Tailored Rolled Blank Press Hardening Against Hydrogen Absorption
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Solution Overview
Problem
Press hardening methods face challenges in preventing hydrogen absorption during austenitization heat treatment, especially in parts with variable thickness, which increases sensitivity to delayed fracture.
Innovation Solution
A method involving flexible rolling of a steel sheet with a zinc- or aluminum-based pre-coating followed by deposition of a hydrogen barrier pre-coating, heat treatment to form a fully austenitic microstructure, and hot-forming to achieve a part with variable thickness and improved resistance to delayed fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If flexible rolling is used to produce variable thickness parts, then weight optimization and load distribution are improved, but hydrogen absorption increases and sensitivity to delayed fracture worsens
Solution Approach 1:
A hydrogen barrier pre-coating is deposited on the steel sheet before flexible rolling to prevent hydrogen absorption during subsequent austenitization heat treatment. This preliminary protective action ensures that even though variable thickness parts absorb more hydrogen, the pre-coating barrier significantly reduces this absorption, maintaining reliability while achieving weight optimization through flexible rolling.
Solution Approach 2:
The steel sheet is provided with a composite structure consisting of the base steel material and a hydrogen barrier pre-coating layer. This composite structure combines the benefits of variable thickness geometry for weight optimization with the protective barrier function to prevent hydrogen absorption, thereby resolving the contradiction between weight reduction and delayed fracture resistance.
2Reliability
If a hydrogen barrier pre-coating is deposited, then hydrogen absorption is reduced and resistance to delayed fracture is improved, but manufacturing complexity increases
Solution Approach 1:
The hydrogen barrier pre-coating is deposited in advance, before flexible rolling and heat treatment. This preliminary action integrates the protective function into the existing manufacturing sequence without requiring additional complex equipment or processes, thereby improving reliability while minimizing increases in manufacturing complexity.
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 method significantly reduces hydrogen absorption and enhances the resistance to delayed fracture by forming thermodynamically stable oxides on the surface, resulting in a part with a martensitic or martensito-bainitic microstructure.
Implementation Method 1
the barrier effect of the pre-coating is highly improved, preventing even more the absorption of hydrogen into the steel sheet
Implementation Method 2
during the thermal treatment, thermodynamically stable oxides are formed on the surface of the barrier pre-coating with a low kinetic. These thermodynamically stable oxides further reduce hydrogen absorption
Implementation Method 3
the heat treatment of the tailored rolled blank to obtain a fully austenitic microstructure in the steel
Implementation Method 4
the cooling of the part having a variable thickness obtained at step G) to obtain a microstructure in steel being martensitic or martensito-bainitic
Data Source
AI summary
A press hardening method including the following steps: A. the provision of a steel sheet for heat treatment being optionally coated with a zinc- or aluminum-based pre-coating, B. the flexible rolling of the steel sheet in the rolling direction so as to obtain a steel sheet having a variable thickness, C. the cutting of the rolled steel sheet to obtain a tailored rolled blank, D. the deposition of a hydrogen barrier pre-coating over a thickness from 10 to 550 nm, E. the heat treatment of the tailored rolled blank to obtain a fully austenitic microstructure in the steel, F. the transfer of the tailored rolled blank into a press tool, G. the hot-forming of the tailored rolled blank to obtain a part having a variable thickness,H. the cooling of the part having a variable thickness obtained at step G).