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 â„ƒ 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 â„ƒ. 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 â„ƒ, 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.
China is the largest country in the world steel consumption and the consumption of Welding Materials . According to 2006 statistics, China's steel output of 420 million tons, accounting for 34% of the world's steel production, welding material production 3.2 million tons, about 50 percent of the world's welding consumables production. This article describes China's future demand trends of welding consumables, analysis by region and by industry demand conditions outlined welding materials in the future development trend. First, the welding consumables market demand trends and the current demand conditions by region and by industry
1, the market demand will continue to rise in the 16th CPC National Congress report makes clear, China in the 21st century the first two decades one of the main task of economic construction, basically accomplish industrialization. Now China is in the medium-term development stage of industrialization. The course of the world show that when a country is in the industrialization period, the consumption of steel and welding consumables will continue to grow. For example, the United States and Japan are basically completed the industrialization in the 1970s, the consumption of steel and welding consumables peak, and then to decline steadily. Next 10 years, China's steel and welding consumables consumption will continue to continued growth, but growth rate will moderate slowdown, and focus on attention to the adjustment of product variety and quality improvement. Measured according to the experts, 10 years after China's steel consumption may reach 6 to 700 million tons. Therefore a corresponding demand for welding materials may reach 400 to 4.5 million tons. 2, according to the geographical distribution of demand conditions in China's economic development, regional differences. 3, the demands of the industry by industry demand, the biggest difference between China's steel and welding consumables and developed countries: in recent years, China's construction steel accounts for about 55%, less than 45% of the industrial manufacturing of steel, while the United States, the construction of steel in Europe and Japan accounted for only 22% to 30%, the industrial manufacturing of steel accounted for 60% to 66%. This difference reflects the characteristics of the current stage of development in China, a large number of infrastructure and urbanization.
Two, the main development trend of the welding material
A welding automation progress to promote the adjustment of the welding consumables structure of varieties the mid-1980s, the proportion of developed countries electrode accounted for welding consumables is about 50%. 2004 in Europe, North America (U.S. and Canada), in the consumption of welding consumables, welding rod ratio have been less than 20%, that is, the developed countries of the automation and semi-self of welding, accounted for the entire welding above 80%.
2, iron and steel scientific and technological progress to promote the upgrading and quality of welding consumables varieties to enhance the country is striving from the direction of the steel power to a steel power has been launched in recent years a large number of upgrading and high-performance high-quality steel, especially the production of iron and steel industry level of equipment and technology has made significant progress, for example, will be put into operation more than 10 sets of plate rolling mill, its performance will exceed the existing mill in Japan and the United States to become the world's new generation of modern plate rolling mill for the realization of controlled rolling and cooling ( TMCP) technology, the production of high-volume, high-performance plate, laid the basic equipment.
Wide range of large ordinary welding consumables should be promoted to higher prices for better quality, market-oriented China's current production and consumption of the most common welding materials, including carbon steel electrode junction 422, HJ431 welding flux, ER50-6 copper wire, etc. products, production capacity expansion, oversupply, and the domestic and export prices of our ordinary welding materials, only the equivalent of 50-60% of the similar high-quality welding consumables prices in international market, some of the welding consumables enterprises adopted a "low-cost, low the vicious competition of quality, low price "means, so quite a few users in recent years reflect the quality of some node 422 welding rod and other common welding consumables, not only no progress, but moving backwards. Foreign markets to reflect some of China's export enterprises ordinary welding consumables is low quality parallel imports ", although the price is cheap but the quality is not good, only minor works to the China Welding Consumables image caused by a bad influence.
4, and promote cooperation with the steel mills, to solve the problem of shortage of wire variety of welding consumables development of the major bottlenecks is the variety and quality of gas shielded solid wires and submerged arc welding solid wires can not meet market demand. Including a variety of different intensity levels of high-strength steel wire, heat-resistant steel wire, low temperature steel welding wire, resistant to atmospheric corrosion of steel wire, Stainless Steel Welding Wires.
As for the domestic and foreign manufacturers have introduced the so-called copper wire, it should be known as special coated wire, the coating composition of the manufacturers and surface treatment differences in the performance of wire there are also different. The excellent performance of the coating and surface treatment process, not only from the rust and the role of lubrication, copper welding does not produce soot, but also to enhance the wire arc stability and reduce spatter.
Domestic and foreign manufacturers in the wire coating and surface treatment technology continues to improve. Expect this wire and precise control of the arc-transition digital inverter welding machine compatible, you can achieve high efficiency, high-current low spatter CO2 welding, reaching the equivalent of the flux cored wire welding process, is the future direction of development.