Steel Sheet Surface Step Differences for Energy Absorption
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Solution Overview
Problem
Current high strength steel sheets used in automobile bodies lack sufficient energy absorption during crushing deformation, leading to potential fractures and inadequate safety in collisions.
Innovation Solution
A steel sheet with a specific chemical composition and surface roughness is produced through an integrated process involving optimized hot rolling and annealing steps, featuring a microstructure of ferrite, pearlite, and martensite, along with surface step differences exceeding 5.0 μm at intervals of 2.0 mm or less, enhancing energy absorption during crushing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high strength steel sheet is used to lighten automobile body weight, then weight reduction is achieved, but energy absorption during crushing deformation becomes insufficient
Solution Approach 1:
The invention creates local quality differences on the steel sheet surface by forming protrusions with specific dimensions (0.1-5.0 μm height, 10-100 μm width). These localized surface features serve as stress concentration points that initiate and guide deformation, enabling the material to absorb more energy during crushing while maintaining overall high strength properties.
Solution Approach 2:
The surface protrusions are formed in advance during the steel sheet manufacturing process (via controlled oxidation or rolling conditions) before the actual crushing deformation occurs. This preliminary structuring of the surface prepares predetermined deformation initiation sites, ensuring that when crushing occurs, the deformation follows a controlled pattern that maximizes energy absorption.
2Reliability
If high strength steel sheet is used to improve collision safety, then passenger safety is enhanced, but fracture resistance during crushing deformation deteriorates
Solution Approach 1:
By creating localized surface protrusions, the invention distributes deformation initiation points across the surface. This prevents localized stress concentration that would lead to fracture, while the overall high strength material properties maintain collision safety. The protrusions guide deformation in a controlled manner throughout the material.
Solution Approach 2:
The invention changes the surface topology parameters (creating protrusions with specific height, width, and spacing) to alter how stress distributes during deformation. This parameter modification enables the high strength steel to undergo controlled deformation without fracture, maintaining both safety and fracture resistance.
3Ease of manufacture
If smooth surface steel sheet is used, then manufacturing simplicity is maintained, but deformation becomes localized and energy absorption decreases
Solution Approach 1:
The invention introduces minimal local quality changes (surface protrusions) rather than completely redesigning the surface. These small-scale features can be created as byproducts of existing manufacturing processes like controlled oxidation or rolling, maintaining ease of manufacture while significantly improving deformation characteristics and energy absorption.
Solution Approach 2:
The surface protrusions can be formed through self-service mechanisms during manufacturing, such as controlled oxidation that naturally creates surface relief or rolling conditions that inadvertently produce the desired topography. This eliminates the need for additional complex surface treatment steps.
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 resulting steel sheet exhibits improved energy absorption and deformation localization, effectively preventing fractures during collisions, thus enhancing safety and performance in automotive applications.
Implementation Method 1
by increasing the surface roughness of a steel sheet to introduce starting points for deformation at the surface of the steel sheet, the steel sheet exhibiting excellent energy absorption in crushing deformation is obtained
Implementation Method 2
using a bell type batch annealing furnace with a gas atmosphere comprised of 75 vol % or more of hydrogen and a balance of substantially nitrogen and unavoidable impurities to perform annealing treatment repeatedly heating the strip by a 20 to 100° C./h heating rate to the Ac1 point to Ac1 point+50° C. for soaking and heating for 8 hours or less
Data Source
AI summary
A steel sheet excellent in energy absorption at the time of crushing deformation, that is, steel sheet having a predetermined chemical composition and steel microstructure which has on the sheet surface a plurality of step differences having height differences of more than 5.0 μm at intervals of 2.0 mm or less.