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Direct welding between spheroidal graphite cast iron (FCD700) and mild steel (SS400) was conducted using electron beam welding to study the microstructure and the mechanical properties of the welds.Results showed that one-pass welding yielded an over-hardened fusion zone exhibiting acicular martensite structure (815 HV) with cracks and porosities. Two-pass welding contained fewer porosities. Both one-pass and two-pass welding displayed acicular martensite and ledeburite within the microstructure of spheroidal graphite cast iron in heat-affected zone. The tensile strength of both one-pass and two-pass welded joints was lower than that of mild steel base metals. These joints ruptured at the fusion zone or the mild steel bond. However, two-pass welded joints demonstrated tensile yield stress values greater than or equal to those of mild steel base metals. Hardening of the fusion zone and the heat-affected zone of spheroidal graphite cast iron made the impact strength values of two-pass welded joints conspicuously lower than those of the spheroidal graphite cast iron base metal. The fatigue strength of two-pass welded joints almost equaled that of mild steel base metal, with a fatigue limit of 209 MPa.

The effect of the microstructure prior to cold rolling on the recrystallization texture and planar anisotropy of the r -value (Δr) in JIS S35C cold-rolled high carbon steel sheet were investigated.When the structure contains fine spheroidized cementite prior to cold rolling, recrystallization is retarded and takes the form of in-situ recrystallization. However, with coarse cementite, recrystallization is completed at a low temperature, and in subsequent grain growth, Ostwald growth of cementite is rate-governing. This difference in recrystallization behavior is inferred to be caused by differences in both the size and the distribution of cementite. Δr in smaller with fine spheroidized cementite than with coarse spheroidized cementites. This is thought to be caused by both the strong development of γ-fiber (‹111›//ND) grains in the recrystallization texture and retardation of {110} grains, which reduce Δr, during annealing. Therefore, it is inferred that refinement of cementite prior to cold rolling contributes to the improvement of the recrystallization texture as it affects Δr.

When spheroidal graphite (SG) cast iron is overlaid with Stellite 1 cobalt-based superalloy by a plasma transferred arc melting process, a carbide-containing interfacial layer can exist between the substrate and the overlayer. Meanwhile, ledeburite can occur in the partially melted zone of the substrate. These microstructures may cause damage during application and thus are undesirable. In the present investigation, Stellite 1 alloy was overlaid on seven ferritic SG cast irons of various silicon content (2.0 to 3.9 mass%) and carbon content (1.5 to 3.8 mass%) under the same overlaying condition (current : 60 A ; voltage : 26 V). The purpose was to characterize the solidification structure with special emphasis on the interface region and the partially melted zone. The results indicate that the overlayer is hypereutectic. The carbide-containing interfacial layer can be eliminated by reducing the carbon content of the substrate. Both reducing the carbon content and increasing silicon content can reduce the amount of ledeburite formed in the partially melted zone. The formation of the ledeburite can be avoided if the silicon content is sufficiently large.

The pearlite in carbon steel appears in different forms according to the conditions cooling from γ-phase. Using three carbon steels, I have obtained different micro-structures by the isothermal transformation in several temperatures quenched from several maximum heating temperatures (below 950°) and its results are shown in charts. The forms obtained are the globular pearlite, lamellar pearlite, sorbite, sorbitic globular, sorbitic lamellar, dotted lamellar, Atols (named by Osmond) and the mixture of these forms. In this study is discussed the formation of these different structures. In hypereutectoid steel, the upper limit of the maximum heating temperature, from which the globular pearlite is formed on cooling, reaches to the temperature immediately below the Acm point, and the lower limit of the transformation temperature is 710° in pearlite steel previously globulized and 700° in those of the other structures. The uniform globular pearlite is obtained by transformation at 710° on cooling from 825° The form of pearlite is remarkably influenced by the form of the cementite in steel before heating. In 0.76% C steel, globular pearlite is formed at the maximum heating temperatures below 825° in globular pearlite steel, but does it not occur in lamellar pearlite steel. In 0.40% C steel, fine globular cementite is formed from globular pearlite and martensite steels heated, but in those of the other structures the coarse globular cementite is formed.