What Are the Advantages of Galvannealed Steel Sheet?

Galvannealed steel is similar to galvanized, but goes through an additional process that improves paintability. It’s also better at resisting corrosion and scratching.

After the metal leaves the zinc bath, it goes through a low pressure, high volume air knife to blow off excess zinc before it solidifies, creating a thinner coating than standard galvanized steel.

Corrosion Resistance

Galvannealed sheet steel has enhanced corrosion resistance when compared to regular galvanized metal. The annealing process diffuses iron from the underlying steel into the zinc coating, creating a zinc-iron alloy. This allows the coating to be harder and more scratch resistant, making it better able to resist surface damage.

It also has a smoother, more matte finish than standard galvanized metal, which makes it easier to paint. The galvannealed coating is more absorbent than standard galvanized metal, so it bonds with paint much better. This is especially important if the metal will be used in an environment where water or salt spray might be present.

Both galvanized and galvanneal steels are stronger than uncoated steel. The strength of a coated steel depends on the coating galvannealed steel sheet as well as the quality of the underlying steel. Galvanneal steel is made of low-carbon steel that contains a small amount of manganese, oxygen, silicon, and phosphorus. The annealing process converts some of these elements into hydrogen, which creates a chemical bond with the zinc layer.

This bond is what gives galvanneal steel its superior corrosion resistance. It can withstand many environmental factors, including high humidity, which might cause other types of steel to rust or corrode faster. It’s often used in industrial settings and other outdoor applications that require corrosion protection.

Weldability

In addition to its corrosion resistance, galvannealed steel is also known for its weldability and formability. These characteristics make it an ideal material for producing automobile body parts. However, the material needs to meet certain requirements before it can be used in this application. For example, the material must have excellent spot weldability and resistance to peeling of the zinc coating during press work.

In order to achieve this, the steel must be reannealed to a temperature of around 770 °C. This process deoxidizes the molten steel and allows it to cool slowly, so that the zinc can re-alloy with the steel. The result is a smooth surface that is less porous and absorbs paints much better than uncoated cold-rolled steel.

The Nb content of the re-annealed steel should not be smaller than 0.005 wt% and the B content should not be lower than 0.0002 wt%. An Nb content that is too low prevents the re-annealing from taking place at normal temperatures and reduces the ductility of the Q195 carbon steel plate sheet. Similarly, a B content that is too low reduces the Lankford value r, which impairs the press-workability of the sheet.

In addition to the above requirements, the welded joint must be resistant to cracking and fatigue in the weldment zone. To meet these demands, the welding parameters need to be adjusted. During spot welding, the width of the heat-affected zone (HAZ) enlarges with increasing welding current and time.

Formability

The galvannealed steel sheet can be easily formed to various shapes, making it useful for manufacturing automobile components. This is possible because the steel is ductile, meaning it can be bent and shaped without damaging it. This also makes it easier to weld. The zinc-iron alloy layer that covers the steel is conducive to welding, and it helps prevent weld spatter and provides an electrically conductive surface. This makes galvanneal steel a better choice than standard galvanized steel for applications that require significant welding.

Galvannealed steel sheets can be postpainted, which is a benefit for manufacturers who want to paint their products. The steel is more porous and abrasive than standard galvanized, which helps the paint adhere to it better. The paintability of galvannealed steel is useful for outdoor applications, such as industrial equipment and building facades.

The present invention relates to a galvannealed steel sheet for use in automobiles having excellent powdering resistance, low temperature chipping resistance and paint bake hardenability. The steel sheet is manufactured by obtaining an ultra-low carbon steel slab having a chemical composition of Ti, Si and N, adding alloying elements effective for solid solution hardening to the base metal thereof, and heating up the resulting steel plate to the plating bath to perform Fe-Zn alloying thereon. This is done while avoiding excessively long processing times, which tend to impair powdering resistance and low temperature chipping resistance of the plated coating.

Paintability

Galvannealed steel is a unique type of sheet metal that undergoes the dual processes of galvanization and annealing. The result is a steel product that has many of the same corrosion resistance benefits of galvanized, but the matte finish and paintability make it ideal for architectural applications, as well as other projects where aesthetics are important.

To create galvannealed steel, the steel first undergoes the hot-dip galvanizing process to get a zinc coating on both sides of the strip. Then, it goes through the annealing process that converts the pure zinc layer into a more durable zinc-iron alloy. This coating provides an impeccable base for paint adhesion, meaning that when the sheet is painted, it will hold the paint longer and not flake or peel as easily as it might with a less durable pure zinc coating.

Because of its ability to withstand the rigors of industrial and outdoor environments, galvannealed steel is used in applications such as agriculture and equipment manufacturing. It is also a popular choice for building parts and components in the automotive industry, such as vehicle body panels. While galvanized steel is often used in these types of applications as well, the ductility of galvanneal makes it a better choice for these jobs that require significant bending and other forming, which can damage or degrade the pure zinc coating on galvanized steel.