Production process of nickel-based alloy pipe

The nuclear steam generator heat transfer tubes are seamless tubes. Because the seamless tubes are integrally formed and have no welded joints, their pressure resistance and corrosion resistance are much better than welded tubes and become the preferred pipe for pressure pipes. Generally speaking, the seamless pipe referred to is a seamless steel pipe such as a low-alloy steel pipe or a non-ferrous metal pipe, and basically adopts a production method of a hot-rolled seamless steel pipe. The basic deformation process of the method can be summarized into three stages: Perforation, extension and finish rolling. The main purpose of the perforation process is to perforate the solid round billet into a hollow capillary tube. It is impossible for the capillary to meet the requirements of the finished product in terms of specifications, precision and surface quality, and further improvement by metal deformation is required. The main purpose of the extender is to further reduce the cross-section to achieve greater axial extension, resulting in improved capillary accuracy, surface quality and tissue properties. The steel pipe rolled by the extension machine is collectively referred to as a waste pipe, and needs to be further formed on the finishing mill to meet the requirements of the finished pipe.
Unlike high-temperature alloy tubes, high-temperature alloy seamless tubes have a high degree of alloying, which brings a series of difficulties to processing, making it more difficult to make seamless steel tubes. Due to the narrow temperature range and poor thermoplasticity, the tube blanks are prone to cracks or even breaks during hot perforation, which directly causes the feasibility of hot perforation to produce high-temperature alloy seamless tubes. Production practices have also shown that the production of high-temperature alloy tubes using the above-mentioned hot-rolled seamless steel tubes does not substantially meet the performance requirements of the tubes. Through scientific research and production, scientists and engineers from all over the world have mastered the hot processing characteristics of high-temperature alloys and the influence laws of various process parameters, and combined with the production experience of seamless steel tubes, proposed drilling/reaming and then hot extrusion. The method of producing waste pipe, and then through the multi-pass cold rolling / cold drawing combined with the intermediate heat treatment process mode to produce superalloy seamless pipe, achieved good results. The tube blank is drilled and reamed to obtain the capillary tube, and then hot extruded to produce the waste tube. The forming function is equivalent to the perforation function and part of the extension function in the production of the hot-rolled seamless steel tube, and the multi-stand cold rolling There is a role in continuing to stretch molding.
For the nickel-based corrosion-resistant alloy seamless pipe, it is difficult to obtain a good production effect, firstly because the nickel-based alloy has a high degree of alloying and a slow heat transfer, which results in uneven temperature distribution of induction heating during reaming; Secondly, the deformable temperature of the nickel-based alloy is very narrow, which requires that the extrusion of the waste pipe should be carried out at high temperature and high speed, and the high-speed extrusion will lead to an increase in the unevenness of the performance of the product, which is likely to cause a large number of defects; The hardness of the alloy is relatively large, the resistance during processing is very large, the requirements for the extrusion die are high, and at the same time, the energy consumption is large. All of these have determined that the production of nickel-base superalloy seamless pipes has many unique characteristics, and it is necessary to have corresponding process specifications to achieve controllable production of pipe quality.

The production of superalloy seamless pipes generally includes the following steps: tube-drilling-induction heating-reaming-induction heating-hot extrusion-solid solution-cold nipple cold drawing-heat treatment-cold rolling 〆cold drawing-heat treatment- Quality Inspection. At present, Baosteel, Panzhihua Steel and Taigang in China use this process model to produce and produce 690 alloy heat transfer tube straight pipe. The results of large-scale trial production and preliminary research show that the process that has a greater impact on the quality of the finished pipe is induction. Heating, reaming, hot extrusion, cold rolling (pulling) and heat treatment are described below.