The size of the stress in the workpiece martensite transformation zone is cooling rate, shape, chemical composition and other factors.
Large diameter steel pipe production process is generally a result of these processes: heating, piercing, bending, seam, weld inside and outside welding, straightening, flat top multi-channel processes, to achieve the American Petroleum Institute standards. Large diameter steel pipe used for large multi-building among the main supporting part to do, such as a bridge piling, underwater piling, piling high-rise buildings.
Large diameter steel pipe has good adhesion, corrosion resistance, which can be resistant to acid, alkali and other chemical corrosion, non-toxic, does not rust, abrasion resistance, impact resistance, permeability, smooth pipe surface will not adhere to any substance, can reduce the transmission of resistance, large diameter steel pipe to improve traffic and transportation efficiency, reduce delivery pressure loss. Coating solvent-free, no leaking substances, and thus will not contaminate the transmission medium, thus ensuring fluid purity and hygiene at -40 ℃ to +80 ℃ range can be used alternately hot and cold cycles, aging, no cracks, which can in cold areas such harsh environments.
Structural steel workpiece in the heating and cooling process, because of the central portion of the cooling surface and the speed and time of inconsistencies, the formation temperature, volume expansion and contraction can lead to uneven stress and the thermal stress. Under the effect of thermal stress, because the surface temperature is below the core part begins, shrinkage core portion by the central portion is greater than the tension, when the end of cooling, since the volume shrinkage of the cooling core section last leaving the surface pressure can not freely central portion tension. That is, in the final thermal stress under the action of the workpiece surface pressure while the heart of tension. This phenomenon is cooled rate, material composition and heat treatment process and other factors. When cooled, the faster, the higher the carbon content and the alloy composition, the cooling process under thermal stress generated in the non-uniform plastic deformation larger, the final form of the residual stress it gets. The other hand, during the heat treatment of steel changes in the organization that the austenite to martensite transition, will be accompanied by an increase in specific volume due to the volume expansion of the workpiece, the workpiece successively all parts of the phase change, resulting in inconsistent grown produce tissue volume stress. The final result of the stress variation is the surface tensile stress, the center of compressive stress, the thermal stress is just the opposite. The size of the stress in the workpiece martensite transformation zone cooling rate, shape, chemical composition and other factors.
