Abstract
Abstract Sulfur is added to low-alloyed steel FAS3420H to improve the free-cutting property of the steel. Elongated MnS inclusions usually deteriorate the mechanical and process performance of steels, so the control of shape and size of MnS is essential. The statistical analysis of MnS inclusions in as-cast and rolled steels at different positions shows that the distribution and aspect ratio of MnS in rolled steel are closely related to the quantity and size of MnS in as-cast one. The in situ observation and experimental results reveal that homogenization treatment effectively reduced MnS inclusions size and transformed their shape to globule or ellipsoid. Significant change of quantity and size of MnS inclusions was identified only when the soaking time exceeds 5 h at 1,250℃. Additionally, a kinetic model is presented to quantitatively characterize the behavior of MnS inclusions during homogenization process.
Highlights
The steel FAS3420H is a low carbon low-alloyed steel that is applied to manufacture components, such as transmission gear, gear shaft, and so on, for heavy-duty truck or coach
The size of MnS increased, the number of MnS inclusions in different size ranges per square millimeter gradually increased with homogenization time, and there were few large-size MnS whose area was greater than 20 μm2
When the homogenization process was at 1,250°C for 5 h or more, suitable MnS was gained with small sizes and big quantity
Summary
The steel FAS3420H is a low carbon low-alloyed steel that is applied to manufacture components, such as transmission gear, gear shaft, and so on, for heavy-duty truck or coach. Size, or type of MnS, it is hard to decrease the micro-segregation of solute elements; the behavior of MnS in high temperature soaking and subsequent hot-rolling process is worthy of attention. Better understanding of the behavior of MnS in ascast steel during soaking could optimize parameters of homogenization process, thereby obtaining appropriate morphology of MnS such as spherical or spindle-like. This optimization can promote more uniform distribution of alloying elements in the steel, which can downgrade the banded microstructure after hot-rolling process.
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