Stainless steel seamless pipe production methods mainly include hot extrusion, hot rolling and cold working processes.
(1) Hot extrusion process
The hot extrusion process is the main production process of foreign hot-processed stainless steel seamless pipes. Compared with the rolling (rolling, cross-rolling) production method, the extrusion method is characterized by the fact that the metal is subjected to three-direction compressive stress during the deformation process. In this optimum state, a good internal and external surface quality and metallographic structure can be obtained for a stainless steel tube having a large deformation resistance and a poor thermoplasticity.
Due to the improvement of the vertical hydraulic perforation process equipment, the wall thickness accuracy of the waste pipe after extrusion can reach 5% to 7%. Extrusion molds are easy to manufacture and replace. They are suitable for the production of small-volume, multi-size stainless steel pipes, especially high-alloy steels that are difficult to process in the production of cross-rolling punches.
(2) Hot rolling process
In China, stainless steel tube blank perforation is generally used in two-roller cross-rolling punching machine. Not only commonly used austenitic stainless steels, but also difficult-to-deformed duplex stainless steels and superalloys can also be produced in batches on two-roll cross-rolling punching machines. If a two-roller conical roller perforator is used, the steel can be produced.
The surface defects of the capillary, especially the inner surface defects such as inner folds and internal cracks, and the thickness of the produced capillary are thinner. The machine (longitudinal rolling, cross-rolling) can thin the pipe wall, thereby reducing the cold drawing (rolling) pass, improving the productivity and the finished product rate, and significantly increasing the economic efficiency.
(3) Cold working process
50%~80% of stainless steel is produced by cold working out the finished pipe. There are basically three types of cold working processes, namely cold drawing process, cold rolling process, and cold rolling-cold drawing combined process. Most of the cold-worked stainless steel pipes adopt the cold rolling-cold drawing combined production process, which is mainly based on cold rolling and cold drawing.
The advantages of cold rolling-cold drawing combined production process are: good quality of steel pipe, high precision of wall thickness of cold rolled steel pipe, good surface quality, cold drawing to ensure the outer diameter precision of steel pipe; short cold working cycle, reducing intermediate degreasing, heat treatment and shrinkage Processes such as mouth and straightening save energy and reduce metal consumption. Large-size waste pipes can be used to produce small-diameter steel pipes, simplifying the types of raw materials.
Cold rolling mills and cold drawing machines are developing in the direction of high speed, high precision, long stroke and multi-line. Modern cold rolling mills can achieve large reductions and large reductions, and 80% of rolling deformation is done on cold rolling mills. It adopts cold rolling and wall fixing, supplemented by cold drawing to change specifications and control outer diameter to meet the requirements of different varieties and specifications.