Method of producing ferritic iron-base alloys and ferritic heat

Details Method of producing ferritic iron-base alloys and ferritic heat Method of producing ferritic iron-base alloys and ferritic heat

1997-01-06

1999-03-30

Ip, Sikyin

Metal treatment

Process of modifying or maintaining internal physical...

Utilizing disclosed mathematical formula or relationship

148506, 148325, 420 34, 420 36, 420 37, C22C 3800, C22C 38302, C22C 3830, C22C 3854

Patent

active

058883185

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method of designing ferritic iron-base alloys on the basis of a predicting system without depending upon conventional trial-and-error experimental procedures. This invention also relates to high strength ferritic heat resistant steels which exhibit high temperature strength and other physical and chemical properties more excellent than those of the conventional ferritic heat resistant steels. The steels are particularly suitable for materials of turbines and boilers.


BACKGROUND ART

Although heat resistant steels are used in various areas, materials of turbines and boilers are the typical uses of the ferritic heat resistant steels. Therefore, the heat resistant steels of this invention will be specified in terms of turbine and boiler materials hereinafter.
Most of conventional heat resistant steels hitherto developed for use in boiler and turbine materials contained 9 to 12% chromium as well as one or more of carbon, silicon, manganese, nickel, molybdenum, tungsten, vanadium, niobium, titanium, boron, nitrogen and copper, in amounts of 0.04 to 2.0%, respectively. It should be noted that "percent (%)" means "mass %" herein unless any explanatory note is given.
Compositions of typical heat resistant steels for materials of turbines and boilers are listed in Table 1 and Table 2 (refer to "Compositions, Structures and Creep Characteristics of Heat Resistant Alloys" distributed as a brief at the 78th conference held under co-sponsorship of Japan Metal Society and Kyushu branch of Japan Iron and Steel Institute . . . Reference 1). All these steels have been developed by many experiments wherein various elements of various amounts were alloyed in turn. The action and function of each said alloying element has come to be known by such trial-and-error experiments and can be roughly summarized as follows.
Chromium:
Chromium improves corrosion and heat resistance of the steel. Chromium content should be increased as the service temperature of the steel is elevated.
Tungsten, Molybdenum:
These elements improve high temperature strength of the steel due to their function for bringing about solid solution hardening and precipitation hardening in the structure of the steel. However, as contents of these elements are increased, the ductile-brittle transition temperature (DBTT) of the resultant steel is elevated. In order to suppress the embrittlement below 1.5%. In accordance with this instruction, the molybdenum equivalent of most of the conventional alloys is around 1.5%.
Vanadium, Niobium:
These elements will bring about strengthening of a steel due to formation of carbo-nitrides through precipitation hardening. The solid solubility of vanadium in a steel is 0.2%, whereas that of niobium is 0.03%, when the steel is annealed at a temperature of 1050.degree. C. If the amount of vanadium and that of niobium exceed their respective solid solubility, the excess amount of vanadium and that of niobium will form their carbides and nitrides in the steel matrix during annealing. Results of experimental work obtained up to the present, in particular that of creep rupture tests, show that the optimum vanadium and niobium contents are 0.2% and 0.05%, respectively. The niobium content "0.05%" in the steel exceeds its solid solubility, and the excess niobium forms NbC which is effective to suppress coarsening of austenitic crystal grains during annealing heat treatment.
Copper:
As copper is one of the austenite stabilizing elements, it suppresses formation of the .delta.-ferrite as well as precipitation of iron carbides. Copper in the steel exhibits a weak action of lowering the Ac.sub.1 point and improves hardenability of the steel. Copper suppresses forming a softened layer in a heat affected zone (hereinafter designated as HAZ). However, addition of more than 1% copper to a steel decreases its reduction of area upon creep rupture.
Carbon, Nitrogen:
These elements are effective to control structure and strength of the steel. Concerning creep properties of the steel, the optimum carbon

REFERENCES:
patent: 3876475 (1975-04-01), Ramqvist
patent: 4824637 (1989-04-01), Yukawa et al.
"Compositions, Structure and Creep Characteristic of Heat Resistant Alloys," 78th Conference of the Japan metal Society and the Iron and Steel Institute, Oct. 25, 1992, pp. 1-8.
Journal of Metal Institute of Japan, vol. 31, No. 7 (1992), pp. 599-603.
Altopia, (Sep. 1991), pp. 23-31.
"Electronic Approach to the Prediction of Phase Stability in Cr-Mo Ferritic Steels," by Hisakazu Ezaki et al., Iron and Steel, vol. 78 (1992) pp. 1377-1382.
"Development and Applications of 9Cr-2Mo Thick-Walled Pipe For Ultra Super Critical Power Plant", Hisao Haneda et al., Technology of Pipe and Tube and Their Preparation, Proceedings of the Third International Conference on Steel Rolling, (Sep. 2-6, 1985) p. 669-676.
Journal of Metal Institute of Japan, vol. 27, No. 3 (1988), pp. 165-172.
Light Metals, vol. 42, No. 11 (1992), pp. 614-621.

Affiliated with

Also associated with

Rating

Method of producing ferritic iron-base alloys and ferritic heat does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of producing ferritic iron-base alloys and ferritic heat , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing ferritic iron-base alloys and ferritic heat will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1210381