US2209248A - Alloy steel - Google Patents

Description

Patented July 23, 1940 UNITED STATES PATENT OFFICE ALLOY STEEL Daniel E. Krause and Clarence H. Lorig, Columbus, Ohio, assignors to Battelle Memorial Institute, Columbus, Ohio Ohio, a. corporation of 2 Claims.

Our invention relates to alloy steels. It has to do, more particularly, with alloy steels which contain phosphorus and vanadium.

The efiect of phosphorus on corrosion and 5 mechanical properties of carbon steels and various alloy steels is well known. Its influence on atmospheric corrosion and corrosion in other media is regarded as very beneficial. By itself, or in combination with other elements, it functions as an alloy and strengthening element and, as such, produces high yield strength and yield ratio. For the above reasons, many of the newly developed low-alloy, high yield strength structural steels contain substantial percentages of phosphorus.

The remarkably great efiect upon mechanical properties and corrosion resistance conferred on steels by small additions of phosphorus is demonstrated by results obtained on a series of very low carbon steels containing increasing percentages of phosphorus. Normalized bar stock of these steels had mechanical properties shown in the following table:

Base composition-0.03% C. 0.10% Mn, 0.01%

25 Si, 0.04% S.

P, Tensile Yield Elong. Red. of Charpy per strength, strength, percent area, impact, cent 1b./sq. in. lb./sq. 1n. 2 percent ft. lb.

" Thus, the above results indicate that phosphorus has a marked-effect on the mechanical proper ties of steels.

In the form of 22 gauge sheet, the above indicated steels showed losses on exposure to the Thus, the above results indicate an increase in the phosphorus content results in an increase in the corrosion resistance of the steel.

In spite of the rather remarkable influence of small amounts of phosphorus on the mechanical properties and corrosion resistance, as shown in the above tables, phosphorus by itself may be objectionable in some cold-forming and colddrawing steels because it increases their hardness. Furthermore, in excess amounts it induces cold-shortness, increases the size of the grain, lowers the ductility and causes segregation in the ingots into which the steels are cast.

One of the objects of our invention is to provide low alloy, high strength steels havinggreatly improved mechanical properties, reduced grain size, increased ductility, and increased corrosion resistance to the atmosphere.

Other objects will be apparent from the following description of our invention.

This application is a division of our co-pending application Serial Number 162,695, filed September 7, 1937.

We have found that additions of vanadium to phosphorus steels greatly improve their mechanical properties, reduce their grain size, increase their ductility, very materially increase their corrosion resistance to the atmosphere, and in other ways improve the phosphorus steels by suppressing some of the detrimental influences of excess phosphorus. Grain size reductions and its control by the use of vanadium in phosphorus steels assist in producing better steels of more uniform properties and with less segregation. As illustrative of the grain size reduction brought about in phosphorus steels by vanadium, two annealed sheet steels, each containing 0.12% carbon and.0.l'7% phosphorus, one without vanadium and one containing 0.20% vanadium, had grain counts of 4,000 and 36,000 grains per sq. in., respectively. Thus, a great decrease in grain size results from the use of vanadium in phosphorus steels.

We have found that steels containing less than 0.5% carbon, up to about 0.5% phosphorus and up to about 0.5% vanadium are readily workable both hot and cold and have decidedly better' properties than steels of the same carbon and phosphorus content but containing no vanadium. For best resistance to corrosion, the carbon content should be less than 0.25% and preferably it should be under 0.15%. The carbon content may be as low as 0.01%. The amount of phosphorus is limited only by its deleterious influences on other properties required of the steels. of vanadium overcome to a degree these deleterious influences and therefore allow higher phosphorus contents to be used. While the resist- Lower carbon contents and the presence ance to corrosion of steels is greatly improved if they contain from 0.08% to 0.50% phosphorus,

we prefer to use from 0.08% to 0.25% phosphorus. We have discovered thatin the presence of phosphorus, vanadium adds greatly to the resistance to corrosion of steels." While we may use percentagesof vanadium as high as 0.5%, the cost of the element in some instances renders its use to this extent inadvisable. We have found that in the less costly steels, vanadium in percentages from 0.025% to 0.25% is satisfactory.

The remaining constituents of the steels, aside from iron, are those incidental to their manufacture. The sulphur is maintained low, preferably not more than 0.20%, though steels containing more than this are within the scope of our invention. The manganese is maintained under 1.5%. 'The preferred percentage of manganese is 0.2% to 0.8%;

The following tables illustrate examples of steels made in accordance with the present invention and compare them with other steels. The mechanical properties were obtained on bar stock after normalizing and after annealing and the atmospheric corrosionlosses were obtained on 22 gauge sheet.

to the vanadium content indicated above. For corrosion resistance, the use of 0.1% to 0.5% copper, in addition to the indicated vanadium content, is decidedly beneficial, although this amount of copper does not measurably increase the strength or'raise the yield point. When the loss in mechanical strength, which would accompany a decrease in vanadium content, is not of serious consequence in the use of the steel, then'it becomes possible to replace some of the much more costly vanadium with copper without impairing the resistance to corrosion. In this case, the use of 1 to 2 times as much copper as the-vanadium which it replaces would not lessen the resistance to corrosion. On the other hand, 0.1% to 0.5% copper, in addition to the indicated vanadium content, can be used to further enhance the resistance to corrosion that results from the joint use of phosphorous and vanadium.

When the strength and yield point of steels having combinations of carbon, phosphorous, vanadium and copper which are particularly satisfactory are to be raised, we prefer to obtain the increased strength and yield point by the use of more copper rather than by the use of additional amounts of one or more of the other three elements. This preference lies in the fact C, P, V, Cu, Tensile Yield Elong Red. Charpy Per- Per- Per- Per- Condition strengt strength, in 2", of area, impact, cent cent cent cent lb./sq. in. lb./sq.1n percent percent ft. lb.

.21 Normalized. 55,000 32,500 44 75 57 Annealed- 52, 500 29, 500 44 75 7 .17 53,000 30,500 as 57 30 75,000 51,500 34 51 10 1a 77, 250 42, 500 so 40 14 55,000 40,000 as 55 a4 80,000 50,000 20 57 4 54,000 47,000 as 72 51 58,000 30,000 as 72 52 70,000 55,500 54 55 :10 75,000 50,000 34 55 20 .005 34,500 25,000 45 s3 42 .008 ..do 50,250 32,000 42 72 51 .25 .10 1.5 Normalized- 70,100 53,300 35 57 a1 .25 .10 1.5 Annealed-.- 75,000 52,300 32 57 30 that copper decreases the ductility far less for a Atmospheric corrosion weight given increase in strength and yield point than C, P, v, Cu, does additions of carbon or phosphorus in steels Per- Per- Per- Per; already containing carbon and phosphorus. In Condition Gmonths if the presence of substantial amounts of phosexmsu" exposure phorus, more carbon is deleterious as it induces brittleness, while in a steel already containing 12. 2.3 substantial amounts of phosphorus, an increase 1 of phosphorus very seriously effects the impact .3 15.5 23.5 3.3 g.; resistance and ductility. The use of vanadium j merely to strengthen the steels, in most instances, 3 3-3 is inadvisable because of its cost. 1 I 1 1 We have found that 1% copper will increase both the strength and yield point of the steels 1... .15 .23 A i 1,5 M f33{f1 5%,, it; from 5,000 to 20,000 lb./sq. in. dependmg upon 15.. .15 .005 .do 23.0 the heat treatments given them, and that additional increases of the same magnitude may be The vanadium-phosphorus steels, having a substantial content of both elements, are char-- be enhanced by the use of copper in addition obtained through precipitation hardening. The latter may be effected with normalized steels containing 0.7% to 3% 'copper by holding them in,

or cooling very slowly through the precipitation hardening temperature range of 750 degrees to 1050 degrees F. The preferred range of copper for improved strength and yield point is about 0.50% to 3%.

Our steel has an advantage in welding. On welding the hardening in the zone immediately adjacent to the weld is not appreciable. One of the secondary advantages of the vanadium in the steel is that it prevents a martensitic zone from forming in the steel near the weld. An-' other function of the vanadium is to prevent grain growth in the overheated zone adjacent to the weld. Phosphorus steel without vanadium will be coarse grained in this zone.

It will be apparent from the above description that we have provided phosphorus-vanadium steels having greatly improved mechanical properties, reduced grain size, increased ductility and increased corrosion resistance. The steel will have a yield strength in the roller, normalized and annealed conditions of more than 40,000 lb./sq. in., a ductility at least equal to that of plain carbon steel of equal strength, a small grain structure, and a resistance to atmospheric corrosion that is greater than that of either plain phosphorus steel of like phosphorus content or phosphorus-copper steel of like phosphorus and copper content.

The phosphorus-vanadium steels with or without copper, or the type disclosed herein, having high physical properties as well as high resistance to corrosion may be made into castings or can be fabricated into rough articles such as structural shapes, sheet, plate, wire and tubing which are to be used where resistance to corrosion, as well as high physical properties are desired.

Having thus described our invention, what we claim is:

1. An alloy steel consisting of from 0.01% to 0.5% carbon, from 0.025% to 0.50% vanadium, from 0.08% to 0.50% phosphorus, from 0.2% to 1.5% manganese and not over 0.20% sulphur, the balance being substantially all iron.

2. An alloy steel consisting of from 0.01% to 0.25% carbon, from 0.025% to 0.25% vanadium, from 0.08% to 0.25% phosphorus, from 0.2% to 0.8% manganese and not over 0.20% sulphur, the balance being substantially all iron.

DANIEL E. KRAUSE. CLARENCE H. LQRIG.