Hot Press Die Hard Layer to Reduce Aluminum Adhesion and Wear
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Solution Overview
Problem
Existing methods for hot press forming of Al-plated steel sheets fail to effectively reduce die wear and maintain surface quality due to the formation of aluminum adhesion and scratches during the process, despite the use of zinc compound or metallic zinc layers for corrosion protection.
Innovation Solution
A method involving a die with a hard layer having a skewness of 1.3 or less and a hardness of HV 2,000 or more, combined with a nitride layer and a hard coating layer, is used to reduce die wear and improve surface quality by minimizing aluminum adhesion and scratches during hot press forming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a steel sheet is heated to a high temperature of 800°C or higher for hot press forming, then the steel sheet can be easily stamped and mechanical strength is enhanced by quenching, but surfaces of the steel sheet are oxidized to cause the generation of scales
Solution Approach 1:
An Al-based metal coating is applied as an intermediary layer between the steel sheet surface and the oxidizing atmosphere. This coating layer prevents direct oxidation of the steel sheet during high-temperature hot press forming, thereby avoiding scale formation while allowing the steel to achieve high mechanical strength through quenching.
Solution Approach 2:
The Al-based metal coating creates a protective environment around the steel sheet surface, effectively isolating it from oxygen during the heating process. This inert barrier prevents oxidation reactions even at temperatures of 800°C or higher, eliminating the need for subsequent descaling steps.
2Reliability
If a steel sheet having Zn-based plating is heated for hot press forming, then corrosion protection is provided, but the plating layer may evaporate at heating temperatures of 700 to 1,000°C and cause a significant deterioration in surface texture
Solution Approach 1:
The invention changes the material parameter of the plating layer from Zn-based to Al-based metal coating. Aluminum has a significantly higher boiling point than zinc, allowing the coating to withstand hot press forming temperatures of 700-1,000°C without evaporation, thus maintaining surface texture quality while preserving corrosion protection through the Al-based coating.
3Productivity
If an Al-based metal coating is provided to prevent scale attachment, then productivity is improved and corrosion resistance is enhanced, but the aluminum-iron alloy layer grows to such an extent that processing defects are formed due to contact with a die during stamping
Solution Approach 1:
The invention optimizes the thickness parameter of the Al-based metal coating to a specific range (5-20 μm). This controlled thickness prevents excessive growth of the aluminum-iron alloy layer during heating, thereby avoiding processing defects such as die contact issues while maintaining the benefits of scale prevention and corrosion resistance.
Solution Approach 2:
The invention applies the Al-based metal coating with controlled local thickness characteristics, ensuring that the coating is thick enough to prevent oxidation but thin enough to limit alloy layer growth. This localized quality control prevents processing defects while maintaining productivity improvements.
4Weight of moving object
If the thickness of steel sheets is reduced to achieve weight reduction, then vehicle body weight is reduced, but the mechanical strength of the structural materials must be maintained
Solution Approach 1:
The invention utilizes the phase transition of steel during hot press forming - heating to austenite phase followed by rapid quenching to martensite phase. This phase transition enables the steel to be formed at high temperature when soft, then achieves superior mechanical strength after quenching, allowing thinner sheets to maintain required strength levels.
Solution Approach 2:
The invention changes the temperature parameter during forming, heating the steel sheet to high temperature to reduce flow stress and enable forming of thin-gauge materials, then rapidly cooling to achieve high strength. This parameter change allows weight reduction through thinner sheets while maintaining mechanical strength requirements.
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 method significantly reduces die wear and enhances surface quality by controlling the skewness and hardness of the die's hard layer, thereby minimizing adhesion and scratches on the die and improving the corrosion resistance and mechanical strength of the press-formed products.
Implementation Method 1
By providing an Al-based metal coating to a steel sheet, attachment of scales to the surface of the steel sheet can be prevented
Implementation Method 2
the Al coating melts, and then transforms into an aluminum-iron alloy layer
Implementation Method 3
transforms into an aluminum-iron alloy layer due to diffusion of Fe from the steel sheet
Implementation Method 4
minimizing aluminum adhesion and scratches during hot press forming
Data Source
AI summary
A method of producing a hot press-formed product includes subjecting an Al-plated steel sheet having a zinc compound layer or a metallic zinc layer, as an outermost layer, provided on an Al plating layer to hot press forming using a die. The die includes a hard layer having a skewness (Rsk), as measured in a direction from the outside of a die hole toward the inside of the die hole, of 1.3 or less and a hardness Hv_Die of HV 2,000 or more, over the entirety of a region of a steel sheet contact surface that is adjacent to a die shoulder portion. The steel sheet contact surface is a surface located outside of the die hole and configured to contact the Al-plated steel sheet that is to be subjected to the hot press forming.