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Bainitic Steel: Structure and Properties

ФИО: Mohamed Yousef Ali Issa

Направление: Материаловедение

Научный руководитель: Associate Professor, PhD

Институт: Институт новых материалов и нанотехнологий

Кафедра: Кафедра Физического материаловедения

Академическая группа: МТМ-14а

Bainite steels demonstrate unique mechanical properties: high wear resistance and tensile strength. Bainite is a non-equilibrium decomposition product of austenite; which is formed as result of so-called intermediate transformation of austenite. Bainite occurs at a temperatures below BS (Bainite start temperature) depending on chemical composition [1]. The aim of the present work is to investigate structure and properties of bainitic steel as a result of different heat treatment conditions.

The chemical composition of material for the research is shown in Table 1 and heat treatment with typical microstructures is represented in Table 2.

C Mn S P Si Al Cu Cr Ni Mo V Nb Ti
0.8 2.03 0.006 0.006 1.51 0.057 0.03 0.22 1.05 0.377 0.004 0.007 0.019

Heat Treatment Microstructure
1 930 °C for 1 h, cooled 0.1 °C s-1 to 550 °C, held for 4 h , air cooled Perlite +ferrite
2 930°C for 1 h, air cooled to 200 °C, held for 10 days , air cooled Bainite
3 930°C for 1 h, air cooled Martensite

After heat treatment №1 three various types of structure elements were observed: perlite, spheroidal and/or oriented ferrite.

Vickers hardness tests were carried out with loads of 0.5 kg or 0.05 kg for 10 s, and the results are shown in Table 3.

P=0.05 kg P=0.5 kg
Bainite 649.83 ±16.78
Perlite 329.95 ±7.46 314.26 ±6.470
Spheroidised ferrite 281.18 ±12.63 295.98 ±8.99
Oriented ferrite 322.50 ±10.62 328.75 ±12.05

To complete the research we are looking for carrying out X-Ray phase analysis, dilatometry to determine phase transformation temperatures and tribological test to confirm high wear resistance.

References:

[1] Bhadeshia, H. K. D. H. «Bainite in Steels». ISBN: 9781909662742: Maney Publishing, London, Third edition, (2015).