Medium carbon non-hardened and tempered steel for fractured connecting rod

Abstract

The invention discloses a medium carbon non-hardened and tempered steel for a fractured connecting rod, which belongs to the field of alloy steel. The medium carbon non-hardened and tempered steel comprises the following chemical components in percentage by weight: 0.35 to 0.55 percent of C, 0.40 to 0.80 percent of Si, 0.80 to 1.50 percent of Mn, 0.04 to 0.15 percent of P, 0.03 to 0.10 percent of S, 0.10 to 0.50 percent of Cr, 0.05 to 0.25 percent of V, 0.0005 to 0.006 percent of B, 0.01 to 0.10 percent of Ti, 0.005 to 0.05 percent of Al, 0.005 to 0.020 percent of N, 0.005 to 0.04 percent of RE and the balance of Fe and other inevitable impurities. Meanwhile, the C content, P content and B content are required to meet a brittleness parameter relationship: the sum of C(percent),P(percent) and 50B(percent) is more than or equal to 0.06 and less than or equal to 1.0. A metallographic structure is composed of ferrite and pearlite. The medium carbon non-hardened and tempered steel is suitable for manufacturing fractured connecting rods with a tensile strength of more than 900MPa. Compared with the prior art, the invention has the advantages that: the steel has low plasticity and high fracturing performance and fatigue performance; and the steel can be used to manufacture fractured connecting rods after being forged and processed and has high economy.

Description

technical field [0001] The invention belongs to the field of alloy steel, and in particular provides a medium-carbon non-quenched and tempered steel for expansion connecting rods, which has low plasticity, excellent expansion (also known as cracking) performance and fatigue performance, and mainly It is suitable for the production of bursting (also known as cracking) connecting rods with a tensile strength above 900MPa. Background technique [0002] The machining process of the traditional automotive engine connecting rod is complex and requires high precision, which often affects the reliability of the engine due to machining accuracy problems. The expansion-broken connecting rod technology developed in recent years has solved this problem. This process is to design and prefabricate a notch (crack groove) at the appropriate position of the big end of the connecting rod to form stress concentration, and then apply a load perpendicular to the predetermined fracture surface t...

AI Technical Summary

Problems solved by technology

The traditionally used steel for breaking connecting rods is high-carbon steel SAE1070 or C70S6 developed on the basis of 0.70% carbon steel [Cao Zheng et al. Automobile Technology and Materials, 2000, (12): 24-27], and its structure is pearlescent A small amount of discontinuous ferrite is added to the body, although it is easy to brittle cracking, it still has obvious disadvantages: low yield ratio and low fatigue performance

The literature [Denji Steel (Japanese), 2000, 71 (1): 81-87] introduces a non-quenched and tempered steel for medium carbon expansion connecting rods, which has good expansion properties, but due to the addition of up to 0.25% The microalloying element V increases the cost of steel, thereby weakening the economy of the steel; too high Si content (2%) also deteriorates the surface quality of forgings and affects the fatigue performance of parts; in addition, in order to improve cutting Machinability, the addition of about 0.1% of harmful element Pb in the steel is not conducive to environmental protection, all of which limit the application of the steel

The literature [Heat Treatment (Japanese), 2007, 47(6): 343-349] also introduced a kind of non-quenched and tempered steel for medium carbon expandable connecting rods. Due to the low carbon content (0.28%), the main effect of adding The content of microalloying elements for precipitation strengthening is too high (0.17%V+0.17%V), which makes the steel less economical

The Japanese patent [JP2003-027178] proposes a medium-carbon non-quenched and tempered steel with good machinability and bursting properties, which can be used to manufacture bursting connecting rods, but the S content in the steel is too high (0.15-0.30%), making The smelting of the steel, especially the continuous casting, is difficult, and the hot workability of the steel is poor, which limits the application of the steel in mass industrial production.

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