高性能的柱塞泵是液压装备的心脏，是其安全、经济运行的前提。 超高压柱塞泵，是鲠在中国装备制造业咽喉的一根刺。 而柱塞泵缸体作为关键部件，实现其材料国产化、保障优异制造性能并控制成本，已成为当前的重中之重。以柱塞泵缸体专用水平连铸 LZQT600-3 球铁型材为研究对象，对比分析了不同部位(边缘、1/2R、心部)的组织特征，并通过正交实验优化了不同部位试样的碳氮共渗参数。 结果表明， 从边缘、1/2R 处至心部球化级别和石墨球数量依次减小， 分别为 554、509 和 492 个/mm2； 石墨球平均直径分别为 29.86、26.78 和 31.03 μm； 基体中的珠光体数量分别为64.4%、65.9%和 70.8%，珠光体片层间距分别为 274、286、316 nm。 根据柱塞泵缸体最佳耐磨性能要求得出的最优碳氮共渗参数方案为，580 ℃×4h，NH3∶CO2 为 4∶3。 渗层组织由氧化层、ε-Fe2-3(N, C)相和 γ′-Fe4N 相组成的化合物层和 α-Fe相组成的扩散层构成。

Ahigh-performance plunger pump, as the heart of hydraulic equipment, provides a prerequisite for safe and economical operation. Ultrahigh-pressure plunger pumps are thorn in the throat of China's equipment manufacturing industry. As a critical component of the plunger pump, achieving the localization of its material, securing superior manufacturing performance, and enabling cost control has become the paramount priority at present. Taking special horizontal continuous casting LZQT600-3 ductile iron dens bars for the plunger pump cylinder as the research object, the microstructure characteristics of different parts (surface, 1/2R,center) were compared and analysed, and the carbonitriding parameters of the samples in different parts were optimized through orthogonal experiments. The results show that the spheroidization level and the number of graphite spheres decrease successively from the surface and 1/2R to the center of the dens bars, which are 554, 509 and 492 per mm2, respectively; the average diameters of the graphite spheres are 29.86, 26.78 and 31.03 μm, respectively; the quantities of pearlite in the matrix are 64.4%, 65.9% and 70.8%; and the lamellar spacings of pearlite are 274, 286 and 316 nm, respectively. The optimal carbonitriding parameter scheme obtained on the basis of the best wear resistance requirements of the plunger pump cylinder is 580 ℃×4h, and the NH3∶CO2 ratio is 4∶3. The diffusion layer structure is composed of an oxide layer, a compound layer composed of the ε-Fe2-3(N, C) phase and γ′-Fe4N phase, and a diffusion layer composed of the α-Fe phase.