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High strength low alloy (HSLA) steels for cold forming

Description

Steels in the HSLA (High Strength Low Alloy) range are hardened by a combination of precipitation and grain size refining, resulting in high strength with low alloy content. This enhances weldability and choice of coatings, since these steels exhibit neither weld zone softening nor grain coarsening. These grades are particularly suitable for structural components such as suspension systems and chassis and reinforcement parts.

For their respective yield strength levels, these steels all exhibit excellent cold forming and low-temperature brittle fracture strength (starting at grade 320).

The entire range of HSLA steels offers good fatigue strength (suspension arm, shock tower) and impact strength (longitudinal beams, cross members, reinforcements, etc.).

Because of their mechanical strength, the weight of reinforcement and structural components can be reduced.

The HSLA range of products is available in hot and cold rolled grades. The various grades are identified by their yield strength.

Hot rolled HSLA grades can be given a Class 1 hot-dip galvanized coating according to the EN 36503 standard (post-galvanizing).

Applications

The steels in the HSLA range are suitable for structural parts such as suspension systems, reinforcements, cross members, longitudinal beams, chassis components, etc. The mechanical properties of  hot rolled HSLA steels and their excellent cold forming performance and low-temperature brittle fracture resistance support cost-effective solutions for many parts and sub-assemblies for which weight, thickness and size reduction are sought, such as:

  • chassis components;
  • wheels;
  • slide rails;
  • cross members.

Rear cross member in Extragal®-coated HSLA 300

Front reinforcement in Dual Phase 780

Shock absorber in HSLA 300

Designation and standard

  Euronorms VDA 239-100
HSLA 260 HC260LA (+ZE) / HX260LAD (+Z, +ZF, +ZA) CR240LA (-UNC,-EG,-GI,-GA)
HSLA 300 HC300LA (+ZE) / HX300LAD (+Z, +ZF, +ZA) CR270LA (-UNC,-EG,-GI,-GA)
HSLA 340 HC340LA (+ZE) / HX340LAD (+Z, +ZF, +ZA) CR300LA (-UNC,-EG,-GI,-GA)
HSLA 380 HC380LA (+ZE) / HX380LAD (+Z, +ZF, +ZA) CR340LA (-UNC,-EG,-GI,-GA)
HSLA 420 HC420LA (+ZE) / HX420LAD (+Z, +ZF, +ZA) CR420LA (-UNC,-EG,-GI,-GA)
 

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
Galfan (EN 10346 :2015): Steel grade name+ZA

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

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

  Euronorms VDA 239-100
HSLA 320 S315MC/HX340LAD (+Z) HR300LA (-UNC,-GI)
HSLA 360 S355MC/HX380LAD (+Z) HR340LA (UNC,-GI)
HSLA 420 S420MC/HX420LAD (+Z) HR420LA (-UNC,-GI)
HSLA 460 S460MC/HX460LAD (+Z) HR460LA (-UNC,-GI)
HSLA 500 S500MC/HX500LAD (+Z) HR500LA (-UNC,-GI)
HSLA 550 S550MC HR550LA (-UNC,-GI)
 

Euronorms
Uncoated (EN 10149-2 :1995): Steel grade name

VDA 239-100
Uncoated: Steel grade name-UNC
Extragal®: Steel grade name-GI

 
 Hot rolled     Cold rolled

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

The above indicative tables summarize the European and VDA standards corresponding to the ArcelorMittal product range.

Technical characteristics

Mechanical properties
Guaranteed for uncoated sheet in the transverse direction.

  YS (MPa) UTS (MPa) ef (%)
L0 = 80 mm
th < 3 mm
 HSLA 260 260 - 320 350 - 410 ≥ 28
 HSLA 300 300 - 360 390 - 450 ≥ 26
 HSLA 340 340 - 400 420 - 490 ≥ 23
 HSLA 380 380 - 450 460 - 530 ≥ 20
 HSLA 420 420 - 520 470 - 590 ≥ 17
 
 Hot rolled     Cold rolled

Guaranteed for uncoated sheet in the rolling direction.

  YS (MPa) UTS (MPa) ef (%)
L0 = 80 mm
th < 3 mm
Ef (%)
L0 = 5,65 √S0 (mm)
th ≥ 3 mm
 HSLA 320 325 - 385 415 - 470 ≥ 24 ≥ 28
 HSLA 360 360 - 435 450 - 520 ≥ 21 ≥ 25
 HSLA 420 420 - 500 490 - 570 ≥ 20 ≥ 23
 HSLA 460 460 - 550 550 - 650 ≥ 17 ≥ 21
 HSLA 500 500 - 590 570 - 670 ≥ 15 ≥ 19
 HSLA 550 550 - 650 650 - 730 ≥ 15 ≥ 18
 
 Hot rolled     Cold rolled

Because HSLA steels can exhibit an extended elastic-plastic transition zone with variations in YS values, by convention only the lower yield strength (LYS) is taken into account in this zone.

Microstructure of a cold rolled HSLA 340 steel

Chemical composition (%)

  C Mn Si
  Max Max Max
HSLA 260 0,080 0,50 0,04
HSLA 300 0,080 0,60 0,04
HSLA 340 0,080 0,70 0,04
HSLA 380 0,080 0,90 0,35
HSLA 420 0,140 1,60 0,40
HSLA 320 0,080 0,50 0,03
HSLA 360 0,080 0,60 0,03
HSLA 420 0,080 0,75 0,03
HSLA 460 0,120 1,60 0,40
HSLA 500 0,090 1,50 0,03
HSLA 550 0,090 1,65 0,35
 
 Hot rolled     Cold rolled

Available coatings and Worldwide availability

  Uncoated Electrogalvanized
  EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI
HSLA 260      
HSLA 300        
HSLA 340    
HSLA 380        
HSLA 420    
HSLA 320            
HSLA 360            
HSLA 420            
HSLA 460            
HSLA 500            
HSLA 550              
  Extragal® Galvannealed
  EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI
HSLA 260        
HSLA 300    
HSLA 340    
HSLA 380    
HSLA 420      
HSLA 320              
HSLA 360              
HSLA 420              
HSLA 460                  
HSLA 500                  
HSLA 550              

 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

Please consult us about the availability of additional HSLA products.

Recommendations for use and secondary processing

Forming
Drawability declines progressively with increasing yield strength. Forming limit curves can be used to define maximum strains without necking for different deformation paths.

Example of forming limit curves calculated for cold rolled HSLA sheet (thickness: 1.0 mm)

We can provide additional forming data for steels in the HSLA range with particular thicknesses and coatings.

Welding

Weldability is determined according to the ISO 18278-2 method.

  Welding range (kA)
HSLA 300 Extragal® (thickness: 2 mm) 3,5
HSLA 340 Extragal® (thickness: 1 mm) 1,1
 
 Hot rolled     Cold rolled

Cold rolled
HSLA steels can be readily welded using all common welding processes.

Based on long experience in the characterization of its products, ArcelorMittal can provide technical assistance in adjusting the resistance spot and arc welding parameters of any steel in the HSLA range.

Fatigue strength

HSLA steels have good fatigue strength.

Examples of Wöhler curves for a variety of HSLA 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 for cold rolled HSLA steels

Because of their high endurance limits, these steels are particularly well suited to parts subject to fatigue stress. To restore the base metal endurance limit adjacent to welds in areas subjected to severe cyclic loading, a post-weld treatment such as TIG melting, hammering, peening or grinding should be applied to the weld toe.

Hot rolled grades above HSLA 420 in thicknesses greater than 6 mm are generally used for fatigue applications and applications involving straightening and stress relieving treatments. These steels cannot be heated above 700°C without risk of impairing the mechanical properties obtained by thermo-mechanical treatment.

ArcelorMittal can make available a comprehensive database concerning the fatigue performance of the steels in its HSLA range.

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