| With the development of heavy-duty locomotive, the security and reliability oftraction gear improve gradually, the gear’s demand is increasingly augmented. Tractiongear, as the core components technical of the heavy-duty locomotive drivetrain, becauseof its complex force, heavy burdens and bad working environment, its security andreliability are strictly requested. However, the heat treatment’s quality control hasbecame the bottleneck of independent research and development to cause its long-termdependence on imports because of the gap of metal melting and quality controltechnique with developed country, so to accelerate the development of technology ofheavy-duty locomotive traction gear, promote the localization process, solve theproblem of long-term imports to meet domestic demand and form the large-scaleindustrialization gradually are necessary. Then more economic value are created bypromoting the application of technology in the field of the heavy gear transmission ofwind power and mine relatively.In this thesis which is under the auspices of International Cooperation Ministry ofScience Cooperation Project (2010DFB83240) and on the back of trial production of theheavy-load locomotive traction gear, those two big problems of intergranular oxidation(IGO) and carbide out of limits that appear time and again on the issues of tractiongear’s heat treatment process are researched specially, the influence of IGO and carbideon the gear’s performance are analysed. Then the IGO’s mechanism is analysed onaspects of thermodynamics&oxidation kinetics，and its process control parameters alsohave analysed combining with metallographic examination, hardness testing, energydispersion spectrum (EDS) scanning and analysis. The process control parameters arefound through the researching of the formation and spheroidal mechanism of carbide，combing with process，the heat treatment process is optimized and its optimized result isproved through process test. The concrete research works include:1) The heat treatment process experiment of the heavy-load locomotive tractiongear which is made of17CrNiMo6is performed with BBH multi-purpose furnace offorvacuum prechamber, and then metallographic examination and hardness testing arerun, two big problems of intergranular oxidation (IGO) and carbide out of limits thathappen repeatedly in the experiment are summarized and their influence on gear’sperformance are analyzed. 2) The mechanism of IGO was explained with some thermodynamic andoxidation kinetics calculations relatively, scanning electron microscope (SEM) andenergy dispersion spectrum analysis (EDS) are done on the sample of place that has ledto a phenomenon of IGO in the experiment, and The results of EDS shows that Cr andO are the major components of black networks produced by the IGO. Through theanalysis of equilibrium curves about Fe, Cr and oxidizing atmospheres, those carburizedprocess parameters, including uniform temperature velocity of heating’s period,temperature, carbon potential, holding time of carbon restoration and diffusion period.3) The formation and spheroidal mechanism of carbide, parameters of affectingcarbide’s spheroidization are expounded through the result of metallographicexamination on the issues of carbide out of limits. The methods of controlling carbideare got as follows: to reduce the carbon potential appropriately later stage ofcarburization; to make the stepped carburizing process heat up progressively andreasonably; to carburize at the temperature of Ac1or Acm as far as possible; to make themulti-level spheroidizing annealing processes reasonably.4) The technological measures of controlling the IGO and carbide are obtained bysynthesizing all conclusions above, heat treatment process is optimized through manytechnology tests, and the optimization results are experimentally validated to beeffective. |
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