Thermal forming manufacturing process is including large-diameter seamless
hot-rolled and hot extrusion of two ways, the former is mainly used to produce composite pipe joints, which applies seamless composite pipe production.
Rolling is a traditional method of preparing
large-diameter seamless steel pipe. Hot rolling the composite is substantially below the pressure welding, if the deformation is large enough, the pressure exerted by the roll of metal would damage the surface of the oxide film, the atomic contact with the surface, so that the two surfaces are welded together. The advantages and disadvantages of the rolling were as follows:
① Advantages: high productivity, good quality, low cost, and can save a lot of loss of metallic materials, and therefore is extremely wide application of composite materials production technology. Roll bonding composite sheet, 90% of the total composite plate, and is often applied to the pipe wall thickness of less than 32mm of the processing.
② Disadvantages: one-time investment, but also a lot of material combinations can not be achieved by rolling complex. Currently the most widely used is the use of rolling processes carbon steel, stainless steel composite pipe joints manufacturing.
Hot extrusion is generally carried out for the double metal tube, called a composite extrusion (coextrude). Composite extrusion is currently the best way to produce stainless steel and high nickel alloy seamless composite pipe, the method of manufacturing a composite tube before squeezing in three ways: by forging billet piercing and amplification by thermal extrusion obtain; direct centrifugal spin casting; with corrosion resistant powder particles. There are two metal raw materials are used inside and outside the powder, called "NUVAL" technology, can develop new alloy, but the preparation of the powder is too costly. Coextrusion 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: Due to the combination depends on the extrusion process elements in a very short time interface diffusion, usually due to the presence of the oxide film is affected, there is currently limited to the composite extrusion composite carbon steel, stainless steel and high nickel alloys between . It should be noted that a small deformation resistance of the hot extrusion, allowing a large degree of deformation of each, resulting in higher surface roughness, so there are then rolled to hot extrusion (or drawing) of the method of manufacturing a composite pipe.