Ni-Mo Steel Billet Casting Mold w/h Ratio for Segregation Control
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Solution Overview
Problem
The continuous casting method struggles to produce high Cr-high Ni—Mo steel seamless pipes due to segregation, cavity, and intergranular cracking issues, which affect the internal quality of round billets and the inner surface of seamless pipes.
Innovation Solution
A method involving continuous casting of high Cr-high Ni—Mo steel into a rectangular billet, followed by shaping into a round billet using a casting mold with a specific w/h ratio and controlled chemical composition, and extended soaking times to reduce Mo segregation and improve internal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous casting method is used to manufacture high Cr-high Ni—Mo steel, then productivity and cost are improved, but Mo segregation, cavity, and intergranular cracking occur in the cast slab
Solution Approach 1:
The patent applies parameter changes by optimizing the chemical composition parameters of the molten steel (specific ratios of Cr, Ni, Mo, and other elements) and controlling casting parameters to minimize segregation and defects while maintaining continuous casting productivity
Solution Approach 2:
The patent applies local quality by ensuring uniform distribution of alloying elements (particularly Mo) throughout the cast slab through controlled composition and casting parameters, preventing localized segregation and improving overall internal quality
2Productivity
If continuous casting is used instead of ingot casting, then cooling speed increases and productivity improves, but cracking occurs in axial center and deformation-related cracking occurs
Solution Approach 1:
The patent changes the chemical composition parameters of the steel to improve cracking resistance during continuous casting, specifically optimizing the ratios of alloying elements to reduce deformation resistance and prevent intergranular cracking under fast cooling conditions
Solution Approach 2:
The patent applies preliminary action by pre-adjusting the chemical composition of the molten steel before casting to prevent cracking issues that would otherwise occur during the continuous casting process, thereby ensuring reliability from the outset
3Ease of manufacture
If rectangular billet is shaped into round billet by rolling or forging, then seamless pipe can be manufactured, but internal quality issues (intergranular cracking, cavity, segregation) affect inner surface quality
Solution Approach 1:
The patent applies preliminary action by ensuring high internal quality in the rectangular billet through optimized continuous casting parameters and chemical composition before the shaping process, thereby preventing internal defects from affecting the final seamless pipe quality
Solution Approach 2:
The patent changes the chemical composition parameters to reduce segregation and improve internal quality of the billet, which directly contributes to better inner surface quality of the manufactured seamless pipe
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances the internal quality of round billets and the inner surface quality of seamless pipes, reducing the reject ratio of seamless pipes to less than 10% by minimizing Mo segregation and intergranular cracking.
Implementation Method 1
continuously casting a molten steel by means of a casting mold, thereby obtaining a rectangular billet
Implementation Method 2
extended soaking times to reduce Mo segregation and improve internal quality
Implementation Method 3
shaping the rectangular billet into a round billet by forging or rolling
Data Source
AI summary
Provided is a method for manufacturing a round billet of Ni-containing high alloy including steps of continuously casting a molten steel by using a casting mold, thereby obtaining a rectangular billet, and shaping the rectangular billet into round billet by forging/rolling, wherein the casting mold has a shape such that a w/h ratio between long side length (w) and short side length (h) of a cross section of the rectangular billet perpendicular to the casting direction of rectangular billet is 1.0 to 2.0, the chemical composition of molten steel is, by mass %: C: 0.005 to 0.250%, Si: 0.05 to 2.00%, Mn: 0.05 to 3.00%, P: 0.04% or less, S: 0.004% or less, Cu: 0.01 to 3.00%, Cr: 10 to 35%, Ni: 10 to 80%, Mo: 1.5 to 10.0%, Al: 0.001 to 0.300%, N: 0.001 to 0.300%, W: 0.00 to 6.00%, Ti: 0.00 to 2.00%, and the balance: Fe and impurities.