JP2009530499A - Manufacturing system for weldable and stainless steel tubular structures having high strength and products obtained therefrom - Google Patents

Abstract

A manufacturing system for weldable and stainless tubular structures having high mechanical strength and products obtained thereby are described, in particular relating to the production using cold drawn stainless steel, with different thicknesses. It can be machined into profile and shape, and is used in the manufacture of lightweight and ultra-light structural frames used in dynamic applications and has excellent mechanical and welding properties. The manufacturing system includes an inclined manufacturing process for reducing the end portion of the tube and an annealing heat treatment process for softening the material and making it easy to deform in order to pass through the drawing device and combine for drawing. The system includes a mechanical test to evaluate the mechanical properties of the material and a metallography that observes the structure of the material and evaluates whether it is within the preset parameters for withdrawal. Is included. After these steps, there is a surface chemical preparation step, which smoothes the contact surface between the tube and the drawing device and suppresses sticking during drawing which permanently deforms the material. The process is repeated until the tube thickness reaches the desired value. After the process is completed, a finishing heat treatment process is performed to modify the deformed steel structure and impart the desired final properties. Finally, a straightening step is performed to straighten the drawn and furnace-treated tube, and a passivation step is performed to produce dense oxide rust and impart corrosion resistance to the steel. Then, cut and perform quality control and packaging.

Description

  The present invention relates to a manufacturing system for weldable and stainless steel tubular structures having high strength and products obtained therefrom, and more particularly, can be processed into different thicknesses and shapes and used in dynamic applications such as racing. Cool, with high performance mechanical and welding properties suitable for the production of competitive vehicles such as cars, high-end bicycles, and lightweight and ultralight structural frames used in aeronautics. The present invention relates to a stainless steel tubular member manufactured by thinning.

  In particular, the structural frame above has special strength and reliability, as well as light weight and excellent properties under dynamic pressure, as in the case of racing vehicles and aeronautical structures. Performance is required.

  As is known, steel structural frames used in dynamic applications are multi-way tubes made of different quality steels and interconnected by metal connecting members. is there.

  An example of one dynamic frame is that used when manufacturing a bicycle.

  When manufacturing high-end bicycle frames, the weight is reduced while ensuring good mechanical strength even in the vicinity of the welds, and the rigidity of the structure is increased. In order to impart rigidity as well, it is necessary to carry out special processing (forming by forming and changing the thickness along the tube by broaching and / or coning).

  As already explained, the tubes in question are preferably connected to each other by welding. In order to achieve a flat connection, it is necessary to maintain the mechanical properties of the material even in the welded part, and it is necessary to weld with a special technique. The first welding example used is called TIG (TIG means tungsten inert gas). In TIG welding, an electric arc is used to heat and melt the metal, and the electric arc is generated between the electrode and the welded part. The protective gas passes through the nozzle and protects the welding bath and the tungsten electrode. The main purpose of the protective gas in TIG welding is to protect the hot and melting zones of the part, the welding material, and the electrodes from the adverse effects of ambient air. Furthermore, the protective gas also affects the arc characteristics and the aesthetic appearance of the weld. Advantages of TIG welding include high quality joints and the absence of slag or spatter. Another welding method is brazing. These techniques require a high degree of accuracy and are elaborate welding methods even if performed by a skilled worker.

  Another more technologically advanced welding method is known as electron beam or laser welding, which are used to manufacture parts used in the aerospace field, but in the field of bicycles. not being used.

  In fact, for example, an electron beam can weld two materials with different properties with high precision and completely adheres them without a welding line. However, in addition to the high initial investment, the cost of using electricity increases exponentially in proportion to the size of the material being welded, making it unacceptably high.

  In addition to the reasons described above, electron beam welding and laser welding are not applicable when joining parts of a specific size such as a frame, so that they can be used in a bicycle frame manufacturing field. Requires a lot of investment. Furthermore, after the welding, further heat treatment is required to finish the frame, resulting in problems such as high movement costs, resulting in a considerable increase in manufacturing costs.

  In all cases, the welding technique used must not give any problematic consequences or other events, and must not be aesthetically damaging.

  Currently, all the quality steels used in the above frame production have the problem that the mechanical properties of the welded part are weak, so that it is necessary to attach a reinforcing member in the vicinity of the joint, There is a problem that a tubular member having a large thickness must be used (except for a tubular member made of steel welded by an electron beam method or a laser method).

Another problem in the manufacture of dynamic frames is that today's most used steel typologies (ie, carbon steels such as 25CrMo ₄ ) have favorable mechanical properties, but are prone to corrosion and tube It is clear from the fact that the inside and outside of the steel deteriorate and the strength and durability are clearly reduced as a result. In order to prevent deterioration, it is necessary to add further protection and finishing with protective paint. However, it is not possible to protect the inside of the pipe where corrosion occurs even if special high-cost technology is used.

  The use of protective enamel has a negative impact on weight in addition to all the environmental impacts caused by the manufacture and maintenance of the frame.

Among the specific non-stainless steels that provide high performance in terms of elasticity, strength and light weight, for example, steel 15CrMoV ₆ is nickel-plated rather than painted, in which case corrosion protection is applied to the interior of the tube. It is done with the outside. When performing nickel plating, it is necessary to consider many adverse effects, and further problems arise if not properly controlled. In fact, the activity of electroplating can adversely affect the environment due to the generation of various harmful substances, such as heavy metals, cyanide compounds, and strong acids (sulfuric acid, hydrochloric acid) that have a great negative impact on the environment in nickel plating processes. Are known. The use of large amounts of inorganic salts, corrosive substances, and solvents creates problems with both wastewater and waste disposal. Furthermore, harmful vapor and powder generated by processing have a great influence on air.

  Among other materials that are difficult to corrode, aluminum and titanium (which are not included in the material categories described here and have many special and unresolved problems), and ferritic stainless steel (mechanical properties) The solution to the above problem has been investigated for stainless steel for the past 10 years, except that it has not been able to meet all requirements to date.

  In fact, austenitic stainless steel (eg, AISI 304, AISI 308, etc.) has good weldability and stainless properties, but weak mechanical properties. That is, they are ductile, not hard, do not cure (single phase), and in fact, their structure does not change and remains austenite even when rapidly cooled after heating above the transformation temperature (AC3). is there.

  In order to impart greater mechanical properties, stainless steel can be hardened by treatment with mechanical force (eg pulling).

  However, in this case, problems related to the welding process are still unsolved. When heated to a temperature above the melting point, the adjacent regions are also heated (and soften), so that the required mechanical properties cannot be obtained. The weld area is formed as a place where the strength is weaker. Since it is necessary to ensure the strength of the structure, an effect that greatly reduces the weight cannot be expected even if the thickness is reduced. Moreover, once hardened by drawing (or another mechanical force), this type of steel presents other processing complications.

  Chrome-nickel stainless steel cannot be hardened, but chromium martensitic stainless steel can be hardened.

  In other words, this type of steel melts during the heat treatment, and the quenched austenite changes to a martensitic structure and high mechanical strength is obtained.

  Martensitic steel with a chromium content of greater than 13% further has good corrosion resistance. However, even in this case, problems related to the welding process occur. That is, when welding is performed, all martensitic steels generate microcracks (in fact, it is recommended to prevent this by making the carbon content greater than 0.20%). Even a slight reduction in strength reduces, inter alia, the strength of structures subjected to dynamic pressure. In either case, since they are self-hardening steels, it is necessary to preheat before welding and then immediately temper or anneal. For this reason, it is undesirable and expensive to use this material to manufacture the pipes to be welded for the manufacture of frames subjected to high pressure for racing vehicles or aircraft.

  Currently, there is also stainless steel (17-4PH steel) by precipitation hardening on the market, which has good stainless steel properties and contains alloying elements (Al, Nb, Ti, Mo, Cu, etc.). The alloy element, after heat aging treatment, precipitates the hardened phase into the matrix, thereby imparting high strength with moderate tensile strength and ductility to the steel.

  As in the case of martensitic steels, these types of steels are difficult to reprocess continuously unless they are costly.

  Furthermore, in this case, no precipitation of carbides occurs in the welding process, so the problem of weldability is unsolved. The formation of weak spots during welding results in reduced reliability of the final structure.

  The only way to avoid that problem is to perform a further heat treatment following the welding process, which results in processing problems that further increase the cost.

  In addition to the steel described above, other stainless steel materials are being considered (eg, AerMet 100 alloy). The material features include more than 5% of one or more alloying elements and are not considered “alloys” in the traditional way of thinking, but are “superalloys” based on iron, cobalt and nickel (ie, The mechanism of structural modification is different and allows specific properties to be imparted, depending not only on the content of the additive elements but also on the complexity of the alloy itself.)

  In particular, these materials have a low modulus of elasticity and are considerably more complicated to process than steel. When using this material, draw and always use pipe welding to make the tube (thus billet extrusion is never used). In addition to complex processing methods and heat treatments, once manufactured to a specific diameter and thickness (like the previously described materials), manufacturing is not economical and does not costly modify. Furthermore, the frame portion close to the welded portion needs to be reinforced using an external reinforcing member (gasket).

  Finally, for the sake of completeness, we will describe the production of Nanoflex tubes, which are innovative steels derived from nanotechnology and do not fall into other steel categories.

  The material is a very promising material that can be expected to have high strength (not by heat treatment but by reduction percentage). In theory, the tube made of this steel is now Has the best mechanical properties, processing properties, and finishing properties. However, apart from the fact that nanoflex also has some problems during welding, this material is not yet commercially available.

  An object of the present invention is to overcome the above-mentioned problems and solve the problems of the prior art by using a manufacturing system of a high-strength, weldable, stainless tubular structure and a product obtained therefrom. Thus, corrosion does not occur, high strength, easy processing for imparting different thicknesses and shapes, easy welding while suppressing the occurrence of weak points in the vicinity of the welded part, Tubes can be manufactured.

  A second object of the present invention is to produce a high strength, weldable, stainless steel tubular structure manufacturing system and products obtained therefrom, thereby producing a tube manufactured without welding. It provides an improved technical measure for the production of lightweight structural frames and welded tubular structures that are structurally uniform for use in dynamic applications.

  A third object of the present invention is to possess a high strength, weldable, stainless steel tubular structure manufacturing system and products obtained therefrom, thereby providing high strength and excellent safety. Pipes with quality can be manufactured, thereby not only being exposed to dynamic pressure, but also in harsh conditions where high strength is required, e.g. space, aeronautics, nuclear, chemistry, sea, motorsport, Machine parts that can be used in fields such as cycling can be manufactured.

  Another object of the present invention is to provide a manufacturing system for a high-strength, weldable, stainless steel tubular structure and a product having a high workability index obtained therefrom.

  Yet another object of the present invention is to provide a manufacturing system for a high strength, weldable, stainless steel tubular structure and the product obtained therefrom, thereby relating to the entire life cycle of the product. Many of the environmental problems can be reduced, i.e., it is possible to reduce the process in the manufacturing process, consequently reducing the consumption of toxic and harmful substances, and extending the lifetime in the effective lifetime of the product, Raise standards, reduce the use of chemicals required for maintenance, and at the end of the effective lifetime, ie at the disposal stage, allow for total recycling without compromising the properties of the raw materials (soft metal Like happening instead in recycling).

  A considerable object of the present invention is to provide a high strength, weldable, stainless steel tubular structure manufacturing system and products obtained therefrom that can be easily manufactured and have superior functionality.

  These and other objects will become apparent during the course of the description of the present invention, and are derived from a manufacturing system for a high strength, weldable, stainless steel tubular structure as set forth in the following claims. It is substantially solved by the product.

  Further properties and advantages of the present invention will become apparent from the detailed description of the manufacturing system and the products obtained therefrom, which are high strength, weldable and stainless steel tubular structures. The present invention is described below with reference to the accompanying drawings. The drawings are for illustrative purposes and do not limit the invention in any way.

  The method of the present invention is used for a steel defined by “austenite-martensite”. As for its chemical composition, austenitic stainless steel contains carbon and molybdenum, and martensitic stainless steel is nickel. And contains chrome. In the present invention, austenitic stainless steel has a martensite ratio reaching about 95%. Therefore, the method of the present invention can also be applied to martensitic steel. An example of steel that can be suitably used in the method of the present invention is called X4CrNiMo 16-5-1.

The manufacturing system of the high strength, weldable and stainless steel tubular structure of the present invention substantially comprises the following steps.
Martensitic steel or austenitic-martensitic steel is heat-processed to produce a blank tube (known as a preform),
Create a tip, thereby reducing the end of the tube, allowing it to pass through the drawing device, and tethering for drawing,
Perform annealing by heat treatment, thereby softening the material and making it deformable,
Perform mechanical tests as needed to determine if the mechanical properties of the material are suitable for subjecting the tube to drawing,
If necessary, perform metallography to observe the structure of the material, and if it is within the specified parameters, determine that it will be subsequently drawn, otherwise soften it for processing. It is determined that it is necessary to perform the annealing treatment of
Chemically prepare the surface, thereby smoothing the contact surface between the tube and the drawing device, preventing sticking,
Pull out the material so that it is permanently deformed,
Heat treatment of the finish, thereby modifying the structure of the deformed steel, giving the desired finish properties,
Straighten the tube that has been pulled out and treated in the furnace,
Passivation treatment is performed, thereby imparting a dense oxide rust to the steel and ensuring corrosion resistance.

  The process of the present invention is completed through conventional processes such as cutting the tube into easier-to-handle parts, quality control and packaging.

  The first step of the present invention is to obtain a “preform” which is the first raw material for carrying out the method of the present invention. Specifically, the preform is a heat-processed tube (at about 1300 ° C.), that is, the preform is wound around a wheel forming the tube or extruded by a press. Preform characteristics are typical of high temperature processing, with oxidized surfaces, weak tolerances, large thickness relative to diameter, and only a standard size. is there.

  The preform is made of a cured and tempered material and has high strength, so that it cannot be pulled out. To reduce the mechanical strength, a single-stage annealing process in a static furnace (or shaft furnace, load furnace, etc.) or a multi-stage annealing process in a continuous furnace or a muffle furnace is required. Let it pass to reduce diameter and thickness.

  The annealing heat treatment used in the production system of the present invention needs to be performed in a furnace in which the atmosphere is controlled, thereby preventing alteration of the internal and external surfaces of the material, oxidation, and decarbonization. “Atmosphere is controlled” means an atmosphere of an inert gas (nitrogen, helium, argon, etc.) or a vacuum atmosphere. In particular, a preferred atmosphere in the present invention is a mixture of about 50% nitrogen and about 50% reducing gas, which may include, for example, a hydrogen-containing gas as obtained from steam reforming. it can.

  More specifically, when performing annealing heat treatment in a continuous furnace, it is necessary to pay attention to the weight of the tube, the moving speed and moving time, and the temperature in different areas of the furnace in order to obtain a workpiece with the desired technical characteristics. There is. This heat treatment is a preliminary treatment of the material for subsequent steps and processing.

  The annealing step includes an initial heating step for heating from room temperature to the annealing temperature, a treatment step at the annealing temperature, and a cooling step.

  The preheating from room temperature to the annealing temperature is usually performed in a time shorter than 1 hour.

  The annealing treatment is performed at 600 ° C. to 750 ° C., preferably 650 ° C. to 700 ° C. In a preferred embodiment of the present invention, the annealing treatment is preferably performed at about 680 ° C. The annealing time is at least 40 minutes, preferably at least 1 hour, more preferably less than 3 hours. In a particularly preferred embodiment of the present invention, the annealing time is 1 hour 20 minutes. The combination of processing temperature and time is important in order to obtain a material with the desired properties, i.e. excellent mechanical and welding properties. In general, it can be clearly said that the heat treatment temperature and the treatment time are inversely proportional. That is, when performing at the temperature close | similar to the minimum of said temperature range, it is necessary to lengthen processing time.

  Cooling the annealed tube is a very important operation. It is important to cool slowly in a controlled atmosphere. Generally, the cooling time is 2 to 4 hours.

  If necessary, subject the material to mechanical testing and metallography to ensure that it has the properties and specifications necessary to send the material to the next process. The metallography is used to evaluate whether the structure of the material is within the specified parameters, and the subsequent extraction is performed based on the results. In order to process it, it is necessary to perform an annealing process for softening. These inspections do not need to be performed on a regular basis, and may be performed only for the completion process of the selected martensite or austenite-martensite steel. In the normal operation of the present invention, these steps need not be performed.

Here, the material is prepared for the next step including chemical preparation of the surface. In this step, the tube is immersed in a first tube containing a suitable acid (nitric acid-hydrofluoric acid type) for a predetermined time (about 40 minutes), rinsed in the water of the second tube, and then washed with Immerse in an acid salt bath for a predetermined time (about 20 minutes) and finally in stearic acid ester (preferably 3% by weight) which smoothes the outer surface of the tube. Preferably, the acid treatment uses 56% nitric acid at 140 kg / m ³ and 38-40% hydrofluoric acid at 40 kg / m ³ . In the oxalate treatment, the oxalate concentration is generally 8 to 16% by weight.

  Here, the material is prepared for the drawing process. At the beginning of the processing step, a ramp was formed to engage the tube with the instrument of the extraction device.

  Drawing is a machining process for permanently deforming the material in the steel case. It is carried out cold using the machine (drawing device) and thus at room temperature. Here, the machine applies a force to the material, i.e. pulls one end of the material, through a drawing device that determines the final shape. In the case of a tube, the drawing device is designed so that the inside and outside of the tube can be machined. The steel pulled at one end is then machined to the shape of the instrument that is drawn from and passed through.

  In the manufacturing system of the present invention, all instruments need to be made of a “hard metal” that has greater mechanical strength than the material being processed.

  In particular, in the drawing process of the present invention, a plurality of passages are provided in order to obtain a tube having a desired thickness, and the thickness can be reduced by about 20% in each passage. The drawing speed depends on the thickness of the material. For example, when the initial thickness is 5 mm to 1.75 mm, the drawing speed may be moderate, and the drawing speed is decreased.

  The pulling described so far uses a mandrel, but other pulling techniques such as bar pulling and cold pilger rolling are not excluded.

  It is preferable to continue the heat treatment by passing through the furnace after passing through the drawing device. Otherwise, you have the risk of breaking the material. The heat treatment is called normalization, and it is necessary to once reduce the thickness of the tube (less than 2 mm for a tube having a diameter of about 5 cm).

  Prior to entering the furnace, the material is cleaned to remove any lubrication residues. Cleaning with surfactant and carbonate is performed by immersing the material in a bath containing the solution.

  Normalizing is normally performed at 950 ° C. to 1150 ° C. for 10 minutes or more and less than 1 hour.

  The material is pulled out, cleaned, normalized by heat treatment in a furnace, and the chemical preparation of the surface is performed separately until the desired thickness is obtained.

  Once the desired thickness of the tube is obtained, the material is subjected to a finishing heat treatment step that imparts mechanical properties (mechanical strength, yield strength, and elongation).

  By adjusting the temperature and processing time defined as a function of both the finished tube shape and the final mechanical and desired microstructural properties, the annealing and heat treatment of the finish and strain are controlled in a controlled atmosphere. Opening occurs. The annealing is performed at 950 ° C. to 1150 ° C. for 10 minutes or more and less than 1 hour. It should be noted that for pipes with a thickness of 2 mm or more, the processing time needs to be longer than for thinner ones.

  In the final normalizing process, a cooling method is important for producing a high-quality product. The heat treatment method is significantly different from the conventional heat treatment in which cooling is performed by immersing in oil in a conventional chamber or muffle furnace. In order to cool the steel faster, incandescent steel (900 ° C.) is now immersed in room temperature oil. The heat exchange capacity of the oil is very high (the oil does not evaporate at 900 ° C.) and can therefore be rapidly cooled. However, in this case, the surface of the tube comes into contact with the oil, where “contamination” occurs that causes oxidation, and therefore a tempering heat treatment is required. However, tempering cannot be applied to thin tubes (less than 1 mm) because it irreversibly deforms.

  In the production system of the present invention, after the heat treatment, it is preferable to perform a rapid cooling process in which the atmosphere around the tube is controlled (specifically, the tube is not in contact with the cooling water) and forcibly cooled, Further, a slow cooling step for returning the tube to room temperature is performed.

  In particular, it is preferable to use a cooled and controlled atmosphere, for example, a cooling water jacket or piping may be placed inside the cooling area downstream of the furnace, in the vicinity of the pipe being processed. it can.

  With the prior art air cooling method, heat moves more slowly from the steel and cooling is slower. However, a sufficient cooling rate can be obtained by making the above improvements to the equipment. In this case, since processing is performed in a controlled atmosphere, the surface of the tube is not destroyed. It is important that the tube be processed in 30 seconds to 2 minutes, preferably about 1 minute, with the temperature dropping rapidly from about 920 ° C. (furnace outlet temperature) to about 450 ° C.

  Furthermore, heating the material can give the steel a specific starting structure related to the desired end product.

  Furthermore, uniformity can be ensured by the processing time. That is, the steel is uniform and has the same structure throughout its entire volume.

  Finally, specific structures and further mechanical properties can be obtained by cooling. That is, different structures can be obtained by changing the cooling rate.

  Here, the manufacturing system of the present invention includes a step of straightening the tube, and further includes a subsequent pickling step and / or a passivating step. In this process, the process produces dense chromium oxide rust on the tube surface, thereby imparting corrosion resistance. The method is the same as the conventional one, and includes acid treatment using an acid bath as in the above (pickling), followed by washing and soaking in a weak acid bath (eg diluted nitric acid). Mobilize.

  Here, the tube is subjected to a cutting process, cut to a desired length according to the needs of the structure, packaged for storage, and sold. The cutting can also be performed before the pickling and passivating steps.

  The production system of the present invention performs all the previous steps under a controlled atmosphere in order to prevent oxygen from coming into contact with the tube surface. This is because the oxidation reaction is very active at high temperatures and is easily amplified.

  Once the manufacture of the tube using the system of the present invention has been completed, it is necessary to combine two or more members to produce a frame as shown in FIG. As shown in Fig. 1, welding is performed using advanced craftsmanship techniques.

  As described above, the present invention can achieve the object.

  In fact, the tubular structure manufacturing system of the present invention makes it possible to manufacture tubes with excellent mechanical properties and excellent quality and safety standards, thereby not only being subjected to dynamic pressure, Mechanical parts can be manufactured that can be used in harsh conditions where high strength is required, such as space, aeronautics, nuclear, chemistry, sea, motor sports, and cycling.

Furthermore, by the tubular structure manufacturing system of the present invention,
It is possible to improve the quality of the structure, in that the finished drawn tube not only retains the martensitic steel crystal structure, but also improves the fine and uniform structure shown in FIG. This is clear from the normalization in a controlled atmosphere, which ensures structural properties, in particular the mechanical strength of the final product is the starting material and conventional heat treatment, where the conventional heat treatment is oil or It is performed in water and requires tempering, but that tempering is not applicable to thin tubes and is superior to any of the materials that have been subjected to, allowing for external and internal surface finish of the tube, 11, which is superior to a tube heat-treated by a conventional method, in which two stainless steel tubes of the same type are compared, one treated with oil and the other Is treated with air using the system of the present invention, the first one is deformed and slightly opaque, while the second one retains its original shape and has perfect gloss ,
Size and shape characteristics can be maintained,
It becomes possible to reduce waste and waste associated with processing, which can solve problems that cannot be avoided with conventional and current heat treatments, such as discarding molded products due to deformation and cracking, Further, the necessity of tempering / strain removal as a finishing treatment, the necessity of an internal / external surface treatment for finishing to remove inevitable dirt due to heat and oxidation as shown in FIG. 11, and the surface treatment , Which can solve the need for chemical satin finish and chemical treatment with acid,
It is possible to reduce the negative impact on the environment, which can reduce all the environmental impacts of the manufacturing process because of the disposal of oil used in conventional heat treatment and satin finish This is because there are no problems related to the disposal of the acid substances necessary for the process, which are stabilized by excellent stainless steel properties, and finally those problems are obsolete by the quality of the final product obtained by performing a mild passivation process. It becomes a problem.

  In addition to the explanation so far, according to the manufacturing system of the present invention, it is possible to reduce adverse effects related to the paint. Moreover, material recovery and recyclability are greatly improved compared to conventional steel.

  Beneficially, the system of the present invention can retain excellent welding properties (shown in FIGS. 3, 4, 5, 6 and 7), and by using materials of a specific chemical composition. Excellent welding characteristics are obtained, and no microcracks are generated during welding as shown in FIG. FIG. 5 is an enlarged photograph of the HAZ (thermally modified region) that surrounds the weld line, where it is clearly recognized that the martensitic transformation is very limited, while the martensitic structure is retained in this region. It can be seen that the second “mixed” structure region is formed by heat during welding. The weld line is clear and no defects are observed.

  Since there is no microcrack, the structure subjected to excessive pressure in the traction test is not cracked at the welded portion, as shown in FIG. ) Explain that it is broken.

  Usually, the cracked part is a welded part (or its vicinity). That is, the material becomes very fragile due to the generation of microcracks, thereby forming a fragile portion.

  In order to solve this problem and to make the vicinity of the weld itself safer, a method of changing the thickness along the pipe is usually adopted, and the thickness of these parts is increased or reinforced. A member is provided.

  On the other hand, according to the welding quality obtained with the pipe described here, the processing process can be simplified, and a new molding method that changes the thickness of the pipe based on a new standard can be used. Opportunities can also be provided. The method aims to improve the shape stability of the frame while reducing weight, and imparts different levels of desired stiffness to different parts of the integrally assembled members.

  To demonstrate the improved mechanical properties of products obtained using the production system of the present invention, a comparison between the best steel types currently on the market and products produced using the system of the present invention went. The results obtained are shown in the following table.

General features:
It has a high elastic modulus of 211,000 MPa, which is twice that of a titanium tube and three times that of aluminum, making it possible to produce a very lightweight frame with high rigidity.

  It has a good expansion coefficient, 20 ÷ 100 ° C. ≦ 0.00001 mm in the field, and the structure has excellent shape stability and dimensional stability during its lifetime.

  Beneficially, the steel obtained by the system of the present invention is stainless steel and can be welded even at a rather thin thickness. This is because the steel in the weld zone and the steel surrounding the weld zone have the same mechanical properties as the other parts of the structure by being heated during welding and then rapidly cooled.

  In addition to the above points, steel manufactured using the manufacturing system of the present invention can be processed using existing equipment, tools, and known techniques, thus significantly reducing the manufacturing cost of the tubular structure. Can do.

  Beneficially, by using the system of the present invention, many of the environmental impacts involved throughout the product life cycle can be avoided. In the manufacturing process, the system can reduce the process, and as a result, can reduce the consumption of toxic and harmful substances that have occurred in the prior art, and has excellent durability with respect to product life And safety standards can be improved, and the amount of chemicals required for maintenance can be reduced. At the disposal stage, it can be recycled without degrading the properties of the raw materials (mild steel). As happening instead in recycling).

  In addition to what has been described so far, the system of the present invention can be used for many applications and enables a clearly innovative and reliable production, where the annular member is made of billet extruded material. If manufactured, welding is not necessary, and it is by cold drawing. Furthermore, since the annular member has both the excellent technical characteristics of martensitic steel and the excellent welding characteristics of austenitic steel, it can be suitably welded to known TIG and MIG. There is no need for complex methods required to obtain high strength and sealing properties.

  In particular, as is apparent from the above description, the obtained annular member has a high strength (1.000 ÷ 1.300 MPa), a high elastic modulus (211,000 MPa, twice the titanium tube and three times the aluminum tube). In addition to its excellent dimensional stability (20 ÷ 100 ° C-0.0001mm), it has excellent shape stability during use, and it is resistant to wear and wear over long periods of time. Can be easily processed into various shapes and thicknesses and has an excellent finished surface.

  As a great advantage of the present invention, the steel pipe of the present invention is very practical, easy to manufacture, and has excellent functions.

  Naturally, many variations and modifications can be made to the present invention, and these are included in the scope of the characteristic concept of the present invention.

It is a microscope enlarged photograph (100 time) of a metal structure after processing using the manufacturing system of the present invention. It is a microscope enlarged photograph (200 times) of a metal structure after processing using the manufacturing system and broaching of this invention. It is a microscope enlarged photograph which shows two different metal structures after welding in the junction part of two pipes. It is another microscope enlarged photograph which shows the metal structure after welding (100 times). It is a microscope enlarged photograph (50 times) which shows the welding part on the metal obtained using the system of this invention. Shows broken tube after traction test. It is a microscope picture of a welding part. The joining by welding of the pipe | tube obtained with the manufacturing system of this invention is shown. The flame | frame manufactured with the pipe | tube obtained with the manufacturing system of this invention is shown. Fig. 6 shows a cross section of the weld for metal analysis in Fig. 5. A comparison is made between the surface appearance of a conventional tube after oil heat treatment and a tube made of the same material and treated with the system of the present invention.

Claims (27)

A manufacturing system for a stainless steel tubular structure having high strength and being weldable,
An annealing heat treatment process for the martensitic steel or austenitic-martensitic steel preform;
A chemical preparation process of the surface to smooth the contact surface between the tube and the drawing device;
An annular structure manufacturing system in which at least one drawing-passing step for permanently deforming a material is continuously performed.   The system for manufacturing an annular structure according to claim 1, further comprising a heat treatment step of finishing to modify the structure of the deformed steel and determine a desired final characteristic.   The manufacturing system of the annular structure according to claim 1 or 2, wherein the drawing passage is performed at least twice until a predetermined thickness is reached.   4. The manufacturing system for an annular structure according to claim 1, 2, or 3, wherein the thickness is reduced by about 20% in each drawing pass.   The annular structure manufacturing system according to any one of claims 1 to 4, wherein the annular structure is subjected to normalization prior to the at least one pull-out pass.   6. The system for manufacturing an annular structure according to claim 5, wherein the normalizing is performed in a temperature range of 950 ° C. to 1150 ° C. for more than 10 minutes and preferably less than 1 hour.   The annealing process of the martensitic steel or austenite-martensitic steel preform has an initial process of heating from room temperature to the annealing temperature, a process at the annealing temperature, and a cooling process. The manufacturing system of the annular structure according to any one of claims 1 to 6, wherein the temperature treatment step is performed at a temperature selected from a temperature range of 600 ° C to 750 ° C, preferably 650 ° C to 700 ° C. .   The annular structure manufacturing system according to claim 7, wherein the annealing temperature is about 680 ° C.   9. The system for manufacturing an annular structure according to claim 7 or 8, wherein the time of the step of treating at the annealing temperature is extended to at least 40 minutes, preferably at least 1 hour, more preferably less than 3 hours.   The system for manufacturing an annular structure according to claim 9, wherein the step of treating at the annealing temperature is extended to about 1 hour and 20 minutes.   The manufacturing system of the annular structure according to any one of claims 8 to 10, wherein the step of heating from the room temperature to the annealing temperature is performed in one hour or less.   The manufacturing system of the annular structure according to any one of claims 8 to 11, wherein the cooling step is performed within a range of 2 to 4 hours.   In the above surface chemical preparation step, the annular structure is immersed in the first tube containing acid for a predetermined time, preferably about 40 minutes, rinsed in the water of the second tube, followed by oxalate. 13. Soak in a bath of water for a predetermined time, preferably about 20 minutes, and finally soak in stearic acid ester, preferably 3% by weight, to smooth the outer surface of the annular structure. The manufacturing system of the cyclic structure as described in any one. In the above acid treatment, 56% nitric acid is 140 kg / m ³ and 38-40% hydrofluoric acid is 40 kg / m ^{3. In} the above oxalate treatment, the concentration of oxalate is generally The system for manufacturing an annular structure according to claim 13, wherein the range is 8 to 16 wt%.   The manufacturing system of the annular structure according to any one of claims 2 to 14, wherein the finishing heat treatment step is performed in a temperature range of 950 ° C to 1150 ° C and longer than 10 minutes and less than 1 hour.   The ring structure manufacturing system according to claim 15, further comprising a rapid cooling step and a subsequent slow cooling step after the finishing heat treatment step.   The manufacturing system for an annular structure according to claim 16, wherein in the rapid cooling step, the annular structure is brought into contact with a cooled and controlled gas atmosphere.   17. In the quenching step, the temperature of the annular structure is decreased from about 920 ° C. (furnace outlet temperature) to about 450 ° C. within a time range of 30 seconds to 2 minutes, preferably about 1 minute. Or the manufacturing system of the cyclic | annular structure of 17.   The manufacturing system for an annular structure according to any one of claims 2 to 18, wherein the annular structure is subjected to a cleaning operation in order to remove a lubricating residue prior to the finishing heat treatment step.   The manufacturing system of the annular structure according to claim 19, wherein the washing step is immersed in a solution containing a surfactant and a carbonate.   The above heat treatment of annealing, normalizing, and finishing heat treatment is performed in a furnace having a controlled atmosphere so that internal and external alteration of the material does not occur and to prevent oxidation and decarbonization. The manufacturing system of the annular structure according to any one of claims 1 to 20.   22. The controlled atmosphere is a mixture of about 50% nitrogen and about 50% reducing gas, which is preferably a hydrogen-containing gas obtained from steam reforming or the like. An annular structure manufacturing system.   23. The preform according to any one of claims 1 to 22, wherein the preform is a blank tube produced by thermal processing, preferably extrusion, of a billet or other source of martensitic steel or austenitic martensitic steel. Manufacturing system for annular structures.   The manufacturing system of the annular structure according to any one of claims 1 to 23, wherein the annular structure is subjected to a pickling treatment and / or a passivation treatment after the finishing heat treatment step.   An annular structure made of martensitic steel or austenitic martensitic steel obtained by the method according to any one of claims 1 to 24 and capable of being welded and having high mechanical strength.   The annular structure according to claim 25, wherein the steel is X4Cr-Ni-Mo 16-5-1. 27. An annular structure according to claim 25 or 26, wherein the steel has a tensile strength of> 1100 N / mm < ² >.

Images