Hot-Pressed Steel Member Bending Collapsibility
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Improving the bending collapsibility of hot-pressed members with a tensile strength of 1.8 GPa or greater is challenging, as existing methods either compromise on strength or fail to enhance toughness sufficiently.
Innovation Solution
Reducing the abundance ratio of inclusions with a longest diameter of 25 μm or greater and inhibiting the formation of retained austenite and bainite by controlling the cooling rate over a specific temperature range, while optimizing the chemical composition and microstructure of the steel sheet to achieve a martensite volume fraction of 70% or greater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of steel sheet is increased to 1.8 GPa class, then the crash safety is enhanced, but the ductility and toughness are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.28-0.45%, Si: 0.01-2.0%, Mn: 0.5-3.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.01-1.0%, N: 0.01% or less, O: 0.0013% or less) and processing parameters (cooling rate ≥20°C/s, heating temperature Ac3-1000°C, heating time 30-600s) to achieve a martensite microstructure with 70% or greater volume fraction, resulting in tensile strength of 1.8 GPa or greater while maintaining toughness through controlled inclusion abundance
Solution Approach 2:
The patent creates a composite microstructure consisting primarily of martensite (70% or greater volume fraction) with controlled inclusion distribution. The inclusion abundance ratio is maintained at 0.003/mm² or less, creating a composite material system where the martensitic matrix provides strength while the controlled inclusion distribution prevents crack initiation and propagation, thereby maintaining toughness at 1.8 GPa strength level
2Reliability
If heat treatment at 150 to 200° C. is applied to improve toughness, then the toughness of hot-pressed parts is enhanced, but cracking still occurs in 1.8 GPa class parts
Solution Approach 1:
The patent applies preliminary action by controlling the base material quality before hot-pressing. The steel sheet is prepared with optimized chemical composition and controlled inclusion abundance ratio (0.003/mm² or less) beforehand, so that when hot-pressing and heat treatment are performed, the material is pre-conditioned to resist crack initiation and propagation, preventing cracking in 1.8 GPa class parts while maintaining toughness
3Reliability
If soft ferrite microstructure is formed in surface layer to enhance ductility, then the crash property is improved, but the yield strength is noticeably reduced
Solution Approach 1:
The patent applies local quality by creating a martensite microstructure (70% or greater volume fraction) throughout the steel sheet, providing locally optimized properties where the martensitic structure simultaneously delivers high strength (1.8 GPa or greater) and adequate ductility through controlled inclusion distribution, eliminating the need for surface ferrite formation that would compromise overall yield strength
4Reliability
If the abundance ratio of inclusions is reduced to improve bending collapsibility, then cracking during collapse is inhibited, but the manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by setting specific compositional parameters (C: 0.28-0.45%, Si: 0.01-2.0%, Mn: 0.5-3.5%, P: 0.05% or less, S: 0.01% or less, Al: 0.01-1.0%, N: 0.01% or less, O: 0.0013% or less) and processing parameters (cooling rate ≥20°C/s, heating temperature Ac3-1000°C, heating time 30-600s) to control inclusion formation and distribution during steelmaking and hot-pressing, achieving inclusion abundance ratio of 0.003/mm² or less through optimized manufacturing parameters rather than additional complex processing steps
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 approach results in a hot-pressed member with a tensile strength of 1.8 GPa and excellent bending collapsibility, as evidenced by a maximum load to yield strength ratio of 0.044 or greater, while maintaining the strength and toughness of the material.
Implementation Method 1
the steel sheet having a microstructure in which martensite is present in a volume fraction of 70% or greater, and a number density of inclusions having a longest diameter of 25 μm or greater is less than or equal to 0.02/mm2
Implementation Method 2
cooling the steel sheet to a room temperature in a manner in which an average cooling rate over a temperature range of 400 to 100° C. is greater than or equal to a specific cooling rate
Data Source
AI summary
A hot-pressed member having excellent bending collapsibility, a method for manufacturing the same, and a method for manufacturing a steel sheet for the hot-pressed member. The hot-pressed member includes a steel sheet as a base material, the steel sheet having a specified chemical composition. The hot-pressed member has a microstructure in which a martensite microstructure is present in a volume fraction of 70% or greater, and a number density of inclusions having a longest diameter of 25 μm or greater is 0.02/mm2 or less. The hot-pressed member has a tensile strength of 1.8 GPa or greater.