Galvanized Steel Sheet Composition for Faster LME-Resistant Hot Pressing
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Solution Overview
Problem
Galvanized steel sheets face challenges during hot pressing due to liquid metal embrittlement (LME) cracks, which reduce the impact resistance and fatigue strength of components, and existing methods to mitigate this issue either require longer heating times, increase costs, or do not effectively suppress LME cracks.
Innovation Solution
A galvanized steel sheet with internal oxides dispersed at a certain depth from the interface between the galvanized layer and the base steel sheet, promoting an alloying reaction that reduces the amount of liquid zinc, thereby suppressing LME cracks, and allowing for shorter heating times during the hot pressing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a galvanized steel sheet is used for hot pressing, then corrosion resistance is improved, but LME cracks occur during press-forming reducing impact resistance and fatigue strength
Solution Approach 1:
A silicate-based coating is applied as an intermediary layer between the galvanized steel sheet and the mold during hot pressing. This coating prevents direct contact between the molten zinc and the mold, eliminating the LME effect while preserving the corrosion resistance of the galvanized layer. The coating acts as a barrier that mediates the interaction between the molten metal and the mold surface.
Solution Approach 2:
The invention changes the chemical composition and physical properties of the surface layer by applying a silicate-based coating. This coating has a higher melting point than zinc and forms a stable barrier layer that prevents zinc from embrittlting the mold. The parameter change involves transforming the surface chemistry to resist LME while maintaining the underlying galvanized structure for corrosion protection.
2Reliability
If heating time is extended to suppress LME cracks, then LME is reduced, but productivity decreases due to longer processing time
Solution Approach 1:
The silicate-based coating is applied in advance to the galvanized steel sheet before hot pressing. This preliminary action creates a protective barrier that prevents LME cracks during the subsequent rapid heating and forming process. Because the protection is pre-established, extended heating times are not required, and productivity is maintained.
3Reliability
If a ductile layer is formed on the galvanized coating to suppress LME, then surface microcracks are prevented, but the ductile layer disappears by rapid alloying during heating
Solution Approach 1:
Instead of relying on a thin ductile layer that is consumed during heating, the invention uses a silicate-based coating that is specifically designed to remain stable at hot pressing temperatures. This coating does not rapidly alloy with zinc and maintains its protective function throughout the process, providing durable crack suppression without being consumed.
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 effectively reduces heating time, enhances productivity, and produces hot press-formed products with high strength and corrosion resistance, while maintaining the required antirust performance.
Implementation Method 1
promoting an alloying reaction that reduces the amount of liquid zinc
Implementation Method 2
zinc liquefied at a high temperature of 900°C
Implementation Method 3
suppressing LME cracks
Data Source
Figure 1~2
Figure 3
AI summary
To provide a galvanized steel sheet for hot pressing which can achieve heating for suppressing the occurrence of LME cracks in a short time during a hot pressing process, and a method of manufacturing a hot press-formed product obtained by performing hot pressing using the galvanized steel sheet. Disclosed is a galvanized steel sheet for use in hot pressing, including a galvanized layer and a base steel sheet, wherein internal oxide is present on a side of the base steel sheet from an interface between the galvanized layer and the base steel sheet, the base steel sheet including defined C, Si, Mn, and Cr, with the balance being iron and inevitable impurities, wherein the base steel sheet satisfies the following formula (1): 2×Si/28.1+Mn/54.9+1.5×Cr/52.0≥0.05 wherein, in the formula (1), [Si] represents a Si content in mass% of the base steel sheet, [Mn] represents a Mn content in mass% of the base steel sheet, and [Cr] represents a Cr content in mass% of the base steel sheet.