Influence of preheating temperature on cold crack sensitivity of 12Cr10Co3W2Mo wear-resistant plate
12Cr10Co3W2Mo steel is a new type of ferritic wear resistant plate, which is based on previous generations of ferritic wear resistant plates such as T23, F11, F12, T/P91, T/P92, etc., by optimizing C, Nb, V and other elements, adding 0.03% of N element, replacing part of Mo element with W, and adding up to 3% of Co element. The creep performance at high temperature has been greatly improved, and the creep fracture strength is expected to reach 180MPa under the conditions of 600℃ and 105h, which is one of the preferred domestic materials for the nozzle structure of ultra-supercritical steam turbines. Turbine nozzle structure is special, welding groove is deep and narrow, welding amount is large and rigid fixed. Due to the uneven heating and cooling in the welding process, the weld and the nearby metal produce non-uniform expansion and contraction, which causes welding residual stress and various welding deformation, and is easy to induce cracks.
The research shows that the ferritic wear-resistant plate is sensitive to cold cracking, and most of them need to be preheated before welding. 12Cr10Co3W2Mo wear-resistant plate is a new material, and there are no reports about its weldability at present. The researchers of Xi 'an Jiaotong University studied the critical fracture stress of 12Cr10Co3W2Mo steel at different preheating temperatures by using the pin test method, and discussed the reasons for the change of cold crack sensitivity, in an attempt to provide a certain reference and theoretical basis for the selection of preheating temperature in engineering applications.
The test results show that:
(1) 12Cr10Co3W2Mo wear-resistant plate has strong cold crack sensitivity, increasing the preheating temperature can significantly increase the critical fracture stress, and the occurrence of cold cracks can be effectively prevented when preheating 320℃ before welding.
(2) When manual arc welding is adopted, the critical fracture stress increases linearly with the increase of preheating temperature, and the fitting formula is σcr=177.5+1.38To.
(3) At each preheating temperature, the microstructure of the coarse crystal zone of the welded joint of 12Cr10Co3W2Mo wear-resistant plate has no obvious change, and all are lat martensitic structure. With the increase of preheating temperature, the hardness in coarse-grained zone decreased slightly, and the increase of critical fracture stress was much larger than the decrease of maximum hardness in heat-affected zone.
(4) At each preheating temperature, the fracture initiation zone morphologic features of cleavage + quasi-cleavage hydrogen-induced cracking were all observed in the latch specimens. With the increase of preheating temperature, the hydrogen-induced cracking fracture features gradually disappeared.
