Abstract

This study investigates the variations in the microstructure and mechanical properties of a medium-carbon high-Si steel (Fe–0.55C–2.3Si) during graphitization heat treatment and subsequent quenching and tempering heat treatment. The microstructure comprising ferrite and pearlite of the as-rolled sample changes to a more ductile microstructure with fine graphites uniformly dispersed in the ferrite matrix after graphitization treatment. These formed graphites are completely dissolved into the ferrite matrix after austenitizing treatment at 900 °C, but preexisting graphite positions remains as voids. The average size and number density of voids are nearly identical to those of the pre-existed graphites. The subsequent tempering treatments at 300 °C and 500 °C cause little changes in the size and number of the voids. Therefore, the formation of voids in the quenched-and-tempered samples is directly related to the graphites of the initial graphitized sample. The average size of graphites and voids is inversely proportional to the logarithm of their number density. When the as-rolled sample is completely graphitized, its ultimate tensile strength decreases from 928 to 494 MPa and its tensile elongation increases from 20.7 to 34.0%, indicating that the medium-carbon high-Si steel is substantially softened through graphitization treatment. Moreover, subsequent quenching and tempering treatment at 500 °C increases its ultimate tensile strength to 1168 MPa. The drastic softening through graphitization and significant strengthening through subsequent quenching and tempering exhibit the possibility of the application of medium-carbon, high-Si steels as cold heading quality steels for manufacturing fastener components.

Graphic abstract

中文翻译：

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石墨化Fe–0.55C–2.3Si钢淬火回火处理后组织和力学性能的变化

摘要

这项研究调查了中碳高硅钢（Fe–0.55C–2.3Si）在石墨化热处理以及随后的淬火和回火热处理过程中的组织和力学性能变化。轧制后的样品中包含铁素体和珠光体的显微组织变为更具延展性的显微组织，在石墨化处理后，细小的石墨均匀地分散在铁素体基质中。在900°C的奥氏体化处理之后，这些形成的石墨完全溶解在铁素体基体中，但预先存在的石墨位置仍保留为空隙。空隙的平均尺寸和数量密度几乎与预先存在的石墨相同。随后在300°C和500°C下进行的回火处理几乎不会改变空隙的大小和数量。因此，淬火和回火样品中空隙的形成与初始石墨化样品的石墨直接相关。石墨和空隙的平均尺寸与它们的数密度的对数成反比。当轧制后的样品完全石墨化时，其极限抗拉强度从928降低到494 MPa，拉伸伸长率从20.7增加到34.0％，表明中碳高硅钢通过石墨化处理已基本软化。此外，随后在500°C进行的淬火和回火处理将其最终抗拉强度提高到1168 MPa。石墨化引起的急剧软化和随后的淬火和回火带来的显着强化显示出可能应用中碳，

图形摘要