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Hot rolled ferrite-bainite steels

Description

This range of hot-rolled high strength steels has been developed to meet weight reduction requirements. It comprises four strength levels: FB 450, 540, 560 and 590. This family of steels extends the HSLA range of micro-alloyed steels to include products combining high tensile strength (UTS) with excellent formability and hole expansion (stretch flangeability) based on their ferrite-bainite microstructure.

Applications

These steels are cold-drawn.
The main applications are:

  • structural parts (longitudinal beams, cross beams, car-body and ground liason parts),
  • wheels,
  • mechanical parts (ground liason parts, gear boxes...).

ArcelorMittal has an extensive database relating to the forming and service properties of the entire range of ferrite-bainite steels. To integrate these steels at the design stage, a team of experts is available to perform specific studies based on modeling or laboratory tests.

Front and rear underseat cross member in galvanised FB 560 (thickness: 1.8 mm)

Suspension arm in uncoated FB 540 (thickness: 4 mm)

Suspension arm in Extragal® FB 560 (thickness: 4 mm)

Pillar reinforcement in galvanised FB 560 (thickness: 1.8 mm)

Wheel in FB 590

Designation and standards

  Euronorms VDA 239-100
FB 450 HDT450F (+Z) HR300Y450T-FB (-UNC,-GI)
FB 540
FB 560
FB 590 HDT580F(+Z) HR440Y580T-FB (-UNC,-GI)
FB 590 HHE* HDT580F HR440Y580T-FB (-UNC)
 

Euronorms
Uncoated (EN 10338 :2015): Steel grade name
Electrogalvanized (EN 10338 :2015 + EN 10152 :2017): Steel grade name+ZE
Galvannealed (EN 10346 :2015): Steel grade name+ZF
Extragal® (EN 10346 :2015): Steel grade name+Z

VDA 239-100
Uncoated: Steel grade name-UNC
Electrogalvanized: Steel grade name-EG
Galvannealed: Steel grade name-GA
Extragal®: Steel grade name-GI

 
 Hot rolled     Cold rolled

HHE: High Hole Expansion.

The above indicative table summarizes the European and VDA standards corresponding to the ArcelorMittal product range.

While the ArcelorMittal grades conform perfectly well to the indicated EN standards, ArcelorMittal grades generally offer tighter mechanical properties (see table below).

Technical characteristics

Mechanical properties
Guaranteed for ISO 20X80 (thickness < 3 mm) or proportional (thickness ≥ 3 mm) test specimen of uncoated sheet.

ST - Transverse direction (perpendicular to the rolling direction) / SL - Rolling direction

  YS (MPa) UTS (MPa) ef (%)
L0 = 80 mm
th < 3 mm
Ef (%)
L0 = 5,65 √S0 (mm)
th ≥ 3 mm
Direction
 FB 450 300 - 380 450 - 510 ≥ 25 ≥ 32 SL
 FB 540 400 - 485 540 - 610 ≥ 18 ≥ 25 SL
 FB 560 450 - 530 560 - 640 ≥ 17 ≥ 22 SL
 FB 590 480 - 600 590 - 670 ≥ 16 ≥ 21 ST
 FB 590 HHE* 480 - 600 590 - 670 ≥ 16 ≥ 21 ST
 
 Hot rolled     Cold rolled

* FB 590 HHE: we recommend this option for parts requiring very high hole expansion (HHE: High Hole Expansion grade). For this grade, the minimum guaranteed JIS elongation is 18%.

Chemical composition (%)

  C Mn Si
  Max Max Max
FB 450 0,17 0,8 0,05
FB 540 0,17 1,5 0,15
FB 560 0,1 1,6 0,15
FB 590 0,1 1,6 0,15
FB 590 HHE 0,05 2,0 0,8
 
 Hot rolled     Cold rolled

Ferrite-bainite microstructure of FB 540

Available coatings and Worldwide availability

  Uncoated Extragal®
  EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI
FB 450              
FB 540            
FB 560              
FB 590          
FB 590 HHE              

 Hot rolled     Cold rolled

Available in non-visible part quality Undergoing customer testing Under development Available in visible and non-visible part quality (Z)

EUR : Europe Region - NAM : North America Region - SAM : South America Region - RSA : South Africa Region - CHI : China

X available product

Recommendations for use and for secondary processing

High hole expansion grade

ArcelorMittal offers an FB590 HHE (High Hole Expansion) grade, which is recommended for parts with sheared edge stretchability requirements (stretch flangeability, edge flanging, edge stress during secondary processing, etc.). The images opposite shows an example of hole expansion behaviour according to the ISO standard for grades FB 590 and FB 590 HHE.

View of hole expansion in grades FB 590 and FB 590 HHE in 4 mm thickness.

The HHE achieves a much higher hole expansion value.

Forming
The graph below gives critical forming limits calculated for the FB family of steels in 2.5 mm thickness.

Forming limit curves for the FB family of steels

Please consult us for further information relating to the forming of steels in the FB range with specific thicknesses and coatings.

Welding

Examples of data relating to resistance spot welding of coated and uncoated steels of different thicknesses in the FB product range, determined according to the ISO 18278 method. These steels can be arc welded.

  Coating Thickness (mm) Welding range (kA)
FB 450 Extragal® 2 2.6
FB 590 uncoated 2.5 4.3
 
 Hot rolled     Cold rolled

The following indicative welding parameters are used in MAG welding:

  • Filler metal: GS2-type wire
  • Protective gas: ATAL 5 or ATAL 18
  • Welding speed: 80 cm/min

ArcelorMittal can provide technical assistance in adjusting the welding parameters of any other steel in the FB range product.

Fatigue strength

As a result of their high tensile strength and their microstructure, FB steels have good fatigue strength.

Examples of Wöhler curves for a variety of FB steels are given in the graph below. The curves plot maximum stress versus number of cycles to failure. They are calculated for a tension-tension loading ratio of R = 0.1.

Wöhler curves of the FB range of steels

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

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