The as cast nodular iron with MS = 0.25cm, 0.50cm and 1.25cm were austenitized and water quenched respectively. Fig.1 shows the position of probe measuring points for carbon content in martensitic structure (austenite at high temperature) between two adjacent graphite spheres in water quenched matrix. The measuring points are uniformly distributed in straight line.
The variation of carbon content in high temperature austenite with austenitizing temperature (t γ) and austenitizing holding time (t γ) is shown in Fig. 2. It can be seen from the figure that the carbon content in high-temperature austenite increases gradually with the increase of t γ, which increases slightly with the extension of t γ, and tends to be stable after 2.0 H.
The carbon content in high temperature austenite of ductile iron with MS of 0.25cm, 0.50cm and 1.25cm is 0.59%, 0.58% and 0.57% at 880 ℃, 0.61%, 0.63% and 0.69% when t γ rises to 920 ℃, and 0.66%, 0.67% and 0.69% respectively when t γ reaches 960 ℃ 71%.