The figure shows the variation curve between Brinell hardness and amplitude of nodular cast iron. It can be seen from the figure that with the increase of amplitude, the Brinell hardness value of nodular cast iron first decreases and then increases. The Brinell hardness value of nodular cast iron prepared at the amplitude of 4mm is larger, while the Brinell hardness value of nodular cast iron prepared at the amplitude of 3mm is smaller.
The higher hardness of nodular cast iron prepared under the condition of amplitude of 0.75mm can be attributed to the small number of graphite balls per unit area and the high content of pearlite in the matrix structure. When the amplitude is increased to 2mm, although the pearlite content in the nodular cast iron produced by this process is slightly higher than that of the nodular cast iron produced by this process when the amplitude is 0.75mm, the larger the pearlite flake spacing and the larger the number of graphite balls contained in the unit area of the nodular cast iron produced by this process make the Brinell hardness value of the nodular cast iron lower. When the amplitude is further increased to 3mm, the Brinell hardness of nodular cast iron continues to decrease, which is mainly due to the decrease of pearlite content in nodular cast iron, the increase of the number of graphite balls per unit area and the presence of more granular pearlite in the pearlite structure. Continue to increase the amplitude. When the amplitude is 4mm, the content of pearlite in nodular cast iron is the most, and the pearlite flake spacing is significantly reduced, so the Brinell hardness of nodular cast iron is significantly increased.