High-strength steels for chassis and exhaust...
Transcript of High-strength steels for chassis and exhaust...
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Dr. Lackmann, 09.04.2013 1
High -strength steels for chassis and exhaust components –Application related developments and materials at Benteler Automotive
J. Lackmann, H-G. Lambers, A. Frehn
Benteler Automobiltechnik GmbH, Paderborn
Outline
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• Benteler Group
• Materials at Benteler Automotive
• Application related materials and developments - Chassis
• Application related materials and developments - Structure
• Application related materials and developments - Exhaust
• Summary
Under the strategic management holding, Benteler International AG, the operative business is organized into the three legally independent business divisions within Benteler Deutschland GmbH.
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Benteler International AG
Benteler Deutschland GmbH
Benteler Automotive Benteler Stahl/Rohr Benteler Distribution
Worldwide activity – Benteler Automotive 2012
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� Sales: 5,530 million euros� 22,400 employees� 74 plants, 20 engineering and
sales offices in 29 countries(Status 12/2011)
Status October 2012
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Mat
eria
l-Str
engt
h : R
m /
UT
S [M
Pa] 2000
1000
1500
500
250 App
licat
ion
in s
erie
s pr
oduc
tion
App
licat
ion
appr
oval
in P
PR
Armoring Steel BSEC510
Armoring Steel BSEC610
Boron Steels /
Surface finished
Multi Phase Steels
Micro Alloyed Steels
Stainless Steels
DDQ Steels
AluminiumSheet / Forged
Boronsteels
High manganese
steel
MG-Forged
MG-Sheet
Plastic-Steel-Hybrid
Plastic Foams
Ultra High Strength Alloys
2500
Carbon Fibre
Al-Profile6000-7000-Alloys
Glass Fibre
Armoring Steels
Carbon Fibre
Materials overview
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Overall application related material requirements
Mechanical – technologicalproperties- Strenght- Hardening behavior- Formability- Modulus- Ductility- Thermo-mechanical properties- Quench propertries
Fatique behavior- Fatique strength- Wöhler diagramms- Crack initiation and - growth
High strain rate behavior- Dynamic strength- Remaining strain- Ballistic resistance
Surface properties- Surface defects- Roughness
Material price- Basic price- Alloying costs
Joining properties- Weldability- Brazeability- Other joining technologies
Corrosion resistance / Coatability- Zinc-coating- Cataphoretic painting- Plasma nitriding- Hot- / wet corrosion properties
„Logistic“ propterties- Available dimensions- Tolerances- Available semi-finished parts- Worldwide availability and quality
Machinability- Die-cutting- Laser-cutting- Drilling
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Requirement – Formability of high strenght steels
- Formability (including thinning) is a key parameter regardingthe produceability of Benteler Automotive products
- Consistently determined characteristic values are needed forfor forming simulations
- Influence of material characteristics along die- or laser-cuttedholes and edges has to be considered for lifetime prediction
- Increasing the formability of high strength steels desired
- Reduction of the variance of mechanical properties (heat dependend)
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Requirement – Dimenional tolerances of high strenght stee ls
Example: Roll-rate of compound crank rear axles
• Influencing factors:• Axle kinematics• Shear center of the torsion profile• Effective torsion lenght• Thickness of the torsion element
Influence of thickness torenances
Basis for analytical estimation: B-segment vehicle (VW) (closed profile, D=115mm, t=2,4mm)
t [mm] ∆∆∆∆2,40 -2,45 4,04%2,50 8,19%2,55 12,43%2,60 16,77%2,65 21,21%
Increasing the sheet thickness of the torsion elementresults in highly variing roll-rates and thereforeconsiderable effects on the vehicle dynamics (over-/ understeering)
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Requirement – Weldability of high strength steels
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Messpunkt Nr.
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S420MC-S420MC BAS100(+A)-BAS100 (+A) BAS100 (+QT)-BAS100 (+QT) TRIP800
Grundmaterial GrundmaterialWEZ WEZSchweißgut
MAG-weldseamConsumables:G4Si1 (S420MC/TRIP800)ESAB13.31 (BAS100)
• Maximum allowable hardness within weldseam and heat affected zone is limited by OEMs• Reduction of hardness steps by changing chemical compositions or annealing parameters• Further examination of hydrogen embrittlement required
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Requirement – Corrosion resistance of high strength steel s
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Increasing requirements regarding corrosion resistance andweight reduction
� Standard cataphoretic painting not allways sufficitent
Possible alternatives� Zinc coating (strip)
� Weldseams highly affected
� Zinc coating (part)� Reduction of fatique strength� Weight increase� Hydrogen embrittlement?� LME-risk?
3 years / ca. 95.000 km
TWIP
Austenitic stainless steel
TRIP
DPMagn.
Alum.
CP 22MnB5MS
IFDDQ
IF-HSBH und P
HSLA
IsotropeStähle
Tensile strenght R m, MPa
Elo
ngat
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atst
rain
A, %
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76
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93 HSLA/Baustähle
Austenitischenichtrostende Stähle
Mehrphasenstähle
Benteler-Stahlsorten(BTR165, BAS100)
Andere Stahlsorten
BAS100+A
BAS100+QT
BTR165HR
BTR165+QT
Steel grades used for chassis components
%
Requirement – mechanical properties of high strength stee ls
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Steel grades used for chassis components – HSLA / mild s teels
Grades:Micro-alloyed and mild steels (Re: 315 – 650 MPa)
Products:Cross member, suspension arms, compound crank rear axles, tube components
Advantages / Disadvantages:+ Low carbon content (weldability – hardness steps)+ Strength / formability ratio+ Minimal variation of mechanical properties within rolled strip+ Different strength levels available+ Worldwide available (Hot- and cold rolled strip)- Reduced formability and springback for high-strentgh grades
Development trends:- Further reduction of grain- and precipitation size (Nano-Hiten)- Perlite-free variants showing increased formability(HSM650HD)
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Steel grades used for chassis components – multiphase ste els
Grades:F/B540, F/B590, F/B780, SZBS800, CP-W800, DP450
Products:Suspension arms, reinforcements
Vorteile/Nachteile:Similar to HSLA / mild steel+ Improved formability and hardening potential+ Significant bake-hardening effect+ Improved hole expensionalbility (FB)- Wordwide availability(different concepts DP/TRIP)- Springback for HSS-grades- Weldeability for TRIP-steel- Hot rolled strip availability for DP/TRIP
Development trends:- Further optimization of F/B-grades- Reduction of C-content of TRIP-steels
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Steel grades used for chassis components – air hardening s teels
Grades:BAS100, BNX120 (Re: 700 Mpa – 850 MPa)
Komponenten:Front subframe
Vorteile/Nachteile:+ High formability in the not hardenend condition combined with
high strength of hardened parts+ No significant hardness steps within the heat affected zone- Alloying costs (Mo und V)- Wordwide availability
Development trends at Benteler:- Optimization of mechanical properties and availability
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Competitor to steel - Aluminium grades used for chassis co mponentsComponent Alloys Condition Strenght Elongation at break
Extruded profiles EN AW-6060EN AW-6005AEN AW-6063
T6 bzw. T5 Re > 225 MPaRm > 270 MPa
A5 > 8%
HF welded tubes EN AW-5454EN AW-5457
H111 Re > 100 MPaRm > 230 MPa
A5 > 20%
Casted parts EN AC-42100 T6 Re > 190 MPaRm > 230 MPa
A5 > 2%
Sheets for pressedparts
EN AW-5454EN AW-5457
H111, H22 and higher
Re > 200 MPaRm > 270 MPa
A5 > 11%
Forged parts EN AW-6062EN AW-6110(Cu limited)
T6 Re > 370 MPaRm > 400 MPa
A5 > 9%
High strength: 300-400 MPa (Rm)Ultra high strenght: > 400 MPa (Rm)
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Potential future steel grades for chassis components
? ? ?
NANO-HITEN, TWIP - steels Steels showing increased elas tic modulus
Reference: JFE, Japan Reference: ArcelorMittal
„Low cost“- air hardening steel, Bainite
Reference: Microstructure of the BSR05-10 (air hardened)
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High strength steels for hot formed structural components and ballisticprotection systems
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Bruchdehnung [%]
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DDQ, UDDQ
P, BH, IFHSHSLA
FB
DPTRIP
CPPM BTR165 hot formed
BTR165
hot rolledHS
SU
HS
SP
HS
BSEC510 hot formed
BSEC610 hot formed
Strain [%]
Tesi
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Perlite
Bainite
Martensite
Martensite
Time (0 -1000 s, log)
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TTT-Diagramm
Ac3
Cooling
Transformation
Ferrite
Ms
Mf
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Partial hardening of high strength steels for structural components
transition T2
duct
ile
T3
high
str
engt
h
T1
0Vickers hardness
dist
ance
•HV0,5
500
Martensite
Ferrite + Perlite
Martensite + Bainite
advantage:strength optimized design properties:
quenched sec.: soft sec.:Rm: 1450 MPa 550 MPa
Re: 1100 MPa 400 MPa
ε (A5): > 6 % > 20%
� good crash performance
� weight reduction
� Part integration
T3
T2Temp 3
Direction of material flow
Temp 1 Temp 2
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Hot formable ultra high strength steels for ballistic pro tection components
Benteler Security Steel (BSEC) // C – Cr – Ni – Mn base d
Benteler steel plant Lingen
BSEC-grades available
BSEC450
Hardness [HB] Impact work [J] Application
410 - 480 40 - 60 Floor parts
BSEC510 480 - 550 25 - 40 Vehicle protection up to STANAG I
BSEC610 570 - 640 10 - 15 Vehicle protection up to STANAG III
BSEC+ Surface hardened BSEC-grades for additional ballistic resistance
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Hot formable ultra high strength steels for ballistic pro tection components
Ballistic protection up to t = 20 mm by fully martensitic microstructure
Parts integration / avoidance of constructional vulnerabilities
Development trends at Benteler:- Reduction of alloying costs- Reduction of CEV
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High Temperature Resistant Ferritic Steel for Exhaus t Application
Reference: ThyssenKrupp Nirosta
BMBF-Project
RUB
Objective: Development of high temperature resistant (quasistatic and thermo mechanical fatique) ferritic stainless steel for exhaust applications, based on Laves – phase precipitation� Close the gap regarding high temperature mechanical properties betweenaustenitic and ferritic stainless steel at cost of ferritc steels
Idea: Manipulation of laves phase andcarbonitride precipitation behavior and solvustemperatures by molybdenum-, tungsten-, silicon- and niobium content � Reliable grain stabilization up to applicationtemperatures of 950°C
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High Temperature Resistant Ferritic Steel for Exhaus t Application
Ferrite950 C Si Mn Cr Mo W V Nb Ti N
ma-% < 0,02 ≈ 0,6 ≈ 0,4 ≈ 18 ≈ 0,5 ≈ 1,5 ≈ 0,1 ≈ 0,8 < 0,1 < 0,05
Laves-phase -(Fe, Cr, Si) 2(Nb, W, Mo)
415
488
548
0 100 200 300 400 500 600 700Zyklen Nf
Ferrite 950
1.4521
1.4509
Ferrite 950 grade: Laves phase and carbonitrides precipitates stabilize grains up to 1000°CThermo-mechanical properties significantly improvedExcellent wet- and hot corrosion resistance� Potential material for components exposed to high exhaust temperatures (downsized engines)
Development activities at Benteler:- Further validation tests on prototypes (manifolds, pipes, converter)
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Summary
Chassis componentsSteel grades with different mechanical strenght will b e the first choice for many chassis componentsHSLA and mulitphase steel are predominantly usedFor components, where rigidity is most important, an inc rease of the elastic modulus is desired
Hot formed structural components and ballistic protectio n systemsPartial hardening of MnB – steel grades allows for tailori ng mechanical propteries within a wide rangeHot formable ultra high strength steels are used for balli stic protection systemsThe reduction of alloying costs while maintaining strengh t-ductility characteristics is attempted
Exhaust componentsChromium oxide based austenitic and ferritic stainless ste el grades are predominantly used for exhaustcomponentsFerritic stainless steel Ferrite 950 is a potential mat erial for closing the gap between austenitic and ferriticstainless steels
FVK / AluminiumFVK (glass / carbon) are getting more and more important f or chassis (e.g. leave-spring) as well as structuralcomponents (e.g. reinforcements) – Joint venture Bente ler – SGLAluminium (5xxx / 6xxx ) is increasingly used for chass is and strucutral components– Benteler Aluminium Systems