Ferritic Spheroidal Graphite Cast Iron Research Articles

Microstructural Features and Erosion Wear Resistance of Friction Stir Surface Hardened Spheroidal Graphite Cast Iron

A ferritic spheroidal graphite cast iron (also named as SG cast iron, ductile cast iron, ductile iron) was treated with friction stir process (FSP) to harden the surface layer owing to a unique microstructure into which the ferritic structure transforms after high temperature deformation and subsequent direct cooling. When the friction stirred surface experiences thermomechanical cycle during FSP (here named friction stir surface hardening, FSSH), a non-traditional bainite structure can be obtained through subsequent cooling process. The bainite structure primarily consists of iron carbide (Fe3C), acicular ferrite and martensite with retained austenite aggregates. It is evident that the FSSH structure caused by deformation at austenite temperature has resulted in a significant increase in the microhardness of about 1000HVyielding a primarily martensitic accompanying bainitic phase transformation. The experimental results also show that the process has resulted in significant improvement in erosion resistance at low angle impingement than that of ferritic specimens. In addition, the maximum erosion rate of ferritic specimens occurs at 20­25°of impact while the peak of the FSSH specimen shifts to higher angle resulting from the formation of continuously cooled martensitic and bainitic structure. [doi:10.2320/matertrans.M2011224]

Influence of Loading Speed on Toughness of Ferritic Spheroidal Graphite Cast Iron with Various Notches

Influence of Loading Speed on Toughness of Ferritic Spheroidal Graphite Cast Iron with Various Notches

Static and Dynamic Three-Point Bending Characteristics of Ferritic Spheroidal Graphite Cast Iron at Low Temperature

Static and Dynamic Three-Point Bending Characteristics of Ferritic Spheroidal Graphite Cast Iron at Low Temperature

Notched-and Unnotched-bar Bending Properties of Ferritic Spheroidal Graphite Cast Iron

Notched-and Unnotched-bar Bending Properties of Ferritic Spheroidal Graphite Cast Iron

Relationship Between Load and Deflection in Bending Test of Ferritic Spheroidal Graphite Cast Iron

Relationship Between Load and Deflection in Bending Test of Ferritic Spheroidal Graphite Cast Iron

Bending Characteristics of Blasted Ferritic Spheroidal Graphite Cast Iron

Bending Characteristics of Blasted Ferritic Spheroidal Graphite Cast Iron

Notch Effects on Impact and Bending Characteristics of Ferritic Spheroidal Graphite and Compacted Vermicular Graphite Cast Irons

Notch Effects on Impact and Bending Characteristics of Ferritic Spheroidal Graphite and Compacted Vermicular Graphite Cast Irons

Fatigue life prediction of components made of spheroidal graphite cast iron

In many cast metals fatigue crack initiates from a defect. The lower bound of the fatigue life in cast components can be estimated based on the maximum defect size which is present in a component. In this research the distribution of defects in a ferritic spheroidal graphite cast iron component was determined. Then, Gumbel distribution was used to estimate the maximum sizes of defects in cylindrical fatigue specimens with different dimensions. Based on estimated maximum defect size, the fracture mechanics approach was used to determine the lower bound of the fatigue life for fatigue specimens with different dimensions and the geometrical size effect was modeled.

Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

Contribution of dual phase (α, G, B) heat treatments to fatigue properties of SG cast irons

Ferritic spheroidal graphite (SG) cast irons are used to make parts that require high ductility and fracture toughness and good high-cycle fatigue resistance. Ferritising anneals have an all-ferritic matrix favouring high fracture toughness and ductility but this does not improve fatigue strength, and even lowers it in some cases. The purpose of the present study was therefore to optimise these heat treatments for the best compromise between fracture toughness and fatigue life. To attain this, the fatigue behaviour of cast irons was studied in the as cast and heat-treated conditions. A comparison of the lives and mechanisms of ferritisation of these metallurgical conditions made it possible to evaluate the influence of various parameters (characteristics of the initiation sites, properties of the matrix). From the present study, a method is proposed to optimise the heat treatments to produce ferrite in association with a stronger phase in the zones where microfissures are initiated. A study of heat treatments favouring the formation of a matrix made up of ferrite and bainite yielded encouraging results. The presence of bainite near the graphite spheroids and zones of porosity can increase resistance to crack initiation. This leads to a substantial improvement of fatigue life of the SG cast iron without at the same time embrittling the material.

Effect of Si Content on the Deterioration of Vibration Fracture Resistance of Ferritic SG Cast Iron under an Aqueous Environment

Ferritic spheroidal graphite cast irons generally exhibit intergranular fracturing even if the specimens are strengthened by silicon in solid solution when tested under wet conditions. The maximum area fraction of intergranular fracture is closely related to the microstructural feature and ambient aqueous environment that caused the deterioration in vibration fracture resistance. In spite of the increasing silicon content, experimental evidence confirms the overall D-N curves can be generalized into three characteristic regions. Intergranular cracks initiated in the vicinity of the nodular graphite; the existence of nodular graphite acting as porosity should be considered as a dominant microstructural factor on the initiation of intergranular fractures. It should be noted that the intergranular cracks can be prevented, resulting in better vibration fracture resistance, when a specimen is covered with oil film. Based on experimental results, when the silicon content is increased, the vibration fracture resistance in general will be improved for all specimens whether they are tested in oil mist, air or aqueous environments. In particular, when the deflection amplitude is fixed, the vibration fracture resistance can be significantly raised for a high silicon sample (4.4Si).

Effect of cyclic heating on ductility deterioration of high silicon ferritic spheroidal graphite cast iron by salt bath

Severe ductility deterioration will be caused when the ferritic spheroidal graphite cast iron undergoes a certain number of heating and cooling cycles. A greater ductility drop resulting from intergranular fracture will be induced when the specimens are cyclic heated in a chloride-rich atmosphere; however, the tensile elongation tended to decrease as the number of heating cycles increased. This significant phenomenon including the ductility deterioration rate of the salt bath heated specimen is higher and the fracture surface of SG cast iron tended to transit from a brittle cleavage fracture to an intergranular fracture as the number of thermal cycles increased. Fractography can confirm that the intergranular crack mainly initiated and propagated at the solidificational eutectic cell wall region, owing to a significant amount of Mg containing inclusion particles clustering at the eutectic cell wall. In addition, crack initiation and propagation will be promoted as a result of the chloride reaction from the surface. IJCMR/427

Static and Dynamic Notched-bar Bending Properties of Ferritic Spheroidal Graphite Cast Iron

Static and Dynamic Notched-bar Bending Properties of Ferritic Spheroidal Graphite Cast Iron

Effect of Microstructural Refinement on Ductility Deterioration of High Silicon Ferritic Spheroidal Graphite Cast Iron Caused by Cyclic Heating

This investigation applies cyclic heating and cooling to elucidate the effect of microstiuctural refinement on the tensile elongation deterioration of ferritic spheroidal graphite cast iron. In order to eliminate the oxidation factor, the cyclic heating/cooling test was performed in a 1.33 ∼ 0.133 Pa ambient vacuum atmosphere with cyclic heating at a maximum temperature of 1023 K. Severe embrittlement accompanied by intergranular fracture occurred after the ferritic spheroidal graphite cast iron was subjected to a certain number of heating and cooling cycles. A fair amount of inevitable inclusion particles were found to agglomerate in the eutectic cell boundary region, and so the cyclic heating induced embrittlement can be recognized to be strongly dependent on the solidification cooling rate of the materials. Based on experimental evidence, the cracking evolution can be divided into three steps: (1) crack initiation from the vicinity of the eutectic cell boundary at the surface, (2) crack linking and major crack formation, and (3) major crack inward extension. Cyclic heating cracks are mainly initiated at the eutectic cell boundary where a fair amount of MgO inclusions dispersed, and consequently propagated along the annealed eutectic cell boundary. While investigating the plastic deformation behaviors around the above mentioned MgO inclusions pertaining to the crack initiation and crack propagation, typical etch pit evidence was observed in the vicinity of the cell boundary area.

Effect of Silicon Content on Intergranular Embrittlement of Ferritic Spheroidal Graphite Cast Iron Suffered from Cyclic Heating

The effect of silicon content on intergranular embrittlement of ferritic spheroidal graphite cast irons after suffer a certain number of thermal cycles is investigated. The tensile elongation tends to increase with the number of thermal cycles, and increased silicon content leads to eventual embrittlement. The fracture surface of a 2.9Si specimen changes from dimple pattern feature to intergranular fracture, whereas the fracture surfaces of both 4.0Si and 4.3Si specimens change from the brittle cleavage to intergranular fracture that following with increasing the number of thermal cycles. The intergranular cracking path will initiate and propagate through the eutectic cell boundaries due to the presence of micro-segregated inclusions that clustered in the eutectic cell boundary region. These inclusions are oxides that mainly contain magnesium, phosphorus and cerium. Experimental analysis detected that the magnesium elements not only segregated in the vicinity of eutectic cell boundaries, but also the annealed ferritic grain boundaries. However the embrittlement resulted from cyclic heating is strongly dependent on the morphology of clustered inclusions and is pertaining to the variation of silicon content. The observed magnesium-containing inclusions located in the central region of the matrix may profoundly affect the overall tensile fracture behavior of heat resistant used SG cast irons.

Effect of Nodular Graphite on the Deterioration of Vibration Fracture Resistance of Ferritic Cast Iron under an Aqueous Environment

An intergranular fracture feature could be observed when ferritic spheroidal graphite cast irons were tested under continuously wet conditions. The maximum depth of intergranular fractures was closely related to the microstructural feature and ambient environment that caused the deterioration in vibration fracture resistance. Experimental evidence has confirmed the overall D-N curves can be generalized into three characteristic regions. Intergranular fractures occurred in the vicinity of the surface; the existence of noular graphite act as porosity should be considered as a dominant microstructural factor on the initiation of intergranular fractures. On the other hand, intergranular fractures can be prevented resulting in better vibration fracture resistance when a specimen of ferritic SG cast iron is covered with oil film, or if an identical test is performed using the Fe-3Si steel specimen containing no nodular graphite.

Impact Test of Ferritic Spheroidal Graphite Cast Iron by Low Energy Blow

Impact Test of Ferritic Spheroidal Graphite Cast Iron by Low Energy Blow

The relationship between inclusion clustering and embrittlement of ferritic spheroidal graphite cast iron at intermediate low temperatures

Four fully annealed ferritic spheroidal graphite cast irons with different carbon equivalents were used to perform tensile tests at temperatures ranging between -120 °C and 40 °C. In addition, all the materials were electro-chemically etched in Morries solution to reveal the distribution morphologies of inclusion particles and thus to explore the influence of inclusion clustering on low temperature tensile properties. The experiment results indicate that elongation deteriorates at a temperature of around -30 °C. This phenomenon is known as intermediate low temperature embrittlement. At this temperature the fracture surface shows a part ductile/partial brittle pattern. We can see that brittle cracks start at the clustering region of the inclusion particles, at the zoned brittle fracture area.Our electro-chemical etching results demonstrated that the specimens with a lower CE value exhibited greater inclusion particle clustering at the eutectic cell walls. Furthermore, the degree of inclusion clustering significantly affected the intermediate low temperature embrittlement of the ferritic SG cast iron. For the materials with a lower carbon content that possess a denser clustering of inclusion particles, the elongation drop was more obvious. It is worth noticing that the inclusion particles are more uniformly distributed in the higher CE materials which will lower the probability of crack initiation and thus the elongation drop is reduced.

球状黒鉛鋳鉄の固相接合 ８ Ｎｉ系ろう材を用いた球状黒鉛鋳鉄接合材の引張特性

The authors have studied the tensile strength, the fatigue strength and the impact characteristics of the joints of the ferritic spheroidal graphite cast iron produced by the solid state bonding method and found that the mechanical characteristics of the joints were comparable to those of the base metal. With respect to practical uses, it is considered that the brazing method with a brazing sheet is easier than the solid state bonding for bonding of the cast iron. In this study, the ferritic spheroidal graphite cast irons were bonded with Ni-base brazing sheets using the high frequency induction heating apparatus. Those sheets were MBF 15 (Ni-Cr-Si-B system), MBF 30 (Ni-Si-B system) and MBF 60 (Ni-P system) in the thickness of 40μm. Furthermore, effects of bonding time, surface roughness of the surfaces to be bonded, and bonding atmosphere on the tensile strength of the joints were investigated. Main results obtained are as follows: (1) When the cast irons were bonded for 2 and 10 minutes with MBF 15 and MBF 60, the joints were fractured at the bonded zone on the tensile test. When the cast irons were bonded for 30 minutes, however, the tensile strength of the joints was nearly equal to that of the base metal. On the other hand, when the cast irons were bonded for 2, 10 and 30 minutes with MBF 30, all of the joints were fractured in the base metal on the tensile test. (2) When the surface roughness was 2.3μm, the tensile strength of the joints bonded with MBF 15 was nearly equal to that of the base metal. When the surface roughness was 13.9μm, however, all of the joints were tensile-fractured at the bonded zone because small shrinkages were formed at the center of the bonded zone. (3) The tensile strength of the joints bonded in argon was a little lower than that of the joints bonded in vacuum with MBF 15 and MBF 60. However, the strength of the joints bonded in air was decreased considerably because the oxides of Cr were produced in the center of the melting zone. On the other hand, when the joints were bonded with MBF 30 in air, in argon, and in vacuum, all of the joints were tensile-fractured in the base metal. (4) In the case of MBF 15 containing Cr, the high density zone of Cr was formed at the center of the melted brazing metal and Cr2O3 particles were produced by oxygen in air. By the final stage of the bonding, Si was accumulated near the Cr2O3 particles, and they were reduced by the Si, and the SiO2 particles were formed instead of the Cr2O3 particles. (5) When the brazing sheets having 5 levels of the Cr content were used for the bonding, the tensile strength of the joints was decreased with an increase of the Cr content.

Effect of microstructure on resonant vibration fatigue fracture of ferritic spheroidal graphite cast iron

The effect of graphite nodule size, counts and eutectic cell wall inclusions on the fatigue fracture behaviour under resonant vibration of spheroidal graphite (SG) cast iron was investigated in this study. Experimental results indicated that the variations of graphite nodule size and counts slightly influence resonant frequency. The D-N curves (deflection amplitude vs. number of vibration cycles) of all test materials show similar manner. The deflection amplitude maintains a constant value for a certain period of vibration cycles (region I) and then decreases significantly with increasing the vibration cycles (region II). The feature of fatigue fracture behaviour under resonant vibration of ferritic SG cast iron can be concisely divided into four steps, namely (1) crack initiation, (2) crack linking, (3) the major cracks formation, and (4) deepening of the major cracks in the through-thickness direction. The initial three steps correspond to the region I period of the D-N curves, and the fourth step occurs in the region II period. Increasing the graphite nodule counts and refining the microstructure increase the region I period, and improve the resonant vibration fatigue life. During fatigue fracture process under resonant vibration, cracks mainly initiate from graphite nodules and some from eutectic cell walls. The eutectic cell wall inclusions are more crowded in SF specimen than that in PF specimen. So, the crack path of SF specimen is more tortuosity. The feature of fracture surface is mostly the brittle fracture.