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The cause of crack on the surface of stainless steel cross

Stainless steel cross is a kind of made by stainless steel pipe fittings, the fittings is divided into four interfaces, and is generally such as diameter, of course, in some cases there is also a reducing, such as the diameter of the stainless steel cross is connected the same size of the pipe body, reducing the different diameter of the pipe body is link. The branch over size less than competent to take over the size. The product is mainly used in pipe branch. In the industry have a four-way called seamless tube manufacturing, the product is hydraulic expansion and extrusion forming of stainless steel cross.

There are several reasons for the crack on the surface of stainless steel cross:

A, processing is too large, in an empty pipe, tube billet by external force for the drawing force, mould wall of the pipe to the positive pressure and friction. Affected by friction, the metal deformation in the process of flow, the outer surface layer along the longitudinal flow more slowly than the inner layer, so as to make the outer metal is attached gallas stress, while the inner metal under compression stress. Processing is larger, difference of inner and outer layer of metal flow rate, the greater the outer metal are attached with William gallas, the greater the stress, the more prone to crack. After drawing, the additional stress disappear, the pipe will produce elastic recovery, the inner metal has a tendency to longitudinal extension, and the outer metal has a tendency to shorten, but the shrinkage of the outer metal is limited by the inner metal, the extension of the inner metal also is limited by the outer layer of metal, so that the outer metal by residual tensile stress, the corresponding inner metal by residual compressive stress. The outer metal by residual tensile stress, is stainless steel cross pipe crack appeared in the process of drawing in place after the main root cause.

In lining pipes, due to the two aspects of mandrel and die wall friction and the effect of tube bloom inside and outside surface layer metal flow velocity is slower than the middle layer velocity, so as to make the internal and external surface metal by gallas attached stress at the same time, when the wall is thin, the metal plasticity is poorer, more prone to crack. At the end of the drawing, the products of the residual stress of pipe inside and outside surface residual tensile stress, residual compressive stress by the middle tier. Due to internal and external surface metal by residual tensile stress at the same time, therefore, line pull thin wall tube in the process of placing more prone to crack.

Two, has deep horizontal tube billet surface scratch. If the pipe outside surface has the deep transverse scratch, will generate stress concentration, whether it is in the process of drawing, or drawing after placement process, are prone to crack.

Three, the pipe annealing is not sufficient. If the pipe annealing is not fully, can appear the endogenous cooked outside. The internal and external surface strength is low, easy to deformation, and the middle layer high strength stainless steel cross’s pipe wall, it is not easy to deformation. Because in the process of drawing tube billet cross-section along the longitudinal deformation of the metal flow is uneven, the intensity distribution of non-uniform deformation have been intensified inhomogeneity, so as to make the easy occurrence crack defects in drawing process. Everyone in the process of using it is important to note that the above said the problem, as far as possible to reduce the damage of the products, to avoid unnecessary waste.

Source: Yaang Pipe Industry Co., Limited (www.yaang.com)

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