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Causes of tensile cracking of stainless steel pipes and preventive measures

Sometimes the cracking phenomenon of tensile stainless steel pipe, the scene appears diversified, there are four kinds of common, respectively after tensile deformation, from the die exit occurs immediately after tensile deformation, impact or vibration occurs after tensile deformation, there is a section of time or in use.
The main reasons are low ductility, high modulus of elasticity and high hardening exponent of stainless steel. The plastic deformation stage of stainless steel is relatively short from yield to cracking.
Specific to the type of stainless steel, the cold hardening index of austenitic stainless steel is relatively high. Austenitic stainless steel is a metastable material. When deformation occurs, it will produce phase transformation, easy to form martensite structure, and martensitic phase is brittle, so it is easy to produce cracking. During plastic deformation, with the increase of austenite phase transformation, the content of martensitic phase will also change more, and the residual stress will also increase, resulting in a vicious cycle. During the processing, the stainless steel will also be more prone to cracking.
So how do the stainless steel pipes prevent cracking in the process of use?
In fact, the use of the appropriate lubricants for stainless steel pipe tensile effect is obvious. The lubricant can produce a layer of thin film with a certain ductility and ductility between the convex and concave dies, which is very beneficial to the drawing of stainless steel.
Polyvinylidene fluoride film can also be used as lubricant for deep drawing parts of stainless steel pipes with large deformation and difficult forming. PVDF film has excellent tearing strength, certain toughness and ductility, and it is very convenient to clean up. Dangtu complex dry film, in the process of drawing the dry film deformation together with the blank, can always put the billet and die isolated, with thin film has its corresponding porosity and fibrous crack, so it can be stored in a certain oil, so that the film is a layer of dry film lubricant. This lubrication method can effectively separate the deformed stainless steel plate and the mold surface from each other, and the lubrication effect is very good. It is helpful for increasing the service life of the die and the qualified rate of the product.
In addition, there are other simple ways, for example, white cast iron is used as the edge blank grinding tool. Because the oil storage property of white cast iron is good, it is easy to produce lubricant film, or the conical blank holder can also be used. It can also make the edges of the workpiece more smooth and remove the small opening gap, which can also effectively avoid the formation and expansion of the cracking.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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