(1) Increasing the level and the use of continuous casting of stainless steel smelting tube present, continuous casting of steel has basically adopted, vertical and curved continuous casting machine in the main. Stainless steel billet and the traditional ingot – Bloom compared to good quality slab, a direct rolling, the metal recovery rate increased by 10% to 15%, saving energy and reducing production costs. Some of stainless steel in the casting process easily oxidized alloying elements, easy to produce oxide inclusions; In addition, the viscosity of molten steel can easily lead to nozzle clogging. As more complex forms of solidification of stainless steel, poor thermal conductivity of molten steel, billet easy to crack, so the casting slab speed of cooling and more stringent requirements; In addition, the use of the tundish heating, no oxidation protection of casting, electromagnetic mixing and automatic control of liquid level and a series of new technologies, thus making greatly improved the quality of billet. Casting of steel is difficult for some species, such as titanium stainless steel, single-phase austenitic stainless steel and martensitic stainless steel casting can be successfully expanded the range of stainless steel billet.
(2) The production of stainless steel seamless tube extrusion process used mainly as production technology, although some units can produce hot-rolled stainless steel tube, but the extrusion unit is the world’s production of stainless steel seamless pipe main unit. 60 sets available in the world extrusion unit, except for a few for extrusion, 70% of the units for the production of steel, the main varieties of stainless steel tube. And rolling (longitudinal rolling and cross rolling) production method, characterized by extrusion of metal deformation process under the three-compression stress.
In this best stress state, for the steel and more resistance to deformation large stainless steel tube, can get better deformation, internal and external surface quality and microstructure. Vertical hydraulic equipment, piercing process improvement, the shortage can extrusion wall thickness deviation of accuracy of 5% to 7%. Extrusion die mechanic is simple, easy to manufacture and replacement, suitable for small-volume, multi-standard stainless steel production. Extrusion unit can also produce a wide range of pipe size, 1 set of 50MN (5000t) in the extrusion unit produces specifications for the 25 ~ 245mm steel pipe, meet the market demand is far higher than other pipe mill. Production of stainless steel by squeeze the maximum benefit can be used directly as a slab of raw materials, product quality, variety replacement of flexible, direct production of finished tube extrusion, but also can produce all kinds of profiled stainless steel tube. However, the disadvantage of extrusion is the production rate of finished steel is low. In order to improve the finished product rate, foreign manufacturers to improve the production process.
High demand for the varieties commonly used pre-drilling, reaming hydraulic punch and squeeze into the pipe production process. Raw materials for the general requirements of the cold tube can be different depending on the circumstances of the production process: small size directly from solid billet steel vertical hydraulic punch a hole and squeeze into a tube; medium size steel billet used in pre-drilled holes as far as possible, legislation Hydraulic punching machine reaming and squeeze into a tube; large size steel billet used in the larger pre-drilled hole, directly into the extruder into a tube.
Clearly, the use of extrusion for the production of cold finished tubes and pipes to provide waste material, thermal processing abroad is widely used stainless steel tube as a more economical production methods. With high-speed, automation, extrusion machine with large tonnage, and the glass lubricants, non-oxidative heating, high strength and toughness of hot die, and other related technologies, with the production of stainless steel seamless pipe hot extrusion method, in particular, deformation of the stainless steel production is difficult, high-alloy steel pipe has been developing rapidly. The use of a single two-roll piercing cold to provide for the shortage of pipe materials, production methods, foreign countries have basically no longer used.
Cold rolled stainless steel tube with the main production process of cold drawing, supplemented by 50% to 80% of the stainless steel finished products need to cold. Therefore, the cold working process equipment has been greatly developed. There are basically three kinds of cold working process, that is drawing process, cold process, cold – cold drawing combined process. Most foreign countries use stainless steel pipe cold rolled – Cold-drawn combination process, and cold-based, supplemented by drawing process. Modern cold rolling mill can be greatly reduced to achieve the wall stainless steel pipe diameter capacity and greatly reduced the amount of deformation of 80% can be completed in the cold rolling mill.
Determined using cold wall, supplemented by drawing specifications and control changes in pipe diameter, different sizes and varieties to meet production requirements. Cold – cold drawing process has the advantage of joint production: good quality steel pipe, cold rolled steel pipe wall thickness accuracy and surface quality high, high precision cold drawn steel pipe diameter; cold period is short, reducing the fat middle, heat treatment, necking, straightening processes and metal consumption and save energy; shortage of large size can be used to produce small size steel pipe material, simplified types of raw material specifications. Currently, the world’s cold-rolled and cold-drawn process technology and equipment level has been greatly developed.
Cold rolling mill forward speed, long travel, ring pass, high-precision direction. The rolling machine of the features are as follows.The vertical inertia force and inertia torque balance of body, rolling machine and from the increased frequency. By loop hole, rolling the length of the block captain than the rolling short stroke 70% rolling improve the uniformity, increased feeding. Using a long tube, pipe shortage of raw materials can increase the length of 12 ~ 15m, improve the utilization of rolling machine, rolling over the efficient utilization coefficient of 0.80. Using curved mandrel and the best parabolic groove, metal deformation and reasonable to raise the tool and die life.
These characteristics, so that the production capacity of cold rolling mill products and the dimensional accuracy greatly improved. Production of stainless steel tube drawing tube machine structural drawing of the machine is still the main chain, there are a few hydraulic drawing tube machine. Multi-line, high-speed, automatic is a drawing of the machine development. There are also warm rolling technology, it is the former cold-rolled stainless steel tubing through a heating device to heat induction to 150 ~ 400 and then the rolling. Warm rolling technology has the rolling force is small, the advantages of a large deformation of 0Cr18Ni9Ti stainless steel tubes 2 to 3 times warm rolling, without the need for intermediate annealing, the total deformation of up to 98%.