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FORGED BACK UP ROLLS

FORGING THE FUTURE NOW

Società delle Fucine (SdF) was founded in 1884 and since 1999 it has been a member of ThyssenKrupp Group.The company is located in Terni, Italy and produces large forgings for rolling mills, energy and heavy industry applications.The production of forged rolls is mainly focused on the back up rolls for steel industry (Plate Mill, Hot Strip Mill and Cold Mill) and for aluminum industry.

A Company of ThyssenKrupp Acciai Speciali Terni Group

A Company of ThyssenKrupp Acciai Speciali Terni Group

Società delle Fucine - Viale B. Brin 218 - 05100 Terni (Italy) Ph +39 0744 4881 - F +39 0744 470912 info.sdf@thyssenkrupp.com

www.fucineterni.it

35

40

45

50

55

60

65

70

75

0 50 100 150 200 250

5% C r

3% C r

3% C r-PM

Core/Neck

FORGED BACK UP ROLLS

Steel QualityThe balance of carbon and alloy elements aims to achieve the best compromise among different properties such as hardenability, hardness, toughness and fatigue, and thermal cracking resistance. Selected scraps and modern steel refining processes allow the residuals content to be minimized: typically, sulphur and phosphorus are below 0.01% and H is less than 1 ppm.2

Ingots are top poured under vacuum. Ingot weight ranges up to 530 t.

Dedicated forging cycleAn optimum forging ratio on the working layer and the necks is obtained thanks to a specific choice of ingot dimensions. Proper heating and plastic deformation parameters allow good physical and metallurgical properties to be achieved throughout the cross-section, especially on the working layer of barrel.

Hardening processIn order to obtain a good combination of necks toughness and high hardness on the working layer, the back up rolls are treated only on the barrel, with a special differential hardening equipment. The heat treatment is then performed by austenitizing the working layer in a high–power heating furnace and then by cooling with blown air and spray water. The uniformity of the treatment is guaranteed by keeping the roll in rotation during the process

Machining and GrindingRolls are supplied according to the customer requests. Società delle Fucine can supply the rolls in the machined status or in fully ground surface (Std Ra = 0.8 µm, on demand till 0.4 µm).Both steps are performed using modern numeric control machines

Typical properties of SdF forged BU Rolls

In comparison with cast rolls, forged rolls with an equal chemical composition show a better combination of metallurgical and physical properties, such as: a compact porosity-free microstructure, good ductility and toughness values and high resistance to fatigue, wear and thermal cracking. In addition, the uninterrupted fibrosity between body and necks, resulting from metal flow during forging, improves the fatigue resistance of the rolls and prevents the failure of necks from arising. The most significant properties of back up rolls are the following:

Fatigue resistance of necks obtained with a minimum forging reduction of 3 on the cross-section, low hardness (35-45 HSC), high tempering temperature and low residual stresses.

High wear resistance of the working layer as a consequence both of the steel chemical composition, rich in carbide forming elements and of the quality heat treatment performed.

Optimized hardness for specific working conditions, with a wide- range variation, even with the same chemical composition. This is possible thanks to different heat treatment conditions, including differential heating, and blown-air cooling water spray.

High thermal cracking resistance by:• specific alloy elements addiction (Cr- Mo);• fine and homogeneous microstructure typical of forged steel;• absence of stress intensity factors, such as porosity, non metallic

inclusions and other discontinuities.

High spalling resistance of the working layer (spalling is often obtained with work hardening) with a proper combination of some factors such as:• good steel micro-cleanliness that prevents local fatigue and

thermal cracking notches from taking place• good material toughness to bear possible cracks caused by

rolling accidents• favourable compressive stresses on the working surface of rolls.

Roll Manufacturing Cycle (flow chart)

Mechanical properties of Sdf forged rolls

Properties Unit Barrel Necks/core

Ultimate tensile strength Mpa 1300 -1800 700 - 1400

Yield strength Mpa 1000 - 1500 600 - 1000

Elongation % >5 >10

Fatigue strength Mpa - 300 - 350

SdF Forged BU Rolls

Other chemical composition are obtained on demand

GRADEAPPLICATION

HARDNESS CHEMICAL COMPOSITION MICROSTRUCTURE

SHC EquotipLD

C CR NI MO

V

MATRIX

CARBIDES

0,05 - 0,20

0,05 - 0,20

3% (M C)3

8% (M C )7 3

3% Cr Plate Mill 45 - 60 586 - 684

0,40 - 0,60

0,40 - 0,60

2,50/3,50 UP TO 0,50

UP TO 1,20

UP TO 0,50

UP TO ,80

TEMPEREDBAINITE

TEMPEREDBAINITE

3% Cr Hot Strip Mill 50 - 65 620 - 710

3% Cr Cold Mill 58 - 68 672 - 734

5% Cr Hot Strip Mill62 - 72 696 - 752 4,50/5,50

5% Cr Cold Mill

Depth from surface (Radius) (mm)

Hard

ness

[ H

Sc

]

01: MELTING 02: REFINING IN ASEA-VODof 60, 100, 130 tonn

03: UNDER VACUUM CASTING 04: FORGING

05: PRELIMINARY H.T. 06: ROUGH MACHINING 07: U.T. BEFORE Q.H.T. 08: QUALITY HEATH TREATMENT

09: FINAL MACHINING 10: GRINDING 11: FINAL TEST(M.T. + DIMENSIONAL CHECK)

12: PACKING AND SHIPPING

Hardness penetration for back up rolls

0,05

0,031

0,011 0,0130,006 0,002

0,26

0,118

0,082

0,027

0,015 0,012

0

0,05

0,1

0,15

0,2

0,25

0,3

HSc 60-3%Cr HSc65-3%Cr HSc65-5%Cr HSc70-3%Cr HSc70-5%Cr HSc75-5%Cr

200 [N]

500 [N]

60,0

62,5

65,0

67,5

70,0

72,5

75,0

55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

Initial Hardness BUR (HS)

Spalling Analysis

Wear test comparison between BUR with 3%Cr and 5%Cr

Unsafe zone

Safe zone

Initi

al H

S+

Wo

rk H

ard

nei

ng

(d

HS

)W

ear-

wei

gh

tloss

[g

]