Structural Organization and Properties of a Natural Ferrite-Martensite Steel Composite
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STRUCTURAL ORGANIZATION AND PROPERTIES OF A NATURAL FERRITE-MARTENSITE STEEL COMPOSITE V. N. Pustovoit,1 Yu. V. Dolgachev,1 Yu. M. Dombrovskii,1 and V. V. Duka1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 15 – 21, June, 2020.
The treatment conditions yielding steel with a natural ferrite-martensite composite structure are proposed. Structural steels having a banded ferrite-pearlite structure after hot rolling are analyzed. It is shown that the strength achievable by the composite is proportional to the volumetric fraction of the strengthening phase. Based on the experimental data obtained as a result of tension and dynamic bending testing, the fracture mechanisms of steels having the ferrite-martensite composite structure are discussed.
Key words: composite, steel, structure, ferrite, martensite, pearlite, segregation banding, fracture.
When using the proposed method, it becomes possible to obtain an almost ideally oriented structure formed during hot rolling with an overall reduction ratio > 70 %. In this case, ductile sulfides (Fe, Mn)S become elongated in the direction of deformation and serve as substrates, on which parallel fibers (plates) of proeutectoid ferrite are formed. A similar form is also acquired by pearlite resulting from the eutectoid transformation of austenite (Fig. 1a). Structural organization of the NFMC can be obtained either by entering the ITR “from below” (i.e., by heating steel with a banded structure to a certain temperature, soaking, and quenching), or “from above” from the austenitic state (i.e., cooling steel in the ITR, soaking at a certain temperature to enable precipitation of proeutectoid ferrite on sulfide inclusions, and quenching). The second option can be implemented directly within a rolling mill process [1]. Depending on the ferrite-to-martensite volumetric ratio, the use of steels with the NFMC structure is feasible for high-load constructions and bridge structures, boilers and high-pressure pipes, rails, special-purpose guides, etc., as well as for manufacturing armor protection systems providing effective resistance to localized high-power impacts (armor protection for military personnel, armored vehicles, mechanized infantry fighting vehicles, armored assault vehicles, and checkpoints in case of small arms and grenade launcher fire). The objective of this work is to study the structure and properties of structural steels with the NFMC structure obtained as a result of treatment under different process conditions.
INTRODUCTION The idea of creating a natural ferrite-martensite composite (NFMC) is based on using the starting materials in the form of proeutectoid steels having a banded ferrite-pearlite structure [1, 2]. Segregation banding (Fig. 1a) is considered a metallurgical defect. However, it is proposed to use this particular flaw to obtain the NFMCs, since after heating such steels in the range (À1 – À3 ) of intercritical temperatures, soaking to allow for ferrite refining, and quenching, a nearly strictly-orient
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