China’s stainless steel pipe production after nearly 50 years of development, especially in the past 30 years, whether it is stainless steel seamless pipe or pipe production technology has made great progress, yield, quality and variety of increasing and improving the quality of a small number of products Reached the international advanced level: but compared with the international advanced level, China’s stainless steel pipe plant in the process technology, equipment level, product quality and so there is a big gap, the need for technological transformation and improvement to meet the national economic development Claim.
One: the world stainless steel pipe production technology development trend
2.1 “three-step” steelmaking and continuous casting process
The use of “three-step” steelmaking and continuous casting production of stainless steel tube blank process, in order to improve the quality of stainless steel tube, to reduce the cost to create the conditions. Some of the world’s major stainless steel plant in the “two-step” on the basis of research and use of the “three-step” smelting stainless steel new technology. At present, most of Japan’s professional stainless steel plants have adopted a “three-step” production process. MANNESSMAN METRO METRO TECHNOLOGIES has developed a process specifically designed for “three-step” technology, which includes an ultra-high-power electric furnace, a MRP-L converter and a VOD unit. The process uses electric furnace melting, MRP-L converter oxygen gun rapid decarburization, VOD vacuum furnace final deep decarburization. The basic starting point of this process is the combination of the advantages of the two processes of AOD and VOD, and overcomes the shortcomings of AOD’s argon and refractory materials and the long processing time to achieve low consumption, shorten the time and reduce costs purpose. Of course, EAF AOD “two-step” smelting stainless steel is also feasible, the current world more than 60% of stainless steel is “two-step” process production. Foreign stainless steel tube has been basically continuous casting caster to vertical and arc-based, but also the use of horizontal caster. Stainless steel continuous casting billet Compared with the traditional ingot-billet, the metal yield increased by 10% ~ 15%, the quality of the tube is better, and the energy saving and the production cost are reduced. Stainless steel in the process of continuous casting some of the alloy elements easily oxidized, easy to produce oxide inclusions; In addition, the viscosity of molten steel, it is easy to cause nozzle clogging. As the solidification of stainless steel is more complex, the thermal conductivity of molten steel is poor, the slab is easy to produce cracks, so the cooling and drawing speed requirements are more stringent, take the tundish heating, no oxidation protection casting, electromagnetic stirring, liquid level control And a series of new technologies, so that greatly improve the quality of slab, so that some difficult to cast steel, such as titanium, stainless steel, single-phase austenitic stainless steel and martensitic stainless steel can be successfully cast, expanded stainless steel continuous casting of steel Species.
2.2 hot extrusion process
Hot extrusion process is the world’s current hot-processing stainless steel seamless pipe of the main production process. With the development of technology, some types of hot-rolled stainless steel pipe units can produce stainless steel pipe, but the extrusion unit is the world’s main production unit of stainless steel seamless pipe. At present, the world has more than 60 sets of extrusion units, with the exception of a few for the profile extrusion, 70% of the units used in the production of stainless steel, the main varieties are stainless steel tube. Extrusion and rolling (vertical rolling, inclined rolling) production method compared to the extrusion method is characterized by metal deformation process to withstand three-way compressive stress. In this optimum stress state, the stainless steel tube with large deformation resistance can obtain better inner and outer surface quality and microstructure. Due to the improvement of the vertical hydraulic perforation process equipment, the thickness of the wall after the extrusion can be 5% to 7%. Extrusion machine tool and die easy to manufacture and replace, suitable for the production of small quantities, multi-standard stainless steel tube. Extrusion unit can also produce a wide range of stainless steel tube, a set of 50MN extrusion unit can produce @ 25-254mm stainless steel tube, the market demand is much higher than other rolling methods. The use of extrusion method to produce stainless steel tube has the outstanding advantages of direct use of continuous casting billet as raw materials, product quality and stability, the replacement of flexible varieties, can directly produce hot extrusion finished product tube, can also produce all kinds of profiled stainless steel tube. It is clear that the production of finished pipes by extrusion and the provision of wastes for cold work are a more economical method widely used in the production of hot-worked stainless steel tubes abroad, with the adoption of high-speed, automated, large tonnage extruders, and Glass lubricants, no oxidation heating, high strength and high toughness hot molds and other related technologies, the use of hot extrusion production of stainless steel seamless stainless steel tube, in particular the production of difficult to deformation of stainless steel, high alloy stainless steel pipe has been rapid development of. With a single two-roll inclined rolling for the cold processing to provide the method of waste pipe material, foreign has been basically not used.
2.3 cold-processing to cold-based, cold drawn for the auxiliary
Cold-processed stainless steel pipe tends to adopt cold-rolled, cold-drawn auxiliary production technology, cold rolling mill, cold drawing machine to high-speed, high precision, long stroke, multi-line direction. 50% to 80% of stainless steel pipe is finished by cold processing. Therefore, the development of cold processing technology equipment to give more attention. Cold processing technology basically three, namely cold drawing process, cold rolling process, cold rolling a cold drawing joint process. Stainless steel tube cold processing Most of the use of cold-rolled cold-drawn joint process, and cold-based, cold drawn auxiliary processing methods. Modern cold rolling mill can achieve large diameter reduction and large reduction in the amount of rolling deformation of 80% in the cold rolling mill to complete. Using cold-rolled fixed wall, supplemented by cold-drawn to change the specifications and control the outer diameter, to meet the requirements of different varieties and specifications. The advantages of stainless steel tube are good quality, cold-rolled stainless steel pipe wall thickness and surface quality is high, Mouth, straightening and other processes, saving energy and reducing metal consumption; can be used to produce large-scale production of small diameter stainless steel tube, to simplify the type of raw materials specifications. At present, the world cold rolling, cold drawing technology and equipment level has been greatly developed. Cold rolling mill is high-speed, long stroke, ring larvae L-type, high-precision direction of development, this mill is characterized by: ① inertial force and inertia torque vertical balance mechanism, rolling mill rounds increased; The length of the rolling deformation zone is 70% longer than that of the short stroke mill, and the uniformity of the rolling deformation is increased and the feed volume is increased. ⑧ The length of the raw material of the long pipe can be increased to 12 ~ 15m, Utilization rate, rolling effective utilization factor of up to 80% or more; ④ using curved core rod and the best parabolic hole type, metal deformation is reasonable, long life and long mold characteristics of the cold rolling mill production capacity and product precision greatly improve the production of stainless steel Tube cold drawn tube machine structure is still based on chain cold drawing machine, there are a small number of hydraulic machine. Multi-line, high-speed, fully automatic development of the current cold-drawn machine direction.
2.4 a variety of welding technology
The progress of welding technology has accelerated the development of stainless steel pipe production, and the application of various welding methods has further improved the welding quality and productivity. At present, the industrial application of stainless steel welding methods are TIG (TIG), high frequency welding, plasma welding and laser welding. Several welding methods have their own characteristics, the most is the use of argon arc welding and high frequency welding:
2.4.1 TIG welding
Stainless steel welded pipe requirements penetration penetration, no oxide inclusions, heat affected area as small as possible, tungsten inert gas protection of the TIG welding has good adaptability, high welding quality, good penetration performance, its products in the chemical , Nuclear industry and food and other industrial areas have been widely used welding speed is not high is the shortcomings of argon arc welding, in order to improve the welding speed, foreign research and development of a variety of methods. Among them, the single electrode single torch to the development of multi-electrode multi-torch, the welding method has been applied in the production. In the 1970s, Germany first used a multi-torch torch along the weld direction to form a long heat flow distribution, the welding speed increased significantly. General use of three electrode torch welding, welding stainless steel pipe wall thickness s ≥ 2ram, welding speed than the single torch to improve 3 to 4 times the welding quality has also been improved. TIG welding and plasma welding can be welded to a larger wall thickness of stainless steel tube. In addition, the use of argon in the use of 5% to 10% of the hydrogen, and then use high-frequency pulse welding power, but also improve the welding speed. Multi-torch welding is suitable for the welding of austenitic and ferritic stainless steel tubes.
2.4.2 high frequency welding
High-frequency welding for carbon steel pipe production has been 50 years of history, but for welding stainless steel pipe is indeed a newer technology. Its production economy, so that its products more widely used in architectural decoration, household appliances and mechanical structure and other fields. High-frequency welding with a large power supply, the different materials, caliber and wall thickness of the stainless steel pipe can achieve a higher welding speed (higher than the maximum welding speed of welding more than l0 times). Therefore, the high-frequency welding production of general-purpose stainless steel pipe with high productivity because of high-frequency welding speed, to the pipe to remove the burrs difficult, which is currently high-frequency welded stainless steel tube is not for chemical, nuclear industry accepted One of the reasons. From the welding material, high-frequency welding can be welded all kinds of austenitic stainless steel tube. At the same time, the development of new steel and the progress of forming welding methods, ferritic stainless steel AISI 409 and other steel can also be successfully welded.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)