Hot extrusion is generally carried out for boiler seamless pipe billet, called a composite extrusion. Composite extrusion is currently the best method for producing stainless steel and high nickel alloy seamless tube boilers. It is a large-diameter composite consisting of two or more metal blank is heated to about 1200 ℃, and then extruded through an annular space formed by the mold and the mandrel. When extrusion billet cross-section is reduced to 10:1, high extrusion pressure and temperature at the interface produced “pressure welding” welding effect, promote the rapid and widespread diffusion of the interface between the combination to achieve metallurgical bonding interface.
Before extrusion composite tube manufacturing method, there are three: the forging billet piercing and enlarged by hot extrusion obtained; direct centrifugal spin casting; corrosion resistant powder particles. There are two metal raw materials are used inside and outside the powder, called “NUVAL” technology, can develop new alloys, but the cost is too high for preparing powder. The coextruded seamless boiler disadvantages are:
① Advantages: The interface is metallurgically bonded; forces involved in the extrusion process is completely stress, it is particularly well suited to the hot workability, high alloy processing low plasticity of metals.
② Disadvantages: As determined by a combination boiler seamless extrusion process elements in a very short time interface diffusion, usually due to the presence of oxide films have been affected, so far limited to the extruded composite carbon steel, stainless steel and high nickel between the composite alloy. It is noted that a small deformation resistance of the hot extrusion, allowing a large degree of deformation of each, resulting in higher surface roughness, and therefore also be further cold rolling the hot extrusion (or drawing) of the method of manufacturing a composite pipe.
Post time: Sep-18-2019