Microstructure and properties of alloy steel connecting rod quenched in different quenching media

doi:10.13251/j.issn.0254-6051.2023.08.011

Abstract

Abstract: Different quenching media including water, quenching oil and AQ251 quenching liquid (concentration 4%, 8%, 12%, respectively) were selected as the research objects. Through the cooling characteristics, microstructure, hardness, tensile properties, impact properties and other tests, combined with the impact fracture morphology analysis, small batch trial testing and quality inspection, the influence of quenching medium on microstructure and properties of the alloy steel connecting rod was analyzed. The results show that after quenching and tempering, tempered sorbite can all be obtained for the five groups of the connecting rods. The quenching medium with stronger cooling capacity has higher microstructure grade, higher hardness and higher tensile strength, while the impact absorbed energy is decreased. Through the analysis of the impact fracture morphology of five groups, all of them belong to ductile fracture. Combined with the small batch testing and quality inspection, the stronger the cooling capacity of the quenching medium, the larger the crack and distortion of the tested connecting rod, the lower the qualified rate of the product. Therefore, after comprehensive consideration of the results of all aspects of data, the quenching oil is the best quenching medium with good internal structure and comprehensive mechanical properties, which includes three levels of microstructure, average diameter of the quenched Brinell hardness indentation of ø2.82 mm, average diameter of the tempered Brinell hardness indentation of ø3.83 mm, tensile strength of 836.87 MPa, yield strength of 705.23 MPa, elongation after fracture of 19.13%, the percentage reduction of area of 62.44% and impact absorbed energy of 86 J. The production practice has proved that the rejection rate is 2.0%. Compared with the other four groups, the quenching oil has more obvious comprehensive advantages and can be given priority in practical application.

Key words: quenching medium, connecting rod, microstructure and properties, flaw detection and quality inspection

CLC Number:

TG162

Qi Yi, Yang Jianquan, Jiao Fei. Microstructure and properties of alloy steel connecting rod quenched in different quenching media[J]. Heat Treatment of Metals, 2023, 48(8): 64-71.

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