ultralight leaf springs for upcoming front truck suspensions · pdf fileultralight leaf...

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


Front truck leaf springs in the world

AMERICA

SIDENOR I+D | R. Elvira3

EUROPA

ASIA



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



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

•

•

•

FAILURE

SAFETY

KITAGAWA Diagram

Defect diameter (µm)

Admisible defect size

Stee

l H

ardn

ess

5



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



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



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

•

•

•

8


Benchmark of leaf spring steel suppliers by component fatigue testing at customer facilities


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…

•

•

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



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

•

•

P D

CA

Fortunately, new characterization methods are available to determine real level of steel quality and to improve manufacturing processes

10



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



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



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



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!

•

•

•

•

•

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



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

•

•

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



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

•

•

•

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

e-mail: [email protected]

ultralight leaf springs for upcoming front truck suspensions · pdf fileultralight leaf...

Documents