Following our discussion on centerline segregation in continuous casting slabs, we move to another important area: large forging ingots. Unlike continuous casting slabs, large forging ingots (used for generator rotors, large marine crankshafts, nuclear pressure vessels, heavy rolling mill rolls, etc.) undergo a much slower solidification process with extremely low cooling rates. Consequently, they face more severe issues of segregation, porosity, shrinkage cavities, and non-metallic inclusions. If these internal defects are not effectively controlled, they will directly lead to rejection of the forging during ultrasonic testing, causing huge economic losses. How can you systematically improve the internal quality of large forging ingots to ensure they withstand the demands of extreme service conditions? Wuxi WeiDa Cored Wire Co.,Ltd provides customized cored wire solutions for ingot mold metallurgy.
The Challenge of Large Forging Ingots: The "Price" of Slow Solidification
Large forging ingots range in weight from a few tons to several hundred tons. Due to their massive cross-sectional dimensions, heat dissipation is extremely slow, and solidification can take hours or even days. This slow solidification process brings a series of problems: First, severe macrosegregation, such as A-segregation (V-shaped) and V-segregation (inverted V-shaped). These segregation bands are difficult to eliminate during forging. Second, center porosity and shrinkage cavities. Solidification shrinkage cannot be effectively compensated, leading to voids in the central region. Third, accumulation of large inclusions. Due to the long flotation path, large inclusions are easily captured by the solidification front, concentrating in the conical bottom or top of the ingot.
Our Solution: Precision Metallurgy Inside the Ingot Mold
Wuxi WeiDa has extended cored wire technology to the forging ingot sector. By feeding specific types of cored wires into the ingot mold during or after teeming, we can "intervene" in the solidification process. First, modifying inclusions with rare earth treatment. Feeding rare earth cored wire (RE-wire) during teeming can completely modify MnS and Al₂O₃ inclusions. This is crucial for improving the transverse properties and fatigue life of forgings. Especially for alloy steel forgings like Ni-Cr-Mo-V, rare earth treatment can significantly reduce the harmful effects of inclusions.
Second, adding solidification nucleants. By feeding titanium, boron, and rare earth composite cored wires, a large number of dispersed, high-melting-point fine particles (e.g., TiN, TiC, rare earth oxides) are formed in the molten steel. These particles act as heterogeneous nucleation sites, refining the as-cast structure, increasing the proportion of equiaxed crystals, and thereby reducing segregation and porosity.
Third, optimizing riser feeding. For large ingots, the effectiveness of riser feeding directly determines the yield of the forging. We provide exothermic and insulating compound cored wires that can be fed into the riser area to improve feeding efficiency and reduce shrinkage cavity depth. Additionally, by feeding aluminum wire or calcium silicon wire for localized deoxidation, the fluidity of the steel in the riser can be improved, allowing it to better feed the ingot body.
Fourth, preventing secondary oxidation. The teeming time for large ingots is long, and the molten steel is exposed to the atmosphere inside the ingot mold for an extended period. We recommend continuously blowing argon into the ingot mold during teeming or feeding protective atmosphere-forming agents to isolate the air, preventing the formation of an oxide film on the steel surface – a major source of surface cracks on forgings.
Practical Case: Significant Internal Quality Improvement
Applying Wuxi WeiDa's ingot mold wire feeding technology to large forging ingots over 60 tons has achieved remarkable results:
•Improved ultrasonic testing pass rate: Center porosity and shrinkage cavity ratings are reduced, and the ultrasonic testing (UT) pass rate increases by 15-20%.
•Improved segregation: Macro-etched samples show significantly reduced severity of A and V segregation.
•Improved isotropy: Due to inclusion modification and structure refinement, the difference between longitudinal and transverse properties of the forging is significantly reduced.
Building a Solid Foundation for High-End Forgings
If you are engaged in the production of large forgings and face challenges like low UT pass rates, unstable properties, and low yield, then ingot mold wire feeding technology is a direction worth your serious attention. Wuxi WeiDa can not only provide you with high-purity, high-stability cored wire products but also collaborate with you to develop customized ingot mold wire feeding processes, formulating the best plan based on your ingot size, steel grade composition, and quality objectives.
To learn about the latest technologies for internal quality control of large forging ingots and obtain a design guide for ingot mold wire feeding processes, please visit https://www.weidamaterials.com/ .