Metal treatment – Stock – Ferrous
Patent
1991-09-13
1993-07-27
Yee, Deborah
Metal treatment
Stock
Ferrous
148610, 420 61, C22C 3820, C22C 3822, C21D 800
Patent
active
052307522
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a ferritic stainless steel which is highly resistant to corrosion in a neutral or weakly acidic chloride-containing medium and more particularly suited for the manufacture of heat exchangers for industry, especially those cooled by brackish water or seawater.
A process for the production of such a steel is also a subject of the present invention.
FR-A-2,377,457 discloses a chromium nickel molybdenum ferritic steel resisting corrosion and containing especially from 18 to 32% of chromium, from 0.1 to 6% of molybdenum, from 0.5 to 5% of nickel and not more than 3% of copper.
Examples of steel which are described in this document relate to steels containing 1.99 to 2.15% of molybdenum. Furthermore, it is stated on page 9, lines 27 to 32, that the steels exhibiting the best alloy compositions are those containing 28% of chromium, 2% of molybdenum and 4% of nickel, and those containing 20% of chromium, 5% of molybdenum and 2% of nickel, because they have a sufficient structural stability and can be manufactured economically on an industrial scale.
FR-A-2,352,893 also discloses a ferritic stainless steel containing from 0.01 to 0.025% by weight of carbon, from 0.005 to 0.025% by weight of nitrogen, from 20 to 30% by weight of chromium, from 3 to 5% of molybdenum, from 3.2 to 4.8% of nickel, from 0.1 to 1% of copper, from 0.2 to 0.7% of titanium and/or from 0.2 to 1% of niobium.
This document claims more particularly a high nickel content of between 3.2 to 4.8% in combination with a limitation on the copper content of between 0.1 and 1% to obtain high ductility values at room temperature.
FR-A-2,473,069 also discloses an iron-based ferritic stainless steel containing up to 0.08% by weight of carbon, up to 0.060% by weight of nitrogen, from 25 to 35% by weight of chromium, from 3.60 to 5.60% by weight of molybdenum, up to 2% by weight of nickel and up to 2% by weight of titanium, niobium and zirconium according to the following equation:
The sum of the said carbon and nitrogen being greater than 0.0275% by weight.
FR-A-2,473,068 discloses a ferritic stainless steel which has the same composition as the above steel, but whose weight content of nickel is between 2 and 5%.
Now, it is known that nickel is a costly element which accelerates the formation of embrittling intermetallic phases and reduces resistance to cavity corrosion in a chloride-containing medium.
The subject of the present invention is therefore a ferritic stainless steel in which the addition of copper is limited to a value of 0.5 to 2% by weight so as to reinforce the impact strength of the alloy while reducing the rate of formation of hard and embrittling intermetallic phases of the sigma and chi type which can form during the heat treatments of manufacture of the welding. This results in the possibility of producing an alloy stabilised with titanium and/or with niobium with a very high content of chromium and of molybdenum, essential for obtaining a maximum corrosion resistance while reducing to a minimum the difficulties of manufacture and the risk of deterioration in the other final properties.
This result is obtained by the invention by virtue of a ferritic stainless steel which has the following chemical composition by weight: 0.60% aluminium, magnesium, calcium, boron and rare-earth materials, the remainder being iron and impurities resulting from the melting of the substances needed for the production.
According to another characteristic of the invention the steel contains less than 0.010% of carbon and less than 0.015% of nitrogen, the sum of the carbon and nitrogen being less than 0.025%.
A further subject of the invention is a process for the production of a ferritic stainless steel from which a steel strip is formed, which is rolled hot, characterised in that the hot-rolled steel strip is subjected to tempering at a temperature of between 900 and 1200.degree. C. and the steel strip is then subjected to a first cold rolling followed by an intermediate tempering at a temperature of between 900 and 1200.degre
Bavay Jean-Claude
Bourgain Pierre
Ugine Aciers de Chatillon et Gueugnon
Yee Deborah
LandOfFree
Ferritic stainless steel and process for producing such a steel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ferritic stainless steel and process for producing such a steel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ferritic stainless steel and process for producing such a steel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2339976