Cold-Rolled Steel Sheet Quenching-Partitioning Process
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Solution Overview
Problem
Current high-strength cold-rolled steel plates face challenges in achieving both high strength and formability while maintaining low material costs, as they often require the addition of expensive alloy elements, which increases production costs and complicates manufacturing processes.
Innovation Solution
A high-formability, super-high-strength cold-rolled steel plate is developed using a composition optimized with C, Si, and Mn, combined with a quenching-partitioning process, which controls the material structure to achieve superior strength and plasticity without the need for expensive alloy elements, employing a continuous annealing process under conventional hot and cold rolling conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If expensive alloy elements (Cu, Ni, Cr) are added to achieve high strength and elongation, then the mechanical properties (yield strength 380-1000 MPa, tensile strength 680-1280 MPa, elongation 15-30%) are improved, but the material cost increases significantly
Solution Approach 1:
The patent changes the chemical composition parameters by limiting expensive alloy elements (Cu≤0.1%, Ni≤0.1%, Cr≤0.1%) and optimizing the content of common elements (C: 0.15-0.25%, Si: 1.00-2.00%, Mn: 1.50-3.00%). This parameter optimization achieves high strength properties while controlling material cost by relying on affordable elements rather than expensive alloys.
Solution Approach 2:
The patent utilizes phase transition during the quenching-partitioning process to achieve high strength without expensive alloys. The steel is heated to Ac3+30-50°C to form austenite, then rapidly cooled to obtain martensite structure with high strength. This phase transition mechanism enables cost-effective high-strength steel production.
2Strength
If traditional phase structures (martensite, bainite) are used to achieve high strength, then the strength is improved, but the plasticity and formability are significantly reduced
Solution Approach 1:
The patent employs a quenching-partitioning process that utilizes controlled phase transitions to achieve both high strength and good plasticity. The steel is heated to austenite region, rapidly cooled to form martensite for strength, then partitioned at 250-600°C to optimize the microstructure. This controlled phase transition sequence produces a balanced microstructure with tensile strength 980-1150 MPa and elongation 17-25%, resolving the contradiction between strength and formability.
Solution Approach 2:
The patent creates a composite microstructure consisting of martensite (for strength) and retained austenite (for plasticity and formability). This microstructural composite achieves super-high strength (980-1150 MPa) while maintaining good elongation (17-25%), effectively combining the advantages of different phases to resolve the strength-formability contradiction.
3Weight of moving object
If the steel plate thickness is reduced to achieve weight reduction, then the vehicle weight decreases (fuel consumption lowered by 5%-8%), but the strength and safety requirements become harder to meet
Solution Approach 1:
The patent uses quenching-partitioning induced phase transitions to achieve super-high strength (tensile strength 980-1150 MPa) in thin steel plates. This enables significant thickness reduction while maintaining strength requirements, directly contributing to vehicle weight reduction and fuel consumption reduction (5%-8% improvement).
Solution Approach 2:
The patent optimizes chemical composition parameters (C: 0.15-0.25%, Si: 1.00-2.00%, Mn: 1.50-3.00%) to achieve high strength-to-weight ratio. This parameter optimization enables the use of thinner steel plates with sufficient strength, facilitating vehicle weight reduction while meeting safety requirements.
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 solution results in a steel plate with a yield strength of 600-900 MPa, tensile strength of 980-1150 MPa, and elongation of 17-25%, suitable for vehicle parts with complex shapes, while maintaining low production costs and simplifying the manufacturing process.
Implementation Method 1
the structure at room temperature of 10%-30% ferrite+60-80% martensite+5-15% residual austenite
Implementation Method 2
combined with a quenching-partitioning process, which controls the material structure to achieve superior strength and plasticity
Data Source
AI summary
A high-formability and super-strength cold-rolled steel sheet and a manufacturing method thereof. The weight percentage of its components is: C 0.15-0.25%, Si 1.00-2.00%, Mn 1.50-3.00%, P≤0.015%, S≤0.012%, Al 0.03-0.06%, N≤0.008%, and the rest are Fe and inevitable impurities. The manufacturing method comprises the following steps: 1) smelting and casting; 2) heating to 1170˜1230° C. and performing thermal insulation; 3) performing hot rolling, the finish rolling temperature being 880±30° C., and coiling at 550˜650° C.; and 4) performing acid washing, cold rolling, and annealing, the cold rolling reduction being 40-60%, annealing at 860-920° C., and performing slow cooling to 690-750° C. with the cooling rate of 3˜10° C./s; performing rapid cooling at 240˜320° C., with the cooling speed ≥50° C./s, then heating to 360˜460° C., and performing thermal insulation for 100˜500 s to cool to the room temperature at last. Finally, a high-formability, low-rebound property and super-strength cold-rolled steel sheet with the yield strength of 600˜900 MPa, the tensile strength of 980˜1150 MPa, the elongation of 17˜25% is obtained.