High strength low alloy (HSLA) steels for cold forming

Transcription

1 Automotive Worldwide High strength low alloy (HSLA) steels for cold forming Extract from the product catalogue -European edition Note: Information contained in this catalogue is subject to change. Please contact our sales team whenever you place an order to ensure that your requirements are fully met. Please contact us if you have a specific requirement that is not included in the range of products and services covered by this catalogue. We are also reachable by the address automotive.request@arcelormittal.com.

2 We are also reachable by the address High strength low alloy (HSLA) steels for cold forming High yield and tensile strength steels 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. HSLA grades can be given a Class 1 hot-dip galvanized coating according to the EN 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 Front reinforcement in Dual Phase 780 Shock absorber in Designation and standard 2

3 Designation and standard HC260LA (+ZE) /HX260LAD (+Z, HC300LA (+ZE) /HX300LAD (+Z, HC340LA (+ZE) /HX340LAD (+Z, HC380LA (+ZE) /HX380LAD (+Z, HC420LA (+ZE) /HX420LAD (+Z, CR240LA (-UNC,-EG,-GI,-GA) CR270LA (-UNC,-EG,-GI,-GA) CR300LA (-UNC,-EG,-GI,-GA) CR340LA (-UNC,-EG,-GI,-GA) CR420LA (-UNC,-EG,-GI,-GA) Uncoated ( EN 10268: 2006+A1: 2013): Steel grade name Electrogalvanized (EN :2006+A1: EN :2017): Steel grade name +ZE Galvannealed (EN :2015): Steel grade name +ZF Extragal (EN :2015): Steel grade name +Z Galfan (EN :2015): Steel grade name +ZA Uncoated: Steel grade name-unc Electrogalvanized: Steel grade name-eg Galvannealed: Steel grade name-ga Extragal : Steel grade name-gi While the ArcelorMittal grades conform perfectly well to the indicated EN standards, ArcelorMittal grades generally offer tighter mechanical properties (see table below). S315MC/HX340LAD (+Z) HR300LA (-UNC,-GI) S355MC/HX380LAD (+Z) HR340LA (UNC,-GI) S420MC/HX420LAD (+Z) HR420LA (-UNC,-GI) S460MC/HX460LAD (+Z) HR460LA (-UNC,-GI) S500MC/HX500LAD (+Z) HR500LA (-UNC,-GI) S550MC HR550LA (-UNC,-GI) Uncoated (EN :1995): Steel grade name Uncoated: Steel grade name-unc Extragal : Steel grade name-gi 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

4 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 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 steel Chemical composition (%) C Max Mn Max Si Max 0,50 0,04 0,60 0,04 0,70 0,04 0,90 0,35 0,140 1,60 0,40 0,50 0,60 0,75 0,120 1,60 0,40 0,090 1,50 0,090 1,65 0,35 Available coatings and Worldwide availability 4

5 Available coatings and Worldwide availability Uncoated Electrogalvanized Extragal Galvannealed Available in non-visible part quality quality (Z) Undergoing customer testing Under development Available in visible and non-visible part : Europe Region - : North America Region - : South America Region - : South Africa Region - : China X Available Please consult us about the availability of additional HSLA products. Recommendations for use and secondary processing 5

6 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 method. Welding range (ka) Extragal (thickness: 2 mm) Extragal (thickness: 1 mm) 3,5 1,1 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. 6

7 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. grades above 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. ArcelorMittal Last update: