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CH Steels for cold stamping

Description

Advanced High Strength Steels

The family of CH steels are the new generation of the Complex Phase grade. These Advanced High Strength Steels provide an improved formability compared to conventional  complex phase steels thanks to their higher elongation. These steels allow the production of  structural elements by a cold forming method such as stamping. The elongation is significantly improved thanks to a small amount of residual austenite.

Applications

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

Typical parts for CH steels

Designation and standard

Show all
ArcelorMittal name Generic name Euronorms VDA 239-100
CR900Y1180T-CH 1180CH - -
CR780Y980T-CH 980 CH - -
  • Euronorms

    Uncoated (EN 10268: 2006 + A1: 2013): Steel grade name
    Electrogalvanized (EN 10268: 2006 + A1: 2013 + EN 10152: 2017): Steel grade name + ZE
    Galvannealed (EN 10346: 2015): Steel grade name+ZF
    Extragal® (EN 10346: 2015): Steel grade name+Z
    Zagnelis® (EN 10346: 2015): Steel grade name+ZM

     

  • VDA 239-100

    Uncoated : Steel grade name-UNC
    Electrogalvanized : Steel grade name-EG
    Galvannealed : Steel grade name-GA
    Extragal®: Steel grade name-GI
    Zagnelis®: Steel grade name+ZM

The above table summarizes, purely for information, the European and VDA standards corresponding to the ArcelorMittal product range.

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
CR900Y1180T-CH 1180CH RD 900 - 1100 1180 - 1350 8 7 8 30
CR780Y980T-CH 980 CH RD 780 - 950 980 - 1140 10 10 11 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)

 

 

 

  • CR780Y980T-CH microstructure

  • CR780Y980T-CH 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 (%)
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH 0.15 1 2.7 0.05 0.01 0.015 - 1.0 0.2 0.005 0.15 1

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)
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH
Show all
ArcelorMittal name Generic name Uncoated (-UNC) Extragal® (-GI) Jetgal® (-ZV)
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH
Show all
ArcelorMittal name Generic name
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH
Show all
ArcelorMittal name Generic name
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH
Show all
ArcelorMittal name Generic name
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH
Show all
ArcelorMittal name Generic name
CR900Y1180T-CH 1180CH
CR780Y980T-CH 980 CH

Please contact us for products under development.

Forming

CH steels have good overall forming properties compared with their level of tensile strength.

 

The figure below shows an example of the forming limit curve for CR780Y980T-CH steel 1.5 mm thick, compared to a conventional lower Yield Stress DP steel with the same Tensile Strength. CH steel of the same strength has slightly better overall ease of forming despite its much higher elastic limit (+ 180MPa).

Forming limit curves for CR780Y980T-CH steel 1.5 mm thick in comparison with lower Yield Stress Dual Phase steel (ArcelorMittal model for Europe)

Forming limit curves for CR780Y980T-CH steel 1.5 mm thick in comparison with lower Yield Stress Dual Phase steel (Keeler model for North America)

The advantage of these steels is above all that they also have excellent local ease of forming/ductility. This high local ductility gives them good ease of forming in cut edges, as well as in ductility behaviour during a crash.

This local ductility was quantified using local measurement of thickness reduction on the section of the tensile test specimen after fracture. The graph below gives the comparison of this thickness reduction for different grades of the same strength (980 MPa).

Welding

Resistance Spot Welding

The CH range of steels has good resistance spot weldability. The welding range, determined according to the ISO 18278-2 standard, is quite wide. The table below shows examples (indicative) of spot welding characteristics for DH steels matching joints, determined according to the ISO 18278-2 standards.

Show all
ArcelorMittal name Coating Thickness (mm) Nugget diameter (mm) Pure tensile (kN) Weld diameter (mm) Tensile-shear (kN)
CR780Y980T-CH GI 1.6 7.2 9.9 6.9 28.1

Fatigue strength

CH steels have good fatigue properties. The table below gives examples of Wöhler curves for CH steels. The curves plot maximum stress versus number of cycles to failure. They are calculated for two loading ratios: tension-compression R=-1 and tension-tension R=0.1.

Wöhler curves or S-N curves for CH steels

The graph below shows the low cycle or EN curves for the same steels. These are expressed as strain amplitude versus number of reversals (one cycle equals two reversals). Other high and low cycle fatigue data are available on request.

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

Impact strength

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

CH steels have been characterized in dynamic axial compression tests using a top-hat structure with a spot-welded closure plate at an impact velocity of 56 kph. These tests have demonstrated the good impact behaviour of these steels similar to Complex Phase steel. The following graph gives as an indication the minimum lightening potential of these steels compared to a CR340LA steel (reference).

 

Mass reduction potential compared to that of a CR340LA steel (reference)

CH steels have been characterized in the 3-point bending test using top hat cross-section specimens impacted at 30 kph. The tests showed good behaviour of these steels, similar to Complex Phase steels. The following graph gives as an indication the minimum lightening potential of these steels compared to a CR340LA steel.

Mass reduction potential compared to that of a CR340LA steel (reference)

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