High-strength steel sheet and production method for same, and production method for high-strength galvanized steel sheet

Abstract

The present invention provides a high-strength steel sheet having a tensile strength (TS) of at least 780 MPa, excellent ductility and stretch flangeability, and excellent material-quality stability, achieved by: having a specific component composition; the Mn volume divided by the B volume being not more than 2100; the steel structure having, in terms of area ratio, a total of ferrite and bainitic ferrite of 25-80%, and 3-20% martensite, and having, in terms of volume fraction, at least 10% retained austenite; the average crystalline particle diameter of the retained austenite being not more than 2[mu]m; the average Mn volume (mass%) in the retained austenite being at least 1.2 times the Mn volume (mass%) in the steel; and retained austenite aggregates, in which seven or more retained austenite crystal particles having the same orientation are grouped together, accounting for, in terms of area ratio, at least 60% of the total retained austenite.

Description

technical field [0001] The present invention relates to a high-strength steel sheet excellent in formability mainly suitable for structural members of automobiles and a method for producing the same, especially to obtain a tensile strength (TS) of 780 MPa or more, excellent in ductility, and excellent in stretch flangeability , and high-strength steel plate with excellent material stability. Background technique [0002] In recent years, the application of high-strength steel plates with a tensile strength (TS) of 780 MPa or more and a thinner plate thickness has been actively promoted in order to ensure the safety of crew members during collisions and improve fuel efficiency due to lightweight vehicles. in the dynamics of automotive structural components. [0003] Furthermore, recently, the application of high-strength steel sheets having extremely high strengths of 980 MPa class and 1180 MPa class TS has also been studied. [0004] However, in general, increasing the str...

AI Technical Summary

Problems solved by technology

[0006] However, the amount of shape change is estimated based on TS. Therefore, when the TS of the steel sheet fluctuates, the deviation between the predicted value of shape change and the actual amount of shape change increases, causing shape defects.

In addition, steel sheets with such poor shapes need to be corrected one by one by sheet metal processing after stamping, which significantly reduces mass production efficiency.

Images