Hot Press Steel Sheet Low-Temperature Heat Treatment
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Solution Overview
Problem
Conventional steel sheets for hot press forming require high temperatures for heat treatment, leading to issues such as reduced strength in thin parts, surface quality deterioration, and increased energy consumption, while also posing challenges in forming ultra-high strength steels with tensile strength above 1000 MPa.
Innovation Solution
A steel sheet composition with specific ranges of carbon, manganese, nitrogen, and other elements, along with controlled processing conditions, allows for hot press forming or post-heat treatment at lower temperatures to achieve tensile strengths of 1470 MPa or more, maintaining strength uniformity and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature heat treatment is performed for hot press forming, then ultra-high strength (1000 MPa or more) can be achieved, but energy consumption increases and surface quality deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the steel sheet (specific C, Si, Mn, P, S, Al, Ti, B content ratios) to enable lower temperature heat treatment. By adjusting these compositional parameters, the steel achieves the necessary hardenability and strength characteristics at reduced temperatures (800-950°C), thereby reducing energy consumption while maintaining ultra-high strength properties
Solution Approach 2:
The patent creates a composite microstructure through controlled alloying, combining multiple elements (C, Si, Mn, Ti, B) in specific proportions to achieve synergistic effects. This composite material approach enables the steel to exhibit both formability and ultra-high strength after heat treatment at lower temperatures, resolving the contradiction between strength achievement and energy consumption
2Strength
If high temperature heat treatment is performed for hot press forming, then ultra-high strength (1000 MPa or more) can be achieved, but surface quality deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters, specifically controlling the content of C (0.15-0.35%), Si (0.01-0.50%), Mn (1.50-3.00%), and other elements to suppress oxide scale formation and surface degradation during heat treatment. This compositional optimization allows surface quality preservation at lower heat treatment temperatures while still achieving ultra-high strength
Solution Approach 2:
The patent introduces specific alloying elements (particularly Si, Al, and Ti in controlled amounts) that act as intermediaries to protect the steel surface during heat treatment. These elements form protective layers or modify the oxidation behavior, preventing surface quality deterioration while enabling the heat treatment process to achieve the desired strength levels
3Strength
If strength of steel sheet is increased to meet motor vehicle requirements, then collision safety improves, but formability degrades due to increased yield strength
Solution Approach 1:
The patent utilizes phase transformation parameters by controlling the steel composition (C: 0.15-0.35%, Si: 0.01-0.50%, Mn: 1.50-3.00%, P: 0.01-0.030%, S: 0.005-0.020%, Al: 0.01-0.10%, Ti: 0.005-0.050%, B: 0.0005-0.010%) to enable transformation-induced plasticity. The controlled presence of these elements facilitates the formation of martensite, bainite, and retained austenite phases during deformation, providing both strength and formability through TRIP effect
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (martensite for strength, retained austenite for plasticity, and bainite for toughness) through controlled alloying. This multi-phase composite material structure enables the steel to exhibit both high strength (≥1000 MPa) and good formability, as each phase contributes different mechanical properties that complement each other during forming operations
4Strength
If high strength steel sheet is used for motor vehicle parts, then collision safety improves, but dimensional precision decreases due to excessive springback
Solution Approach 1:
The patent optimizes the chemical composition parameters, particularly the C (0.15-0.35%) and Mn (1.50-3.00%) content, along with controlled amounts of Si, P, S, Al, Ti, and B, to achieve optimal hardenability and phase transformation characteristics. This compositional control enables the steel to undergo complete austenite transformation during heat treatment followed by uniform martensitic transformation during quenching, minimizing differential transformation strains and reducing springback while maintaining ultra-high strength
Solution Approach 2:
The patent exploits controlled phase transitions through its compositional design. The specific alloy content enables complete austenitization at heat treatment temperature, followed by uniform martensitic transformation during rapid cooling. This controlled phase transition sequence ensures uniform dimensional changes throughout the part, minimizing springback and improving dimensional precision while achieving the required ultra-high strength properties
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 proposed solution enables the production of steel sheets with high tensile strength and improved yield strength, enhancing the collision performance and structural integrity of motor vehicle parts while reducing energy consumption and surface defects.
Implementation Method 1
heating the blank at a temperature of 820° C. to 950° C.; and die-quenching the formed steel sheet
Implementation Method 2
heating the blank at a temperature of 820° C. to 950° C.
Implementation Method 3
die-quenching the formed steel sheet. Thereby, either martensite phases or phases in which martensite and bainite are mixed are finally formed
Data Source
AI summary
A steel sheet for forming having low-temperature heat treatment property, in which heat treatment is performed within a range of lower temperature than a conventional steel sheet in the event of hot press forming or post-heat treatment after cold forming, a method of manufacturing the same, and a method of manufacturing parts using the same. The steel sheet has a composition of, by weight, carbon (C): 0.15 to 0.35%, silicon (Si): 0.5% or less, manganese (Mn): 1.5 to 2.2%, phosphorus (P): 0.025% or less, sulfur (S): 0.01% or less, aluminum (Al): 0.01 to 0.05%, nitrogen (N): 50 to 200 ppm, titanium (Ti): 0.005 to 0.05%, tungsten (W): 0.005 to 0.1%, and boron (B): 1 to 50 ppm, wherein Ti/N: less than 3.4, where Ti/N is the atomic ratio of the corresponding elements, Ceq expressed by the following formula ranges from 0.48 to 0.58, and temperature Ar3 ranges from 670° C. to 725° C. Wherein Ceq C+Si/24+Mn/6+Ni/40+Cr/5+V/14 where C, Si, Mn, Ni, Cr and V indicate the contents (wt %) of the respective elements.