Metal treatment – Stock – Ferrous
Patent
1997-02-04
1998-03-31
Yee, Deborah
Metal treatment
Stock
Ferrous
148542, 148609, C22C 3844, C21D 802
Patent
active
057333874
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a duplex stainless steel for use in corrosive environments, such as in sea coast facilities and the like, and a manufacturing method therefor. More specifically, the present invention relates to a duplex stainless steel and a manufacturing method therefor, in which the steel consists of a ferrite phase and an austenite phase.
DESCRIPTION OF THE PRIOR ART
Generally, a duplex stainless steel in which ferrite and austenite phases are mixed together (called a "duplex stainless steel" below) is superior in corrosion resistance and in stress corrosion cracking resistance. Therefore it is widely used in applications requiring high corrosion resistance, such as oil well drilling pipes, power generating plant desulphuring facilities, paper manufacturing tank facilities, acid manufacturing tanks, sea water pumps, marine structures and the like.
Generally duplex stainless steel which is known to be superior in the corrosion resistance contains a large amount of Cr which is an alloy element used for promoting pitting corrosion resistance. In addition, Mo and Ni are employed as basic alloying elements. Duplex stainless steels are grouped roughly into two classifications.
One classification is UNS 31803 which is composed of: 21-23 weight % (to be called merely % below) of Cr, 4.5-6.5% of Ni, 2.5-3.5% of Mo, 0.08-0.20% of N, less than 2% of Mn, and less than 0.03% of C.
The other classification is SAF 2507 which is composed of: 24-26% of Cr, 6-8% of Ni, 3-5% of Mo, 0.24-0.32% of N, less than 0.5% of Cu, less than 1.2% of Mn and less than 0.03% of C.
The above stainless steels provide corrosion resistance almost equivalent to that of a super austenitic stainless steel. However, they are low in the hot ductility, and therefore, when these stainless steels are formed into a steel sheets, they are liable to form edge cracks during hot rolling. If edge cracks are formed, it leads to sheet ruptures and a decrease in the actual yield. Therefore, it is desirable that duplex stainless steel possesses a superior hot ductility.
A conventional method for improving the hot ductility of duplex stainless steel, involves adding Ce into the duplex stainless steel (J. I. Komi, et al., Proc. of Int. Conf. on Stainless Steels, ISIJ, Tokyo, 1991, p807). In this method, the S content is lowered to 30 ppm, and Ce is added, so that the segregation of S is prevented, thereby improving the hot ductility.
In addition, according to A. Paul et al., in order to promote the recrystallization of the austenite phase during hot rolling of duplex stainless steel, the strain rate is made high, thereby improving the hot ductility (Innovation of Stainless Steel, Florence, Italy, 1993, p3297).
However, the above described methods have the problem that they cannot be applied to a facility in which the temperature can be complemented by adjusting the temperature during the hot rolling.
All the above described duplex stainless steels do not contain W but Mo. However, a composite duplex stainless steel in which Mo and W are added has more superior hot ductility and corrosion resistance. Therefore, recently, studies have been made on duplex stainless steel in both Mo and W are added. For example, in a duplex stainless steel which was proposed by B. W Oh et al., a part of Mo is replaced with W in a steel which contains 20-22% of Cr. It is reported that a duplex stainless steel containing 2.7% of W and 1.05% of Mo has an improved corrosion resistance compared with that containing 2.78% of Mo (Innovation of Stainless Steel, Florence, Italy, 1993, P359).
However, the above steel has an excessively low Mo content, and therefore, the corrosion resistance is decreased.
As another example, European Patent EP 0,545,753A1 by H. Okamoto proposes a duplex stainless steel in which 2-4% of Mo and 1.5-5.0% of W are added. This steel is known to have high strengths and a high corrosion resistance. However, it is liable to cracking during a hot rolling, and the phase stability tends to be lowered.
In addition, there are s
REFERENCES:
patent: 4765953 (1988-08-01), Hegenfeldt et al.
patent: 5284530 (1994-02-01), Azuma et al.
patent: 5298093 (1994-03-01), Okamoto
J.I. Komi et al., "Effects of Sulphur Phosphorus and Cerium on the Hot Workability of a Ferritic-Austenitic Stainless Steel", Proc. of Int. Conf. on Stainless Steels. 1991. ISIJ. Tokyo. p. 807.
A. Paul et al., "Behaviour of 2205 Duplex Stainless Under Hot Working Conditions", 1993, Innovation of Stainless Steel, Florence, Italy, p. 3.297.
Kim Bong Un
Kim Kwang Tae
Lee Yong Deuk
Lee Yong Heon
Pohang Iron & Steel Co. Ltd.
Research Institute of Industrial Science & Technology
Yee Deborah
LandOfFree
Duplex stainless steel, and its manufacturing method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Duplex stainless steel, and its manufacturing method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Duplex stainless steel, and its manufacturing method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-47826