Lightweight Steel Sheet Austenite Retention Decarburization Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge is to develop a lightweight steel sheet with improved strength and ductility that maintains a sufficient amount of austenite during thermal treatment, even with small amounts of carbon and manganese, to prevent decarbonization and ensure high mechanical properties.
Innovation Solution
A lightweight steel sheet composition including carbon (0.1-1.2 wt%), manganese (2-10 wt%), aluminum (3-10 wt%), phosphorus (0.1 wt% or less), sulfur (0.01 wt% or less), and optional nickel, copper, antimony, or boron, with a specific formula B* (B*=Ni+0.5Cu+100Sb+500B) to control decarbonization, and a manufacturing method involving reheating and hot rolling at specific temperatures followed by cold rolling to maintain austenite and improve mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If carbon and manganese are added to steel to improve strength and ductility, then mechanical properties are improved, but decarbonization occurs during thermal treatment reducing austenite content
Solution Approach 1:
Silicon is introduced as an intermediary element that preferentially reacts with oxygen during thermal treatment, forming silicon oxide. This protects the carbon-austenite system from decarbonization by acting as a sacrificial protective layer, allowing austenite to be maintained while still achieving high strength through controlled carbon and manganese addition
Solution Approach 2:
The invention changes the chemical composition parameters by adding silicon within specific ranges (0.01-2.0 wt%) in combination with controlled carbon (0.15-1.0 wt%) and manganese (1.0-3.0 wt%) contents. This parameter adjustment prevents decarbonization during thermal treatment while maintaining the desired mechanical properties and austenite content
2Weight of moving object
If aluminum is added to reduce specific gravity, then weight is reduced, but tensile strength decreases to about 400 MPa
Solution Approach 1:
The invention creates a composite microstructure containing both ferrite and retained austenite phases through controlled aluminum addition (2.0-10.0 wt%) combined with silicon and carbon-manganese interactions. This dual-phase composite structure achieves both lightweight properties from aluminum and high strength through the synergistic effect of ferrite-austenite combination, preventing the strength reduction that occurs with aluminum alone
Solution Approach 2:
The invention creates local quality differences by controlling the distribution and content of alloying elements throughout the steel matrix. Silicon preferentially segregates to certain regions during thermal treatment, creating localized protection against decarbonization while maintaining overall lightweight properties through aluminum addition and achieving high strength through controlled carbon-manganese distribution
3Strength
If dual phase steel with large amount of residual austenite is manufactured to improve strength and ductility, then mechanical properties are improved, but decarbonization during reheating reduces austenite content
Solution Approach 1:
Silicon serves as a protective intermediary that prevents carbon loss during thermal treatment. By adding silicon (0.01-2.0 wt%), it forms silicon oxide during reheating, creating a protective barrier that prevents oxygen from reacting with carbon. This maintains the carbon content necessary for sustaining residual austenite, thereby preserving the dual-phase microstructure and its associated high strength and ductility properties
Solution Approach 2:
The invention applies preliminary action by adding silicon to the steel composition before thermal treatment. This preliminary addition of silicon prepares the steel for subsequent thermal processing by establishing a protective chemical environment that prevents decarbonization during reheating, ensuring that the austenite content is maintained throughout the thermal treatment 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 solution effectively controls decarbonization, maintaining a sufficient amount of austenite and carbide dispersion in a ferritic base material, resulting in a steel sheet with tensile strength of 700 MPa or more and elongation percentage of 30% or more, reducing material anisotropy and enhancing moldability for lightweight vehicle bodies.
Implementation Method 1
the dual phase lightweight steel sheet is decarbonized and causes a problem in that the amount of austenite is reduced along with the loss of carbon
Implementation Method 2
a dual phase lightweight steel sheet having no ridging and having improved strength and ductility was developed by containing a large amount of residual austenite to cause transformation induced plasticity
Implementation Method 3
when the dual phase lightweight steel sheet is reheated to hot roll a slab
Implementation Method 4
cold rolling the hot rolled steel sheet at a cold reduction ratio of 40% or more
Data Source
AI summary
The present invention relates to a lightweight steel sheet and a method of manufacturing the same, wherein high strength and ductility can be achieved in the lightweight steel sheet even when a small amount of carbon and manganese is added, by preventing loss of austenite due to decarburizing through inhibiting decarburization, which occurs during a heat treatment step of a steel sheet containing austenite.