MATERIAL

Wallace Douglas - doug.wallace@fcagroup.com

SPRING STEELS
MORGANO ENRICO - enrico.morgano@crf.it

STANDARD
Fiat Group Carbon Steel
Automobiles C.72 52554
NORMAZIONE [MS.90028] Page: 1/12
Date: 16-JUN-2016

TMD
Code
-
PURPOSE

Ch.
To specify the requirements to be met by Grade C 72 carbon steels supplied in the form of patented and
Co-Author

drawn wires or of strips and to provide instructions for drawing call - out.
Author

A
Edition
This Standard consists of 12 pages.

Change Date Description

FCA ITALY -- GROUP MATERIALS LABS (CRF) - METALS

-- Mar., 1990 Edition 4 - Revised for updating and harmonization with the
corresponding A.R. Standard 3200.0433 - Class B. (GF)

A Oct., 1990 Data processing code under para. 5.3 deleted (was 21060 - C72

DISPUTE THE ONLY VALID REFERENCE IS THE ITALIAN EDITION. IF THE ITALIAN
EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
Nastro) (BM)

THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD

PARTIES WITHOUT PRIOR WRITTEN CONSENT BY FGA S.P.A. IN CASE OF
FCA US -- METALLIC MATERIALS - 5810

- 17-OCT-2014 Edition 5 - Reference norms:

. 50231 replaced by 50225 and 50235
. 5.00432 replaced by 9.57408
. 5.00401 superseded
. Reference to MS.90028 added in the title. (DC)
Rev A 16-JUN-16 Updated documents cited in the text (GL)

VALID REFERENCE.
CONFIDENTIAL
Co-Author Department
Author Department

ANY PRINTED COPY IS TO BE DEEMED AS UNCHECKED; THEREFORE THE UPDATED COPY MUST BE CHECKED IN THE APPROPRIATE WEB SITE

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1. GENERAL
1.1. Steel grade
Spring carbon steel, supplied as wires and strips.

1.2. Intended use

- Round hard drawn wire - Springs for general purposes statically stressed.

- Round hard drawn patented wire - Springs for general purposes for which a more marked
characteristic uniformity and better quality are required.

- Round or polygon hardened-and-tempered wire - (hardened - and - tempering is carried out on

finished springs)
Springs having a complex shape (with highly severe forming). Unless otherwise specified the properties
indicated in the chart of Fig. 7 shall be obtained on the finished part; therefore when different properties
are needed, the required value of the hardness shall be added to the normal designation "C 72 Filo
Bon", e.g. "C 72 Filo Bon HV 415 to 435".

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- T3 strips - For exceptional use: fatigue stressed flat springs, obtained from pre - treated strips for which
characteristics shown in Figs. 2 and 3 are sufficient.

- T2 and T1 strip - For exceptional use: severely fatigue stressed flat springs obtained from pre-treated
and re-rolled strip, for which higher characteristics than those of T3 are required (see Figs. 4, 5 and 6).

- Nastro Bon (hardened - and - tempered strip)

Springs, hardened - and - tempered after forming obtained by means of strip bending. Resistance being
equal, these springs will have fatigue limit and elastic limit lower than those of T2 or T1 strip springs.

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For resistance/hardness comparison of these springs, the scale shown on the chart of Fig. 2 can be
EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
WRITTEN CONSENT BY FGA S.P.A. IN CASE OF DISPUTE THE ONLY VALID REFERENCE IS THE ITALIAN
THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR

used. The HRC hardness values obtainable on these springs are specified in para. 4.3; if different
hardness values are required, such values shall be added to the designation on drawing, e.g. C 72
Nastro Bon HRC 43 to 47. The Supplier, at his discretion, may use T3 T2 T1 strips, on condition that
the specified requirements are met.

1.3. Equivalences with other Standards

Equivalences quoted below are FOR GUIDANCE ONLY. Before adopting any substitution always consult
the F.C. - Central Laboratories.
VALID REFERENCE.

17223 Afnor 1429

CONFIDENTIAL

DIN NF B.S. SAE

UNI 3283 EURONORM 17222 A47 - 301 1408 C

Nastro MK75G 42 C Grade 2 J113

FILO B - FILO TIPO B Class B1 (Filo Pat. Traf.) Class2

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2. REQUIREMENTS
2.1. Chemical composition
2.1.1. Ladle analysis %

C Mn Si S P Fe
0.65 to 0.80 0.50 to 0.80 0.20 to 0.40 ≤ 0.035 ≤ 0.035 balance

2.1.2. Check analysis

For permissible deviations from limit values given in para. 2.1.1 see Std. 52120.

2.2. Physical, chemical and fabrication properties

2.2.1. Physical properties (indicative)
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Density at 20ºC : 7.85 kg/dm³

Modulus of elasticity : Longitudinal (E) : 206.000 N/mm²

Transversal (G) : 78.500 N/mm²

-6
Linear thermal expansion coefficient at 20 to 100ºC : 11.2 x 10 /ºC
Thermal conductivity coefficient at 100ºC : 0.102 cal/cm sec ºC
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2.2.2. Fabrication properties (indicative)

Fabrication characteristics are rated as follows: excellent, good, acceptable, fair, poor, bad, very bad,

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
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impossible.

Material condition Material condition

Property Hardened Property Hardened

Annealed Annealed
and tempered And tempered

- Corrosion resistance
Hot formability Good Bad Bad
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Cold Good Bad Core toughness - -

formability
Weldability Impossible Impossible Hardening depth Excellent -

Hardening
Machinability Fair Bad Acceptance Acceptable
non-deformability

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2.3. Mechanical properties for material inspection

In accordance with Std. 50225, no material inspection is performed because of the wire and strip
dimensions; therefore the mechanical properties are measured directly on the semifinished product (See
para. 3.3).

3. SEMIFINISHED PRODUCTS
3.1. "As supplied" condition and relevant designations

- Drawn wire: C 72 Filo - Cold rolled annealed strip: C 72 Nastro Lmtf Rct

- Patented and drawn wire: C 72 Filo Pat Trf - Cold rolled hardened - and - tempered strip: C
72 Nastro T3

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- Drawn, annealed, size wire: C 72 Filo Trf Rct - Cold rolled hardened - and - tempered re - rolled
Calb (*) strip: C 72 Nastro T2

- Cold rolled strip: C 72 Nastro Lmtf - Cold rolled hardened - and - tempered hard
re-rolled strip: C 72 Nastro T1

(*) Complete, if necessary, by indicating the wire section shape (round or polygonal).

3.2. Acceptance inspections

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
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THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR

According to Std. 50225 - 50235 , besides the characteristic checks specified in para. 3.3, the cooling
test, the continuous torsion test and the bending test shall be performed for the drawn wires, the bending
test for annealed wires, and the micrographic test (for the control of structural characteristics specified in
para. 3.5) and macrographic examination (for the surface appearance control indicated in para. 3 4) for all
wires and strips.
VALID REFERENCE.
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3.3. Inspection mechanical properties (See Std. 50225 and 50235 ) (1)

Elastic limit (min)

Diameter Elongation Fatigue Bending
Material R Tension e Tension limit Ft
or A test
shape and (U.T.S.) e Hardness
thickness (indicative) (10) α = 180°
condition N/mm² (indicative)
mm (2) % min D/a (5)
N/mm² (4)
Filo Trf
Fig.1, -
0.1 to 9 Fig.1, d -
Filo Pat Trf B
23 ± 23 -
Filo Trf Rct (6)
Calb 1 to 8 HV ≤ 196
- - 20 ± 20
Nastro Lmtf (3) HRB
- 0 (8)
Rct ≤ 90 (7)
Mastro Lmtf (3) HRB
0.08 to 3 -
≤ 105
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-
Nastro T 3 Fig. 2, Fig. 2,
Fig. 2, C 7 Fig. 3 (9)
A-B A-B
Nastro T 2 Fig. 4, Fig. 4,
Fig. 4, C Fig. 5 (9)
A-B A-B
0.08 to 2 -
Nastro T 1 Fig. 6, Fig. 6,
Fig. 6, C -
A-B A-B

(1) Mechanical properties of wires are referred to stress relieved, non shot-peened
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semifinished products

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
(2) For standard production dimensions see Std. of class 54. Strips may be supplied in 5 through

THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR
500 mm width. For the tolerances, see Stds. 54307 and 01485 for wires and strips
respectively.

(3) The hardness inspection shall be carried out using different scales depending on thickness:
HRB for thickness (a) >0.9; HR 45 - T for a >0.6 to 0.9; HR 30 - T for a = 0.4 to 0.6;
HR 15 - T for a < 0.4. The values shall be converted according to Std. 50109.

(4) Stress corresponding to a 0.02% permanent elongation.

(5) Ratio between the bending diameter (D) and the specimen thickness (a).
VALID REFERENCE.
CONFIDENTIAL

(6) On an exact length of wire quenched in oil at 820 to 850°C and tempered at 400°C to
430°C.

(7) If a lower hardness is required (e.g. U - flex rings), hardness HRB <60 (obtainable by
spheroidizing) may be specified.

(8) Test to be carried out according to Std. 50125, single bending.

(9) Test to be carried out according to Std, 50125, single bending by means of a U - shaped
die.

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 CONFIDENTIAL
THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR
WRITTEN CONSENT BY FGA S.P.A. IN CASE OF DISPUTE THE ONLY VALID REFERENCE IS THE ITALIAN
EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
VALID REFERENCE.

Strip thickness (mm)

Wire diameter ( mm)

52554

Fig. 2
2
R (da N/mm )

C72 wire T3
Fig. 1
2
R (da N/mm )

C72 wire Tri

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2
δ e (da N/mm )
Fig. 3

Bending
C72 Nastro T3

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Strip thickness (mm)

Strip thickness (mm)

2
R (da N/mm )

Fig. 4

Fig. 6
R (da N/mm )
C72 Nastro T2

C72 Nastro T1

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Page 7

Change

2
δ e (da N/mm )

2
δ e (da N/mm )
52554

Fig. 5

Bending
C72 Nastro T2

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THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR
WRITTEN CONSENT BY FGA S.P.A. IN CASE OF DISPUTE THE ONLY VALID REFERENCE IS THE ITALIAN
EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
VALID REFERENCE.
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3.4. Surface condition

The surface shall be free from slivers, pittings, machining defects or any other flaws prejudicial to
serviceability; light scratches, small marks and pittings are permitted on drawn (not patented) wires, on
condition that they are not prejudicial to part performance.

3.5. Structural properties

Grain size
Non-metallic
Decarburized layer (accoring to
Semifinished inclusions
Structure ASTM-E-112)
products
Total Partial
Filo Trf Structure heavily None ≤ 3% of diameter or Not required
deformed thickness; anyway
Nastro Lmt lengthwise not ≤ 0.15 mm 7 or finer

•
UNI 3244-66 ) shall not be larger
than the number 2 of the Scale JK
Filo Pat Trf None ≤ 1.5% of diameter; 7 or finer

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The inclusions (according to
any way not
≤ 0.04 mm

Filo Trf Rct Calb Pearlite-ferrite None ≤ 3% of diameter or 7 or finer

thickness; anyway,
Nastro Lmtf Rct not ≤ 0.13 mm

Nastro T 3 Tempered None 1.5% of the thick- 7 or finer

martensite and ness; anyway, not
sorbite ≤ 0.04 mm

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
WRITTEN CONSENT BY FGA S.P.A. IN CASE OF DISPUTE THE ONLY VALID REFERENCE IS THE ITALIAN
THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR

Nastro T 2
Tempered
martensite and
Nastro T 1
sorbite.*

 When the semifinished product size does not allow the checks according to UNI 3244-66,
inclusions shall be inspected by examining in its totality, with a 100% magnification, the longitudinal
section of a semifinished cut section abt. 20 mm, polished and subjected to a light Nital etching (1 to
2%); for each examination field, inclusions shall not result larger than those corresponding to Scale
VALID REFERENCE.

JK number 2.
CONFIDENTIAL

* Structure is heavily deformed lengthwise.

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4. FINISHED PARTS
4.1. Production of finished parts (*)
- Wire: the finished spring (when not hardened-and-tempered) shall be stress relieved, and when
specified on drawing, shall be subjected to setting treatment, shot-peening and surface coating. Stress
relieving treatment consists of heating to 230 to 250°C with at least 30 min soaking. Normally, the
spring setting shall be run at the torsion elasticity limit and shall be such as to meet the requirements
set forth inspection class specified on drawing.

- Nastro T 2 and T 1 - Parts are obtained from the hardened-and-tempered and re-rolled strip; after
forming, they shall be subjected to stress relief treatment by heating to a temperature from 230 and
250°C with at least 30 min soaking.

- Nastro T 3 - Parts are obtained from hardened-and-tempered strip and shall be subjected to a stress
relief treatment by heating to a temperature from 230 to 250°C with at least 30 min soaking.
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- Nastro Bon - Parts are obtained from the cold rolled annealed strip. Finished parts shall be hardened-
and-tempered at such a temperature as to ensure meeting of the property requirements in para. 4.3 or
specified on drawing.

4.2. Structural properties

Decarburized layer Grain size

Semifinished Non-metallic
Structure (according to
products inclusions
Total Partial ASTM-E-112)
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Filo Bon Tempered ≤ 3% of diameter or

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
martensite and None thickness; anyway not See para. 3.5 7 or finer

THIS DOCUMENT MUST NOT BE REPRODUCED OR CIRCULATED TO THIRD PARTIES WITHOUT PRIOR
Nastro Bon sorbite ≤ 0.13 mm

Filo Trf

Filo Pat Trf

Nastro Lmtf
The requirements indicated in para. 3.5 apply
Nastro T 3

VALID REFERENCE.
CONFIDENTIAL

Nastro T 2

Nastro T 1

(*) For information only. As regards production, the processing cycle requirements shall apply.

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4.3. Finished part properties

Torsion fatigue limit

U.T.S (std. Elastic limit,
2 Load loss 50225 and min.
Semifinished Ft (10) min.,kg/mm (2) after 72 h 50235 )
product at 120°C R Torsion Tensi
shape and Hardness Fluctuating with on δ e
(3) t e
2
Repeated stress daN/mm
material stress t = 70 (4) 2 daN/
daN/m mm2
2
condition N/mm
not shot shot not shot shot (3)
(indicative values)
peened peened peened peened
Filo Trf - - - - - 7% Fig. 1, B Fig. 1, C -

Filo Pat Trf - 23 ± 20 33 ± 33 35 ± 21 45 ± 31 7% Fig. 1, B Fig. 1, C -

Filo Bon Fig. 7, 20 ± 20 - - - 4% Fig. 7, A & B Fig. 7, C -
A & B (5) (5) (5)

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Nastro Bon HRC 41 to 45
(*) (6)
HRC 43 to 47 - - - - - (8) - 0.8 R
(7)
Nastro T 3 Fig. 2, A & B - - - - - Fig. 2, A & B - Fig. 2,
C
Nastro T 2 Fig. 4, A & B - - - - - Fig. 4, A & B -
Fig. 4,
C
Nastro T 1 Fig. 6, A & B - - - - - Fig. 6, A & B - Fig. 6,

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EDITION. IF THE ITALIAN EDITION IS NOT AVAILABLE OR NOT UPDATED, THE ENGLISH EDITION IS THE
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C
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(1) Minimum values for calculation. Normally a spring is fatigue calculated when the load varies by more
than 10,000 times during its life.
(2) Values corrected to Wahl's coefficient for compression and tension springs, stress relieved and set;
they are particularly reliable if the wire has 2.5 to 5 diameter. For helical flexure springs, these values
shall be increased by 40% for wire with ø ≤ 3 mm, and by 30% for larger wires. The maximum
amplitude for a completely reversed stress is 1.2 to 1.3 times the maximum amplitude allowed for the
repeated stress.
(3) On spring subjected to stress relief treatment (when not hardened-and-tempered) and set spring:
these values are corrected to Wahl's coefficient.
(4) On wire or strip cut sections. stress relieved after straightening the spring; the yield strength Rs is
VALID REFERENCE.
CONFIDENTIAL

0.9 R.
(5) Unless a particular hardness is specified on drawing.
(6) For springs obtained from strips having thickness over 0.7 mm
(7) For springs obtained from strips having 0.2 to 0.7 mm thickness.
(8) Correspondence between R and hardness specified on drawing is the same as that for strip T 3
(see F g. 2).
(*) In exceptional cases for parts obtained from strip, fatigue stressed or extremely stressed and of vital
importance, grade C 72 Extra may be called out on drawing; this strip has the same chemical analysis
except for S and P which are ≤ 0.020 and ≤ 0.025% respectively and offers the same properties of
grade C 72 but these show a marked uniformity in whatever location of every single semifinished item.

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52554

Hardness
2
R (daN/mm )
(mm)
Wire diameter
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Fig. 7
C72 Filo Bon
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t e (daN/mm )
2

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4.4. Protective coatings
As a rule, according to the following indications:

- Phosphating, as per P.S. 9.57408- for springs in contact with aggressive substances in ground.

- Phosphating- for springs located inside the occupant compartment

5. DRAWING CALL-OUT AND DATA PROCESSING CODE

5.1. Condition of the finished part and relevant designations
VALID REFERENCE.
CONFIDENTIAL

Finished part condition Standard designation on drawing (1)

Drawn C 72 Filo (2) (3)
Patented and drawn C 72 Filo Pat (2) (3)
C 72 Filo Bon (4)
Hardened-and-tempered C 72 Nastro Bon (5)
C 72 Nastro T 3 (2)

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(cont'd)

Finished part condition Standard designation on drawing (1)

Hardened-and-tempered and re-rolled C 72 Nastro T 2 (2)

Hardened-and-tempered and hard re- rolled C 72 Nastro T 1

(1) Quote also the indication of shot peening and/or protective coating (if any); for tension straight
helical springs, whilst inspection class selected among those listed there- in; in the C 72 Filo Pat
case, add the suffix "F" if the control of fatigue strength is required.
(2) If a stress relief treatment is required after spring forming (this heat treatment increases the
elasticity limit considerably), add the symbol "Dist", e.g. C 72 Filo Dist.
(3) The Supplier is free to use C 85 Filo indicated in Std. 52556, instead of the C 72 specified on
drawing.
(4) If mechanical properties different from those of Fig. 7 are required, the designation shall be
completed with the value of the required hardness.

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(5) If hardness different from those listed in para. 4.3 are required, the relevant symbol shall be
added to the designation on drawing.

5.2. Example of standard designation on drawing

Class Steel
Mat.: C 72 Filo
Std. 52554

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5.3. Data Processing Code

Designation Data processing code (See Std. 50020)

C 72 Filo 21009

6. REFERENCES
VALID REFERENCE.

01485 - 50020 - 50109 - 50225 - 52120 - 50235 - 52556 - 54307 -– 9.57408- UNI 3244-66 -
CONFIDENTIAL

ASTM E 112.

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