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Hot-dip coated sheet – The standard in terms of corrosion protection and formability

Hot-dip coated sheet Z from thyssenkrupp Steel for stamped parts.

Hot-dip coated sheet (Z) from thyssenkrupp is a quality sheet protected against corrosion by a firmly adhering zinc coating. The cold rolled sheet is continuously coated by immersion in a bath of molten zinc.

Hot-dip galvanized sheets in accordance with DIN EN 10346 are available with different coatings from Z100 to Z600, and in finish types A to C, depending on the intended use. In the industrial sector, hot-dip galvanized flat rolled products are used in a wide range of components with increased requirements for corrosion protection and surface finish. Areas of application include structural elements in the construction industry, gates and racking structures, ducts in ventilation and air-conditioning technology, washing machines and refrigerators in the household appliances industry, and sections and telescopic rails in the furniture industry.

In addition, hot-dip zinc coated sheets serve as a substrates for the coil-coated pladur® products.

Availabe steel grades

Hot-dip galvanized sheet for household appliances.
Hot-dip galvanized sheet for household appliances.

Hot-dip coated sheet (Z/GI) is available in different grades of deep-drawing steels, general structural steels, micro-alloyed steels, and multi-phase steels.

For the automotive sector, we supply hot-dip coated sheet (GI) in accordance with VDA 239-100.

Deep-drawing steel
DIN EN 10346

SURFACE FINISHING
Steel grade Z
DX51D
DX52D
DX53D
DX54D
DX56D
DX57D
DX58D

Hot-dip coated structural steel
DIN EN 10346

SURFACE FINISHING
Steel grade Z
S220GD
S250GD
S280GD
S320GD
S350GD
S390GD
S420GD
S450GD

High-strength IF steel
DIN EN 10346

SURFACE FINISHING
Steel grade Z
HX160YD
HC180Y / HX180YD
HC220Y / HX220YD
HC260Y / HX260YD

Bake hardening steel
DIN EN 10346

SURFACE FINISHING
Steel grade Z
HC180B / HX180BD
HC220B / HX220BD
HC260B / HX260BD

Micro-alloyed steel
DIN EN 10346

SURFACE FINISHING
Steel grade Z
HC260LA / HX260LAD
HC300LA / HX300LAD
HC340LA / HX340LAD
HC380LA / HX380LAD
HC420LA / HX420LAD
HC460LA / HX460LAD
HC500LA / HX500LAD

Dual-phase steel
DIN EN 10346

SURFACE FINISHING
Steel grade Reference grade
DIN EN 10346
Z
DP-K® 290Y490T
HCT490X
DP-K® 330Y590T
HCT590X
DP-K® 330Y590T DH
DP-K® 420Y590T
DP-K® 440Y780T HCT780X
DP-K® 440Y780T DH
DP-K® 440Y780T HHE
DP-K® 500Y780T
DP-K® 590Y980T HCT980X
DP-K® 700Y980T HCT980XG
DP-K® 780Y1180T
DP-K® 900Y1180T

Complex-phase steel
DIN EN 10346

SURFACE FINISHING
Steel grade Reference grade
DIN EN 10346
Z
CP-W® 660Y760T HDT760C
CP-W® 800 -
CP-K® 570Y780T HCT780C -
CP-K® 780Y980T HCT980C
CP-K® 900Y1180T -

Chassis steel
DIN EN 10346

SURFACE FINISHING
Steel grade Reference grade
DIN EN 10346
Z
CH-W® 660Y760T HDT760C

Retained-austenite steel (TRIP steel)
DIN EN 10346

SURFACE FINISHING
Steel grade Reference grade
DIN EN 10346
Z
RA-K® 400Y690T
HCT690T

Ferritic-bainitc-phase steel
DIN EN 10346

SURFACE FINISHING
Steel grade Reference grade
DIN EN 10346
Z
FB-W® 300Y450T HDT450F
FB-W® 460Y580T HDT580F

Hot-dip galvanized flat product with very close thickness tolerances
DIN EN 10346

SURFACE FINISHING
Steel family Steel grade Standard name Z
Mild steel for cold forming

scalur®+Z DX51D DX51D
scalur®+Z DX52D DX52D
Hot-dip coated structural steel scalur®+Z S220GD S220GD
scalur®+Z S250GD S250GD
scalur®+Z S280GD S280GD
scalur®+Z S320GD S320GD
scalur®+Z S350GD S350GD
scalur®+Z S390GD S390GD
scalur®+Z S420GD S4250GD
scalur®+Z S450GD S450GD
Microalloyed steel scalur®+Z HX260LAD HX260LAD
scalur®+Z HX300LAD HX300LAD
scalur®+Z HX340LAD HX340LAD
scalur®+Z HX380LAD HX380LAD
scalur®+Z HX420LAD HX420LAD
scalur®+Z HX460LAD HX460LAD
scalur®+Z HX500LAD HX500LAD
Complex-phase steel scalur®+Z HDT760C HDT760C

Serial production

Tolerances
Dimensional and shape tolerances to EN 10 143.

Surfaces

Available surface finishes, hot-dip coated

Minimum coating two-sided sample [g/m2] Auflage je Seite an Einflächenprobe [μm]
Coating Specification Triple spot sample Single spot sample Thickness Typicl thickness
Z100 DIN EN 10346 100 85 5 – 12 7
Z140 DIN EN 10346 140 120 7 – 15 10
Z200 DIN EN 10346 200 170 10 – 20 14
Z225 DIN EN 10346 225 195 11 – 21 16
Z275 DIN EN 10346 275 235 13 – 27 20
Z350 DIN EN 10346 350 300 17 – 33 25
Z450 DIN EN 10346 450 385 22 – 42 32
Z600 DIN EN 10346 600 510 29 – 55 42
Other coatings and different coatings per side are available on request.

Processing of hot-dip coated sheet (Z)

Forming

All common forming processes used for cold rolled sheet can be used for hot-dip coated sheets if the die geometry and die surface are matched to these materials. The hot-dip galvanization (coating) of sheets in conjunction with the surface topography exerts a decisive influence on the tribology of the forming process.

The characteristic parameter is the friction coefficient μ. At thyssenkrupp Steel, the friction coefficient is determined in the drawing test between plane parallel tools. Compared with uncoated sheet (0.14 ≤ μKB ≤ 0.18), hot-dip galvanized sheet has a lower mean friction coefficient (0.08 ≤ μZ ≤ 0.12). The scatter band results from the roughness spectrum, which is set in production to customer requirements. When changing over from a different surface finish (coating) to hot-dip galvanized sheet, the blank shape, blankholder forces or the geometry of the drawing bead may have to be adapted to the flow behavior of the material in the flange area. The only exception is the changeover from zinc-aluminum coated galfan® sheet to hot-dip galvanized sheet.

To avoid coating abrasion, which tends to occur more when forming with short cycle times, the die surface must be completely smooth. thyssenkrupp Steel measures abrasion using the draw-bead test. Hot-dip galvanized sheet displays almost comparable measurable abrasion rates (0.2 to 0.8 g/m2) to uncoated sheet on which abrasion can also be measured (0.5 to 1.0 g/m2).

Processing instructions for joining

All thermal and mechanical joining techniques can be used, as can adhesive bonding and sealing. However, the particular properties of the hot-dip zinc coating require the processing parameters for some joining techniques to be adapted from those used for ungalvanized cold rolled sheet. Joining techniques which do not impair the surface, i.e., which preserve the anticorrosion properties of the coating, such as clinching and adhesive bonding are continually gaining in importance. However, resistance spot welding, inert gas, and laser welding remain the most frequently used joining processes. The first of these, in the form of spot, projection and roll seam welding, has largely come to dominate in automobile manufacturing. These processes are easy to automate, cause little surface damage or component distortion and do not require weld fillers.

In comparison with uncoated cold rolled sheet, a higher welding current and higher electrode force must be applied when resistance spot-welding galvanized sheets, as the coating has a lower contact resistance. The higher thermal and mechanical loads and the tendency to electrode pick-up with the zinc coating reduce the tool life in terms of components processed.

These factors can be counteracted by the use of a suitable electrode material, e.g. CuCrZr, an adapted electrode geometry and adequate electrode cooling coupled with optimized process control. For example, a stepper control is used to increase the welding current in stages and so considerably increases the number of components that can be processed by a set of electrodes. Milling the electrodes after a specific number of weld points has also proved effective in this respect.

When fusion welding is used, the coating metal in the area of the weld seam burns. A fusion welding process that does not introduce much heat to the weld seam area should therefore be selected in order to produce the minimum possible degradation of the corrosion protection.

Laser welding has proven to be the ideal fusion welding method. A slower welding speed than that used with cold rolled sheet improves degassing of the weld pool and avoids the formation of pores. Fumes containing Zn oxides arise when welding galvanized sheet. The quantity of these fumes is largely determined by the coating thickness and the welding process. Adequate ventilation and extraction is essential in any event. Under unfavorable conditions, e.g., in small rooms, an extraction system should be fitted as close as possible to the source of the welding fumes.

Corrosion protection

The assignment of the protective effect of hot-dip galvanized sheet according to DIN EN 55634-1 to the corrosivity categories/corrosion loads C1 to C5 is given as C2(L) and C2(M) for coating Z100 with a coating thickness of 7 μm and as maximum C3(L) for coating Z275 with a coating thickness of 20 μm. In general, the corrosion protection increases with increasing zinc coating.

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