US2334869A - Chromium steel - Google Patents

Description

Patented Now. 23, 1943 nssell Frank. m Falls, N. Y alslgnor to Electro Metallurgical Company, a corporation No Drawing. Application February 4. 1942,

Serial N- 429,499

I 6 Claims. (CI. 75-126) This invention relates to chromium steels and i to articles made therefrom, and has as its primary object the improvement of the corrosion resistance of such steels.

Chromium steels find numerous and varied uses primarily because of their exceptional resistance to attack bycorrosive media and the ready amenability or the steels to be fabricated into different kinds -of equipment. In general, the steels exhibit excellent resistance to oxidizing corrosive media, although the ability of the steels to resist attack by reducing corrosives is generally less great. v

Broadly the present invention comprises chromium steel containing between 4% and 30% chromium wherein the resistance oi the steel to" reducing corrosives is considerably enhanced by a small but effective content of antimony.

More specifically, the invention contemplates alloy steels containing in addition to antimony;

chromium between 4% and 30%; up to 0.50%

carbon; up to 0.30% nitrogen; up to about 3% each of manganese and silicon, although normally these elements should not exceed 1% each; the remainder being principally iron. In steels which are to be wrought it has been found that the amount of antimony which can be present without excessive impairment of the hot working properties of the steel is influenced-by the chromium content. For example, 12% chromium steels with up to 1.50%- antimony can be readily hot worked; as can 18% chromium steels with up to 1% antimony and 25% chromium steels with up to 0.75% antimony. In chromium steels to be used in the cast form the antimony content may be somewhat greater but should not exceed The chromium steels of this invention may also contain one or more of the elements columbium,

tantalum, titanium and molybdenum, in small percentages not exceeding 5% in the aggregate. Columbium in amounts 5 to times the carbon content, tantalumin amounts 8 to times the carbon content, and titanium in amounts 3 to '7 times the carbon content, decrea'se' or eliminate the martensitic structure of low carbon chromium steels and thus soften the material and decrease'or eliminate hardenability. Moderate amounts of molybdenum enhance the resistance of the steel to certain types of corro sion.

It has been found that in the manufacture of chromium steels a high recovery of antimony is obtained, in fact 95% of the antimony introduced in themolten steel is retained in the flnished product. Antimony, when used within the limits hereinbefore described, enters into solid.

solution with the steel and hence results in a product of uniform characteristics.

Little or no antimony is lost when antimonybearing chromium steel welding rods are used for fusion-deposition welding. Thus, the inherent corrosion resistance imparted by the antimony addition is retained in the resulting weld;

this is particularly important when the base metal and welding rod are of similar composition. The general practice in welding chromium steels has been to employ welding rods having a somewhat higher-chromium content than is desired in the resulting weld in order to compensate for losses during welding and to assure comparable corrosion resistances in both the weld and the I base metal.

' Experimental test data are set forth in' the table to illustrate the superiority of antimonycontaining chromium steels in resisting reducing type corrosive media over antimony-free chromium steels of otherwise similar composition. The data show the corrosive efiectsof both dilute hydrochloric acid and dilute sulphuric acid over a 48 hour test period on wrought strips of 12%, 18% and 25% chromium steels, each respectively with and without antimony additions.

Hydrochloric and sulphuric acid tests at room temperature on 12%, 18% and 25% chromium steel j Inch penetration er Analysis of steel Condi month in one iii-b om- Heat 7 on t test period metal Or Sb 0 10% H01 10% 11,30.

Per-v Per- Percent cent cent 1 12.68 None 0. 05 v A 0.12 0.21 2 12.79 0.31 0.05 A 0.023 0.08 3 12.86 0.65 0.05 A 0.015 0. 050 12.75 0.95 0.05 A 0.01 0.027

18.53 None 0.08 A 0.44 18. 76 0. 42 0. 05 A 0.029 0. 12 18.53 0.63 0.06 A 0.023 0.079 18.50 1. 10 0.06 A 0.017 0.032

9 24.81 None 0. 13 B 0.13 0.24 10 25.34 0.33 0.09 B 0.045 0.15 11 25.28 0.63 0. 10 B 0.038 0. l1

1 Condition of metal:

A-Heated 3 hours at750 C. and-air cooled. B--Hcated 0 hours at 900 0. and air cooled. I All the steels in the table also contain appro mately 0.35% silicon and 0.50% manganese, remainder substantially alliron;

0.15% nitrogen.

The data indicate that the resistance or 12% chromium steels containing antimony (heats 2- to 4) to attack by weak hydrochloric and sulphuric acids at room temperature is. considerably improved over the antimony-free sample (heat No. 1). In fact the antimony-tree steel (heat No. 1) has a corrosion rate in both hydrochloric and sulphuric acids approximately 10 times as great as steel No. 4 containing 0.95% antimony but otherwise of like composition. Similar eil'ects are noted in the 18% chromium steels by a comparison of antimony-containing steels (heats 6 to 8) with the antimony-free sample (heat No. In these steels the antimony-tree sample (heat No. 5) was attacked at a rate about 14 times as great as heat No. 8 containing 1.19% antimony but otherwise of similar composition. The substantial improvement in corrosion resistance imparted by antimony to 25% chromium steels is seen by a comparison of the antimony-containing steels (heats 10 and 11) with the antimony-' free steel (heat No. 9). In these steels an antimony addition of 0.63%, (heat No. 11) reduced the corrosion rate to between one-quarter and onehalf that of the antimony-free steel (heat No. 9)

These results are particularly significant in view of the fact that chromium itself tends to decrease the corrosion resistance of steels to reducing type corrosive media. This effect is readily seen by a comparison of the antimony-tree 12% and 18% chromium steels (heats 1 and 5). It will be noted that the 18% chromium steel has a corrosion rate more than double that of the 12% chromium steel. An addition, however, of less than half a per cent of antimony to the 18% chromium steel (heat N0. 6) improves the corro- .sion resistance oi this steel to reducing type corrosives until it is better than that exhibited by antimony-free "12% chromium steels. Thus the present invention permits the use 01 higher percentages of chromium when the special properties thereby imparted are required without the loss in resistance to reducing type corrosives heretofore inherent in such increase in chromium content. This condition is most desirable when the properties of a steel require the addition of high percentages of chromium and the steel at the same time is required to resist attack from reducing type corrosive media.

It is to be understood that the invention is in no way limited by the particular compositions set forth in the table. The cpositions and data recorded therein are merely illustrative of the a,as4,eee v eitect oi antimony in preferred embodiments of.

the present invention.

In my copending application Serial No. 429,500. filed February 4, 1942, there is disclosed the effect of small additions or antimony upon the properties of austenitic chromium-nickel steels.

I claim:

1. Alloy steel having substantially the compontion: chromium between 4% and 30%, antimony between 0.1% and 2%, remainder principally iron together with incidental impurities; the antimony serving to increase the resistance of the alloy in both the wrought and cast condition to attack from reducing-typecorrosives.

2. Alloy steel containing between 4% and 30%- chromium, between 0.1% and 2% antimony, at least 0.1% but less than 1% each of manganese and silicon, carbon not over 0.50%, nitrogen not antimony serving to increase the resistance of the alloy in both the wrought and cast condition to attack from reducing type corrosives.

4. Alloy steel containing between 12% and 18% chromium, between 0.1% and 1.00% antimony, carbon not over 0.50%, remainder iron together with incidental impurities including manganese and silicon in amounts less than 1% each; the antimony serving toincrease the resistance of .the alloy in both the wrought and cast condition to attack from reducing type corrosives.

5. Alloy steel containing'between 4% and 12% chromium, between 0.1% and 1.50% antimony,

up to 0.50% carbon, remainder principally iron,

together with incidental impurities including manganese and silicon in amounts less than 1%- each; the antimony serving to increase the resistance oi the alloy to attack from corrosive media of a reducing type. I Y

6. A welding rod characterized in that it contains between 4% and 30% chromium, between about 0.1% and 2% antimony, remainder principally iron with incidental impurities; said welding rod being particularly suitable for producing welds having high resistance to attack from corrosives of a reducing nature. 1