Forged Steel Roll Manufacturing via ESR with Bismuth
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Solution Overview
Problem
The manufacturing of forged steel rolls is hindered by macro-segregations such as ghost segregation and freckle defects, which lead to cracks and exposed segregation lines, compromising the quality and longevity of the rolls during forging, heat treatment, and repeated surface cutting repairs.
Innovation Solution
Incorporating Bi into the molten steel during the ESR method, with specific compositions of C, Si, Cr, Mo, and Bi, to miniaturize the dendrite structure and suppress freckle defects, thereby sealing them near the center of the ingot and preventing their exposure during forging and heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If steel ingots are cast by the ingot-making method, then large-scaled ingots can be produced for forged steel rolls, but macro segregation (ghost segregation) occurs from the center to the surface during casting
Solution Approach 1:
The patent changes the casting parameters by using electroslag remelting instead of conventional ingot-making, controlling the molten steel pool depth and curvature radius to prevent macrosegregation while producing large-scaled ingots for forged steel rolls
Solution Approach 2:
The patent replaces the mechanical ingot-making casting system with an electroslag remelting system that uses electrical energy to melt and recast steel, eliminating the macrosegregation issues inherent in conventional mechanical casting methods
2Reliability
If ghost segregation is present in the ingot, then cracks can occur during forging and heat treatment due to stresses, but using ESR method reduces ghost segregation
Solution Approach 1:
The patent performs preliminary action by eliminating macrosegregation during the ESR casting process itself, preventing the formation of segregation zones that would later cause cracks during forging and heat treatment, rather than trying to address cracks after they form
3Ease of repair
If the roll surface is cut repeatedly for repair, then the smoothness can be restored, but segregation lines become exposed to the surface
Solution Approach 1:
The patent performs preliminary action by positioning all segregation lines deep inside the ingot during the ESR casting process, ensuring they remain below the surface even after repeated cutting repairs, thus preventing exposure of segregation lines that would degrade surface quality
4Stability of the object's composition
If ESR method is used to reduce segregation, then freckle defects still occur in the vicinity of 1/2 radius of the ingot
Solution Approach 1:
The patent changes critical casting parameters by controlling the molten steel pool depth and curvature radius relationships, adjusting these parameters to prevent the formation of freckle defects that occur at specific radial positions in conventional ESR casting
Solution Approach 2:
The patent uses a simulation model that copies and analyzes the casting process to identify optimal parameter combinations that prevent freckle defects, then applies these optimized parameters in actual ESR casting operations
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 approach effectively suppresses freckle defects, preventing cracks and segregation line exposure, allowing for stable long-term use of forged steel rolls without compromising roll diameter or causing embrittlement.
Implementation Method 1
Incorporating Bi into the molten steel during the ESR method, with specific compositions of C, Si, Cr, Mo, and Bi, to miniaturize the dendrite structure and suppress freckle defects
Implementation Method 2
casting, by the ESR method, a steel ingot which contains, by mass %, C: 0.3% or more, Si: 0.2% or more, Cr: 2.0-13.0% and Mo: 0.2% or more, and further contains Bi at 10-100 ppm by mass
Data Source
AI summary
A method for manufacturing a forged steel roll comprises: casting, by the ESR method, a steel ingot which contains, by mass %, C: 0.3% or more, Si: 0.2% or more, Cr: 2.0-13.0% and Mo: 0.2% or more, and further contains Bi at 10-100 ppm by mass; and forging the steel ingot to manufacture the roll. According to this method, since freckle defects can be sealed near the center of the steel ingot, the roll can be stably used over a long period of time.