Large Diameter Thick-walled SMLS Pipes Can Replace Imported Ones!

20# seamless steel pipes are low carbon steel pipes. Carbon steel can be generally divided into three kinds of steel: low carbon steel, medium carbon steel and high carbon steel. The prices of seamless steel pipes continue to be steady, however the business shipments are weak. Most of the resources continue to be in the state of little or no goods. As for the inventory, most of the steel mill inventory is high, and traders are also very few. 
 
The performance indicators of China's electric power with high-end heat-resistant steel seamless steel pipes fully meet the industry standards, which broke the foreign monopoly and achieved real localization. 
 
According to reports, China's ultra-supercritical power generation of high-end heat-resistant steel large-diameter thick-walled seamless steel pipes has all been dependent on imports for many years, seriously restricting the healthy development of the country's power industry. In 2019, North Heavy Industry Group of China North Industries developed and built the world's largest 360MN ferrous metal vertical extruder and debuted the large-diameter thick-walled seamless steel pipes’s production line successfully, breaking the long-term foreign monopoly at one blow and laying a solid foundation for the domestication of high-end heat-resistant large-diameter thick-walled seamless steel pipes.                                             
　
Through continuous technical breakthroughs, the high-end and heat-resistant large diameter thick-walled seamless steel pipes produced by North Heavy Industry Corporation of China have gradually entered China's large-scale power generation projects, successfully replacing the imports. It made North Heavy Industry Corporation of China to be the only state-owned enterprise capable of producing such pipes in China. 
 

 
The first application of domestic high-end heat-resistant large-diameter thick-walled seamless steel pipes will greatly reduce the construction cost of large power generation enterprises in China, save nearly 10 billion yuan for the country every year, and further enhance the international competitiveness of China's electric power construction projects. 
 
The sellers were more eager to ship the goods to get funds. Therefore, they were more cautious about replenishment. Sometimes, they even refuse to replenish the goods. The price of raw materials, iron ore and coking coal was down. And the iron ore futures limited down for the first time. The overall market mentality weakened. Let's take into account the two sessions. The favorable policies have not been clear. It is expected that Shanghai seamless steel pipes prices in the short term will be in weak consolidation operation. Among them, 45# steel is medium carbon steel. The steel lower than 45# is low carbon steel. That higher than 45# is high carbon steel. If there are no special requirements for seamless steel pipes, 20# seamless steel pipes are generally used.
 
20# seamless steel pipes material is 20# steel whose strength is slightly higher than that of 15#. It rarely quenches and has no tempering brittleness. The arc welding and contact welding performance are good. The thickness is low because of gas welding. The parts are prone to crack for the strict shape requirements or with complex shapes. 

The material of 20# seamless steel pipes is high quality carbon structural steel.

Grade: 20 steel

Standards:
GB8162-2008
GBT8163-2008
GB3087-2008
GB9948-2006
GB5310-2008
 
Chemical compositions:
Carbon C: 0.17 - 0.2 
Si: 0.17 - 0.37 
Mn: 0.35 - 0.65 
S: ≤0.035 
P: ≤0.035 
Cr: ≤0.25 
Ni: ≤0.25 
Cu: ≤0.25
 
Mechanical properties:
Tensile strength σb (Mpa): ≥410(42) 
Yield strength σs (Mpa): ≥245(25) 
Elongation Δ5 (%): ≥25 
Section shrinkage ψ(%): ≥5
Hardness: ≤156HB, no heat treatment
Sample size: 25mm
 
Heat treatment specifications and metallographic structures:
Heat treatment specifications: normalizing, 910℃, air cooling
Metallographic structures: ferrites + pearlites
　
Delivery status: as for the hardness test of stainless steel, its mechanical properties should be taken into account, which relate to the deformation, stamping, cutting and other processing performance and quality of stainless steel. Therefore, all seamless steel pipes should be tested for mechanical properties. So what are the hard test methods of seamless steel pipes? The mechanical property test method is mainly divided into two categories. One is a tensile test, and the other is a hardness test. 

The tensile test is that the samples are made of seamless steel pipes. The samples will be pulled to break in the tensile testing machine, and then determine one or several mechanical properties. In general, only several indexes will be tested, such as the tensile strength, yield strength, elongation after fracture and section shrinkage. The tensile test is the most basic test method of mechanical properties of metal materials. There is a requirement for mechanical properties for almost all metal materials. They all have a tensile test. Especially for those materials whose shapes are not convenient for hardness tests, the tensile test becomes the only means of mechanical properties testing.
 
The hardness test is that a hard indentation head with hardness tester is slowly pressed into the sample surface, and then test the indentation depth or size according to the specified conditions in order to determine the size of the material hardness. The hardness test is the most simple, the most rapid and the most easy to implement methods in the material mechanical property test. Hardness tests are non-destructive, and there is an approximate conversion relationship between the material hardness value and the tensile strength value. The hardness value of the material can be converted into the tensile strength value, which has great practical significance.
 
As the tensile test is not convenient to be tested. And it is easy for the conversion from hardness to strength. Therefore, people increasingly only test the hardness of materials and less test their strength. In particular, due to the continuous progress of hardness tester manufacturing technology and innovation, some of the original test methods can not directly test the hardness of materials, such as seamless steel pipes, stainless steel plates and stainless steel belts. Now, the hardness may be directly tested. Therefore, there is a tendency that hard tests gradually replace tensile tests.
 
Tensile tests and hardness tests are both stipulated in most national standards for stainless steel materials. Only the tensile test is stipulated for those materials which hardness tests are not convenient to be done, such as seamless steel pipes.