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Tubes heating temperature refers to the billet baking temperature. It should be determined to ensure that the steel in the plastic within the best range of the implementation of the main deformation to determine the basis of heating temperature is iron, carbon balance diagram, in practice, the general should consider the following factors. ① steel. Different steel grades correspond to their different heating temperatures. ② temperature drop. The temperature drop (outside) of the new product from the ring heating furnace to the rolling mill process line should generally ensure that the metallographic structure before the final deformation is in the single phase zone. ③ heating defects. Should prevent the billet overheating or even burned.
The main quality defects of pipe heat treatment are discussed, and the quenching and tempering heat treatment process is described as typical process.
The quality problems caused by the heat treatment of the pipe are mainly reflected in several aspects (performance, organization, defects, size, surface, etc.).
Performance and organizational issues
Performance and organizational issues, depending on the material composition and the original state and the rationality of the heat treatment process and process control level, which is the core of the quality of heat treatment content.
If the heat treatment process is developed or performed poorly, the performance of the pipe (such as yield, tension, extension) will exceed the requirements specified in the standard; organizations that will appear in the organization such as weir and ribbon will not exist.
Mainly in the length of the direction (axial) bending and cross-sectional direction (radial) of the oval and outside diameter tolerance.
Cause of bending of steel pipe
Seamless steel pipe heating uneven bending
Uneven heating of the steel pipe, the temperature in the axial direction of the pipe is different, the change time of the steel during quenching is different, the volume change time of the steel pipe is different and the bending occurs.
Steel pipe quenching bending
Quenching is the preferred heat treatment for high strength casing and high grade pipe production. During the quenching, the tissue transformation is very rapid, and the change of the steel structure leads to the change of the volume. Due to the cooling rate of the various parts of the steel pipe is not consistent with the rate of change in the organization is not consistent, will produce bending. Tubes bends cause bending
If the chemical composition of the steel pipe segregation, even if the cooling conditions are exactly the same, in the cooling will produce bending.
Uneven cooling produces a curved alloy steel pipe after the heat treatment, usually to the side of the steel pipe side of the natural cooling. At this time the axial and circumferential cooling rate of the steel pipe is not uniform, will produce bending. If the bending of steel pipe can not meet the requirements, will affect the subsequent processing (such as transportation, straightening, etc.), and even affect its performance.
Drilling of steel pipe on the sizing machine, especially the narrower diameter of the pipe (such as pipe, casing) in the tempering after the general requirements of the sizing. If the centerline of the sizing rack is inconsistent, the pipe will bend.
The Main Causes of Ovalness and Outer Diameter of Steel Tubes
Quenching, due to the transformation of the various parts of the steel pipe is inconsistent, the steel will produce ellipticity; due to the existence of oval, so most of the steel pipe in the quenching and tempering treatment needs to be sizing, if the sizing control process is not good, difference.
Defects and surface problems of quenching cracks in steel Tubess
The quenching temperature of the steel pipe is too high, or the heating time is too long, or the heating temperature is not easy to cause quenching crack. If the chemical composition of segregated steel pipe, steel pipe is also easy to cause inclusions cracks.
Steel pipe overheating or over-burning steel pipe quenching heating temperature is too high or heating time is too long, easy to cause overheating or over burning, serious, the steel pipe will collapse.
The surface of the steel pipe is decarburized or severely oxidized
When the steel pipe is heated, the surface is seriously decarburized or severely oxidized due to improper heating temperature and heating time control or air conditioning ratio adjustment.
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