High-strength and high-yield-ratio non-quenched and tempered steel for automobile engine stretch-broken connecting rod and production method thereof

Abstract

The invention discloses high-strength and high-yield-ratio non-quenched and tempered steel for an automobile engine stretch-broken connecting rod and a production method thereof. The steel comprises the following chemical components in percentage by weight, 0.40-0.50% of C, 0.40-0.60% of Si, 1.00-1.30% of Mn, 0.040-0.060% of S, 0.10-0.20% of V, 0.020-0.035% of Nb, 0.10-0.30% of Cr, 0.10-0.30% of Ni, 0.010-0.020% of N, and the balance Fe and impurity elements. Through the combination of the group distribution ratio and a controlled rolling and controlled cooling process, the mechanical propertyRel of the connecting rod material is greater than or equal to 850 MPa, the Rm is greater than or equal to 1000 MPa, and the yield ratio can reach more than 0.84, so that the light weight of an automobile engine is facilitated.

Description

technical field [0001] The invention discloses a steel for a broken connecting rod of an automobile engine, which belongs to the field of non-quenched and tempered steel, and specifically relates to a niobium-vanadium composite strengthened non-quenched and tempered steel for a broken connecting rod of an automobile engine. Background technique [0002] The connecting rod of an automobile engine is one of the five key components in an automobile engine. The connecting rod transmits the pressure of the piston to the crankshaft, and together with the piston, it forms a moving part. As the core force-bearing part of the engine, the connecting rod bears strong alternating loads, and its quality directly affects the performance and reliability of the engine. [0003] Connecting rod processing mainly includes two processes: cutting and breaking. The traditional machining process of connecting rods is complex and often affects the stability of the engine due to machining accuracy e...

AI Technical Summary

Problems solved by technology

At present, the high-carbon non-quenched and tempered steel C70S6 is widely used. C70S6 steel is prone to brittle cracking, but there are still obvious shortcomings: low yield ratio; fatigue performance is lower than that of quenched and tempered steel; brittle lamellar cementite High hardness and high content make the cutting performance of steel poor

The effect of the P element on the tensile strength of the material is greater than the yield strength, which is not conducive to the increase of the yield ratio; in addition, the effect of the V element on the yield ratio is not large when it is above 0.20%, and the content of the Nb element in the medium carbon steel reaches More than 0.035% due to the increase in the probability of forming large-grained liquefied carbides, the strengthening effect is weakened, and it is not conducive to the fatigue performance of the product. In addition, V and Nb alloys are expensive, which increases the cost of the product

[0008] CN201410421719.2 discloses a free-cutting steel for automobile connecting rods with a tensile strength of ≥1200MPa and a production method thereof. The strength of the steel is improved by increasing B, the tensile strength is ≥1200MPa, and the yield strength is ≥850MPa; Polymerization improves the strength of steel, but due to the better plasticity of grain boundary strengthening steel, it is not conducive to the increase of steel yield ratio

[0009] CN201510092255.X discloses a high-strength toughness non-quenched and tempered steel suitable for composite forging. By adding V 0.01-0.15%, Nb 0.005-0.05%, RE 0.001-0.0075, P 0.005-0.03, N 0.008-0.02, Ti 0.01-0.15%, and reduce the C content to 0.25-0.40%, the tensile strength of forgings R m ≥900MPa, yield strength R p0.2 ≥750MPa, the yield ratio can reach 0.85 and above, the strength is low, and it is difficult to add rare earths in the steelmaking process, and the rare earth oxides generated are not easy to float up and remove, thus reducing the cleanliness of the steel

[0010] As can be seen from the above prior art, it is not an easy task to obtain a connecting rod material with a high yield ratio while maintaining high strength.

This is because even though the influence of elements on the strength is known, the influence of each element on the yield ratio is still unclear and there are different opinions in the current literature

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