1.Connector corrosion control and prevention measures
(l) Intergranular corrosion control
①Metallurgy measures.Weld components from the control of manpower, a Canadian selection of ultra-low carbon austenitic stainless steel welding material; add Nb, Ti and other stabilizing elements to form a stable carbide NbC, TiC; the formation of γ + δ-phase organization (3% to 5% δ ) and so on.
②Technological measures. Using a small amount of heat input, fast cooling and crafts. If necessary, heat treatment after welding can be used, such as solution-treated or stabilized.
(2) To prevent stress corrosion
①In structural design, corrosion resistant material to a reasonable choice, while minimizing stress concentration and reduce the high stress areas.
②In the construction manufacturing, a reasonable first choice of welding materials, such as the selection of a γ + δ-phase organization of welding consumables and so on.Second, we must develop a reasonable assembly and welding processes to avoid stress concentration or welding defects.Finally, to eliminate the stress treatment, you can use the residual deformation and residual stress relaxation hammer method, or by low temperature (less than 300 a 350 ℃) annealing can also be implemented more than 850 ℃ heat treatment to eliminate residual stress.Must pass the test to determine the optimum specification parameters.
③Production management, to implement the control of impurities in the media, to carry out treatment and corrosion monitoring and analysis and so on.
2.Joint measures to prevent hot cracking
(1) First, choose a metallurgical measures γ + δ-phase organization of welding materials, chrome-nickel when compared to control Creq / Nieq, in order to guarantee access to "first δ ferrite to" freeze mode. Second, we must limit the harmful impurities in the weld, such as S, P and other content
(2) Process measures
① limit overheating. You can use a small welding current and a small welding speed, reduce the amount of welding heat input.
② control form factor. Form factor of the control parameters associated with the welding, a reasonable form factor (without the premise of increased welding speed, welding current technology used reduces obtained) to have a role in controlling hot cracking..
③ reduce the fusion ratio. In reducing the base metal of the weld dilution rates, the same request to reduce the welding current.
④ reduce the degree of binding.
⑤ control assembly gap, improving the quality of assembly
3.Low temperature and high-temperature toughness of the joint control measures
(1) the adjustment to adjust the weld seam composition of γ phase and the formation of δ phase element contents and their ratio to obtain tissue weld single-phase γ (s phase does not appear as much as possible), add the appropriate amount of rare earth elements to improve the joint low-temperature toughness.For the dry heat of austenitic joints to prevent γ → δ transformation is a prerequisite,Adding inhibition of the transition elements (including REE) and control content, in order to suppress the high-temperature embrittlement of joints.：(2) measures the use of welding without preheating, limit the amount of heat input, as rapid cooling process, enabling control of joint embrittlement.
4.Measures to prevent weld porosity
(1) First, eliminate the source of gas before welding on the workpiece and the wire surface rust, oil and clean up the oxide film to prevent harmful gases into the arc zone.While welding material must be moisture-proof, according to specification requirements before use for drying and heat, used with the check;Secondly, the welding process but also to strengthen the protective measures, such as gas welding must be wind, shielding gas flow and purity also need control.
(2) The correct selection of welding material into the molten pool when welding focus to consider the amount of water vapor and gas pool in the ease of escape.
(3) Control of welding process conditions selected welding method and welding process parameters, the general principle is that the total amount of gas into the arc in less, and bath with better conditions in the gas escape; taking into account other properties of austenitic stainless steel fittings requirements, such as corrosion resistance, crack resistance and so on.
In general the following aspects can be improved from the quality of welding of austenitic stainless steel：
(1) improve the joint performance of corrosion resistance and thermal cracking of the main metallurgical measures: use the weld as low C, containing a small amount of δ phase (3% to 5%), containing stabilizing element Nb weld material.
(2) welding of austenitic stainless steel to ensure the quality of the main process measure is the use of focused energy welding welding method; process parameters should follow the principle of cooling as much as possible to speed up connection, process measures should be beneficial to reduce the welding residual tensile stress.Such as the use of small current, short-arc welding, without preheating, forced cooling, not yaw and small fusion ratio; Also note that the welding sequence, in contact with corrosive media must be the last seam welding; avoid duplication of heating should not be used more layer welding and so on.
(3)To improve the joint's resistance to intergranular corrosion, can be used when necessary, stabilization annealing or solution heat treatment.
(4)austenitic stainless steel weld in the holes to prevent a fundamental measure is to limit the source of gas and improve pool conditions in the gas escape.
Source:
Tags:
