Two-phase stainless steel pipes used in severely corrosive environments must have corrosion resistance. However, when the carbon content is large, due to thermal effects during heat treatment, welding, etc., the precipitation of carbides tends to be too much, which leads to the corrosion and workability of steel from the viewpoint of corrosion, especially from the viewpoint of corrosion. It is necessary to reduce the steel Content.
(B) When the carbon content is reduced, its strength is not enough for any other operation; however, the material tube produced by the thermal processing of two-phase stainless steel material or the solid solution heat treatment made of two-phase stainless steel material can be Increase the strength when cold stretching is subsequently applied. Here, it should be noted that when the work rate exceeds 35%, the area is reduced, high strength is maintained, but work hardening occurs, and therefore, ductility or toughness deteriorates. On the other hand, when the work rate is less than 5%, in reducing the area, the expected high strength can not be achieved. Therefore, it is necessary to set the work rate of cold stretching at 35% to 5 to reduce the area.
(C) At the same time, it has been found that the work ratio RD during cold drawing is a reduction in area ranging from 5 to 35%, and it is more important for the cold drawing work of duplex stainless steel pipes than the final development. The YS with high yield strength is more effective. For duplex stainless steel pipes, the relationship between working ratio RD and yield strength YS is linear. It has also been found that the strength of duplex stainless steel pipes is significantly affected by the Cr content, and high-strength duplex stainless steel pipes can be obtained from materials with Cr content in steel. In addition, it has also been found that the strength of duplex stainless steel pipe is significantly affected by the content of Mo and W, and the content of Mo or W can produce high-strength duplex stainless steel pipe.fig. 1 is a plot of the yield strength (MPa) versus the YS working ratio RD tensile test value (%) in the area reduction value. The example for duplex stainless steel pipes with different chemical compositions is as follows. Figure 1 shows the linear relationship between the work ratio YS that occurs in terms of reduced area and yield strength.
(R&D) In the next step, the inventor believes that the yield strength of the two-phase stainless steel pipe depends on the working ratio of the cold drawing and the chemical composition of the two-phase stainless steel pipe during execution, and establishes an appropriate component design based on this Two-phase stainless steel pipes with targeted yield strength for technology and pipeline working conditions. In other words, in order to achieve the yield strength, the purpose of the targeted duplex stainless steel pipe is not based on the circuit adjustment of the chemical composition of the duplex stainless steel pipe, but the basis of fine-tuning can be achieved by cold drawing. The work ratio RD . In addition, it is not necessary to perform a large amount of molten two-phase stainless steel preparation