Mitigating liquid metal embrittlement in zinc-coated press hardened steels

Abstract

Methods of reducing liquid metal embrittlement (LME) in zinc-coated high-strength steel alloys are provided. In one variation, the method includes decarburizing an exposed surface of a high-strength steel alloy to form a decarburized surface layer. The decarburized surface layer has a thickness of less than or equal to about 50 micrometers. The decarburized surface layer may have greater than or equal to about 80 volume % ferrite. The method also includes applying a zinc-based coating to the decarburized surface layer. A blank is formed from the high-strength steel alloy. The method also includes heating and press hardening the blank to form a press-hardened component having an ultimate tensile strength of greater than or equal to about 1,100 MPa that is substantially free of liquid metal embrittlement.

Description

INTRODUCTION[0001]This section provides background information related to the present disclosure which is not necessarily prior art.[0002]Press-hardened steel (PHS), also referred to as “hot-stamped steel” or “boron-steel” (e.g., 22MnB5 alloy), is one of the strongest steels used for automotive body structural applications, typically having tensile strength properties on the order of about 1,400 megapascals (MPa) or higher. Such steel has desirable properties, including forming steel components with significant increases in strength-to-weight ratios. PHS components have become ever more prevalent in various industries and applications, including general manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like.[0003]For example, when manufacturing vehicles, especially automobiles, continual improvement in fuel efficiency and performance is desirable, thus PHS components have been increasingly used. PHS component...

AI Technical Summary

Benefits of technology

The patent text provides a method to improve the strength and ductility of high-strength steels used for load-bearing components in vehicles. This is achieved by using a process called decarburization to form a thin layer of ferrite on the surface of the steel, which is then coated with zinc to create a galvanized layer. This results in a high-strength steel component that is resistant to liquid metal embrittlement and has improved performance. Additionally, the method reduces the likelihood of cracking and fatigue in the steel components, which can prolong the life of the components and increase safety for vehicle occupants.

Problems solved by technology

However, liquid metal embrittlement (LME) may occur when a metallic system is exposed to a liquid metal, such as zinc, during forming at high temperature, resulting in potential cracking and a reduction of total elongation or diminished ductility of a material.

LME may also result in decreased ultimate tensile strength.

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