High-Strength Steel Manufacturing via Single-Heating Martensite Formation
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Solution Overview
Problem
Traditional hot stamping processes for producing martensite steel result in high manufacturing costs and energy losses due to the need for multiple heat treatments and low yield strength, making it difficult to achieve high tensile strength and yield ratio.
Innovation Solution
A method involving a single heating step followed by hot rolling, cold rolling, annealing, and controlled cooling to achieve a high volume ratio of tempered martensite without retempering, which includes specific temperature and time parameters to produce steel with high tensile strength, yield strength, and yield ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional hot stamping process is used to produce martensite steel, then high tensile strength is achieved, but manufacturing cost and energy loss increase due to multiple heat treatments
Solution Approach 1:
The patent combines multiple heat treatment steps into a single heating process. The steel slab is heated once to austenite region, then undergoes hot rolling, cold rolling, and direct quenching to form martensite structure. This eliminates the need for separate tempering and re-heating steps, reducing energy consumption while maintaining high tensile strength through the martensitic microstructure achieved by controlled cooling.
Solution Approach 2:
The patent performs preliminary hot rolling and cold rolling on the steel slab before final quenching. These preliminary deformation processes are conducted while the steel is in the austenite region, preparing the microstructure for subsequent martensitic transformation. This preliminary action allows the steel to achieve desired shape and initial microstructure without requiring additional heating cycles.
2Strength
If traditional hot stamping process is used to produce martensite steel, then high tensile strength is achieved, but manufacturing cost increases due to additional equipment investment
Solution Approach 1:
The patent integrates forming and heat treatment operations into a single continuous process. The steel slab is heated once, then directly formed through hot and cold rolling, and finally quenched in the same production line. This eliminates the need for separate hot stamping presses and tempering equipment, reducing capital investment while achieving high tensile strength through the martensitic structure formed by controlled cooling.
3Ease of manufacture
If single-stage cooling is used in hot stamping process, then manufacturing is simplified, but yield strength remains low and yield ratio is difficult to increase
Solution Approach 1:
The patent divides the cooling process into multiple stages with different cooling rates. After heating to austenite region, the steel is first cooled at a moderate rate during hot rolling, then at a faster rate during cold rolling, and finally rapidly quenched to form martensite. This segmented cooling approach allows control over microstructure development, achieving high yield strength and yield ratio through the martensitic transformation while maintaining process feasibility.
4Manufacturing precision
If multiple heat treatments are applied to produce martensite steel, then microstructure control is improved, but processing time increases
Solution Approach 1:
The patent performs preliminary deformation and microstructure preparation during hot rolling and cold rolling while the steel is in the austenite region. These preliminary actions establish the desired shape and create a fine-grained austenite structure that will transform uniformly during subsequent quenching. This eliminates the need for separate tempering and re-heating steps, reducing processing time while maintaining precise microstructure control through the martensitic transformation.
Solution Approach 2:
The patent maintains continuous processing from heating through hot rolling, cold rolling, and quenching without interrupting the production flow. The steel remains in the austenite region throughout hot and cold rolling, then undergoes continuous cooling to form martensite. This continuous action eliminates idle time between heat treatment steps while maintaining microstructure control through careful management of temperature and deformation parameters throughout the process.
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 manufacturing costs and energy losses while achieving steel with a tensile strength of at least 1300 MPa, yield strength of at least 1050 MPa, and a yield ratio of at least 0.8, with a volume ratio of tempered martensite not less than 95%, thus improving the efficiency and cost-effectiveness of steel production.
Implementation Method 1
cooling the annealed steel plate to no less than 680° C. at a cooling rate between 5° C./second and 20° C./second; cooling the annealed steel plate to no higher than 400° C. at a cooling rate between 30° C./second and 300° C./second; and cooling the annealed steel plate to between 250° C. and 300° C. at a cooling rate between 10° C./second and 40° C./second
Implementation Method 2
a volume ratio of tempered martensite of the high-strength steel is not less than 95%
Implementation Method 3
a heating step is performed on the slab to obtain a heated slab
Data Source
AI summary
The present disclosure relates to a high-strength steel and a method of manufacturing the same. Slab with specific composition is subjected to a rolling process and a heat treatment process with specific conditions for changing the metallographic structure of the obtained steel. The obtained steel includes at least 95% tempered martensite, and has a high tensile strength and a high yield strength.