US2069718A - Turbine blade - Google Patents

Description

Patented Feb. 2, 1937 UNITED STATES PATENT OFFICE mesne assignments, to Rustless Iron and Steel Corporation, Baltimore, Md., a corporation of Delaware No Drawing.

3 Claims.

This invention relates to rustless irons and steels and more particularly to articles wrought therefrom.

Among the objects of my invention is the pro- 5 duction of rustless irons and steels which are strong, tough, durable, corrosion-resistant, heatresistant and the like and yet which may be forged, swaged, cut, hammered and otherwise shaped, especially in successive stages of working and reheating, Without developing strain cracks or other defects, thus permitting the production of forged turbine blades of desired physical characteristics, such as strength, toughness, durability, corrosion-resistance and heat-resistance, all

with maximum efliciency, economy and reliability.

The invention accordingly consists in the combination of elements, composition of ingredients and mixture of materials and in the products, articles and parts manufactured therefrom as described herein, the scope of the application of which is indicated in the following claims.

As conducive to a clearer understanding of certain features of my invention it may be noted at this point that in the manufacture of certain articles fashioned of rustless irons and steels, that I is alloy irons and steels containing as essential ingredients chromium from about 12% to carbon from about .05% to .40%, and the balance principally iron, difliculties are encountered in 30 consistently producing sound, wrought metal articles free from surface cracks and free from other defects of working strain. In the production of heretofore known wrought turbine buckets or turbine blades, especially where the shaping or forming of these blades require a number of successive periods of working of the metal alternated by periods of reheating to desired working temperatures, sound articles free from surface cracks and like defects arenot consistently obtainable. One of the objects of my invention is the production of a relatively inexpensive rustless iron or steel alloy of desired physical characteristics, which is readily adapted to working, shaping or forming into turbine buckets or blades with a minimum of flaws or defects and a maximum of economy and reliability.

Rustless irons and steels, due to the relatively large chromium content are relatively diilicult to work or shape asiby hammering, swaging, upsetting or the like, where the metal is subjected to impact. In order to effect the necessary reduction of area to achieve a turbine blade of desired form or shape from available bar stock 55 for example, the metal, which is ordinarily hot Application September 29, 1933, Serial No. 691,572

worked, is subjected to the treatment of alternate periods of heating and working.

During the working periods the metal cools. Inherently, rustless irons and steels because of relatively high chromium contents employed are 5 subject to air hardening. In the ordinary course of the working of the metal, then, a hardness develops incident to the'normal cooling during working. This hardening, of course, limits the duration of each working period and necessitates 10 a number of alternate periods of working and reheating the metal in order to complete the forming of the desired product. 1

In the working of the metal it is inescapable that certain portions of the metal cool more quick- 15 1y than other portions and where, as in heretofore known processing or working of rustless irons and steels certain portions of the metal, because of the inherent air hardening characteristics referred to above, become harder than other por-, 20 tions. With continued working internal stresses are set up between various portions of the product and minute strain cracks develop which upon further working, especially where the metal is worked in several periods alternated by periods 25 of reheating, grow to noticeable proportions rendering the product undesirable or unfit for use.

In the practice of my invention desired analyses of rustless irons and steels are supplemented by a small amount of a ferrite forming ingredient, 30 such as molybdenum. This supplementary addition promotes the formation of free ferrite throughout the metal and moderates the inherent air hardening characteristics. Instead, then, of the hard air hardening, incident to the normal 35 cooling during working of the metal with the attendant production of strain cracks as indicated above, there is a relatively mild air hardening promoting a more even hardness throughout the metal with a consequent reduction in internal 4o stresses and the effective limitation of these stresses to values below a point where strain cracks appear. Furthermore, this moderation of the air hardening characteristics of the rustless iron or steel permits, in the fashioning of turbine 45 buckets or-blades, a somewhat prolonged working of the metal during each period, consequently reducing the average number of alternate periods of heating and working with consequent savings in time, labor and the like and permitting an 5 improved eiiiciency and economy in processing the metalJ' Incident to the moderation of the air hardening characteristics of rustless irons and steels by the introduction of a supplementary amount of molybdenum, there is a perceptible decrease in the ultimate hardness of the metal. This reiuction in hardness is objectionable where rustless irons and steels of maximum hardness are desired, so that the amount of molybdenum added to the metal is preferably limited to a value just suflicient to produce the desired result of permitting a ready working, shaping, or forming of the alloy, into turbine blades of desired size and shape, free from strain cracks or other defects of a like nature and yet of maximum strength, hardenability and the like.

In rustless iron and steel turbine blades of the character indicated, good results are achieved by the supplementary addition of from about .2% to .4% of molybdenum. This small addition of molybdenum is sufficient for most purposes and although molybdenum is a comparatively expensive addition the use of this amount does not greatly increase the cost of the turbine blade over that of the straight chromium analysis.

This supplementary addition renders the metal readily workable or formable without materially decreasing the hardenability. Other characteristics, such as corrosion-resistance and heat-resistance are noticeably improved by the supplementary addition of molybdenum, the improvement in these characteristics being almost directly in pro JItiOll to the amount of molybdenum added.

In general a higher percentage of molybdenum up to about 1.0 is employed in the rustless iron or steel turbine blades of higher chromium contents, while a lower percentage of molybdenum, for example about .2 is used in the iron and steel turbine blade stock of lower chromium contents. For most analyses, however, especially the chromium analyses of from to a molybdenum content of from .3% to .7% produces satisfactory results, although this percentage may be increased to about 1.0% when desired without greatly increasing the cost of the iron or steel or without objectionably decreasing the hardenability.

Thus it will be seen that there is provided in this invention alloy iron or steel turbine blade 6 stock of desired physical characteristics which may be forged into turbine blades which are strong, hard, corrosion-resistant, heat-resistant and the like and which are particularly free from strain cracks or like defects resulting from such 10 working.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments herein set forth, it is to be understood that all matter hereinbefore 15 described is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. In manufactures of the class described, a forged corrosion-resistant iron or steel turbine 20 blade comprising as essential ingredients carbon from .05 percent to .10 per cent, chromium from 12 per cent to per cent, molybdenum from about .2 per cent to about 1.0per cent, and with the balance substantially iron.

2. In manufactures of the class described, a forged corrosion-resistant iron or steel turbine blade comprising as essential ingredients carbon from .05 per cent to .10 per cent, chromium from 15 per cent to 20 per cent, molybdenum about .3 30 per cent to .7 per cent, and with the balance substantially iron.

3. In manufactures of the class described, a corrosion-resistant iron forged turbine blade comprising as essential ingredients carbon from about .05 per cent to .10 per cent, chromium from about 12 per cent to 20 percent, molybdenum about .4 per cent, and the balance substantially iron.

. ALEXANDER L. FEILD.