Made by the student of the 832 AMS group Gerasenko K.

Pridneprovs’ka State Academy of Civil Engineering and Architecture

MECHANICAL PROPERTIES OF STEELS WITH ACICULAR FERRITE

STRUCTURE

Scientific supervisor : Ph.D. O. Uzlov

Language supervisor : K. Kuznetsova

Dnipropetrovsk 2011

Martensite

Bainite

Acicular ferrite(x5000)

Microstructures of steels in different structural states martensite structure is characterized by high

strength properties with decreasing of plasticity.

Obtaining of bainite structure in steel allows to raise its strength properties without lowering plastic properties of the steel (as it happens in martensite structure). But at the time the lowering of plastic characteristics at lowered temperatures takes place.

The growth of impact toughness in the steels with acicular ferrite structure comparing with tempered martensite and bainite structure steels takes place.

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Such growth of impact toughness can be explained by the features of main crack formation.

Main crackAcicular ferrite

structure

Bainite structure

Fig. 1.1. Main crack spreading: a) along accicular ferrite grain, b) along bainite grain

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Chemical compositions of investigated steelsSystem of alloying

%, Wt.

C Mn Si P S Cr Mo V Ni Cu Al Ti N

Al-Ti-N 0,1

9

0,63 0,28 0,015 0,014 0,1

8

- - 0,13 0,20 0,02

9

0,00

3

0,019

Al-Ti-N 0,2

0

0,71 0,30 0,016 0,010 0,2

2

- - 0,13 0,18 0,02

8

0,01

6

0,018

Ti-V [1] 0,3

7

1,45 0,6 0,010 0,043 0,0

4

0,025 0,1

1

- 0,14 0,02

4

0,01

5

0,016

2

Ti [1] 0,3

5

1,56 0,33 0,010 0,043 0,0

4

0,025 - - 0,14 0,02

7

0,02

8

0,008

9

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steel grade structural state y(0,2), (YTS)

MPа

В, (ULS)

МPа

5, % , %

16Г2АФ [5]

(C+Mn+V+N)

Tempered

martensite(Quenchi

ng 9200С tempering

6800С,2 h.)

390...555 555...710 18...28 N/A

09Г2ФБ

(C+Mn+V+Nb)

Ferrite+perlite,

controlled rolling

550 640 23 N/A

Al-Ti-N

acicular ferrite +

packed bainite

580...590 800...820 21...22 41...43

Al-Ti-N acicular ferrite +

packed bainite

620...630 860...870 21...22 37...39

Ti-V [1] acicular ferrite 560...666 N/A N/A N/A

Ti [1] acicular ferrite 519 N/A N/A N/A

Obtained mechanical properties of steels

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Mechanical tests have been conducted according to valid State Standard and Technical Requirements. For impact toughness estimating the U-notched specimens were chosen.

KC

U,

J/cm

2

Testing temperature, 0C6

Conclusion

Microalloyed constructional steel (on the base of steel 0,2C+Mn+Al+Ti+N) with acicular ferrite structure has the strength and plastic property complex similar to property complex of steels alloyed V, Nb and Mo. Therefore, in case of applying for high-strength shaped and strip rolling investigated constructional low-alloyed steel with acicular ferrite structure can substitute higher alloyed and more expensive steels such as 16Г2АФ and 09Г2ФБ.

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Thank you for attention

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