Hot-rolled and annealed ferritic stainless steel sheet and method for manufacturing the same

Abstract

The present invention provides a hot-rolled and annealed ferritic stainless steel sheet which has sufficient corrosion resistance and in which cracks can be prevented during blanking into a thick flange, and a method for manufacturing the same. A hot-rolled and annealed ferritic stainless steel sheet has a chemical composition containing, in percent by mass, C: 0.001% to 0.020%, Si: 0.05% to 1.00%, Mn: 0.05% to 1.00%, P: 0.04% or less, S: 0.01% or less, Al: 0.001% to 0.100%, Cr: 10.0% to 19.0%, Ni: 0.65% to 1.50%, Ti: 0.10% to 0.40%, and N: 0.001% to 0.020%, with the balance being Fe and unavoidable impurities, and has a threshold stress intensity factor K_IC of 35 MPa·m^1/2 or more.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is the U.S. National Phase application of PCT / JP2018 / 016545, filed Apr. 24, 2018, which claims priority to Japanese Patent Application No. 2017-087756, filed Apr. 27, 2017, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.FIELD OF THE INVENTION[0002]The present invention relates to a hot-rolled and annealed ferritic stainless steel sheet having excellent workability and being suitable for use in flanges and the like and a method for manufacturing the same.BACKGROUND OF THE INVENTION[0003]In recent years, there has been increased tightening of regulations on exhaust gas in automobiles and there has been an urgent need to improve the fuel efficiency. Accordingly, an exhaust gas recirculation (EGR) system, in which exhaust gas from an automobile engine is used again as intake air of the engine, has been increasingly used. The exhaust gas from the engine is passed through a...

AI Technical Summary

Benefits of technology

[0008]It is an object according to aspects of the present invention to solve the problem described above and to provide a hot-rolled and annealed ferritic stainless steel sheet which has sufficient corrosion resistance and in which cracks can be prevented during blanking into a thick flange, and a method for manufacturing the same.

[0009]In order to solve the problem, the present inventors have conducted detailed studies, and as a result, have found that by increasing a threshold stress intensity factor KIC of a steel sheet, the steel sheet can be worked into a thick flange having a burring working part without occurrence of cracks. Specifically, it has been found that, by setting the threshold stress intensity factor KIC at 35 MPa·m1 / 2 or more, when a steel sheet worked into a thick flange having a burring working part, occurrence of cracks in the burring working part can be effectively prevented, and the steel sheet can be sufficiently put into practical use for a thick flange having a burring working part.

[0010]It has also been found that, by performing hot-rolled sheet annealing at an appropriate temperature on a hot-rolled steel sheet obtained by subjecting ferritic stainless steel having an appropriate chemical composition to finish hot-rolling with multiple passes including three or more passes while appropriately controlling the accumulated rolling reduction of final three passes (=100−(final sheet thickness / sheet thickness before start of final three-pass rolling)×100[%]), the threshold stress intensity factor KIC is improved. Aspects of the present invention have been made on the basis of the findings described above, and are as follows.

Problems solved by technology

However, when the present inventors tried to work the hot-rolled ferritic stainless steel sheet described in Patent Literature 1 into the shape of a thick flange having a burring working part, in spite of the fact that the steel sheet had a sufficient Charpy impact value, in some cases, cracks occurred in the burring working part, in particular, at the central part in the sheet thickness direction, and it was not possible to obtain a predetermined flange shape, revealing that the hot-rolled ferritic stainless steel sheet was not sufficient enough to be used as a thick flange.