20 steel and 20G, 20g seamless steel pipe difference
20 steel and 20G, 20g seamless steel pipe difference
20, 20G, 20g, 20R these four steel are carbon content of 0.20% carbon structural steel. But there is a big difference between them, the price difference is also very poor.
20, 20G, 20g, 20R these four steel are carbon content of 0.20% carbon structural steel. But there is a big difference between them, the price difference is also very poor. If the design and use can not be properly selected often heavy cases of destructive accidents, the light will also affect the service life or cause good material bad use.
Now the difference between the four steel and the design and use of the place should be noted as follows:
1. Applicable standards and uses are different
(1) 20 steel for general steel pipe, there are three standards.
Standard GB8162 for structural seamless steel pipe;
Standard GB8163 is suitable for general seamless steel pipe for conveying fluid;
Standard GB3087 for low and medium pressure boiler seamless steel pipe, the standard for the manufacture of various structures Low and medium pressure boiler superheated steam pipe, boiling water pipes and motor boilers with superheated steam pipe, smoke pipe, small pipe and arch brick with high quality Carbon structural steel hot - rolled and cold - drawn (rolled) seamless steel tubes.
(2) 20G is a high-quality carbon structural steel for producing steam boilers and pipes for high pressure and the like. Such as widely used to create medium temperature ≤ 430 ℃ of the economizer, superheater, water wall, water supply, the main steam pipe.
Standard GB5310 for high pressure boiler with seamless steel pipe.
(3) 20g for the manufacture of various boiler pressure components with a thickness of 60-120ram carbon steel plate.
The standard GB713 is suitable for use in boiler carbon steel and low-application alloy steels.
(4) 20R for medium temperature and pressure vessel pressure components with a thickness of 6-100mm carbon steel. Standard GB6654 for pressure vessel steel plate.
2. The nuances of chemical composition
The chemical composition of the four steel grades is basically the same. But compared to the corresponding applicable standards, the chemical composition is also slightly different.
(1) Cu and Ni elements in the carbon steel as impurities in the residual steel, but the two components of the nature of the steel will only bring benefits. Copper is also used as an impurity in carbon steel. When the copper content exceeds the standard, the surface of the steel is rich in copper, and the secondary heating in the hot working process will further thicken the copper layer and diffuse to the austenite grain boundary in the surface area, making the austenite grain boundary serious Brittle, resulting in the workpiece under the action of external load caused by surface brittle fracture. Therefore, when the steel is to be hot for forging and stamping, excessive copper content will cause cracking of the workpiece. The content of copper in the steel must be limited. May be taken into account the complexity of 20 steel smelting materials and as a workpiece when more heat pressure processing. In the applicable standard GB699 (GB8162, GB8163, GB3087 indicate chemical composition deviation should meet the standard GB699) in the text 3 1.1.1 provides that "the use of scrap steel smelting steel agreed to the amount of copper is not greater than 0.30%."
(2) 20g steel plate to meet the performance requirements of the case, the lower limit of manganese content can be 0.40%, thickness greater than 25ram steel plate carbon content up to 0.22%. To improve the performance of 20R, trace elements can be added.
Applicable standard GB699 also provides "hot-pressing steel for processing steel should not be more than 0.20%."
(3) steel smelting with manganese when the manganese residue in the steel. In general, manganese is a beneficial element. Manganese is mainly dissolved in the ferrite body to strengthen the iron body, in addition, manganese can also increase the relative amount of pearlite and make it refined, so manganese can improve the strength of steel. But the high manganese content of the welding performance is unfavorable. Taking into account the overall performance of steel, manganese content and carbon content should be properly matched. Therefore, the 207 steel plate in the GB713 standard and the carbon content of the 20R steel plate in the GB6654 standard are lower than those of the other two types of steel, and the upper limit of the manganese content is more than 0.20- 0.22% And 0.50 to 0.90% and 0.40 to 0.90%, respectively.
(4) silicon is also a deoxidizer, and its deoxidation is stronger than manganese. Silicon solid solution in the ferrite, to improve the strength of steel, but also reduce the plasticity and toughness of steel. Therefore, in order to ensure that 20g and 20R steel has good plasticity and toughness, especially the impact of toughness and long-term use of medium temperature performance. The upper limit of silicon content in these two steels is lower than that of the other two steels, which is not more than 030%.
3. The difference in mechanical properties
The mechanical properties of 20g and 20R steel are different with the thickness of steel plate, and the thickness grade is thinner. With the increase of thickness, the strength, yield point and impact toughness index are reduced. 20G is divided into two kinds of vertical and horizontal specimens.
Four kinds of high temperature of 20 steel specified residual elongation stress (MPa), not less than the values in the table below.
Four steel high temperature requirements Residual elongation stress MPa thickness temperature (℃ steel standard number
