| With the development of industry, the world demand of oil and natural gas resource iscontinually increased．In the further exploitation of low-permeability oil and gas fields, theoil and gas output will be affected if the space between the gas layer and oil&gas well isnot clear in the complex geological structure. By expanding the extension and dredgingstrata gap to improve penetration ability, the production of the oil&gas will be raised. Itwas found that fracturing process is one of the most effective measures to achieve thisgoal currently, after various research and practice. The Implement fracturing process of theequipment is mainly composed of the fracturing machine units，the pump head is thecrucial component of the units. The pump head work in the harsh environment, somecrack had appeared in the pump head body within the validity period, or size toleranceoccur in some parts of the pump head body when they are machined. Pump head can’twork normally when these problems come up, therefore it is very important for theremanufacturing technology research of the25Cr2Ni4MoV pump head.This paper firstly studies the heat treatment process and the mechanical properties of25Cr2Ni4MoV steel, and the welding procedure of the quenched and tempered steel.Secondly, analyzes the weldabiltiy of the25Cr2Ni4MoV steel concretely, which includethe cold crack tendency, the hot crack tendency, HAZ’s microstructure types, brittlementwithin the coarse-grained zone and the softening etc. According to the steel’s weldability,the parameters for the experiment can be set：welding materials, preheat temperature andlayers temperature, welding energy and post-weld heat treatment etc. Thirdly, analyzes thecold crack tendency to the different preheat temperature and the relevant factors of coldcrack through the Y-shape groove test. Finally, Simulate the pump head’s crack repairingand tolerance repairing, butt welding and surfacing welding experiments are set. By meansof tensile test, impact test, hardness test and microstructure analysis, the influence ofdifferent procedure to the microstructure and performance is systematically studied.The results of the Y-shape groove test show that25Cr2Ni4MoV quenched andtempered steel is preheated above200℃that can be effectively in preventing weldingcold cracks. The emergence of the cold cracks was relevant to the bulky hard brittlemicrostructure of the coarse grain area. In generally, the cold crack initiate from weldgroove in the stress concentration. The crack expanded along the welding fusion line. Some crack expand throughout the melt fusion line, also some expended to the weld zoneand stop at the weld zone.According to the tests of the butting welding and surfacing welding, it can be cameto the following conclusion：the best procedure is using the CHE857CrNi electrode weldingin accordance with the following condition： the225℃preheating1hour, layerstemperature is maintained at220±10℃,250℃post-weld heat treatment1hourimmediately after welding, and then air cold. The butt welding specimen’s mechanicalproperties can meet the base metal’s requirements, the surfacing welding specimen’stensile strengthen and horizontal toughness can also reach the requirements, but theLongitudinal toughness is less than base metal10%.Based on the results of the test and the actual pump head’s characteristics can comeup with a reasonable welding procedure, which is applied to the actual wielding repairing.it is found that the repairing effect is good after inspection. |
PDF Full Text Request