Zhengheng Power’s high-grade cast iron

Precision casting and intelligent manufacturing of heavy-duty components

High-grade cast iron (including high-grade gray cast iron, vermicular graphite cast iron, and high-strength ductile iron) has become the core material for heavy-duty power components such as commercial vehicle diesel engines, construction machinery, and generator sets, due to its high strength, low deformation, and high heat resistance. This type of material is sensitive to solidification shrinkage, and the graphite structure is difficult to control. Shrinkage porosity and leakage defects are prone to occur in thick-walled parts, making the manufacturing threshold extremely high. Relying on Tonglin Foundry’s profound accumulation in the field of high-end cast iron, Zhengheng Power has established an exclusive intelligent manufacturing system for high-grade cast iron. Especially in the field of high-strength ductile iron, it has successfully achieved stable mass production of QT900-6 grade, providing customers with high-density, high-stability, and high-durability heavy-duty cast iron component solutions.

Zhengheng Power adopts CAE casting simulation technology to optimize the runner layout and filling rhythm, and construct a reasonable temperature gradient for high-grade castings with complex wall thickness and internal cavity structures. Coupled with modular resin sand core assembly technology, it achieves precise assembly of complex internal cavities, uniform cavity rigidity, and avoids slag inclusion, shrinkage cavity, and deformation defects from the source. Taking the QT900-6 bridge housing as an example, the solidification behavior of the part with a wall thickness of only 10mm was accurately predicted through simulation, effectively preventing the tendency of shrinkage porosity and ensuring the accuracy and quality consistency of mass production.
Addressing the challenges posed by the significant shrinkage of cast iron and the difficulty in feeding shrinkage in thick-walled (as well as thin-walled high-strength components), Zhengheng Power has adopted a bottom vertical pouring process. This process ensures a smooth filling of the molten iron layer without turbulence or oxidation slagging. Leveraging a top-down positive solidification gradient, a stable feeding channel is formed, significantly reducing porosity and shrinkage defects. In the mass production of QT900-6, this process has successfully addressed the issues of shrinkage porosity and deformation that are particularly prevalent in large-sized thin-walled components (with a bridge housing wall thickness of only 10mm). As a result, the density, rigidity, and airtightness of the castings have been significantly improved, meeting the requirements for heavy-load, high-temperature, and alternating working conditions.

Zhengheng Power adopts standardized cast iron metallurgical control, with a tapping temperature of 1520-1550℃ and a inoculation temperature of 1480-1420℃. Through refining and degassing before the furnace, instantaneous inoculation with the flow, graphite morphology refinement, and uniform matrix structure, structural segregation is improved. For the breakthrough grade QT900-6, the technical team has gone through 14 rounds of iterations and verified hundreds of schemes, establishing a precise control model from chemical composition, spheroidizing inoculation to cooling parameters. Finally, it achieves mechanical indicators of tensile strength ≥880MPa, yield strength ≥540MPa, and elongation ≥5.5%, far exceeding the national standard QT900-2 (elongation is only 2%), achieving a rare balance of ultra-high strength and high plasticity.
Given the characteristic of cast iron being prone to stress deformation, all castings undergo a stress relief annealing process (holding at 500-550°C for 2-8 hours, followed by furnace cooling) to release internal stress and stabilize metallographic and dimensional accuracy. The core components undergo precision machining with strict tolerance control, and are subjected to comprehensive inspections including hydraulic and air tightness testing, metallographic analysis, mechanical testing, and non-destructive testing. In the inspection of QT900-6 products (such as new energy heavy-duty truck axle housings and wind turbine gearbox components), both batch consistency and air tightness meet stringent installation standards, fully demonstrating Zhengheng Power’s process control capabilities.
Zhengheng Power is capable of flexibly mass-producing high-grade gray iron, vermicular graphite cast iron, and high-strength ductile iron castings, meeting the needs of new product development, small-batch customization, and large-scale production. We independently complete the entire process from casting, heat treatment, finishing, to inspection. Our products are widely used in commercial vehicle powertrains (especially new energy heavy-duty truck axle housings), construction machinery, generator sets, ships, heavy-duty agricultural machinery, and wind turbine gearboxes,
Zhengheng Power continuously iterates on high-grade cast iron metallurgy, molding, and quality control processes. Whether it’s traditional high-grade gray iron, vermicular graphite cast iron, or high-strength and tough ductile iron representing the industry’s cutting edge, Zhengheng Power can provide a one-stop reliable solution from material design to mass production delivery.