Hot Strip Inductive Hardening for Strength and Weldability
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Solution Overview
Problem
Conventional hot strip production methods result in non-homogeneous properties near weld seams and require labor-intensive, cost-intensive piece-by-piece heat treatments, which can negatively affect weldability and mechanical properties due to high alloy concentrations.
Innovation Solution
A method involving short-term inductive hardening or quenching and tempering with rapid heating and cooling rates, achieving a predominantly martensitic structure with homogeneous isotropic properties, including optional annealing to improve weld seam properties and increase yield strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional hot strip production methods are used with high alloy concentrations, then strength can be improved, but weldability deteriorates
Solution Approach 1:
The patent changes the thermal processing parameters by applying short-term inductive hardening (heating to Ac3 + 30-50°C and holding for 3-10 seconds) followed by rapid cooling. This parameter change enables achieving high strength (tensile strength ≥1200 MPa) without requiring high alloy concentrations, thereby maintaining good weldability
Solution Approach 2:
The patent replaces conventional slow heating methods with inductive heating technology, achieving rapid heating rates (10-100 K/s) that enable short-term heat treatment. This substitution allows for precise control of austenite grain formation and subsequent martensitic transformation, achieving high strength properties with reduced alloy content
2Strength
If piece-by-piece heat treatment is applied to improve mechanical properties, then strength and toughness can be improved, but production efficiency deteriorates
Solution Approach 1:
The patent applies short-term inductive hardening directly to the hot strip while it is still in the rolling mill, before the strip is cut into individual pieces. This preliminary action on the continuous strip eliminates the need for subsequent piece-by-piece heat treatment, significantly improving production efficiency while achieving the desired mechanical properties (tensile strength ≥1200 MPa, elongation ≥10%)
Solution Approach 2:
The patent enables continuous heat treatment of the hot strip through the rolling mill using inductive heating technology. The heating and cooling process occurs continuously along the strip length without interruption, maintaining production flow and eliminating downtime associated with batch heat treatment of individual pieces
3Use of energy by moving object
If conventional cooling rates are used after rolling, then energy consumption is reduced, but microstructure homogeneity deteriorates
Solution Approach 1:
The patent employs a two-stage thermal process: first, conventional cooling after rolling to reduce energy consumption; second, short-term inductive heating to Ac3 + 30-50°C followed by rapid cooling (10-100 K/s). This periodic action achieves homogeneous martensitic microstructure with fine grain size (5-15 μm) while minimizing overall energy consumption compared to continuous rapid cooling
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 approach produces ultra-high-strength hot strip products with enhanced toughness, isotropy, and weldability, allowing for inline heat treatment and eliminating the need for separate component hardening or quenching, while achieving superior mechanical properties such as high tensile strength and notched bar impact work.
Implementation Method 1
heating takes place with the use of an inductive heating device with a temperature increase of more than 5 K/s
Implementation Method 2
a cooling takes place at a cooling rate of more than 10 K/s
Implementation Method 3
for hardening purposes, is briefly heated to a temperature >Ac3 and cooled again... achieves a predominantly martensitic structure
Data Source
AI summary
The invention relates to a method for producing hot-rolled hot strip products in which a steel alloy is melted; the melted steel alloy is cast into slab ingots and after being heated to a temperature above Ac3, the slab ingots are hot rolled until they reach a desired degree of deformation and a desired strip thickness; the rolling is performed above the recrystallization temperature of the alloy; after the rolling, the strip is cooled to room temperature and for hardening purposes, is briefly heated to a temperature >Ac3 and cooled again, characterized in that the heating takes place with a temperature increase of more than 5 K/s, more than 10 K/s, more than 50 K/s, or more than 100 K/s and is kept at a desired target temperature for a period of 0.5 to 60 s before cooling to yield improved mechanical properties.