The advantages of the extrusion production process for stainless steel seamless pipes

Currently, the production of stainless steel mostly adopts continuous casting technology. The continuous casting machines are mainly of vertical and arc types. Compared with traditional steel ingots and rolled billets, the performance and quality of stainless steel continuous casting billets are better, with a metal yield increase of 10%-15%. This has a significant effect of cost reduction and efficiency improvement. At present, the mainstream process for manufacturing seamless stainless steel pipes is hot extrusion. While the hot rolling pipe production lines are gradually being phased out, the extrusion lines are becoming the main production lines for stainless steel seamless pipes worldwide. 

These extrusion machines, except for a few which are used for extruding profiles, are mostly employed for manufacturing steel pipes. The main type is stainless steel seamless pipes. Compared to the rolling process, the characteristic of the extrusion process is that during the metal deformation process, it will be subjected to compressive stress in three directions. Under this optimal stress condition, for stainless steel pipes with a large variety of models and high deformation resistance, satisfactory deformation, internal and external surface quality, and microstructure state can be achieved. 

The greatest advantage of manufacturing stainless steel pipes through the extrusion process is that it can directly use the continuous casting billets as raw materials. The quality of the stainless steel pipes is stable, and the replacement is flexible. It can directly produce hot extrusion finished stainless steel pipes, and can also be used to manufacture various special-shaped stainless steel pipes. However, the disadvantage of extrusion method for manufacturing stainless steel pipes is that the yield rate is relatively low. 

To increase the yield rate of stainless steel pipes, some production enterprises have optimized their production processes. For high-quality products, the production process usually involves pre-drilling, hydraulic drilling and expansion, and extrusion to form the pipes. For general cold-processed raw pipe materials, different production processes are adopted according to the actual situation. For example, small-sized stainless steel pipes directly use solid billets to be drilled and extruded on a vertical hydraulic drilling machine; medium-sized stainless steel pipes use pre-drilled small holes, a vertical hydraulic drilling machine for expansion, and extrusion to form the pipes; for large-sized steel pipes, the pre-drilled larger holes are used, and then they directly enter the extrusion machine for extrusion. It is obvious that using the extrusion method to produce finished pipes and providing raw pipe materials for cold processing are now a relatively economical and cost-effective production method widely adopted by foreign hot-processed stainless steel pipes. 

In addition, most cold-processed stainless steel pipes adopt a production process mainly consisting of cold rolling and supplemented by cold drawing. 50% to 80% of the stainless steel pipes need to be processed through cold working to become finished products. Therefore, the development of cold processing equipment has been significant. The cold processing techniques mainly include three types: cold drawing process, cold rolling process, and the combined cold rolling-cold drawing process. In foreign countries, the cold processing of stainless steel pipes mostly uses the combined cold drawing-cold drawing process, where cold drawing is the main method and cold drawing is the auxiliary method. 

The current cold rolling tube machine is capable of achieving significant reductions in wall thickness and diameter for stainless steel tubes. 80% of the deformation can be completed directly on the cold rolling tube machine. By using cold rolling for setting the wall thickness and combining it with cold drawing to change the tube specifications and control the outer diameter, production requirements for different specifications and varieties can be met. 

The advantages of this production process are that the quality of the finished stainless steel pipes is excellent, the wall thickness and surface quality of the pipes are high, the outer diameter accuracy of the cold-drawn steel pipes is high, the cold processing cycle is short, the intermediate processes such as degreasing, heat treatment, reduction, straightening, etc. are omitted, and the consumption of pipe materials is reduced, which effectively saves energy. Moreover, it can simplify the specifications of raw materials, thereby expanding the production scale.