P91 steel is filled with pearlite heat-resisting steel and austenitic heat-resisting steel, martensitic heat-resisting steel in the temperature range of new soda pipe line steel 600~650°C. The maximum temperature is 650°C in the original 9Cr-1Mo. Actual production based on steel. Added strengthening elements such as V, Nb, and N to form a new type of steel deterioration.
P91 welding performance
P91 steel can be welded according to the existing methods, including argon arc welding (TIG). Electrodes and fluxes should be selected as close as possible to the chemical composition of the weld and base metal so that the weld metal has the same or better creep and sustained strength than the base material. Since steel is insensitive to hot cracks, weld cracking does not occur after preheating to 150-200°C, and various steels are used, such as P22 steel (penetrite heat resistant steel), X20CRMOV121 (martensitic hot rolled steel) and TP304H ( Austenitic heat-resistant steel) steel welding. The following describes the welding of P91 steel:
a) P91 steel and P91 steel welding, use 9Cr-1Mo (T9) or improved 9Cr-1Mo (T91) electrode, wall thickness greater than 25 mm, the latter using a preheat temperature of 200 °C, slowly cooled to room temperature after welding, Then temper at temperatures above 730 °C;
B) When welding P91 steel and 10CRMO910, the welding material should be matched with 10CRMO910. After releasing at 730°C, it should be cooled in air for 2 h because the two parts of the welding part are decarburization areas. If 10CRMO910 electrode welding is used, the carbon content is ensured. The weld metal NT is high enough to meet the durability requirements;
C) P91 steel and P22 steel welding, the electrode can be used 2.25Cr-1Mo electrode, preheat temperature is 200 °C, slowly cooled to room temperature after welding, and then tempered 700 ~ 725 °C, but also in the P91 steel side welding 5C1 -1Mo electrode, then welded with P22 steel;
d) P91 steel and X20CRMOV121 welding, using two matching welding materials, such as P91 steel electrode, preheating temperature of 250 °C, slowly cooling after welding to 80 ~ 100 °C, tempering temperature higher than 750 °C;
E) Welding of P91 steel and TP304H, using Inco nickel 182Ni alloy electrode, preheating temperature 200 °C, after welding to room temperature, tempering at 700 ~ 730 °C.
The heat treatment temperature after welding depends on the tube wall thickness. The small diameter tube is treated for 0.5 h and the large diameter tube wall thickness is treated every 25 mm for 1 hour. Because of the high creep strength of P91, the wall thickness is thinner than THA under the same conditions. P22 steel has a relatively small amount of T and weld filler metal, while P91 steel is sensitive to weld type IV cracks. Therefore, it is necessary to minimize the system stress of P91 steel. Pipes with a wall thickness greater than 12.5 mm require cold welding and tempering at temperatures above 100°C.
