The production of high quality polished stainless steel tubing is divided into cold processing and hot processing, regardless of which processing process will have a certain impact on stainless steel tubes.
In metal technology, cold working refers to the processing technology of plastic deformation of metal below the recrystallization temperature, such as cold rolling, cold drawing, cold forging, stamping, cold extrusion and so on.
high quality polished stainless steel tubing, especially austenitic stainless steel has excellent plasticity, making these cold working methods are easy to realize, however, these cold working actually like welding, will give the performance of stainless steel pipe, especially corrosion or heat resistance performance will bring unavoidable impact.
The effect of cold working on high quality polished stainless steel tubing
- The resulting lattice dislocations or phase transitions occur at the surface of the material, which becomes the starting point for localized corrosion such as pore corrosion. This phenomenon has a direct adverse effect when the degree of deformation reaches 20% minus the section rate.
- Will lead to material lattice dislocations and other microscopic defects and surface roughness increase, and induced martensitic phase transformation and carbide precipitation. For example, austenitic steels show an increase in magnetism after cold working.
The degree of cold working also has an adverse effect on the high temperature endurance strength of austenitic stainless steels. Generally, the higher the working temperature or the higher the fracture life requirement, the lower the permissible degree of cold working.
After cold working, residual stresses will be left in the material, and the residual stresses are extremely unfavorable to the material’s resistance to stress corrosion cracking (SCC). Any degree of cold working will greatly increase the sensitivity of the material to SCC.
For stainless steel tubing applications subjected to alternating loads, cold working can be detrimental due to the reduced elongation and residual elongation, which increases the rate of crack propagation.
How to minimize damage to high quality polished stainless steel tubing?
- The stainless steel tube standards of most countries, especially the European unified stainless steel tube standards, stipulate that all seamless high quality polished stainless steel tubing and pipes must be supplied in solution or annealed condition to eliminate the performance damage caused by cold working and welding and other processing.
- Solution treatment should pay attention to three key parameters: heating temperature, rapid cooling method and high temperature residence time. Excessively high solution treatment temperatures or residence times can be detrimental to the corrosion resistance of the material. To determine whether solid solution is in place, hardness measurement, flaring, crimping, flattening, and tensile data can be determined, of which hardness measurement is the easiest.
- Because solid solution or annealing significantly increases manufacturing costs and production cycles due to high-temperature heating and pickling treatments, coupled with acid mist and other emissions and wastewater discharge, some companies omit this process and use such products, which are prone to production and personal accidents after use.
- For some products or application conditions may be difficult to implement solution or annealing, control the degree of cold working (cold working deformation) and local low-temperature stress relief annealing is a practical way to reduce the harmful effects.
High quality polished stainless steel tubing: a small industry with high added value
Industrial stainless steel tube application environment is special, high requirements for production technology, processing difficulty, and usually has more specifications, batches, customized features. Especially high-end stainless steel tube market, need to overcome the product technology based on the production license, qualified supplier qualification, product safety records, etc., there are more obvious barriers to entry, enterprises to achieve import substitution as an important development direction. The industry generally adopts the pricing model of “raw materials / material rate + processing fee”, so the material rate and product structure optimization has become a stainless steel tube enterprises to obtain higher profit margins of the two ideas. The material rate is mainly determined by the material of the steel pipe, outer diameter, wall thickness, process, technology and other factors. Product processing fees fluctuate with labor costs and changes in the market supply and demand environment, relatively speaking, higher value-added products, demand for more prosperous products can obtain higher processing profits.
Thermal power demand explosion, boiler tube products in short supply
Supercritical and above with high quality polished stainless steel tubing due to the existence of barriers, the industry order is relatively good, the long-term formation of some enterprises dominated the development pattern. After experiencing a downturn in demand for thermal power tubes in the previous few years, the supply is once again cleared, and the industry supply is centralized. Demand, with the accelerated approval of coal power, ultra (ultra) critical units to increase the use of high-end boiler tube demand has risen sharply. According to each million kilowatts of ultra (super) critical unit consumption Super304H and HR3C and other high-pressure boiler tube number of about 1250 tons, if the new 80 million kilowatts of coal power units, corresponding to the demand for boiler tube up to 100,000 tons. Superimposed on the replacement of the transformation of boiler tube demand will rise sharply.