The formation of retained austenite in nodular cast iron by austenitizing and heat treating at 450 or 350 C has been studied by X-ray measurements and metallographic examination. It has thus been related to the detailed mechanism of the bainite transformation.

The effects of the addition of a few tenths of a percent of Mn, Cr and Mo were examined and the effect of higher contents was estimated from literature data. Already small additions increase the maximum amount of retained austenite but larger additions are needed in order to increase the time for complete transformation substantially.

A small addition of Sn which has a strong effect on the transformation to pearlite had no effect on the transformation to bainite.

Structure and properties of whitoheart malleable iron cast in gray iron permanent molds are examined. The results of test bars and industrial castings are compared to those of green sand molds. Malleable iron is predestined for casting in permanenet molds, because it must solidify completely white. Faster cooling achieved Dy the permanent mold refines primary austenite dendrites, promotes formation of ledeburite (metastable eutectic) and allows higher contents of graphitizing elements. Silicon content can be raised. The yield improves, annealing time decreases, combination of mechanical properties is improved. Combined metallurgical, technological and environmental advantages can improve economy.

Laser surface melting and alloying provide a flexible route for modifying surface structures and properties. Potential technological benefits include improvement of properties such as resistance to corrosion and wear. The technique can also be used to obtain basic structural information for materials solidified over a range of rapid solidification rates. Laser surface melting of cast irons has been quite widely investigated [e.g. 1–4] using various initial structural states, including flake and spheroidal graphite irons; substantial surface hardening has been achieved from the white iron structures resulting from the rapid solidification. In the field of laser surface alloying a number of investigations have used ferrous substrates [5–9].

The microstructure obtained in the heat-affected zone (HAZ) and the carbide zone in the weld metal adjacent to HAZ has been studied in multipass welds in ferritic ductile cast iron. The effects of postweld anneal were also studied. The amount of martensite in the HAZ and the carbide zone can be reduced by the heating cycles of subsequent weld beads during multipass welding. The amount of martensite in the structure affects the graphite morphology after postweld annealing in both the HAZ and the carbide zone. It is also proposed that the graphite in the carbide zone, when arc-welding ductile cast iron with no or moderate preheat, is formed from cementite by grafitization.

The rupture behaviour of lamellar grey cast iron under tension depends on the overall damage suffered by the heterogeneous microstructure. In order to quantify the influence of microstructural components on the rupture behaviour of the material, it is therefore preferable to apply “Damage Mechanics” concepts rather than “Linear Fracture Mechanics”. In this preliminary study the damage process is assumed to be isotropic and two parameters are considered; firstly a damage limit σ0 and secondly, a damage rate B. Measurements made on a grey cast iron, cast in three different cross sections, show that these damage parameters may be used to separate the contributions of the graphite network and the matrix wich interact in the degradation process of the heterogeneous microstructure of lamellar grey cast iron.

The paper present the results of investigation into the directional solidification of Fe-C-Cr alloys containing about 30% Cr and various contents of carbon. The main types of the structure of these alloys were given and the zone of a coupled growth of the eutectic was determined as well as an effect of the growth rate on the interfacial distance λ and on the tensile strengthof these alloys. It was proved that the additions of titanium and cerium considerably reduce the distance λ and increase the tensile strength, which in the case of an Fe-Cr-C-Ce alloy can reach a value of about 3250 MPa. The alloys solidified in the form of bars and plates which also enabled the determination of an effect of angle between the axis of the carbide fibres and the direction of loading on the ultimate tensile strength. of these alloys.

The effects of composition and process variables on the tensile strength of flake graphite cast iron are well established. However, when compared with most metallic materials, there is little quantitative understanding of the way in which the microstructure controls the mechanical properties. In this paper a fracture mechanics approach is used to develop a mechanistic interpretation of the relationship between the microstructure and tensile strength. Flake graphite cast irons have been studied in which matrix microstructures of pearlite, ferrite and tempered martensite have been developed by heat treatment. For a given eutectic cell size, a linear relationship exists between the tensile strength and the fracture toughness KIC, for all of the matrix structures studied. The tensile strength is interpreted as a brittle fracture stress which is determined by the fracture toughness of the iron and an inherent defect size which is defined by the eutectic cell size.

When a ferritic Spheroidal Graphite Cast Iron(SG iron) is submitted to a large tensile load, the graphite nodules in the iron are deformed into oval shape. It has been recognized that a large deformation under tensile stress produces a kind of voids at the graphite edges. However, the breaking process of the graphite nodules has not been clarified yet.

Remarkable elongations have been obtained on cast iron samples subjected to alternate thermal cycles around the A1 critical point, under a tensile stress lower than the yield stresses of the stable phases. This procedure makes use of the “phase transformation plasticity”, characterised by an apparent softening of the material during its structural evolution. The influence of the applied stress, as well as the heating and cooling rates,on the elongation per cycle has been studied. A quantitative comparison between this “soft” technique and the more classical high-temperature metal forming techniques (deformation in stable α or γ domains, or in α + γ domain, high temperature creep) showed that, for an equal strain, the internal cavitation resulting from the thermomechanical cycling deformation of spheroīdal graphite cast iron is much smaller than for other techniques. This soft technique leads to higher mechanical characteristics at room temperature.

The influences of silicon and phosphorus contents and cooling rate on JIC fracture toughness of ferritic spheroidal graphite cast iron were investigated by 15mm thick compact tension test-pieces. The JIC values were measured by means of the R-curve method for most cases at 20°C, and by means of the maximum J value method for the cases at -100° C. The results obtained are summarized as follows. At 20WC, the specimens with silicon contents less than 3.2% showed the ductile Load-COD relations, but a specimen with 3.5%Si showed a brittle Load-COD relation and the JIC decreased greatly. Increasing phosphorus content between 0.006% and 0.26% made the JIC value decrease gradually and made the slope of the R-curve decrease greatly. Difference in cooling rate produced differences in graphite nodule diameters and ferrite grain sizes. At 20°C, the larger the specimen's average graphite nodule diameter was, the larger the JIC value was. At -100° C, the Jic values of all the specimens tested decreased largely, and the influences of these factors became very different from those at 20° C.

Intergranular fracture had been observed in the temperature range from 573K – 673K, where the ductilit miniTum appears at 673K for the strain rate of sec−1 in ferritic spheroidal graphite cast irons.

The cause of intergranular fracture at about 673K has been investigated. The following two points are emphasized. The first is the role of hydrostatic tensile stress in triaxial stress field developed in ferrite matrix among graphite nodules, relating to the effect of graphite volume fraction on the intergranular fracture. The second is the role of carbide precipitation during dynamic strain ageing, relating to the strain rate and the temperature dependence of the intergranular fracture.

As cast microstructures of chromium-manganese white cast iron containing about 2.5 % carbon, 0.7 % silicon, 4.5 % manganese and 11.5 % chromium reveal discontinuous plate like eutectic carbides embedded in a mainly austenitic matrix[1](Fig.1). This austenitic matrix accounts for a higher impact strength and a lower wear resistance. It has been reported elsewhere [2] that a martensitic matrix containing uniformly distributed fine alloy carbides exhibits a very good wear resistance, but lower impact strength.