1. Made by the student of the 832 AMS group Gerasenko K. Pridneprovs’ka State Academy of Civil Engineering and Architecture Scientific supervisor : Ph.D. O. Uzlov Language supervisor : K. Kuznetsova Dnipropetrovsk 2011

2. 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.

3. Such growth of impact toughness can be explained by the features of main crack formation. Main crack Acicular ferrite structure Bainite structur e Fig. 1.1. Main crack spreading: a) along accicular ferrite grain, b) along bainite grain

4. Chemical compositions of investigated steels System of alloying %, Wt. CMnSiPSCrMoVNiCuAlTiN Al-Ti-N 0,190,630,280,0150,0140,18--0,130,200,0290,0030,019 Al-Ti-N 0,200,710,300,0160,0100,22--0,130,180,0280,0160,018 Ti-V [1] 0,371,450,60,0100,0430,040,0250,11-0,140,0240,0150,0162 Ti [1] 0,351,560,330,0100,0430,040,025--0,140,0270,0280,0089

5. steel gradestructural state  y(0,2), (YTS) MPа  В, (ULS) МPа  5, % , % 16Г2АФ [5] (C+Mn+V+N) Tempered martensite(Quenching 920 0 С tempering 680 0 С,2 h.) 390...555555...71018...28N/AN/A 09Г2ФБ (C+Mn+V+Nb) Ferrite+perlite, controlled rolling 55064023N/AN/A Al-Ti-N acicular ferrite + packed bainite 580...590800...82021...2241...43 Al-Ti-N acicular ferrite + packed bainite 620...630860...87021...2237...39 Ti-V [1]acicular ferrite560...666N/AN/AN/AN/AN/AN/A Ti [1]acicular ferrite519N/AN/AN/AN/AN/AN/A Obtained mechanical properties of steels

6. Mechanical tests have been conducted according to valid State Standard and Technical Requirements. For impact toughness estimating the U- notched specimens were chosen. KCU, J/cm 2 Testing temperature, 0 C

7. 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.