Surface Grain Refining Hot-Shearing Steel Sheet
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Solution Overview
Problem
Existing methods for hot-shearing steel sheets with high carbon content face issues such as reduced tool service life, delayed fracture due to residual stress, and dimensional inaccuracies, which are not adequately addressed by current techniques like quenching press, laser cutting, or local electric-heating methods.
Innovation Solution
A surface layer grain refining hot-shearing method that involves heating the steel sheet to austenitize it, then shearing at a temperature calculated based on equivalent plastic strain and Ar3 point, followed by rapid cooling, to optimize the microstructure and reduce residual stress without increasing shearing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching press is used to form high-strength members, then strength is improved, but tool service life deteriorates due to high hardness
Solution Approach 1:
The invention applies preliminary heating to the steel sheet before shearing, softening the material in advance to reduce deformation resistance during shearing. This preliminary thermal preparation allows subsequent quenching to achieve high strength while the initial soft state protects the tool from excessive wear, resolving the contradiction between strength and tool service life.
Solution Approach 2:
The invention changes the temperature parameter dynamically: heating the steel sheet to austenite region (above Ac3 point) before shearing to reduce hardness and deformation resistance, then rapidly cooling during or after shearing to achieve high strength. This parameter transformation allows the material to exhibit different properties at different stages, protecting the tool during shearing while achieving high strength in the final product.
2Strength
If shearing is performed on quenched material, then strength is maintained, but delayed fracture occurs due to residual stress
Solution Approach 1:
The invention performs preliminary heating to austenite temperature before shearing, which reduces the material's deformation resistance and allows for more uniform plastic deformation. This preliminary thermal preparation minimizes localized stress concentrations that would otherwise lead to delayed fracture, while the subsequent quenching maintains the required strength.
Solution Approach 2:
The invention utilizes phase transition of steel from austenite to martensite during quenching. By shearing in the austenite phase (above Ac3 point) where the material is more ductile and less prone to stress concentration, and then transforming to martensite phase for high strength, the invention achieves both delayed fracture resistance and strength through controlled phase transition timing.
3Reliability
If shearing temperature is increased to prevent delayed fracture, then reliability is improved, but dimensional accuracy deteriorates due to thermal expansion
Solution Approach 1:
The invention applies preliminary heating to a specific temperature range (above Ac3 point but controlled) to achieve the necessary ductility for preventing delayed fracture. By carefully controlling this preliminary heating temperature and duration, the invention minimizes excessive thermal expansion while still achieving the austenite transformation needed for improved reliability during shearing.
Solution Approach 2:
The invention changes the temperature parameter precisely: heating to just above the Ac3 point to achieve austenite transformation and improved ductility, then rapidly cooling to room temperature. This controlled parameter change achieves the minimum necessary temperature elevation for reliability improvement while minimizing thermal expansion and dimensional inaccuracies through efficient heat dissipation.
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 effectively prevents delayed fracture and improves dimension accuracy of the workpiece by controlling the shearing temperature and microstructural transformation, enhancing the toughness and structural integrity of the sheared surface layer.
Implementation Method 1
heating the steel sheet to austenitize it
Implementation Method 2
quenching by rapidly cooling the sheared steel sheet
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Provided is a surface layer grain refining hot-shearing method including: heating and keeping a steel sheet in a temperature range of from Ac3 to 1400°C to austenitize the steel sheet; subsequently shearing the steel sheet in a state in which the steel sheet is placed on a die; and quenching by rapidly cooling the sheared steel sheet, wherein a start temperature of the shearing is set to be a temperature (°C) obtained by adding a temperature of from 30°C to 140°C to a previously measured Ar3 of the steel sheet.