Tailor-Welded Press Hardened Steel with Q&P Tailored Microstructures
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Solution Overview
Problem
Conventional press hardened steels lack the ability to achieve tailored properties with high strength and high energy absorption, as they typically result in components with uniform microstructures, limiting their application in structural members requiring varying intrusion resistance and energy absorption.
Innovation Solution
A tailor-welded blank composed of a higher alloyed steel (Alloy A) and a lower alloyed steel (Alloy B) is created using a modified cooling process, where Alloy A forms a predominantly martensite microstructure and Alloy B retains austenite, achieving strengths up to 2000 MPa and 900 MPa respectively, through a quenching and partitioning (Q&P) process that involves rapid cooling and a controlled holding temperature to stabilize austenite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional press hardening process is used, then high strength is achieved, but uniform microstructure limits energy absorption capability
Solution Approach 1:
The patent applies local quality by creating different microstructures in different regions of the steel component. Through controlled cooling rates during press hardening, the material achieves martensite structure in high-strength regions and retained austenite in energy-absorbing regions, allowing each area to have optimized properties for its specific function
Solution Approach 2:
The patent creates a composite microstructure within the steel component by combining martensite and retained austenite phases. This multi-phase microstructure enables the material to simultaneously exhibit high strength from martensite and high energy absorption from retained austenite, effectively creating a composite material system at the microstructural level
2Adaptability or versatility
If tailor-welded blanks with different steel compositions are used, then tailored properties are achieved, but process complexity increases
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate parameter during press hardening to achieve different microstructures from a single steel composition. By varying the cooling rate, the same material can transform into martensite at faster cooling rates or retain austenite at slower cooling rates, eliminating the need for multiple steel compositions and simplifying the manufacturing 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 enables the production of components with tailored properties, achieving high strength and moderate elongation, suitable for applications requiring both high intrusion resistance and energy absorption.
Implementation Method 1
quenched in the stamping die at sufficient cooling rates such that martensite is formed
Implementation Method 2
the steel is deformed at high temperatures at which austenite is stable
Implementation Method 3
a relatively large fraction of retained austenite is maintained in one steel comprising the tailor-welded blank
Data Source
Figure 1
AI summary
A tailor-welded blank is created by forming a blank from a steel of composition A and a steel of composition B and welding said two steels together, heating said welded blank to a temperature above the Ac1 temperature associated with the steel of composition A, transferring said blank to a forming die, and then cooling said blank to a temperature between the martensite start temperature and martensite finish temperature of the steel of composition B and holding said blank at such temperature or at a higher temperature, cooling said blank to room temperature. The tailor-welded blank comprises Alloy A and Alloy B, wherein Alloy A comprises 0.10 - 0.50 wt % C, 0.1 - 0.5 wt % Si, 2.0 - 8.0 wt % Mn, 0- 6.0 wt% Cr, 0.0 - 2 wt% Mo, and 0.0 - 0.005 wt% B and wherein Alloy B comprises 0.06 - 0.12 wt% C, 0.1 - 0.25 wt% Si, 1.65 - 2.42 wt% Mn, 0.0 - 0.70 wt% Cr, 0.08 - 0.40 wt% Mo, 0.0 - 0.05 wt% V, 0.01 - 0.05 wt% Ti, and 2 wt % A1 or less, and wherein said tailor-welded blank is subject to a quench and partition thermal cycle in a forming die.