Welded Steel Sheet Rolling to Prevent Joint Fracture
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Solution Overview
Problem
The conventional method of manufacturing thin cold-rolled steel sheets concentrates deformations in welded joints, leading to geometrical, metallurgical, and mechanical singularities that can cause fractures during rolling, especially in high-strength steels like dual-phase, high-formability, martensitic, and press-hardening steels, which are challenging to cold roll due to limited rolling capacity and risk of premature fracture.
Innovation Solution
A method involving sequential butt welding and cold rolling of hot-rolled sheets with controlled deformation ratios to minimize the concentration of deformations in welded joints, using a two-step cold rolling process where the first step achieves an intermediate thickness with a deformation ratio between 0.35 and 0.65, and the second step reaches the final thickness with a deformation ratio between 0.4 and 0.7, reducing the risk of fracture and maintaining surface reactivity for subsequent annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hot-rolled sheets are welded and then cold rolled to high strength grades (tensile strength >600 MPa), then the sheets achieve high strength and formability for automotive parts, but the welded joints are prone to premature fracture due to deformation concentration
Solution Approach 1:
The cold rolling process is divided into multiple passes with controlled deformation ratios. The first pass applies a limited deformation ratio (0.15-0.35) to reduce deformation concentration in welded joints, followed by intermediate annealing, then subsequent passes achieve the final thickness and high strength properties without causing fracture
2Volume of moving object
If the cold rolling deformation ratio is increased to achieve thinner sheets, then the final thickness is reduced, but the welded joints fracture more easily due to excessive deformation concentration
Solution Approach 1:
The total deformation is segmented across multiple rolling passes. The first pass uses a controlled deformation ratio (0.15-0.35) to avoid fracture, intermediate annealing restores material properties, and subsequent passes progressively achieve the target thin thickness without exceeding deformation limits that would cause welded joint fracture
Solution Approach 2:
Intermediate annealing is performed after the first cold rolling pass to restore the material's ductility and reduce internal stresses before applying further deformation in subsequent passes, preventing fracture during the overall thinning process
3Productivity
If conventional cold rolling is used on welded sheets, then the sheets are processed efficiently, but geometrical and metallurgical singularities concentrate deformations in welded joints leading to production interruptions
Solution Approach 1:
The cold rolling process is segmented into multiple controlled passes with intermediate annealing, distributing the deformation across time and process stages. This prevents sudden deformation concentration that would cause welded joint fracture and production interruptions, while maintaining overall productivity through optimized process flow
Solution Approach 2:
Intermediate annealing is applied after the first cold rolling pass to preliminarily restore material properties before subsequent deformation passes, preventing defect formation and ensuring continuous production capability throughout the manufacturing process
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 reduces the risk of premature fracture in welded joints by distributing deformations evenly, achieving high tensile strength and homogeneity in mechanical properties, while allowing for a wider range of thicknesses beyond the limitations of existing rolling facilities, and maintaining surface reactivity for annealing processes.
Implementation Method 1
in a step (L1), the assembly of at least two hot-rolled sheets is cold rolled and welded to an intermediate thickness eint... such that: 0.15≤ε1≤0.35
Implementation Method 2
in a step (L2), cold rolling is carried out on the assembly of at least two intermediate cold-rolled and welded sheets, to a final thickness ef... such that: 0.40≤ε2≤0.70
Data Source
AI summary
A steel sheet that is welded and then cold rolled to a thickness between 0.5 mm and 3 mm, the deformation ratio created by cold rolling in the base metal is equal to εMB, for which the deformation ratio created by the cold rolling in the welded joint is equal to εS, where:0.4≤ɛSɛMB<0.7.