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DH steels for cold drawing

Description

The DH family of steels is quoted to comply with standard VDA239. These very high strength steels provide enhanced formability compared to that of conventional Dual Phase steels thanks to their higher elongation. This gives them added value in the case of critical parts during drawing, bearing in mind that their welding performance remain equivalent to those of conventional dual phase grades. These steels enable structural elements to be produced using a cold-forming process such as drawing.

Applications

Thanks to their excellent mechanical properties, these grades are particularly suitable for automotive safety parts for crash resistance. Typical parts are shown in the figure below:

Typical parts for DH steels

Typical parts for DH steels

Designation and standard

Show all
ArcelorMittal name Generic name VDA 239-100
CR330Y590T-DH DP600 DH CR330Y590T-DH
CR440Y780T-DH DP780 DH CR440Y780T-DH
CR700Y980T-DH DP980 DH CR700Y980T-DH

By way of indication, the above table summarises the cross-references between the ArcelorMittal range, European standards and standard VDA 239-100.

Mechanical properties

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ArcelorMittal name Generic name Direction Yield stress Rp0.2 (MPa) Tensile strength Rm (MPa) Type 1 Min. A50mm (%) Type 2 Min. A80mm (%) Type 3 Min. A50mm (%) Min. BH2 MPa n4-6 n10-20/Ag
CR330Y590T-DH DP600 DH RD 330 - 440 590 - 700 28 26 28 30 0.18 0.16
CR440Y780T-DH DP780 DH RD 440 - 550 780 - 900 19 18 19 30 0.18 0.13
CR700Y980T-DH DP980 DH RD 700 - 850 980 - 1130 14 13 14 30

A80mm %: Percentage elongation after fracture using a specimen with gauge length L0 = 80 mm (ISO 6892-1 type 2 (EN20x80))
A50mm %: Percentage elongation after fracture using a specimen with gauge length L0 = 50 mm (ISO 6892-1 type 1 (ASTM12.5x50) or type 3 (JIS25x50)
A%: Percentage elongation after fracture using a proportional specimen with L0 = 5.65 (So)1/2
Ag %: Percentage plastic extension at maximum force
BH2: Increase in yield strength between a reference condition after a 2% plastic pre-strain and the condition obtained after heat treatment (170°C-20minutes)

  • CR330Y590T-DH microstructure

  • CR450Y780T-DH microstructure

Chemical composition

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ArcelorMittal name Generic name Max. C (%) Max. Si (%) Max. Mn (%) Max. P (%) Max. S (%) Al (%) Max. Cu (%) Max. B (%) Max. Ti + Nb (%) Max. Cr + Mo (%)
CR330Y590T-DH DP600 DH 0.15 0.8 2.5 0.05 0.01 0.015 - 1.0 0.2 0.005 0.15 1.4
CR440Y780T-DH DP780 DH 0.18 0.8 2.5 0.05 0.01 0.015 - 1.0 0.2 0.005 0.15 1.4
CR700Y980T-DH DP980 DH 0.23 1.8 2.9 0.05 0.01 0.015 - 1.0 0.2 0.005 0.15 1.4

Global availability


Under development     Customer trials     Commercial unexposed only     Commercial exposed and unexposed    

Show all
ArcelorMittal name Generic name Uncoated (-UNC) Extragal® (-GI) Jetgal® (-ZV)
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH
Show all
ArcelorMittal name Generic name Uncoated (-UNC) Extragal® (-GI) Jetgal® (-ZV)
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH
Show all
ArcelorMittal name Generic name Extragal® (-GI)
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH
Show all
ArcelorMittal name Generic name Extragal® (-GI)
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH
Show all
ArcelorMittal name Generic name
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH
Show all
ArcelorMittal name Generic name
CR330Y590T-DH DP600 DH
CR440Y780T-DH DP780 DH
CR700Y980T-DH DP980 DH

Please check with us for products under development.

Forming

DH steels show good ductility relative to their tensile strength level.
The illustration below provides an example of a forming limit curve for CR450Y780T-DH and CR700Y980T-DH steels in a thickness of 1.5 mm.

Forming limit curves for the DH steels family of 1,5 mm thickness (ArcelorMittal model for Europe)

Forming limit curves for the DH steels family of 1,5 mm thickness (Keeler model for North America)

Welding

Spot weldability

The DH steel range boasts good spot weldability. The scope of weldability obtained for welding conditions recommended by standard ISO18278-2 is broad. By way of indication, the table below lists a number of properties of spot welds on DH steels in uniform combinations in accordance with standard ISO18278-2.

Show all
ArcelorMittal name Coating Thickness (mm) Nugget diameter (mm) Pure tensile (kN) Weld diameter (mm) Tensile-shear (kN)
CR440Y780T-DH GI 1.5 7 10 8 25

Fatigue strength

DH steels show good fatigue properties. By way of example, the two graphs below show the Wöhler curves for DH steels. These are expressed in terms of maximum stress against the number of cycles applied. They are obtained using two stress ratios, either in symmetric fluctuating tension R = -1, or repeated tension R = 0.1.

The graph below shows the oligocyclic curve or EN curves for the same steels. It is expressed in forming amplitude according to the number of alternations (one cycle equals two reversals). Other fatigue data at high or low numbers of cycles is available upon request.

ArcelorMittal can provide a database on the fatigue performance of DH steels.

Impact strength

Due to their high tensile strength, DH steels are particularly suitable for safety parts.

The DH steels were characterised in axial compression using an omega structure with a spot-welded cover plate at an impact velocity of 56 km/h. These tests have shown good impact behaviour for these steels, similar to that of Dual Phase steels. By way of indication, the following graph shows the minimum weight-saving potential offered by these steels compared to CR340LA steel.

 

Weight saving potential compared to CR340LA steel (reference)

Weight saving potential compared to CR340LA steel (reference)

The DH steels were characterised in dynamic 3-point bending at 30 km/h on an omega section test piece. These tests have shown good impact behaviour for these steels, similar to that of Dual Phase steels. By way of indication, the following graph shows the minimum weight-saving potential offered by these steels compared to CR340LA steel.

 

Weight saving potential compared to CR340LA steel (reference)

Weight saving potential compared to CR340LA steel (reference)

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