Microstructure and properties of connecting rods made of medium carbon non-quenched and tempered forging steel 43MnS with different sulfide morphologies

doi:10.13251/j.issn.0254-6051.2020.07.025

Abstract

Abstract: Sulfide morphologies, microstructural characteristics and mechanical properties of different parts of connecting rods made of commercial medium carbon non-quenched and tempered steel 43MnS with sulfide-modification (No.1) and without sulfide-modification (No.2) were studied by using optical microscopy, scanning electron microscopy, tensile testing machine and hardness tester. The results show that the sulfides in No.1 steel connecting rod are distributed relatively uniform and most sulfides exhibit a spindle shape, which are slightly elongated during forging deformation process and have an average aspect ratio (the ratio of length to width of sulfide) of 3.5-3.9. The sulfides in No.2 steel connecting rod are elongated and partially fractured during forging, thus poorly distributed and exhibit a highly elongated shape with a average aspect ratio of 5.5-7.0. The strength and hardness of No.1 steel connecting rod are higher than that of No.2. The fracture mechanism of both kinds of specimens is plastic fracture of dimples, and sulfide inclusions often exist at the bottom of large size dimples. Mainly caused by the forging deformation difference and the cooling rate difference at different parts of the connecting rod, according to the order of the big-end, small-end and shank of the connecting rod, the microstructure is gradually refined, and the content and hardness of both the ferrite and intragranular ferrite are gradually increased.

Key words: medium carbon non-quenched and tempered steel 43MnS, sulfide, deformation amount, microstructure, mechanical properties

CLC Number:

TG142.1

Chen Zhen, Hui Weijun, Wang Zhanhua, Zhang Nian, Zheng Wenchao. Microstructure and properties of connecting rods made of medium carbon non-quenched and tempered forging steel 43MnS with different sulfide morphologies[J]. Heat Treatment of Metals, 2020, 45(7): 124-129.

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