Ultralight Leaf Springs for Upcoming Front Truck Suspensions
International Conference on Steels in Cars and TrucksSCT2017 June 18/22 • 2017
Amsterdam-Schiphol, NL
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
Longer road distances require higher transport efficiency
SIDENOR I+D | R. Elvira
Reduce chassis weight to Increase payload
Freight (tons/km)
2
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
Front truck leaf springs in the world
AMERICA
SIDENOR I+D | R. Elvira3
EUROPA
ASIA
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Leaf spring nominal stresses are rising and approaching to those typical of suspensions springs
Less leaves / less weight / higher stresses•
Less number of leaves Higher stressesThicker leaves Higher hardenability
Higher fatigue requirements
-17% Weight -42% Weight
Weight reduction
44
SIDENOR I+D | R. Elvira
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
Higher Stresses: Smaller Admissible Defects
Higher stresses imply much higher failure risk
Admissible defects must be smaller
Steels used for multileaf springs are not suitable any more
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•
•
FAILURE
SAFETY
KITAGAWA Diagram
Defect diameter (µm)
Admisible defect size
Stee
l H
ardn
ess
5
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Early fatigue failures occur when lighter leaf springs must cope with higher stresses in the presence of surface and internal defects
Higher stresses lead to fatigue issues
Surface defects Internal defects
6
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Current leaf spring manufacturing route
Steelmaker Springmaker OEM
Re-rolling Eye forming StresspeeningSteelmaking
Flat Bar Products
Hot rolling AssemblyHeat treatment
• Internal and surface flat bar inspections are not automatic, but manual
• A guarantee of “zero defects” is not possible nowadays
• Fatigue failures are due to defects non-detectable by current inspection methods
7
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Apparently similar steel batches lead to a totally different fatigue performance
Scatter among different industrial heats and steelmakers might lead to a 60% reduction in average of the fatigue life from higher to lower
A certain risk of service failures could be expected, as no standard method can rank properly steel suppliers’ quality
Similar… but not the same
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•
•
8
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
Benchmark of leaf spring steel suppliers by component fatigue testing at customer facilities
SIDENOR I+D | R. Elvira
Even the average performance of steelmakers shows a big scattering, doubling the lifetime from top to bottom supplier.
Component fatigue tests are able to sort out steel quality, but unfortunately they are not economically appropriate for the regular control of leaf spring serial production
Leaf spring testing is not the solution…
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Supplier 6
Supplier 3
Supplier 2
Supplier 7
Supplier 1
Supplier 5
SIDENOR Supplier 4
20000
0
40000
60000
80000
100000
120000
140000
160000
18000051CrMoV4
Average B50
9
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Standard controls consist in:Visual inspection (for surface defects)Metalographic inspection (for internal defects)
But, as these controls are clearly insufficient and inadequate…:“Effective CHECK” activities are:Component fatigue testing (for homologation of new references)Service failures!!!
Ineffective Quality Control
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•
P D
CA
Fortunately, new characterization methods are available to determine real level of steel quality and to improve manufacturing processes
10
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
3-point fatigue testing correlates satisfactorily with component testing and allows a proper product characterization
Fatigue testing
1300
1350
1400
1450
1500
1550
1600
1650
1700
1750
1800
1850
1,0E+ 04 1,0E+ 05 1,0E+ 06 1,0E+ 07 1,0E+ 08
L ife tim e (cyc le s)
Failures Steel-1
Failures Steel-2
Failure Steel-3
Runouts Steel-2
Runouts Steel-1
Runouts Steel-3
14 5 0 M P a
1 65 0 M P a
1 55 0 M P a
Same grade, same strength, different steelmaking practices!!!
11
Max
imum
Ben
ding
Str
ess
(Mpa
)
12
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Quality assessment
0%
20%
40%
60%
80%
100%
0
5
10
15
20
25
30
Clase
A
Frecuencia % acumulado
0 %
1 0 %
2 0 %
3 0 %
4 0 %
5 0 %
6 0 %
7 0 %
8 0 %
9 0 %
1 0 0 %
0
5
1 0
1 5
2 0
2 5
3 0
C l a s e
B
F r e c u e n c ia % a c u m u l a d o
0%
20%
40%
60%
80%
100%
0
5
10
15
20
25
30
Clase
C
Frecuencia % acumulado
6 6 7 Inicio: Profundidad ( m m ) / DSR8 t - 1 A
20 SamplesA : Dep th (mm)/ Defect size
6 6 7 Ce ntro: Profundidad ( m m ) / DSR8 t -1 B
20 SamplesB : D ep th (mm)/ D efect size
Profundidad (m m )/ tam año de fectos C -scan 8 t -1 C
20 SamplesC : D ep th (mm)/ Defect size
12
13
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Surface and internal defects can be examined deeply and determined the root causes of fatigue failure to take corrective actions on the process
SEM Identification of failure causes
14
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Conventional characterization methods cannot differentiate properly between “good” and “bad” steel batches, leading to an inacceptable scatter
Conventional characterization is useless
Same strength
Same toughness
Equivalent microcleanliness evaluation
Similar hardenability…but
Different supplier!
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•
•
•
•
Benchmark of leaf spring steel suppliers by component fatigue testing at customer facilities
51CrV4
Heat-1
50000
0
150000
+120
%
100000
Heat-2 Heat-3 Heat-4
L10
(No.
cyc
les)
15
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
New testing methods allow checking steel quality in a suitable way and improving service performance
Using them, even downgraded steels might beat more alloyed grades with well-known best fatigue behavior
New methods discriminate and help to improve
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•
Supplier-4
B10
(No.
cyc
les)
Supplier-3 Supplier-2 SIDENOR
20000
0
40000
60000
80000
100000
120000
140000
160000
180000
200000
51CrV4 52CrMoV4
+30%
70% less
New testing methods 2016
16
Sidenor | Ultralight Leaf Springs for Upcoming Front Truck Suspensions
SIDENOR I+D | R. Elvira
Upcoming Ultralight Leaf Springs must cope with much higher stresses and traditional leaf spring steels are not valid any more
Conventional characterization methods are inappropriate and misleading and cannot predict service performance properly
New characterization methods can adequately CHECK steel quality and use it to improve steelmaking and spring making practices
Conclusions
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•
•
P D
CA
FAILURE
SAFETY
KITAGAWA Diagram
Defect diameter (µm)
Admisible defect size
Stee
l H
ardn
ess
51CrV4
Heat-1
50000
0
150000
+120
%
100000
Heat-2 Heat-3 Heat-4
L10
(No.
cyc
les)
Supplier-4
B10
(No.
cyc
les)
Supplier-3 Supplier-2 SIDENOR
20000
0
40000
60000
80000
100000
120000
140000
160000
180000
200000
51CrV4 52CrMoV4
+30%
70% less
New testing methods 2016
Barrio Ugarte s/n - 48970 Basauri (Bizkaia)C.I.F.: B01292903
Teléfono: +34 94 487 1500Fax: +34 94 487 1615
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