Austenite-type stainless steel hot-rolling steel material with excellent corrosion resistance, proof-stress, and low-temperature toughness and production method thereof

Abstract

An austenitic stainless steel hot-rolled steel material can be provided which has sea-water resistance and strength superior to conventional steel. Low-temperature toughness can be maintained, which is preferable in a structural member of speedy craft. The steel material can include an austenitic stainless steel hot-rolled steel material which excels in the properties of corrosion resistance, proof stress, and low-temperature toughness. In such austenitic stainless steel hot-rolling steel material, e.g., PI[=Cr+3.3(Mo+0.5W)+16N] ranges from 35 to 40, δ cal [=2.9 (Cr+0.3Si+Mo+0.5W)−2.6 (Ni+0.3Mn+0.25Cu+35C+20N)−18] ranges from −6 to +2, and a 0.2% proof stress at room temperature is not less than 550 MPa, Charpy impact value measured using a V-notch test piece at −40° C. is not less than 100 J/cm2, and the pitting potential measured in a deaerated aqueous solution of 10% NaCl at 50° C. (Vc′100) is not less than 500 mV (as it relates to saturated Ag/AgCl).

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a structural steel material which excels in corrosion resistance and is used in a marine (chloride) environment, for example; an austenite-type stainless steel hot-rolling steel material, as a hull-structural material which excels in strength as well as seawater resistance, and low-temperature toughness, upon being used as a material for an outer shell, a bulkhead, an frame, a hydrofoil, etc.; and a production method thereof. [0003] Priority is claimed on Japanese Patent Application No. 2005-26177, filed Feb. 2, 2005, Japanese Patent Application No. 2005-26176, filed Feb. 2, 2005, and Japanese Patent Application No. 2006-012569, filed Jan. 20, 2006, the contents of which are incorporated herein by reference. [0004] 2. Background Art [0005] Hitherto, coated steel sheets to which a heavy corrosive protection was applied were used for hull structures. The demand for speedy craft equippe...

AI Technical Summary

Benefits of technology

[0034] An austenitic stainless hot-rolled steel material having excellent corrosion resistance, and low-temperature toughness, including: not more than 0.03 mass % of C, 0.1 to 1.5 mass % of Si, 0.1 to 3.0 mass % of Mn, not more than 0.05 mass % of P, not more than 0.003 mass % of S, 15.0 to 21.0 mass % of Ni, 22.0 to 28.0 mass % of Cr, 1.5 to 3.5 mass % of Mo, 0.15 to 0.35 mass % of N, 0.005 to 0.1 mass % of Al, and not more than 0.007 mass % of O, in which the PI value expressed by the following formula (1) ranges from 35 to 40, δ cal value expressed by the following formula (2) ranges from −6 to +4, the remnant consists of Fe and substantially inevitable impurities, and the content of intermetallic compounds contained in the steel material is not more than 0.5 mass %,

[0035] A ninth aspect of the present invention is the austenitic stainless hot-rolled steel material having excellent corrosion resistance, and low-temperature toughness, as set forth in the eighth aspect of the present invention, further including one or more selected from the group consisting of 0

Problems solved by technology

Among these, although Patent document 2 discloses a production method of an austenitic stainless steel having a high proof stress while maintaining a low-temperature toughness, the sea water resistance is not taken into consideration in this austenitic stainless steel while maintaining low-temperature toughness.

On the other hand, a high strength steel material of an austenitic-type high corrosion resistance stainless steel having a PI value over 35 has not yet been put in practical use.

Stainless steel is more susceptible to crevice corrosion when it is shaped into a crevice form than when it is not shaped i.e. flat.

Among Cr, Mo and N, which increase corrosion resistance, as for Mo and Cr, it is not sufficient to simply add, because processability in hot-rolling will decr