1, The principle
The production method of the seamless steel pipe is roughly classified into a cross rolling method and an extrusion method.
There are two methods for cold working: one is cold drawing, which is to pull the steel pipe through the extruding die to make the steel pipe become thinner and longer; the other method is cold rolling, which is invented by the Mengnesmann brothers. The hot rolling mill is applied to the method in cold working. Cold working of seamless steel tubes can improve the dimensional accuracy and processing finish of steel pipes and improve the mechanical properties of materials.
2, The production method
Cold rolling sometimes has heating, but the temperature is relatively low, because work hardening occurs after cold rolling, and if the molding requirements for the material are relatively high, annealing is also required.Cold rolling and hot rolling are generally with sheets or profiles materials, while cold drawing is generally a cylindrical section of wire. In addition, the hot-rolled sheet is generally a steel with a high alloy content and high strength, while the cold-rolled steel is a low-carbon low-alloy steel, which can be used to improve the strength and ensure the surface quality of the material by cold rolling.
The difference between cold drawn seamless steel pipe and hot rolled seamless steel pipe is different from that of the plate. Seamless steel tubes are divided into hot-rolled (extruded) seamless steel tubes and cold drawn (rolled) seamless steel tubes due to their different manufacturing processes. Cold drawn (rolled) tubes are divided into two types: round tubes and shaped tubes: Cold drawn steel pipes generally need to be drawn multiple times, and there must be corresponding stress relief annealing between each drawing to ensure the next cold drawing smoothly.
From the outside, cold-rolled seamless steel pipes are often small-diameter, and hot-rolled seamless steel pipes are often large-diameter. The accuracy of cold-rolled seamless steel tubes is higher than that of hot-rolled seamless steel tubes, and the price is also higher than that of hot-rolled seamless steel tubes. Cold drawn seamless pipes generally have a small diameter, mostly below 108 mm, especially the precision of the outer diameter of the cold drawn seamless pipe is very high, and the length of the cold drawn seamless pipe is generally shorter than that of the hot rolled seamless pipe. The wall thickness is cold and the seamless pipe is evener than the hot rolled seamless pipe.
3, The performance
Hot rolling and cold drawing is the difference between the production process, hot rolling is processed at high temperature, which does not change the structural properties of the metal. While cold drawing is to pierce the round steel at high temperature, and then cold drawn on the pipe puller Processing, in the absence of tempering, such processing affects the crystal structure of the metal. In general, hot rolling has better mechanical properties than cold rolling. The heat-treated steel has improved tensile strength, yield strength, ductility and toughness. In addition, heat treatment can eliminate residual stress, while cold rolling may Because of the uneven deformation of the yielding of the steel during the machining process, residual stress is generated, which has a great influence on the stability.