Hot dip galvanized steel sheet having excellent resistance to cracking due to liquid metal embrittlement

Abstract

A hot-dip galvanized steel sheet having excellent resistance to cracking caused by liquid metal embrittlement is provided. The hot-dip galvanized steel sheet having excellent resistance to cracking caused by liquid metal embrittlement includes a base steel sheet having a microstructure in which an austenite fraction is 90 area % or more; and a hot-dip galvanizing layer formed on the base steel sheet, wherein the hot-dip galvanizing layer includes an Fe—Zn alloy layer; and a Zn layer formed on the Fe—Zn alloy layer, and the Fe—Zn alloy layer has a thickness of [(3.4×t) / 6]μm or more, where t is a thickness of the hot-dip galvanizing layer. In addition, provided is the hot-dip galvanized steel sheet in which plating layer delamination easily occurring in vehicle welding and molding conditions according to the related art, is prevented, and cracking caused by liquid metal embrittlement is suppressed.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a hot-dip galvanized steel sheet having excellent resistance to cracking caused by liquid metal embrittlement.BACKGROUND ART[0002]In general, body components of a vehicle are required to be lightweight while having stability. To this end, it is required to ensure high strength, ductility, and corrosion resistance in a steel sheet used for a component for a vehicle.[0003]A representative technique therefor is disclosed in Patent Document 1. The technique relates to a Twinning-Induced Plasticity (TWIP) type ultra high strength steel sheet including 0.15 wt % to 0.30 wt % of carbon (C), 0.01 wt % to 0.03 wt % of silicon (Si), 15 wt % to 25 wt % of manganese (Mn), 1.2 wt % to 3.0 wt % of aluminum (Al), 0.020 wt % or less of phosphorus (P), 0.001 wt % to 0.002 wt % of sulfur (S), and iron (Fe) as a residual component thereof, and inevitable impurities, and a microstructure of steel is formed of a structure in an austenite phase. Ultr...

AI Technical Summary

Benefits of technology

The patent is about a way to make a hot-dip galvanized steel sheet that will not develop plating layer delamination or cracks during vehicle welding and molding. This can improve the quality of the finished products and make them more reliable.

Problems solved by technology

At this time, when tensile stress is applied to the HAZ, a crack having a size of about 10 μm to 100 μm may occur, thereby causing a brittle fracture phenomenon.

In addition, as a grain boundary is expanded by a high thermal expansion coefficient, a liquid metal embrittlement problem may occur severely.

As a result, without external tensile stress, the thermal stress is applied to a welded portion, whereby the possibility of the occurrence of liquid metal embrittlement may be very high.

When an LME crack occurs as illustrated in FIG. 1, the LME crack causes fracturing of a steel sheet, whereby it may be difficult to use GI TWIP steel as a component for a vehicle and the like.

Images