Three groups of hypereutectic cast irons alloyed with Cu, Ni and microalloying additive like Ti and Nb were examined for its hardness and wear resistance in the austempered (360 °C/3. h) and quenched and tempered conditions at varying tempering temperatures. It is observed that the cast irons in the quenched and tempered condition showed good wear resistance and moderate hardness at 400 °C. This was comparable with the wear resistance in austempered condition. The study also showed that in quenched and tempered condition, increasing Cu content in cast irons improved its wear resistance moderately while increasing Ni content has decreased its wear resistance. The presence of strong carbide formers (Nb, Ti) did not give significant improvement in wear resistance in quenched and tempered condition. Even in austempered alloys, higher Cu content increases its wear resistance and higher Ni content decreases their wear resistance. The austempered alloys showed ausferritic microstructure with 20% austenite phase which enhances wear resistance through transformation induced plasticity effect. On the other hand, the quenched and tempered alloys showed good wear resistance at 400. °C due to fine tempered carbides in the matrix. © 2011 Elsevier Ltd.

M. Kamaraj

Department of Metallurgical and Materials Engineering

Austenite phase

CU CONTENT

GRAY CAST IRON

matrix

NI CONTENT

Tempering temperature

Transformation induced plasticity

Wear behaviors

Alloys

Carbides

CAST IRON

Copper alloys

Hardness

Iron

Wear resistance

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IIT Madras

Materials and Design

The effect of tempering temperature (100-600 °C) on the hardness and wear resistance of a series of quenched and tempered hypereutectic alloyed gray cast irons has been studied in this work. Hardness was observed decreases with increase in tempering temperature and this trend is influenced by alloying additions and the volume of graphite flakes. Hardness of alloyed gray irons is also influenced by solid solution strengthening of tempered ferrite and carbide content and their distribution. The wear loss of alloyed cast irons was found to be lowest at a tempering temperature of 100 °C and 400 °C. The optimum tempering temperature is 400 °C with moderate hardness and low wear rate. This has been attributed to strengthening of the matrix at this temperature. Beyond 400 °C, the wear rate increases significantly due to carbide coagulation. © 2010 Elsevier Ltd.

Mechanical and wear behavior of quenched and tempered alloyed hypereutectic gray cast iron

The austempering behavior of a series of hypereutectic alloyed gray iron compositions with carbon equivalent from 4.37 to 5.14 was studied to understand the influence of microstructure on its mechanical and wear properties. The alloying elements in the alloys included Ni, Mo, Cr and inoculation by micro-constitution of Ti, Nb and Ce. The alloys were austempered at 360 °C and upper bainitic type feathery ferrite was observed in the matrix. While the graphite content determined by optical metallography varied between 16 and 24 vol%. The volume of austenite determined by XRD analysis showed values between 20 and 26%. The ferrite lath size was determined using XRD peak broadening. The tensile property varying between 188 and 270 MPa, showed no significant variation with volume percentage of carbon or austenite in the ausferrite. However the wear rate varying between 0.5 and 2.6 × 10-7 g/Nm, showed a decreasing trend with graphite content attributed to the higher lubricating effect of released carbon during sliding wear. The specific wear rate of hypereutectic alloys, increased with increasing ferrite lath size due to enhanced softer ferrite phase on the sliding surface. The wear rate was found to increase with volume of austenite, austenite carbon content and austenite lattice parameter, which is attributed to increased stability of austenite against strain induced martensite formation and the increased formation of bainitic carbides in the second stage tempering. The various technical aspects in correlating the microstructure with the mechanical and wear properties of hypereutectic austempered gray iron are described. © 2009 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Structure-property correlation in austempered alloyed hypereutectic gray cast irons

Alloyed gray cast iron of varying compositions was studied for their wear behavior. In general, the alloyed gray irons studied have higher graphite volume fraction (∼20%) with Type-A graphite flake morphology. Base cast iron showed two to three times higher wear rates than the alloyed gray irons. Tensile strength and wear rates show decreasing trend with increase in graphite and carbide volume fraction. Wear track analysis shows three body abrasive wear mode resulting in debris generation and smudging along the wear tracks. The graphite gets released during sliding to form films along the wear tracks and then forms irregular debris. © 2009 Elsevier Ltd. All rights reserved.

Tribology International

Wear behavior of alloyed hypereutectic gray cast iron

The mechanical and wear behavior of a series of as-cast gray iron alloys were compared with properties obtained after austempering at 360 °C. The austempered alloys showed equivalent or moderately enhanced mechanical strength than the as-cast pearlitic gray irons. The specific wear rates of all the austempered alloys decreased significantly by 7-15 times and friction coefficient reduced by 30-50% compared to pearlitic alloyed gray irons. The dry sliding wear studies of as-cast alloys against high carbon 1%Cr through-thickness hardened steel shows that the specific wear rate ranged from 5.6 to 19.1 (×10-7) g/Nm with friction coefficient from 0.55 to 0.7. While, the austempered alloys showed wear rates from 0.5 to 2.6 (×10-7) g/Nm with friction coefficient ranging from 0.23 to 0.4. The improved wear resistance was attributed to the layer wise surface phase transformation associated with strain induced martensite formation of the stabilized austenite in the austempered matrix, lubrication of the interface by the flake graphite and better heat conduction from the rubbing interface by higher volume fraction of the graphite. Cast iron alloyed with Ni shows enhanced mechanical properties and wear resistance. The tensile strength shows decreasing trend with increase in carbon equivalent and graphite volume. The specific wear rate and friction coefficient shows decreasing trend with increase in hardness and graphite flake volume. © 2009 Elsevier Ltd. All rights reserved.

Studies on mechanical and wear properties of alloyed hypereutectic gray cast irons in the as-cast pearlitic and austempered conditions

Alloyed gray cast irons were made with and without misch metal inoculation (0.1%). The mechanical and wear properties were compared with conventional gray cast iron used for a typical clutch application in heavy commercial vehicles. Alloyed gray iron without misch metal showed higher volume fraction of pearlite (89%) and lower flake graphite (11%). Misch metal inoculated gray irons showed higher volume of flake graphite (15%) with 85% pearlite as matrix. Alloyed gray irons produced tensile strength from 300 to 344 MPa and hardness in the range of 221-247 VHN. Misch metal inoculation has slightly increased the graphite volume (40-60%) with corresponding decrease in strength and hardness (9-13%) in alloyed gray irons. The specific wear rates of all alloyed gray irons are significantly lower (<34%) compared to unalloyed base at two different sliding speeds (1.6 m/s and 2.5 m/s). The friction coefficient is less than 0.4 for alloyed gray irons as against 0.5-0.7 for unalloyed base gray iron at both the sliding speeds. This is attributed to the presence of alloying additives within the matrix which resists adhesive and abrasive wear loss. Among the inoculated alloyed gray irons, the alloy with lower S content (0.08%) showed higher wear rate at higher sliding speed due to lower graphite flake density compared to higher S containing iron (0.12%). This indicates that the wear rate is influenced by the amount of graphite which is released into the interface during sliding to provide lubrication and reduce wear. Inoculation with rare earth misch metal has a positive influence over graphite morphology in gray iron. © 2009 Elsevier Ltd. All rights reserved.

Journal	Materials and Design
ISSN	02641275
Open Access	No