Research On The Application Of Pack Boronizing In Petroleum Machinery

Some parts of petroleum machinery work under severe conditions. The conditions involve hard particles such as grit and corrosion mediums such as H2S,HCO3- so that these parts must be wearable and corrosion-resistant. Because of the high hardness of the borided layer and its fine wear resistant, oxidation-resistant in high temperature and corrosion-resistant capacity, the boronizing technology has been used widely. Because of simple to operate and easy to clean, pack boronizing has received extensive attention in recent years. Extending the application of pack boronizing can improve the quality and prolong the life of petroleum machinery parts. Therefore, it is necessary and practically meaningful to research the application of pack boronizing in petroleum machinery.However, pack boronizing has some disadvantages. For example, high temperature and long time is required when boronizing. Due to distinct brittleness, easily-craze and easily-spall liability of borided layer, the mechanical properties of the substrate are debased and the wear resistant and corrosion-resistant properties are affected. These restrain further development and application of pack boronizing. In the present work, the microstructure, mechanical properties, friction and wear properties and corrosion resistant properties of the boronizing samples of sucker tube and sucker rod joint were studied by using different heat treatment methods and adding rare earth compound in boriding agent. All of these will offer theoretical and practical foundations for extending applications of pack boronizing in petroleum machinery.Under the condition of boronizing, the borided layer of 36Mn2V steel is composed of FeB phase and Fe2B phase. The amount of pearlite increases, whereas the amount of ferrite decreases with the increasing of cooling velocity. As the cooling velocity increases, the mechanical properties are remarkably improved. The fan-cooled sample with graphite bar inside has the highest ultimate strength and yield strength. Fractography analysis indicates that the fractured surface of tested 36Mn2V steel samples at room temperature has many ductile dimples and tearing ridges. All of the fractured surfaces accord with typical ductile fracture feature.The microstructures of 36Mn2V steel which is boronized with lanthanum chloride mixed rare earth and 45 steel which is boronized with neodymium oxide rare earth were studied. The results demonstrate that with the increasing rare earth content, FeB phase reduces and Fe2B phase increases. Rare earth has a catalytic effect on borided layer. The content of rare earth added has an optimized range; the thickness of borided layer will decrease with excessive content of rare earth.Carbon content of 45 steel which is boronized with neodymium oxide rare earth increases from the layer to the transition zone, and it reaches a maximum in the transition zone. The fracture toughness values of FeB and Fe2B phases are higher than that of boronized sample. The brittleness of borided layer reduces.In the present work, friction and wear resistance of boronized and RE-boronized samples were studied. The results indicate that the wear rate of boronized 36Mn2V steel increases with the increasing of test loads, whereas the friction coefficient decreases. The samples of 36Mn2V steel which is boronized with lanthanum chloride mixed rare earth were given the test load of 130N. The wear rate of the samples with less lanthanum chloride mixed rare earth is lower than that of boronized samples. The friction coefficient of the samples increases with increasing content of rare earth. The wear rate of boronized 45 steel and 45 steel which is boronized with 3% neodymium oxide rare earth increases with the increasing of tested loads and the friction coefficient decreases. Under the condition of high test loads, the wear rate of RE-boronized samples is relative lower than that of boronized samples. The analysis of worn surfaces reveals that the wear mechanism of boronized and RE-boronized samples is abrasive wear.The corrosion resistance of the boronizing samples was studied. The test results show that the corrosion resistance of boronized 36Mn2V steel is remarkably improved than that of non-borided samples. The corrosion potential of 36Mn2V steel which boronized with lanthanum chloride mixed rare earth is higher than that of boronized and non-borided samples, and the corrosion resistance of RE-boronized samples is improved.The analysis of dynamics reveals that the thickness of borided layer of boronized 45 steel and T12 steel increases with the increasing of boronized temperature. At the same temperature, the thickness of borided layer decreases with the increasing of carbon content. The calculated values of activation energies for the boronizing process in the 45 and T12 steels are about 184kJ/mol and 261kJ/mol, respectively.