780 MPa hot-rolled high-strength steel with high hole expansion ratio and manufacturing method thereof

Abstract

The invention provides a 780 MPa hot-rolled high-strength steel with high hole expansion ratio and a manufacturing method thereof. The 780 MPa hot-rolled high-strength steel with high hole expansion ratio comprises the following chemical components in percentage by mass: more than or equal to 0.03 percent and less than or equal to 0.07 percent of C, less than or equal to 0.2 percent of Si, more than or equal to 1.0 percent and less than or equal to 2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, more than or equal to 0.02 percent and less than or equal to 0.05 percent of Al, less than or equal to 0.005 percent of N, more than or equal to 0.08 percent and less than or equal to 0.20 percent of Ti, more than or equal to 0.15 percent and less than or equal to 0.25 percent of Mo, less than or equal to 0.003 percent of O and the balance of Fe and inevitable impurity elements, wherein Ti/Mo is more than or equal to 0.25 and less than or equal to 1.5, and (Ti-3.42N)/4+Mo/8 is more than or equal to 0.03 percent and less than or equal to 0.07 percent. The 780 MPa hot-rolled high-strength steel with high hole expansion ratio is obtained through smelting, casting, high-temperature heating, hot rolling and reeling processes, and is more than or equal to 750 MPa in yield strength, more than or equal to 780 MPa in tensile strength, more than or equal to 20 percent in extensibility, more than or equal to 70 percent in hole expansion ratio when the thickness is 3-6 mm.

Description

technical field [0001] The invention belongs to the technical field of hot-rolled high-strength steel, and in particular relates to a 780MPa grade hot-rolled high-strength high-hole expansion steel and a manufacturing method thereof. Background technique [0002] With the increasingly stringent national environmental protection laws and regulations and the implementation of the country's restrictions on automobile emissions, in the field of automobiles, especially passenger cars, high-strength thinning or lightweight automobile structures have become an important research direction for international automobile manufacturers. From the perspective of energy saving and emission reduction, there are two main ways to improve the fuel efficiency of automobiles: one is to develop engines with higher fuel efficiency; the other is to use high-strength steel or light steel to reduce the weight of the car body and thereby reduce emissions. [0003] Due to the complex structure of the c...

AI Technical Summary

Problems solved by technology

From the perspective of structure type, ferrite and bainite structures have relatively high hole expansion performance, but their strength is relatively low, and it is difficult to reach 780MPa and above. This is why the current high hole expansion steel is mainly concentrated at 440 and 590MPa. Main reasons on two intensity levels

Although ferrite and martensite have lower yield ratio and higher strength, due to the large difference in the two-phase properties of ferrite and martensite, their hole expandability is at the same strength level as that of different structure types. worst performer in steel

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