Cold-Rolled Welded Steel Sheets With Staged Deformation Control
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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 increase the risk of fracture during cold rolling, particularly in high-strength steels like dual-phase, high-formability, martensitic, and press-hardening steels, which are challenging to produce efficiently and with uniform properties.
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, where the sheets are first cold rolled to an intermediate thickness, then re-welded and rolled to the final thickness, with the direction of cold rolling aligned with the hot rolling direction, and the deformation ratio controlled between 0.35 and 0.65 to reduce the risk of premature fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the welded joint is cold rolled in a single step to achieve final thickness, then the cold rolling process is simple and fast, but the deformation concentrates in the welded joint leading to fracture risk
Solution Approach 1:
The cold rolling process is divided into multiple stages with intermediate annealing. The total deformation is split into several passes, with the welded joint being annealed between passes to restore ductility and prevent deformation concentration that would lead to fracture.
Solution Approach 2:
The welded joint undergoes preliminary annealing treatment before the final cold rolling pass. This preliminary action restores the metallurgical structure and ductility of the welded joint, preparing it to withstand the subsequent deformation without fracturing.
2Length of moving object
If the total deformation during cold rolling is increased to achieve thinner sheets, then the final sheet thickness is reduced, but the deformation concentration in welded joint increases fracture risk
Solution Approach 1:
The large total deformation required to achieve thin sheet thickness is segmented into multiple smaller deformation passes. Intermediate annealing treatments are applied between passes, particularly to the welded joint, to prevent deformation concentration and enable accumulation of total strain without fracture.
Solution Approach 2:
The metallurgical parameters of the welded joint are changed through controlled annealing treatments. By adjusting temperature and time parameters of the annealing process, the ductility and microstructure of the welded joint are optimized to withstand the cumulative deformation required for producing thin sheets.
3Productivity
If flash welding or laser welding is used to ensure continuity, then the welding quality is high, but the geometrical and metallurgical singularities are concentrated in the welded joint
Solution Approach 1:
The welded joint with concentrated singularities is extracted and subjected to separate annealing treatment. This allows the welded joint to be processed differently from the base metal, addressing its specific metallurgical needs to reduce singularities while maintaining the benefits of continuous welding.
Solution Approach 2:
The thermal parameters of the welded joint are changed through controlled annealing. By adjusting temperature, heating rate, and holding time, the metallurgical structure of the welded joint is modified to reduce geometrical and metallurgical singularities, improving uniformity while maintaining process continuity.
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 fracture in welded joints by achieving uniform deformation across the sheet, maintaining surface reactivity for annealing, and producing high-strength steel sheets with consistent mechanical properties across a wider range of thicknesses, thereby enhancing manufacturing efficiency and productivity.
Implementation Method 1
These welds are generally made by flash welding or by Laser welding
Implementation Method 2
These welds are generally made by flash welding or by Laser welding
Implementation Method 3
the hot-rolled sheets are welded, so as to ensure the continuity of the subsequent process steps... the sheets or strips are pickled by passing through a suitable bath
Implementation Method 4
They are then rolled on a cold rolling mill and recoiled. Finally, they are continuously annealed... a hot-rolled sheet of thickness ei=3 mm can be cold rolled to a thickness ef=1 mm, by successive passages through rolling stands
Implementation Method 5
the cold-rolled sheet then undergoes a treatment in a continuous annealing furnace
Data Source
AI summary
A method for the manufacture of a cold-rolled steel sheet of thickness ef between 0.5 mm and 3 mm is provided. At least two hot-rolled sheets of thickness ei are supplied and butt welded, so as to create a welded joint (S1) with a direction perpendicular to the direction of hot rolling. The at least two hot-rolled sheets are pickled by continuous passage through a bath, then the assembly is cold rolled, in a step (L1), to an intermediate thickness eint, the direction of cold rolling (DL1) coinciding with the direction of hot rolling. The cold rolling is carried out with a reduction ratioɛ1=Ln(eieint)such that:0.35≤Ln(eieint)Ln(eief)≤0.65,then the welded joint (S1) is removed so as to obtain at least two intermediate cold-rolled sheets. Then the two intermediate cold-rolled sheets are butt welded, so as to create a welded joint (S2), the direction of which is perpendicular to the direction of hot rolling, then the assembly of the at least two intermediate cold-rolled and welded sheets is cold-rolled, in a step (L2), to the final thickness ef, the direction (DL2) of the cold rolling step (L2) coinciding with the direction of rolling (DL1).