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In the building materials, the stainless steel round steel and the screw steel are the common forms of address for different kinds of steel bars. The difference between them is quite obvious, mainly five points. The first is the difference in shape. The outer surface of the stainless steel round steel is very smooth, while the outer surface of the screw steel has a spiral rib. Secondly, the production standards of both are different. In the modern standard, stainless steel refers to HPB235 steel, the production standard is based on the “hot-rolled smooth steel reinforced concrete and steel”, usually refers to the HRB335 and HRB400 grade steel, the production standard is based on “the reinforcement of concrete hot rolled ribbed bar”. The third point is that they are different in their strength. The design strength of stainless steel round steel is 210MPa, while the strength of rebar is higher than that of stainless steel round bar. The design strength of HRB335 is 300MPa, and the design strength of HRB400 is as high as 360MPa. The fourth point is that the steel is different, that is to say, the chemical composition in the steel body is different. The stainless steel round carbon is carbon steel, the steel is Q235, the rebar is low alloy steel, the HRB335 grade reinforcement is 20MnSi (20 MN SI), and the HRB400 grade reinforcement is 20MnSiV or 20MnSiNb or 20MnTi. It is because the chemical composition is different, so the physical and mechanical properties of the two are different. The better performance of cold-formed stainless steel, can hook 180, screw steel can be just 90 degrees straight hook, stainless steel weldability is good, as long as the use of ordinary carbon welding line, screw steel must use low alloy steel electrode; the toughness and anti fatigue properties etc. than the excellent stainless steel round bar. Steel reinforced concrete is often used to build facilities, material is generally low alloy steel grades is generally 16Mn (16 Mn low-alloy steel), or 45 carbon just, yield strength are higher than 350Mpa, the tensile strength was less than 500Mpa, compared with the ordinary low carbon steel stainless steel round up very much, one thread the strength of the steel after heat treatment of the low carbon stainless steel round steel is nearly twice as high or even more. Because the surface has a thread shape, it can increase the bond with the concrete. The concrete member should choose the thread steel first with the longitudinal reinforcement and the stirrup. So in general, because steel is a kind of low alloy steel, the price than the low carbon stainless steel round steel is high, the construction units from the ordinary civil construction of affordable angle positioning for reducing the quality of the project, will instead use low carbon stainless steel instead of steel. While some large key projects, usually in bribe related personnel, with stainless steel instead of steel rebar to “substitution”, so as to reduce the construction cost. From the design perspective, because members without stirrups give principal stress support, the main role is to keep in shape and position, and because the stainless steel round bar surface is relatively smooth, the strapping easy positioning accuracy, so in addition to longitudinal reinforcement, can be used as a steel reinforced stainless steel round bar. But the longitudinal bar must be completely threaded steel. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

As a special kind of special steel with excellent performance, stainless steel is widely used in the production and life of people. Usually the stainless steel material in molding process, most of them are subject to various heat treatment processing, this time such as annealing, quenching, welding and forging process, it will form a layer of black oxide on the surface of stainless steel, the oxide skin will not only affect the appearance quality of stainless steel, will have a negative impact the stainless steel machining process, so in the following processing prior to this layer of oxide skin removing. The oxide scale of stainless steel is mainly composed of NIO2, Cr2O3, FeOOCr2O3, FeOOCr2OO3Fe2O3 and other dense spinel oxides. It is very firmly combined with the matrix of stainless steel and is hard to remove by ordinary acid washing. In addition, the difficulty of removal also varies with the steel and the manufacturing conditions. Therefore, it is of great practical significance to grasp the methods of various stainless steel oxide pickling and to choose the production process reasonably. Below is a simple way to remove the acid washing of the oxide skin. The first is the three acid washing method, the acid is sulfuric acid, nitric acid and hydrochloric acid. It is a more effective acid cleaning method for removing the stainless steel oxide skin. The proportion of the three acids is probably 15%-20%H2SO4, 5% ~ 7%HCl, 5% ~ 7%HNO3, and the pickling temperature of three acids should be kept at about 70-800 degrees. The specific pickling time should be decided by the composition and condition of stainless steel oxide scale, usually 20 to 50min. The three method can successfully remove acid stainless steel oxide, but because the pickling process will precipitate a lot of nitrogen dioxide, which will worsen labor conditions, environmental pollution. In addition, the acid washing process is easy to form the phenomenon of acid washing. The second method is nitric acid and hydrofluoric acid pickling, this kind of acid washing is a better way of stainless steel pickling. The commonly used proportioning method is 4%-6% hydrofluoric acid and 8%-12% nitric acid. The temperature of the acid is 50 to 600 degrees. The pickling time depends on the oxide scale of the stainless steel surface, usually 20 to 40min. The operation process must be looked over diligently to avoid pickling. In fact, the acid pickling speed is faster, the operation is easy and the quality is good. However, hydrofluoric acid is highly toxic, and requires better ventilation and wastewater treatment. The third is alkali cooking, also called the acid washing compound method. In order to solve the weakness of tricarboxylic acid method, the compound method of alkali boiling and pickling can not only optimize the quality of pickling, but also reduce the consumption of metals. Alkali cooking can loose oxide, then remove the oxide using acid washing. Most of the ingredients in the alkali boiled liquid are the mixture of sodium hydroxide and sodium nitrate, with a ratio of 8:2. The temperature of alkali boiling is controlled at 500 to 550 degrees C. The time of alkali cooking is related to the steel, specification, quantity and oxidation skin state of stainless steel, usually from 30min to 1.5h. Stainless steel material after alkali boiling to immediately immersed tank burst to the scale, then the use of three acid washing to remove oxide. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The surface quality of 304 stainless steel plate, usually the main heat treatment after pickling process, if the heat treatment before a surface oxidation process to generate thick skin, or uneven microstructure, surface roughness and uniformity that cannot improve the use of pickling stainless steel plate. Therefore, attention should be paid to heat treatment and prior surface cleaning. If uneven surface oxide thickness of stainless steel plate, metal surface finish thick and thin places of the following is not the same degree, dissolution and oxidation skin and pickling board surface oxide skin attachment site of base metal was also different, so the degree of corrosion, stainless steel surface is not uniform. Therefore, in the heating of stainless steel plate heating, it is necessary to make it evenly oxidized skin. And to meet this requirement, we must pay attention to the following problems. Once the stainless steel plate is heated, there is oil on the surface of the workpiece, and the thickness and composition of the oxide scale and other parts of the oxide in the oil attachment area are different, and the part will also be carburized. The carburized parts of the oxidized stainless steel matrix are strongly eroded. The oil droplets ejected from the heavy oil burner at the initial combustion will also be greatly affected if it is attached to the stainless steel plate. The fingerprint of the operator is also attached to the stainless steel plate. Therefore, the operator is best not to touch the stainless steel directly with his hands, even if you want to touch, you should bring clean gloves and then operate. 304 stainless steel plate surface of the workpiece if attached when processing cold lubricating oil, it must use warm water to clean the trichloroethylene degreasing agent, caustic soda solution fully after degreasing, followed by heat treatment. Stainless steel plate, if the surface is still debris, especially organic or gray in the stainless steel plate surface, heating will certainly affect the oxide skin. Stainless steel plate furnace atmosphere will lead to different parts of the difference, the formation of oxide skin will also produce change, and this is also lead to stainless steel plate after acid uneven cause of formation. Therefore, when heating the stainless steel plate, the atmosphere in each part of the furnace must be the same. In order to solve this problem, we should also consider the cycle of good atmosphere. In addition, the formation of heating bench used brick, asbestos, if there are water, so when heated, water will evaporate, direct contact with the water vapor of the stainless steel plate part and other parts of the atmosphere will be different, the oxide coating is also different. Therefore, the direct contact with the heating stainless steel plate workpiece must be completely dried before use. However, after drying, such as placed at room temperature, moisture in high condition, the water will still condense on the surface of the workpiece. Therefore, it is better to dry before use. 304 stainless steel plate if the oxide skin remnants of the local heat treatment before, there will be residual oxide parts and parts without oxide after heating, the difference of composition and thickness of oxide is formed on the skin, resulting in pickling stainless steel plate surface is not uniform, so should pay attention not only to the final heat treatment, but also pay attention to intermediate heat treatment and pickling. Source: China Plate Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The surface treatment technology of stainless steel plate is pided into many kinds, such as sand blasting, passivation, electroplating, acid washing, coating, degreasing and degreasing, rust removal and anodic oxidation. However, there are three common types, which are passivation, acid washing and degreasing. Passivation for stainless steel The surface of the surface, which uses this surface treatment process, does not contain iron. For example, the stainless steel particles on the surface of cast iron, low carbon steel, medium carbon steel or low alloy steel will lead to pitting corrosion of stainless steel on the surface of “free” iron and stainless steel. The problem is very serious, so the passivation treatment is only suitable for the treatment of stainless steel. The purpose of stainless steel passivation is to avoid the oxidation and corrosion of the surface of the stainless steel plate. Stainless steel pickling The purpose of stainless steel pickling is to remove the oxide skin on the surface of stainless steel after high temperature welding, heat treatment or hot processing. It is also able to remove the contaminants of steel, iron or steel particles that are corroded by red rust. It should be noted that if the acid on the surface of stainless steel plate is not cleaned after pickling, the surface of stainless steel will soon be corroded and rusted. The corrosion resistance of the stainless steel matrix is reduced. The stainless steel pickling treatment process can be applied to the surface treatment of all 200, 300 and 400 stainless steel. All pickling operations will make the surface of stainless steel plate slightly change the size of the impurities while removing impurities, so the result is to a certain extent, the extinction of the visual brightness will even lead to a smaller size. The heat treatment in vacuum or a good controlled atmosphere, such as bright annealing, eliminates the need for acid pickling, which usually makes the stainless steel get a better light cleanser. Degreasing and degreasing of stainless steel cleaning agent Before the surface treatment, the stainless steel must first remove the grease, cutting fluid, draw compounds and other lubricants, and then passivate the stainless steel parts before the surface heat treatment. The stainless steel plate must also weld the components before the degreasing process to prevent the pickup from precipitating carbon elements at high temperatures. Generally speaking, when using stainless steel cleaning agent, as long as the material soaked for ten minutes at room temperature, it can remove all kinds of oil pollution. The operation is relatively simple, the labor intensity is also very low, and it can be recycled repeatedly, which can significantly reduce the production cost. Source: China Stainless Steel Plates Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In order to choose stainless steel fasteners with good quality, first of all, we should understand the common manufacturing materials of fasteners. There are many kinds of materials that can be used to make stainless steel fasteners. Among them, stainless steel is the most satisfactory material. Stainless steel fasteners are characterized by high surface quality, high working intensity, and excellent corrosion resistance, easy processing and welding. Fasteners made of stainless steel can be used for electroplating or heat treatment. With the excellent performance of stainless steel, it can be completely recycled and reused. In addition, if the fasteners are made of stainless steel material manufacturing, its application in all aspects of manufacturing, processing or have showed very obvious advantages, so although fasteners for stainless steel material manufacturing will have higher costs, but considering the use of stainless steel materials cycle is very long, so in the choice of fastener materials in the scheme, is still very cost-effective. However, in the use of stainless steel fasteners, there are two problems to be paid attention to. The first is the cost problem. When fasteners were made of stainless steel, they used to rely heavily on the use of nickel. However, the price of stainless steel fasteners has changed greatly as the price of nickel metal has increased worldwide. In order to alleviate the pressure of material cost and improve the competitiveness of stainless steel fastener products, some fastener manufacturers are looking for alternative materials in all kinds of stainless steel materials, and finally produce low nickel stainless steel fasteners. One more problem is the magnetic problem. When making fasteners with stainless steel materials, it is necessary to understand the magnetic problem of the stainless steel itself. People usually think of stainless steel materials are not magnetic, but actually austenitic stainless steel by stainless steel processing technology, magnetic or produces weak, so not to have the quality as the standard to evaluate the magnetic properties of stainless steel fasteners. Specifically, in the selection of stainless steel fasteners, stainless steel does not prove whether there is magnetic material quality, because there is no chromium manganese stainless steel with magnetic stainless steel, but it can not replace the Cr Mn stainless steel 300 series stainless steel is used, especially in the medium high corrosive environment is this. Source: China Stainless Steel Fasteners Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Generally speaking, there are three kinds of polishing processing technology for stainless steel pipe elbow, they are mechanical polishing, chemical polishing and electrolytic polishing. Among them, the machine polishing has three terms, need to understand, first of all, abrasive said is stainless steel pipe elbow polishing wax, eliminate excess particles, so that the surface shows very neat. The grease is said to make the elbow have lubrication and cooling function by polishing wax, so that the surface of the pipe has some effective substances such as stearic acid, fatty acid and paraffin wax. Cutting force is to say, the polished stainless steel pipe elbow friction leveling process needs to complete the force. When stainless steel pipe elbows are placed for a long time, be sure to check and maintain them regularly. For the stainless steel pipe elbow exposed on the outside of the part has to ensure clean, remove dirt, keep clean, stainless steel pipe elbow should be placed in the indoor ventilated and dry place, can not be completely exposed to the outdoors and accumulation. Stainless steel pipe elbow itself ball valve, wafer check valve, gate valve use time, can only be fully open and fully closed, the middle can not adjust the flow over time can prevent the sealing surface from corrosion and wear damage, usually the valve and the valve on the screw contained within the inverted sealing for manual hand wheel rotation to the the upper head surface can achieve long-term rust free, no corrosion. In addition, the installation of adjustable stainless steel pipe bend, it is necessary to maintain its seal status, otherwise it will cause it can not work properly. There are two main types of forming process of stainless steel pipe, one of which is hot forming, hot forming process is the use of stainless steel pipe elbow‘s bend drawing machine, mould and heating device, the set of billet in the mold on the forward movement in the push for the machine, and in the movement to be heated and expanded diameter and bending. The deformation characteristics of the hot pushing elbow is based on stainless steel pipe elbow plastic law of constant volume deformation before and after determining the tube diameter, tube diameter less than the diameter of the elbow, the deformation process of mould blank control, the metal flow in the arc compressed, compensation due to expanding and reducing other parts of thin thus, the uniform wall thickness of elbow. The other is a stamping, stamping of stainless steel pipe elbow is the earliest to forming process for the production of large quantities of seamless elbow, elbow now commonly used in the production of specifications have been replaced by hot method or other molding process, but in some specifications of the stainless steel tube bend in production quantity and the wall thickness is too thick or too thin. Before the stamping, the stainless steel tube blank is placed on the lower die, and the inner core and the end die are loaded into the tube blank, and the die is moved downward to start pressing, and the stainless steel pipe bend is formed by the constraint of the external die and the supporting action of the internal model. Source: China Pipe Elbow Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

According to the difference between heat treatment and chemical composition, heat treatment process of 304 austenitic stainless steel plates are often used solid solution treatment, stable annealing process, should eliminate several processing and sensitizing treatment, the following is to deal with these hot technology introduction. Solid solution treatment 304 austenitic stainless steel plate melting treatment is to heat the plate to excess phase, fully dissolved into a solid solution in a certain temperature, after a certain period of time to cool the rapid cooling process. Austenitic stainless steel plate solution heat treatment is to be before the carbide formation or precipitation and sigma each processing phase in re dissolved into austenite, resulting in austenite stainless steel single, so as to ensure that the board has excellent mechanical properties and corrosion resistance, so as to maximize the elimination of stress and the cold hardening. The Austenitic 304 stainless steel plate is suitable for any component and grade. Stabilization annealing The stable annealing process is a heat treatment method for Austenitic 304 stainless steel plates containing stabilizing elements, titanium or niobium. The purpose of using this method is through the use of titanium and niobium with carbon strong binding properties, stable carbon, as far as possible to reach the stable with chromium binding, chromium, chromium in austenite and enhance the stability of the grain boundaries, prevent from security, sub corrosion resistance of stainless steel plate. 304 austenitic stainless steel plate stabilization cooling mode and cooling rate on the stabilization effect will not have much impact, therefore, in order to prevent the deformation of complex shaped workpieces or stainless steel to ensure minimum stress, cooling rate can be smaller, such as air cooling or cooling furnace. Stress relief treatment The determination of the stress treatment process to eliminate 304 austenitic stainless steel plate, according to the material type, the use of the environment, eliminate stress and to stainless steel shape and size etc., need to pay attention to grasp some of the principles. Remove the stress produced during the processing or remove the residual stress after processing, can be treated with solid solution heating temperature and rapid cooling, class I and class II Austenitic 304 stainless steel plate can be used more slowly cooling into. To ensure the final dimensional stability of the stainless steel workpiece, lower heating temperature and slow cooling rate can be used. To eliminate the great residual stress. To eliminate the residual stress in the work environment which may produce new stress or to eliminate the welding stress of the large section weldment, the austenitic stainless steel plate must be fast cooled due to the melting heating temperature of the type III. In this case, it is better to choose I or II Type Austenitic 304 stainless steel plate. After heating, it can be cooled slowly, and the effect of stress elimination is better. In order to eliminate the residual stress of the workpiece which can only be used in the local heating mode. Low temperature heating and slow cooling shall be adopted. Sensitization treatment Sensitization process does not essentially belong to the heat treatment process required by the Austenitic 304 stainless steel plate or its products in the manufacturing process. But as a procedure used to test the intergranular corrosion resistance of Austenitic 304 stainless steel sheets. In fact, sensitization treatment is to make Austenitic 304 stainless steel plate more sensitive to intergranular corrosion. On some special occasions, for the intergranular corrosion resistance of more stringent assessment materials, in some standard, the system of austenite be sensitized by the future more demanding, temperature and carbon materials used in and whether contained elements using different systems and sensitization. Some of them also control the speed of lifting and cooling. Therefore, in order to judge the intergranular corrosion tendency of austenite 304 stainless steel plate, it is necessary to pay attention to the sensitization system used. Cold work strengthening and stress relief treatment Austenitic 304 stainless steel sheets can not be strengthened by heat treatment, but can be enhanced by cold working deformation (cold hardening, deformation strengthening), will improve the strength of the material and reduce plasticity. 304 austenitic stainless steel plate or products by cold deformation strengthening, with a larger processing stress, the stress would make use of stress in the corrosive environment, increase the stainless steel plate material stress corrosion sensitivity, thus affecting the stability of materials. In order to reduce stress, stress relief treatment can be used. Usually it is heated to 280 DEG C to 400 DEG C and kept cool after 2-3 hours. The stress treatment can not only reduce the stress of the workpiece, but also increase the hardness, strength and elastic limit under the condition that the elongation is not changed obviously. Source: China Sheet Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Many of the advantages of the 304 stainless steel plate, such as surface appearance, application forms, excellent corrosion resistance, long service life, high strength materials, so the use of the field of stainless steel sheet is very extensive, because there are good oxidation resistance, so the stainless steel plate can effectively fire resistant products. Stainless steel material is very easy to be machined at normal temperature. Because there is no need for surface treatment, stainless steel products are easy to use, easy to maintain, and the surface is bright and beautiful. The most important difference between 316 and 304 stainless steel in chemical composition is that 316 stainless steel contains molybdenum alloy element, and it is generally believed that 316 stainless steel has better corrosion resistance. In high temperature, 304 stainless steel is also more resistant to corrosion. Therefore, in the high temperature operating environment, 316 stainless steel parts are usually used. However, if it is in a concentrated sulfuric acid working environment, even if the temperature is higher, it is absolutely not possible to use 316 stainless steel, because in order to avoid thread killing when exposed to high temperature, it is necessary to apply solid lubricant. 304 stainless steel, because the yield point of stainless steel itself is relatively high, and the hardness is also high, so the cold hardening effect is obvious. 304 stainless steel plates will have the following characteristics when doing bending processing. The first is due to thermal conductivity is lower than the ordinary low carbon steel, low elongation, so the deformation force needed is relatively large, the bending process and springback tendency is very strong compared to the existence of carbon steel stainless steel sheet, stainless steel plate bending steel workpiece in bending angle is larger than that of carbon steel to have cracks. Because of the relatively high hardness of 304 stainless steel plate, cold hardening effect is obvious, so choose the tool steel heat treatment hardness greater than 60HRC in the choice of bending tool, the surface roughness than the bending tool steel is an order of magnitude higher. Based on the above characteristics, usually in the unit size, the thick plate bending strength, the greater the need, and with the margin of plate thickness increase in the choice of bending equipment when the bending force is much higher, in size, higher tensile strength, the elongation rate is lower, the greater the need of bending force the bending angle is bigger also. According to the actual situation, a bending workpiece is the sum of the right angle side unfold size minus two thickness, can fully meet the design requirements of precision, outspread quantity can simplify the calculation and greatly improve the production efficiency is calculated in accordance with the empirical formula, stainless steel material yield strength increases, elastic recovery amount is high, in order to obtain the bending part 90 degrees, need to press the knife angle to lower the design. Compared with carbon steel, the 304 stainless steel plate with the same thickness has larger bending angle. This aspect needs special attention, otherwise there will be bending cracks, which will affect the strength of stainless steel plates. Source: China Stainless Steel Plates Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

If the surface of the stainless steel plate is not uniform, it is necessary to make a uniform oxide skin in the process of heat treatment. To achieve this goal, in addition to the high surface quality of stainless steel plates, it also depends on whether the pickling process is in place. Therefore, we must pay attention to the surface cleaning of stainless steel plates before heating and heat treatment before heat treatment. The following is to focus on the relationship between the surface quality of the stainless steel plate and the heat treatment process. First of all, if the surface of stainless steel plate is attached to oil when heated, the thickness of oxide scale on the area of oil attachment is different from that of other parts, and it will also lead to carburizing. The parts of the oxidized subcutaneous stainless steel matrix that are carburized are seriously eroded by acid. The oil droplets that are sprayed at the beginning of the burning of the heavy oil burner will have a larger impact if they are attached to the stainless steel plate. In addition, the operator’s fingerprints also have adverse effects on the stainless steel plate. Therefore, the operation can not directly touch the stainless steel plate, stainless steel plate, don’t let the dip in the new oil, such as oil plate cold processing if there is left, must be in the trichloroethylene degreasing agent, caustic soda solution and then use fully skimmed warm water to thoroughly clean, then do heat treatment processing. If the surface of stainless steel plate has impurities, especially when organic matter or ash is attached to the surface of stainless steel plate, heat treatment will have a negative effect on the oxide scale. In addition, the surface of the stainless steel directly exposed to the flame is also different from that produced in the area without contact. Therefore, when heated, it must not be allowed to contact the flame directly. If the local processing of stainless steel in heat treatment before there is a residual oxide, oxide and residual parts and no oxide parts after heating, different thickness and composition can produce oxide on the surface resulting after pickling is not uniform, so should pay attention not only to the final heat treatment, but also completely note that the middle heat treatment and pickling. The surface finish of stainless steel will also be affected. If the surface finish is different, even if the same heating is applied, the surface roughness area of the stainless steel plate is different from that of the fine area. For example, in the area where the partial defects are cleared and not cleaned, the oxide scale is also different, which will lead to the uneven surface of the stainless steel plates after pickling. The last point is the difference of the atmosphere in the furnace. The different atmosphere in each part of the furnace will also lead to different changes in the oxide scale. This will also lead to uneven after acid washing. Therefore, in the heating, the atmosphere in the various regions of the furnace must be kept the same, and this must consider the circulation of the atmosphere. Source: China Stainless Steel Plates Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The common element of stainless steel plate in more than 10, in addition to the basic elements of the iron and steel, properties and microstructure of stainless steel plate is the greatest impact elements including carbon, chromium, nickel, manganese, silicon, molybdenum, titanium, niobium, titanium, manganese, cobalt, copper, nitrogen etc.. When some elements coexist in the whole stainless steel, the influence of far is much more complex than when they exist independently, because not only to consider the elements of its function, but also pay attention to their effects caused by each other, so the performance of stainless steel is the sum of various elements affect the decision by the. Chromium plays a decisive role in stainless steel. As long as it is stainless steel, it contains a certain amount of chromium. This is because the addition of chromium to the steel will lead to the movement of contradictions within the stainless steel to the benefit of resistance to corrosion damage. The main reason is to increase the electrode potential of Fe based solid solution. In addition, chromium also absorbs iron to make iron passivated. Again, carbon is one of the major elements of industrial steel. The properties and organization of steel are largely determined by the content and distribution of carbon in steel, and the effect of carbon is more pronounced in stainless steel. Effect of carbon on microstructure in stainless steel is mainly manifested in two aspects, one is the stable austenite carbon element, and the effect extent is 30 times higher than the nickel effect, the second is because due to carbon and chromium and chromium affinity, forming a series of complex carbide. Therefore, from the two aspects of strength and corrosion resistance, the role of carbon in stainless steel is contradictory. The role of nickel in stainless steel is to play with chromium to play out, nickel is an excellent corrosion resistant material, but also an important alloying elements alloying steel. Nickel in stainless steel is austenite formation elements, but the low carbon nickel steel to obtain pure austenite, nickel content must be as high as 24%. And only with nickel 27%, will make the stainless steel in some medium corrosion resistance has changed significantly. Therefore, nickel cannot be made into stainless steel separately. However, when nickel and chromium are present in stainless steel, nickel containing stainless steel has a lot of valuable properties. Nickel as alloying element in stainless steel, is the high chrome organization changes, so as to improve the corrosion resistance of stainless steel materials and process performance. In addition of manganese and nitrogen can replace nickel chromium nickel stainless steel, chromium nickel austenitic stainless steel has the advantages of many, but over the years because refractoloy and heat resistant steel containing nickel below 20% a large number of development and application, and the chemical industry development needs more and more and the stainless steel, nickel deposits the relatively small and concentrated in a few areas in the world, so there is a contradiction in the supply and demand of nickel. Therefore in many other fields of stainless steel and alloy forging steel, tool steel, heat resistant steel etc., especially nickel less resources, widely carried out section of nickel and nickel with other elements of the generation of scientific research and production practice, the research in this aspect and is widely applied to manganese and nitrogen instead of nickel in stainless steel and heat resistant steel. Manganese acts as an element of austenite, similar to nickel. More specifically, the role of manganese is not only lies in the formation of austenite, critical quenching speed can reduce the stainless steel, increase the stability of austenite during cooling, inhibit decomposition of austenite, the austenite under high temperature can be generated to maintain normal temperature. The corrosion resistance of stainless steel increased, little effect of manganese, nickel manganese austenite is about half the stability in the role of low nickel stainless steel, stainless steel and nickel free CrMnN Stainless steel has been used in the industry, some areas have been successfully used to replace 18-8 chromium nickel stainless steel. Source: China Sheet Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

(1) welding methods: due to the majority of stainless steel pipes and sizes, according to the welding characteristics of stainless steel, as far as possible, reduce the amount of heat input, the manual electric arc welding, argon arc welding is adopted two kinds of methods, d > 159 mm Φ adopts argon arc welding, manual arc welding covering. D ≦ Φ 159 mm all use argon arc welding. The welding machine adopts the manual arc welding/argon arc welding of the WS7-400 inverter arc welding machine. (2) the welding material: austenitic stainless steel is special steel, to meet the joint with the same performance, should follow the principle of “the composition such as” to choose the welding material, at the same time to strengthen the joint between the thermal crack and corrosion ability, make a small amount of ferrite appear in the joint, choose HooCr19Ni12Mo2 argon arc welding with welding wire, hand arc welding with electrode CHSO22 as filling material, its composition is shown in table 1 and table 2. Table 1 chemical composition of welding wire HOOCr19Ni12Mo2 (%) C Si Mn P S Ni Cr Mo 0.012 0.13 1.70 0.019 0.007 13.23 18.72 2.38 Table 2 chemical composition of welding rod CHS022 (%) C Cu Si Mn P S Ni Cr Mo 0.03 0.20 0.64 0.75 0.02 0.007 11.77 19.66 2.05 (3) welding parameter. The outstanding feature of austenitic stainless steel is that it is sensitive to overheating, so it is necessary to control the interlayer temperature strictly under the condition of small current and fast welding, and the interlayer temperature is less than 60 degrees. (4) Groove form and assembly position welding. Using V groove, groove form with lower welding current, penetration is small, thus groove blunt edge is smaller than carbon steel, approximately 0-0.5 mm, groove Angle is bigger than carbon steel, which is about 65 ° to 700 °. Due to the large thermal expansion coefficient of stainless steel, the welding stress can be produced when welding, and strict positioning welding is required. For d ≦ Φ 89 mm tube adopts two positioning, d = Φ 89 – Φ 219 mm USES three positioning, d ≧ 219 mm by four o ‘clock positioning; Position weld length 6-8 mm. (5) Welding technical requirements: 1. The welding machine adopts dc inverse when manual arc welding, and dc is used when argon arc welding. 2. Before welding, the wire should be brushed with stainless steel wire to remove the oxide skin of the surface and clean with acetone. Electrode should be in 200-250 ℃ drying 1 h, as you take; 3. Before welding, clean the oil on both sides of the slope of the workpiece by 25 mm, and wash the sides of the slope with acetone. 4. Argon arc welding, the nozzle Φ 2 mm in diameter, extremely rich tungsten tungsten electrode, specifications Φ 2.5 mm; 5. When the argon arc welding stainless steel, the back must be protected by argon gas to guarantee the back forming. The flow rate is 5-14l/min, and the positive argon flow rate is 1213l/min. The seam thickness should be as thin as possible at the bottom of the bottom welding, and it should be in good shape with the root, and the arc should be formed in a gentle slope. If the arc is retracted, the grinding machine will be worn out. The arc must be filled in the groove and the arc crater should be filled to prevent the cracks. Due to the stainless steel to austenitic stainless steel, to prevent the carbide precipitation sensitization and intercrystalline corrosion, should strictly control the interpass temperature and cooling rate after welding, the welding interlayer temperature control under 60 ℃, must immediately after welding water-cooled, by subsection welding at the same time. The specific section method is shown in figure 1. This symmetrical dispersion welding sequence can increase the cooling speed of the connector and reduce the welding stress. Figure 1. Welding schematic of different pipe diameters 2 the results (1) the appearance inspection has no porosity, welding tumor, sag and biting edge etc., forming well. (2) to stretch and bend test pieces, all mechanical property indexes meet the requirements, and no defects such as fusion and cracks are found. (3) macroscopic metallographic examination, found that the weld bead was well fused, and the penetration was 1-1.5mm. Microscopic metallographic examination, parent material and the heat affected zone is all austenitic organization, weld metal for ten ferrite austenite (4%) of the organization, fully meet the requirements of intergranular corrosion resistance and resistance to brittle, after incoalation company site construction to ensure the welding quality. Source: China 316L Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steel welded pipe is mainly used in landscape decoration, light industry, pharmaceutical industry, water supply and other industries. It is also applied to petrochemical industry. It usually selects medium and low pressure pipelines above the size of 159mm. Besides, the automobile muffler can also be made of stainless steel welded pipe. Stainless steel seamless pipes are mainly used in chemical industry, fertilizer, chemical fiber (three), oil, power boilers, machinery, aerospace, nuclear industry, defense industry and other demanding industries. Oil drilling can be made of stainless steel pipes, stainless steel non-magnetic drill collar, high resistance CO, CO2 and Cl- corrosion super ferrite stainless steel Cr13, Cr25 and other oil and casing are used in oil field drilling, but most of such stainless steel pipes still rely on imports. Stainless steel pipe for thermal power boilers Heat – resistant and stainless steel austenitic steel boiler tubes are used in thermal power boilers. 1 tons of 600 thousand kW supercritical thermal power unit boiler need 200-500 tons of rust resistant steel tube, which is also more dependent on import. “Three” industrial use of heat-resistant stainless steel tubes The heat resistant stainless steel pipe is mainly used for heat exchange and fluid transportation in the “three industry”. The market capacity is the largest, and the domestic market demand is about 160 thousand tons per year. And the requirements of this kind of stainless steel pipes are very strict, and it is also necessary to meet the requirements of the import. The potential market is used to transport oil pipe pipe and low temperature cracking furnace of large diameter, heat and corrosion resistance because of its special requirements and equipment installation and maintenance inconvenience, and requirements of equipment life cycle is long, through the material properties and performance optimization control of material composition and special heat treatment. The other potential market is the special steel pipe for the fertilizer industry (urea and phosphate), the main steel types are 316Lmod and 2RE69. At present, the above stainless steel tubes are basically imported. Duplex stainless steel pipes (fluid, heat exchanger) The duplex stainless steel is mainly used in chemical and chemical fertilizer fields. Its characteristics are good stress corrosion resistance and the application temperature is less than 350 degrees C. Because of its high strength, resistance to stress, corrosion resistance and economy, duplex stainless steel pipes are now used in the manufacture of heat exchangers and fluid tubes. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)