Microstructure and properties of nodular cast iron plunger pump block by nitrocarburizing process

From the development and research trend of chemical heat treatment in atmosphere in recent years, it is still a hot research topic to improve the infiltration rate, multi-element co infiltration and low temperature co infiltration and select the suitable economic and green technology in actual production. At present, the way to improve is physical field intensification and infiltration, such as glow ion carbon nitrogen or nitrogen carbon co-infiltration, flow particle furnace or Nitrocarburization. Because it mainly depends on the new heat treatment furnace, but domestic development of new heat treatment furnace is relatively backward and many small and medium-sized enterprises are difficult to bear the cost of adding equipment. Under the premise of market economy tension, the energy consumption directly affects the cost of products, and will have a certain impact on the survival and development of enterprises. Therefore, how to reduce energy consumption and improve product quality while saving cost is a very valuable research. Therefore, the experiment uses tl1200 tube furnace to explore reasonable co permeability parameters under the co infiltration process of low temperature, short time and different proportion of NH3 and CO2 flow, which provides theoretical basis for the actual production of enterprises.

The as cast structure of lzqt600-3 horizontal continuous casting ductile iron profile was studied, the difference between the structure and performance of different parts was studied. The random sampling of three parts was conducted to provide the basic data for the subsequent nitrogen carbon co infiltration of different parts of samples. According to the requirements of wear resistance and hardness of piston pump cylinder block friction pair, the surface of nodular iron profile can be strengthened by nitrogen carbon gas CO osmosis technology. The co permeable layer with certain thickness and excellent effect can be obtained at a lower temperature (540-570 ℃) and a short time (1-7 h). The specific research is as follows:

(1) The microstructure and properties of different parts of the horizontal continuous casting ductile iron profile were studied. The change rules of the number, equivalent diameter, shape factor and pearlite content of graphite balls at the edge, 1/2r and the center were quantitatively analyzed by image J. the wear resistance and corrosion resistance of the samples in different parts were obtained through friction and wear experiments and electrochemical tests.

(2) Based on the investigation of the change rules of structure and performance between different parts of lzqt600-3 ductile iron profile, the experimental parameters of nitrogen carbon co infiltration of three parts were determined by orthogonal experiment method, and orthogonal design table with three levels and three factors was selected. The last column is set as empty column, which considers three levels of change of the co permeability temperature T, the holding time t and the gas ratio s. The main and secondary factors influencing the surface properties (thickness of the co permeability layer, surface hardness, effective hardening layer depth and wear resistance) of different parts of lzqt600-3 ductile iron profile are discussed by means of the analysis of extreme difference and variance. Finally, the best co infiltration technology under the combination of the above three factors is obtained.

(3) The wear resistance and wear mechanism of the as cast and nitrogen carbon co infiltrating samples of lzqt600-3 ductile iron profile were studied. The surface morphology and wear mechanism of the sample after wear are analyzed by friction and wear experiments.

(4) The surface hardness and microhardness of lzqt600-3 ductile iron profile samples after the best technological parameters were tested, and compared with the as cast samples and other process samples.

The research status of horizontal continuous casting technology and surface chemical heat treatment is introduced. The advantages and development prospects of the current technology are studied.

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