Complex-phase steel having high hole expansibility and manufacturing method therefor

Abstract

Disclosed in the present invention is complex-phase steel having high hole expansibility. The complex-phase steel has a microstructure of ferrite and bainite. The complex-phase steel having high hole expansibility comprises the following chemical elements in percentage by mass: C: 0.06-0.09%, Si: 0.05-0.5%, Al: 0.02-0.1%, Mn: 1.5-1.8%, Cr: 0.3-0.6%, Nb≤0.03%, Ti: 0.05-0.12%, and the balance of Fe and inevitable impurities. In addition, also disclosed in the present invention is a manufacturing method for the foregoing complex-phase steel having high hole expansibility. The method comprises the following steps: (1) smelting and casting; (2) heating; (3) hot-rolling; (4) phosphorous removal; (5) laminar cooling: a relaxation time period is controlled to be 0-8 s, and a laminar cooling rate is 40-70° C./s; (6) coiling; (7) leveling; and (8) pickling. The complex-phase steel having high hole expansibility can simultaneously satisfy the requirements for hole expansibility and good plasticity.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a steel and a manufacturing method thereof, and particularly relates to a complex-phase steel and a manufacturing method thereof.BACKGROUND ART[0002]With the strength-weight development of automobiles, more and more models use 80 kg grade hot-rolled pickling steel plate to produce automobile chassis parts, such as control arm, tie rod, spring seat and so on. For example, the forming process of automobile chassis parts such as control arm includes stamping, flanging, reaming, etc. Therefore, it not only has certain requirements for strength and elongation, but also has certain requirements for reaming performance.[0003]CN103602895A with the publication date of Feb. 26, 2014, entitled “high-hole-expansion-ratio steel plate with tensile strength of 780 MPa and manufacturing process thereof”, discloses a high-hole-expansion-ratio steel plate with tensile strength of 780 MPa and manufacturing process thereof. The steel plate has a Si...

AI Technical Summary

Problems solved by technology

It is difficult to obtain strip steel with high-grade surface in this patent application.

Meanwhile, because the red iron scale on the surface of the steel plate is difficult to control, it is difficult to measure accurately in the process of hot rolling temperature measurement, resulting in the instability of product performance.

Meanwhile, a three-stage cooling mode is adopted in this patent application, which has low production stability.

Meanwhile, the steel plate has an Nb content of 0.03-0.08%, which is also relatively high, the cost is high, and sectional cooling is required after rolling, and the cooling process is complex.

In the prior art, the higher the strength of the material, the more difficult it is to control the length and width stability of the material.

However, silicon in the steel is easy to form the surface defect of fayalite (2FeO—SiO2) iron oxide scale on the surface of the steel plate, which has a bad impact on the surface quality.

At the same time, the appearance of red iron scale is not conducive to the temperature control in the hot rolling process, resulting in the instability of product performance Based on this, in the complex-phase steel having high hole expansibility of the present disclosure, the mass percentage of silicon is controlled to be 0.05-0.5%.

However, the high mass percentage of aluminum will produce oxidation and further affect the continuous casting production.

The low mass percentage of manganese will lead to insufficient strength, but the high mass percentage of manganese will reduce the plasticity o

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