Cold Rolled Steel Sheet Grain Refinement for Drawn Can Formability
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Solution Overview
Problem
Existing cold rolled steel sheets for drawn cans face challenges in achieving simultaneous improvements in press formability, surface roughening resistance, and earing resistance while maintaining non-ageing properties, with issues related to crystal grain size, adhesion of Ni-plated layers, and corrosion resistance.
Innovation Solution
A cold rolled steel sheet with a chemical composition of C: 0.0060% to 0.0110%, Si: 0.50% or less, Mn: 0.70% or less, P: 0.070% or less, Sol. Al: 0.005% to 0.100%, N: less than 0.0025%, and Nb satisfying a specific ratio, forming a ferrite single-phase structure with a crystal grain size number of 11.0 or more, and optionally featuring a Ni diffusion plated layer with appropriate Fe concentration and adhesion, to enhance mechanical properties and prevent ageing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the crystal grain size is increased to improve surface roughening resistance, then press formability deteriorates due to reduced material ductility
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystal grain size to fall within the range of 5.0 μm to 10.0 μm, and by adjusting the chemical composition parameters (C: 0.0030-0.0100%, Si: 0.05-0.35%, Mn: 0.50-1.00%, P: 0.010-0.050%, S: 0.010-0.050%, Ti: 0.010-0.050%, Nb: 0.008-0.030%, B: 0.0002-0.0007%) to achieve the optimal balance between surface roughening resistance and press formability. This quantitative parameter optimization resolves the contradiction by finding the precise range where both requirements are satisfied simultaneously.
2Reliability
If Ni plating is applied to improve corrosion resistance, then adhesion problems occur during harsh pressing operations
Solution Approach 1:
The patent employs composite material strategy by creating a multi-layer plating structure consisting of Ni plating combined with underlying metal layers (such as Cu or Zn layers). This composite structure provides both corrosion resistance from the Ni layer and improved adhesion to the base metal through the intermediate layers, thereby resolving the contradiction between corrosion resistance and adhesion strength during harsh pressing.
Solution Approach 2:
The patent introduces intermediary layers (such as Cu or Zn layers) between the Ni plating and the base metal. These intermediary layers act as mediators that enhance the bonding between the Ni coating and the substrate, preventing adhesion failures during harsh pressing while maintaining the corrosion protection function of the Ni outer layer.
3Reliability
If harsh multiple stages of drawing and ironing are applied to improve can performance, then material defects such as cracking occur
Solution Approach 1:
The patent applies parameter changes by optimizing the crystal grain size (5.0 μm to 10.0 μm) and chemical composition parameters to enhance the material's formability and ductility. These parameter optimizations enable the material to withstand harsh multiple stages of drawing and ironing without developing defects such as cracking, thereby improving can performance while preventing material failures.
Solution Approach 2:
The patent applies preliminary action by pre-treating the steel sheet with controlled rolling and plating processes before the harsh drawing and ironing operations. The controlled rolling creates an optimized microstructure, and the plating provides protective and adhesive layers in advance, enabling the material to better withstand subsequent harsh forming operations without developing defects.
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
The solution results in a steel sheet with improved press formability, surface roughening resistance, and earing resistance, along with non-ageing properties, ensuring high yield strength, tensile strength, and total elongation, while maintaining corrosion resistance and preventing stretcher strains.
Implementation Method 1
a first relationship between an amount of C and an amount of Nb is defined by Expression (1): F1 (=Nb/C)≥500×C... (Nb) satisfying Expression (1)... to refine crystal grains
Implementation Method 2
a crystal grain size number is 11.0 or more... GS. No of a recrystallized grain is 8.5 to 11.0
Data Source
Figure 1
AI summary
A steel sheet for a drawn can has a predetermined chemical composition and has a ferrite single-phase structure with a crystal grain size number of 11.0 or more, the sheet thickness is 0.15 to 0.50 mm, in an L direction of the steel sheet after an ageing treatment at 100°C for one hour, an yield strength YP is 220 to 290 MPa, a tensile strength TS is 330 to 390 MPa, a total elongation EL is 32% or more, an yield point elongation YP-EL is 0%, an average plastic strain ratio rm is more than 1.35, and an in-plane anisotropy Δr is -0.30 to +0.15.