measures to prevent stress corrosion cracking: (1) to develop a reasonable forming and assembly processes to minimize the degree of cold deformation, avoid forcing the assembly to prevent all injuries caused during assembly (the assembly of various wounds and burn marks arc will become SCC the crack source, could easily lead to corrosion pits). (2) a reasonable choice of welding consumables: weld and base metal should be a good match, does not produce any adverse tissue, such as grain coarsening and brittle martensite, etc.; (3) take appropriate welding process: to ensure that the weld forming well, does not produce any stress concentration or pitting defects, such as undercut, etc.; take reasonable welding sequence, reducing the welding residual stress level; (4) eliminate the stress treatment: post-weld heat treatment, such as fully annealed or annealed after welding; used in difficult to implement post-weld heat treatment or shot peening hammer, etc. (5) Production management: media control of impurities, such as liquid ammonia medium O2, N2, H2O, etc.; liquefied petroleum gas in H2S; chloride solution O2, Fe3 +, Cr6 +, etc.; corrosion treatment: such as coating, lining or cathodic protection; added inhibitor.
4, low-temperature embrittlement of weld metal: for austenitic stainless steel welded joints at low temperature use, the plastic weld metal toughness is the key issue. At this point, weld metal ferrite in the presence of low-temperature toughness is always worse.
Preventive measures: The use of pure austenitic welding consumables and adjust the welding process to obtain a single austenitic weld.
5, the welded joints of σ phase embrittlement: weldment to withstand a certain time in the heated to high temperatures in a brittle weld precipitation of σ phase, the entire joint embrittlement, ductility and toughness decreased significantly. σ phase precipitation temperature range of 650-850 ℃. In the high temperature heating process, σ phase mainly formed by the ferrite transformation. The longer the heating time, σ phase precipitation more.
Preventive measures: (1) limit in the weld metal ferrite content (less than 15%); ultra alloy welding materials, namely high nickel welding consumables. (2) the use of small practices to reduce the weld metal at high temperatures the residence time; (3) precipitation of σ phase have been when conditions allow for solution processing, the σ phase dissolved in austenite.
Second, the austenitic stainless steel electrode selection points:
Stainless steel is mainly used for corrosion-resistant, but also as a heat-resistant steels and low-temperature steel. Therefore, the welding of stainless steel, the electrode performance must be consistent with the use of stainless steel. Stainless steel electrode and the base material must be based on working conditions (including temperature and exposure to media, etc.) to use.
1, in general, the choice of electrode material can refer to the base metal, base metal component selection and the same or similar electrode. Such as: A102 corresponding 0Cr19Ni9; A137 corresponding 1Cr18Ni9Ti.
2, the carbon content on corrosion resistance of stainless steel have a great impact, therefore, generally used in the carbon content of deposited metal is not higher than the base material of stainless steel electrode. If you must use A022 316L electrodes.
3, austenitic stainless steel weld metal mechanical properties should be guaranteed. Can be verified by the welding procedure qualification.
4, for work in high-temperature heat-resistant stainless steel (austenitic heat-resistant steel), the choice of electrode should be able to meet the main thermal crack resistance of weld metal and welded joints of high-temperature performance.
(1) of the Cr / Ni ≥ 1 of the austenitic heat-resistant steel, such as 1Cr18Ni9Ti, etc., generally are used austenitic - ferritic stainless steel welding rod to weld metal ferrite containing 2-5% is appropriate. Ferrite content is too low, the weld metal cracking and poor; if too high, or long-term use in high temperature heat treatment is easy to form σ-phase embrittlement, resulting in cracks. Such as A002, A102, A137.
In some special applications, may require the use of fully austenitic weld metal, can be used such as the A402, A407 electrodes and so on.
(2) of the Cr / Ni <1 the stability of the austenitic heat-resistant steel, such as Cr16Ni25Mo6, etc., generally should be to ensure the weld metal and base metal with similar chemical composition roughly the same time, increase the weld metal Mo, W, Mn and other elements of content, making the heat to ensure a strong weld metal at the same time, improve weld crack resistance. Such as the use of A502, A507.
5, for work in a variety of corrosive media in the corrosion resistance of stainless steel, the temperature should be medium to select the electrode and work, and to ensure its resistance to corrosion (corrosion of welded joints to do test).
(1) For operating temperature over 300 ℃, there is a strong corrosive media, shall be stabilized with Ti or Nb elements or ultra-low carbon stainless steel electrode. Such as A137 or A002.
(2) media containing sulfuric acid or hydrochloric acid, often used with Mo and Cu or Mo-containing stainless steel electrode, such as: A032, A052 and so on.
(3) work, corrosive pollution weak or just to avoid corrosion of equipment, may use Stainless Steel Welding Electrodes Ti or Nb.
To ensure the weld metal resistance to stress corrosion, the use of ultra-alloyed welding consumables, that the corrosion resistance of weld metal alloying elements (Cr, Mo, Ni, etc.) were higher than the base metal. Such as the use 00Cr18Ni12Mo2 types of welding material (such as A022) welding 00Cr19Ni10 weldment.
6, for work in low temperature conditions, austenitic stainless steel, welded joints should be used to ensure that the temperature of the low-temperature impact toughness, so pure austenitic electrodes. Such as A402, A407.
7, can also be used nickel-based alloys electrodes. Such as the use of 9% Mo welding consumables welding of nickel-based super austenitic stainless steel Mo6.
8, electrode selection of drug skin type:
(1) The two-phase austenitic steel weld metal itself contains a certain amount of ferrite, with good ductility and toughness, crack resistance of weld metal from the point of comparison, alkaline drug skin leather with titanium calcium type Unlike carbon steel electrode welding difference as significant. Therefore, in practical applications, from welding performance, focus more, mostly by drug skin type code 17 or 16 of the electrode (eg, A102A, A102, A132, etc.).
(2) only in the rigid structure of a large crack or poor weld metal (such as certain martensitic chromium stainless steel, pure austenitic chromium-nickel stainless steel, etc.) only when considering the selection of drug, code-named 15 of the skin alkaline drug skin stainless steel electrode (eg, A107, A407, etc.).
In summary, the austenitic stainless steels have their own unique characteristics, austenitic stainless steel welding electrode selection of particular note, the only way to achieve the implementation of different materials for different welding methods and different electrode materials, stainless steel electrode must be based on the base metal and working conditions (including temperature and contact media, etc.) to use. It was possible to achieve the desired weld quality.