Flat Steel Surface Waviness Control via Tempering Roller Parameters
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Solution Overview
Problem
Existing methods for producing flat steel products, particularly those made from soft IF steels or bake-hardening steels, face challenges in maintaining optimal surface properties and minimizing waviness, which is critical for automotive body construction where filler-free painting is used.
Innovation Solution
A method involving specific steel compositions and processing steps, including hot rolling, cold rolling, recrystallizing annealing, and temper rolling, is employed to achieve a flat steel product with reduced waviness and optimized surface properties, characterized by a Wsa (1-5) value of less than 0.35 µm and planar anisotropy within a controlled depth, ensuring operational safety and formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If smooth tempering rollers are used to reduce waviness, then surface smoothness is improved, but impressions are left on the flat steel product and minimum surface texture requirements are not met
Solution Approach 1:
The invention changes the parameters of the tempering roller surface by specifying a controlled arithmetic mean roughness Ra of 0.4-1.6 μm and peak count Rp of 60-100/cm, rather than using perfectly smooth rollers. This parameter optimization allows the roller to reduce waviness while maintaining sufficient surface texture to avoid impressions.
Solution Approach 2:
The invention applies local quality by creating a specific surface structure on the tempering roller with controlled roughness and peak distribution. The roller surface is engineered to have specific local characteristics (Ra and Rp values) that differ from both completely smooth and conventional rough surfaces, enabling selective waviness reduction without impression formation.
2Object-generated harmful factors
If skin rolling with rough work rolls is used to create surface texture, then minimum surface texture requirements are met, but waviness increases
Solution Approach 1:
The invention optimizes the skin rolling parameters by specifying work roll roughness Ra of 0.8-2.5 μm and peak count ≥100/cm2, and limits the skin rolling degree to 0.4-0.7%. These controlled parameters ensure sufficient surface texture is created while minimizing waviness transfer to the steel product.
3Manufacturing precision
If the Wsa value is kept low in the undeformed state, then surface smoothness is improved, but the value deteriorates to unacceptable levels during subsequent forming
Solution Approach 1:
The invention applies preliminary action by performing skin rolling with specifically parameterized work rolls before final temper rolling. This preliminary surface structuring creates a robust surface texture that is resistant to deterioration during subsequent forming operations, preventing waviness development while maintaining adequate surface quality.
4Adaptability or versatility
If recrystallization annealing is performed to optimize formability, then formability is improved, but surface properties and waviness control become more difficult to maintain
Solution Approach 1:
The invention segments the manufacturing process into distinct stages with specific surface treatment operations. Recrystallization annealing is performed followed by skin rolling and then temper rolling, with each stage optimized for its specific function. This segmentation allows formability to be improved through annealing while subsequent rolling stages restore and maintain surface quality.
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 method effectively reduces waviness and enhances surface properties, ensuring the flat steel products meet stringent requirements for automotive applications by minimizing waviness and maintaining formability and strength, thus improving the reliability of components produced from these steels.
Implementation Method 1
b) Heating the slab in an oven to a slab-pulling temperature Bzt of 1200 - 1270 °C
Implementation Method 2
d) Cooling the obtained hot-rolled steel flat product to a coil temperature of 620 - 780 °C, with a cooling rate of 4 - 30 K/s
Implementation Method 3
h) recrystallizing annealing of the cold-rolled steel flat product at an annealing temperature of 650 - 900 °C
Data Source
AI summary
The invention enables the production of flat steel products provided with a corrosion protection coating, which, after 5% biaxial deformation on one of their surfaces, have a Wsa(1-5) value of < 0.35 µm, a planar anisotropy Δr of -0.5 to +0.5, and a nanohardness H of > 0.1 to < 3.0 GPa from its surface down to a depth of < 200 µm. For this purpose, a slab of (in wt.-%) 0.0003 - 0.050 % C, 0.0001 - 0.20 % Si, 0.01 - 1.5 % Mn, 0.001 - 0.10 % P, 0.0005 - 0.030 % S, 0.001 - 0.12 % Al, 0.0001 - 0.01 % N, each optionally 0.0001 - 0.15 % Ti, 0.0001 - 0.05 % Nb, ≤ 0.005 % B, ≤ 0.15 % Cu, ≤ 0.15 % Cr, ≤ 0.15 % Ni, ≤ 0.10 % Mo, ≤ 0.05 % Sn and as residue from Fe and impurities to a slab drawing temperature BZT of 1200 The steel is heated to 1270 °C, pre-rolled with a thickness reduction of 80–90%, and then hot-rolled again with a thickness reduction of 85–95% at a final temperature of 850–950 °C, achieving a total deformation of 95–99.5% and a thickness reduction ΔdF in the last hot-rolling pass of 1–25%, resulting in a 3–5 mm thick flat steel product. This product is then cooled at a rate of 4–30 K/s to a coiling temperature HT of 620–780 °C and coiled. After pickling, it is cold-rolled with a total deformation of 70–90% and recrystallized annealing at 650–900 °C.BZT, GLZ, ΔdF, and HT satisfy the condition −0.529653*Q+0.944372*HT_t+0.711559*ΔdF_t<−0.1889459, where BZT is in °C, GLZ in min, HT in °C, and ΔdF in %, and Q = ((BZT/GLZ)-5.553°C/min)/(1.777°C/min); HT_t = (HT-728.13°C)/42.300°C and ΔdF_t = (ΔdF12.43384%)/2.306328%. The steel flat product is coated with a corrosion protection coating.