Thin Slab Cast Press Hardening Steel With 1500 MPa Formability
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Solution Overview
Problem
Current methods for producing ultra-high-strength steel with a tensile strength of 1500 MPa or more are inefficient, leading to high manufacturing costs and inability to meet the demands for lightweight automobile parts due to long processes and low strength levels, along with issues like cracking and springback during forming.
Innovation Solution
A press hardening steel is produced using thin slab casting and direct rolling with specific chemical compositions and a streamlined process involving hot melt desulphurization, continuous casting, soaking, hot rolling, and quenching, which includes multiple descaling steps and controlled temperatures and pressures to achieve a tensile strength of 1500 MPa or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultra-high-strength steel with tensile strength of 1500 MPa or more is produced using existing cold-rolled annealed methods, then the strength requirement is met, but the production process becomes long and costly
Solution Approach 1:
The invention extracts and eliminates unnecessary intermediate processes from the traditional production chain. By removing the cold-rolling and annealing steps and directly producing ultra-high-strength steel through controlled rolling and cooling from hot-rolled slabs, the process time is significantly reduced while maintaining the required tensile strength of 1500 MPa or more
Solution Approach 2:
The invention skips the conventional cold-rolling and annealing stages by rapidly cooling the hot-rolled slabs to achieve martensitic microstructure directly. This rushing through of intermediate steps reduces production time while achieving the target strength level through controlled cooling rates and composition optimization
2Strength
If the strength of steel is increased to 1500 MPa or more, then the collision safety is improved, but the formability deteriorates with cracking and springback
Solution Approach 1:
The invention changes the microstructural parameters by controlling the chemical composition (C: 0.18-0.25%, Si: 0.15-0.30%, Mn: 0.80-1.50%, etc.) and processing parameters (finishing rolling temperature, cooling rate, coiling temperature) to achieve a martensitic microstructure that provides both ultra-high strength and improved formability compared to conventional methods
Solution Approach 2:
The invention utilizes phase transition during rapid cooling from austenite to martensite. By controlling the cooling rate and finishing rolling temperature, the steel undergoes a controlled phase transition that produces a fine martensitic microstructure, achieving tensile strength of 1500 MPa or more while reducing springback and cracking during forming
3Loss of time
If existing medium and thin slab casting and direct rolling methods are used, then the production process is shortened, but the tensile strength only reaches 600-750 MPa which is insufficient
Solution Approach 1:
The invention changes the chemical composition parameters by optimizing C (0.18-0.25%), Si (0.15-0.30%), Mn (0.80-1.50%), and adding microalloying elements (Ti: 0.01-0.05%, Nb: 0.01-0.05%, V: 0.01-0.05%) to enable ultra-high strength. It also changes processing parameters including finishing rolling temperature (850-950°C) and cooling rate to achieve tensile strength of 1500 MPa or more while maintaining the shortened direct rolling process
Solution Approach 2:
The invention creates a composite microstructure through controlled alloying and processing. The combination of base steel with optimized composition and microalloying elements (Ti, Nb, V) creates a martensitic microstructure with enhanced strength properties, achieving ultra-high strength of 1500 MPa or more through the synergistic effect of composition and microstructure control in the direct rolling 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 process results in a high-strength steel with improved surface quality, precision, and reduced springback, enabling complex deformations and meeting the quality requirements for cold-rolled products, thus reducing manufacturing costs and enhancing the strength of automobile parts.
Implementation Method 1
Hot melt desulphurization, and controlling S≤0.005%
Implementation Method 2
soaking, and heating the slab, and controlling a temperature of the slab entering the furnace to be 820-1050° C. and a temperature of the slab leaving the furnace to be 1190-1210° C.
Implementation Method 3
quenching, controlling the quenching cooling speed to be 20-40° C./s
Implementation Method 4
hot rolling, controlling a first pass reduction rate to be 52-63%, a second pass reduction rate to be 50-60% and a final pass reduction rate to be 10-16%
Data Source
AI summary
A press hardening steel by a thin slab casting and direct rolling has a tensile strength of 1500 MPa or more. The press hardening steel has a components by weight percent: C: 0.21-0.25%, Si: 0.26-0.30%, Mn: 1.0-1.3%, P≤0.01%, S≤0.005%, Als: 0.015-0.060%, Cr: 0.25-0.30%, Ti: 0.026-0.030% or Nb: 0.026-0.030% or V: 0.026-0.030%, or a mixture of two or more of the above in any proportion; B: 0.003-0.004%, and N≤0.005%. A method for producing the press hardening steel includes following steps: hot metal desulphurization; electric-furnace or converter smelting and refining; continuous casting; descaling, then entering a soaking furnace; heating and soaking; high-pressure water descaling, then entering a rolling mill; hot rolling; cooling; coiling; austenitizing; die deforming and quenching.