Tensile properties of partially austenitised and austempered ductile irons with dual matrix structures

Abstract

In the present study, an unalloyed ductile iron containing Fe-3 . 50C-2 . 63Si-0 . 318Mn-0 . 047Mg (wt-%) were intercritically austenitised (partially austenitised) in two phase region azc at various temperatures of 795, 805, 815 and 830uC for 20 min and then quenched into salt bath held at austempering temperature of 365uC for various times to obtain different ausferrite volume fractions (AFVFs). Results showed that dual matrix structure containing proeutectoid ferrite, new ferrite (also called epitaxial ferrite) and ausferrite (bainitic ferritezhigh carbon austenite, which is retained or stabilised austenite) has been developed. Within each of the austempered series in azc temperature range, new ferrite volume fraction increased with increasing intercritical austenitising temperature (ICAT). Although, transforming percentage of new ferrite from parent austenite present at ICAT increased with decreasing ICAT. Some specimens were also conventionally austempered from 900uC for comparison. The new ferrite was absent in these samples. The volume fraction of proeutectoid ferrite, new ferrite and ausferrite can be controlled to determine the strength and ductility. Austempered specimens in azc temperature range exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing AFVF. On the other hand, the ductility increased with increasing proeutectoid ferrite and new ferrite volume fractions at the expense of strength. The specimen with ,47 . 2%AFVF exhibited the best combination of high strength and ductility. The strength and ductility of this material is much higher than that of ferritic grades. Its strength is at the same level as while ductility almost more than four times higher than that of pearlitic grades. Meanwhile, the specimen with ,75%AFVF exhibited the best combination of high strength and ductility compared with those of pearlitic grades. The strength of this material is much higher and its ductility is almost more than two times higher than that of pearlitic grades yet slightly lower than that of ferritic grades. This material also meets the requirements for the strength of quenched and tempered grades and its ductility is higher than that of this grade.

Development and Characterization of a New Type of Ductile Iron with a Novel Multi-phase Microstructure

“…The matrix of a dual phase ADI is composed by ausferrite (as in regular ADI microstructure) and free or allotriomorphic ferrite, in an attempt to combine the high tensile strength and toughness of the ausferrite with the high ductility of ferrite. [15][16][17][18][19][20][21][22][23][24] Different methodologies have been applied to obtain dual phase microstructures. [15][16][17][18][19][20] The simplest method seems to be that described by Basso et al 21,22) and Kilicli et al, 23,24) which consists of an incomplete austenization stage at temperatures within the intercritical interval, where austenite (γ) ferrite (α) and graphite (Gr) coexist (Fig.…”

Mechanical Characterization of Dual Phase Austempered Ductile Iron

“…The results have revealed that a strong relationship exists between tensile strength and elongation until failure in the case of some Dual Phase ADI microstructures. [4][5][6][7][8] Along these lines, fracture toughness tests have yielded interesting values when compared to those of fully ferritic or fully ausferritic matrices. 4) In view of the fact that many mechanical components used in the industry need tolerate cyclic loads at elevated stresses; another property to be analyzed is fatigue resistance.…”

“…8, in which the tensile strength-deformation until failure ratio is shown for DI with different microstructures, considering our results as well as those reported by other authors. [4][5][6][7][8][9] …”

“…[4][5][6][7] An adequate handling of the heat treatment variables allows to control the amount, morphology and distribution of the micro constituents (free ferrite and ausferrite), thereby enabling to attain a wide range of mechanical properties.…”

High Silicon Ductile Iron: Possible Uses in the Production of Parts with ^|^ldquo;Dual Phase ADI^|^rdquo; Microstructure

“…This improvement is explained by the novelty of this DI microstructure, which is composed of different amounts of free (or allotriomorphic) ferrite and ausferrite (ADI regular structure). [1][2][3][4][5][6][7][8][9][10][11] Special thermal cycles have been developed by different researchers in order to obtain Dual Phase ADI. One of them has been advanced and used by Kilicli et al 7,8) and Basso et al [4][5][6] It consists in subjecting fully ferritic DI parts to an incomplete austenitization stage, at different temperatures within the intercritical interval of the Fe-C-Si diagram (see Fig.…”