The temperature of cutting and welding repair shall not exceed 250 ℃, and the cooling method can be water cooling or air cooling.
The castings are qualified through RT and Pt inspection, chemical composition and mechanical properties. Metallographic examination shows that ferrite and austenite account for 50% respectively.
| Tensile strength / MPa | Yield strength / MPa | Elongation /% | Remarks |
| ≥ 730 | ≥ 530 | ≥ 25 | — |
See Table 1 and table 2 for technical requirements and measured mechanical properties (mechanical properties are tested according to ASTM SAF2507 standard).
| Tensile strength / MPa | Yield strength / MPa | Elongation /% | Reduction of area /% |
| 734 | 541 | 25 | 64 |
(1) As the austenitic duplex temperature of sa2507 stainless steel increases γ Phase ferrite α Phase transformation, i.e. austenite γ Phase is decreasing, ferrite α The phase is increasing. When the temperature continues to rise, it will change into ferrite in the structure α The phase is much larger than that of austenite γ Phase.
(2) During heat treatment, secondary austenite is easy to precipitate in the region rich in Cr, Ni and Mn in the super duplex stainless steel SAF2507 matrix.
(3) Carbide precipitation. If the duplex stainless steel SAF2507 after heat treatment is heated at a lower temperature (340 ~ 950 ℃) or kept warm, carbides and intermetallic phases will precipitate, mainly chromium carbide, which is mainly distributed on the crystals of austenite and ferrite. The precipitated intermetallic phases mainly include α Phase σ Phase harmony γ These phases are very hard and brittle, which can lead to the strengthening effect of ferrite matrix and easy to crack.
(4) When the valve casting is reheated in the process of cutting riser and repair welding, it shall be firstly α The phase is formed into fine secondary austenite γ Phase, and then precipitate σ Phase. The results show that brittle cracking occurs in σ Phase and matrix σ At the interface of the phase.
By analyzing the mechanism of crack generation, ZHY casting adopts to avoid carbide precipitation and precipitation in the production process σ Temperature range of the phase. In addition, the temperature of both cutting riser and welding repair shall not exceed 250 ℃.