Cold processing of stainless steel pipes

There are five main properties that can cause damage to stainless steel pipes. First, it will increase microscopic defects such as lattice dislocations and surface roughness of the tube material, and will also induce martensitic phase transformation and precipitation of carbides. For example, austenitic stainless steel shows an increase in magnetism after cold working.
Secondly, it will also cause lattice dislocation or phase transformation of the stainless steel pipe material to occur on the surface, and it will also become the starting point of local corrosion such as pitting corrosion. This phenomenon will have direct adverse effects when the deformation reaches 20% area reduction.
After cold working, residual stress will be left in the stainless steel pipe material. The residual stress is very detrimental to the pipe's resistance to stress corrosion cracking. Any degree of cold working will significantly increase the material's susceptibility to stress corrosion cracking.
The degree of cold working will also have an adverse effect on the high-temperature durability strength of austenitic stainless steel. Generally, the higher the working temperature or the higher the fracture life requirements, the lower the degree of cold working can be performed.
For the application of stainless steel pipes subjected to alternating loads, cold working will cause adverse effects due to the decrease in elongation and residual elongation and the increase in the cracking expansion rate.
In order to solve the above problems, there are several solutions. First of all, the stainless steel pipe standards of most countries, especially the unified European stainless steel pipe standards, stipulate that all stainless steel seamless steel pipes must be supplied in a solid solution or annealed state, thereby eliminating performance damage caused by cold working and welding.
Secondly, three key parameters should be paid attention to during solid solution treatment, namely heating temperature, rapid cooling method and high temperature residence time. Excessively high solution treatment temperature or residence time will be detrimental to the corrosion resistance of stainless steel materials. To determine whether the solid solution is in place, hardness measurement, flaring, curling, flattening, and stretching data can all be judged, among which hardness measurement is simple.
Since solid solution or annealing requires high-temperature heating and pickling, the manufacturing cost and production cycle are increased, and there are waste gases such as acid mist and wastewater emissions. Some companies omit this process. Using this product, it is easy to Cause production and personal accidents.
Finally, for some stainless steel pipes that may be difficult to solidify or anneal, it is necessary to control the degree of cold working and perform local low-temperature stress relief annealing, which can effectively reduce harmful effects.