In order to improve the performance of stainless steel, often need to adopt a certain way of cold work, such as cold drawing, cold rolling, cold rolling, cold, cold, cold bending distortion and so on, but the effect will be to arrive at the same time can also cause certain damage, all of these cold actually like welding, would give the performance of the stainless steel tube, especially corrosion resistant brings the inevitable damage or heat resistant performance. Concrete is:
1, will lead to material lattice dislocation and other microscopic defects and surface roughness increase, and induce martensitic transformation and carbide precipitation. For example, after cold processing, austenitic steel shows an increase in magnetism.
2, resulting in material lattice dislocation or phase transformation occurs on the surface, will become the initial location of local corrosion such as pitting. This phenomenon will have direct adverse effects when the deformation degree reaches 20% reduction of section rate.
3, after cold processing, residual stress will be left in the material, residual stress on the resistance to stress corrosion cracking (SCC) of the material is very adverse. Any degree of cold processing will greatly increase the SCC sensitivity of the material.
4, the degree of cold processing on the high temperature endurance strength of austenitic stainless steel also has a bad effect. Generally, the higher the operating temperature or the higher the fracture life requirements, the lower the allowable degree of cold processing.
5, for the application of stainless steel pipe under alternating load, cold processing will cause adverse effects by reducing the elongation and residual elongation so that the cracking expansion rate increases.
In view of the above problems, we should try to solve them:
1, the vast majority of countries’ stainless steel pipe standards, especially the European uniform stainless steel pipe standards stipulate that all stainless steel seamless steel pipe must be supplied in solution or annealing state, in order to eliminate the performance damage caused by cold processing and welding.
2, solution treatment should pay attention to three key parameters: heating temperature, rapid cooling method and high temperature residence time. Too high solution treatment temperature or residence time will be detrimental to the corrosion resistance of materials. To determine whether the solution is in place, hardness test, flaring, rolling, flattening, stretching data can be determined, hardness test is the most convenient.
3, because of solution or annealing due to high temperature heating and pickling treatment, so that the manufacturing cost and production cycle increased significantly, coupled with acid fog and other waste gas and wastewater discharge, some enterprises omit the process, using this product, easy to produce production and personal accidents after use.
4, for some products or application conditions may be difficult to implement solution or annealing, control the degree of cold processing (cold processing deformation) and local low temperature stress relief annealing, is a practical method to reduce harmful effects.