US1712030A - Stable-surface alloy steel resistant to acids - Google Patents

Description

Patented May 7, 1929. 0

UNITED STA TIES PATENT, OFFICE- RALPH P. DE VRIES, OF MENANDS, AND HENRY A. DE FRIES, 0F ALBANY, NEW YORK,

ASSIGNORS TO LUDL'UM STEEL COMPANY, OF WATERVLIET, NEW YORK, A COR- ronn'rron or new JERSEY.

STABLE-SURFACE ALLOY STEEL RESISTANT TO ACIDS.

No Drawing. 7

This invention relates to alloys of steel and more particularly to such alloys which are commonly designated as stable surface acid resistant steels.

The main objects of our invention are to provide an alloy steel of new composition which will be resistant to sulphuric acid in all percentages of dilution, whether the acid be used in the cold or in the hot condition, and which will further be resistant to mixtures of sulphuric and nitric and to certain dilutions of hydrochloric acid.

The invention is of particular utility for steel tanks, valves, and fittings of various kinds which are used where they come into contact with acids such as are employed in commercial or manufacturing operations, and finds particular application where steel is required for strength and is at the same time exposed to sulphuric acid diluted to any degree.

The alloy steel of our invention contains nickel from 14%130 30%, chromium from 6% to 20%, silicon from 1% to 3%, tantalum from 1% to 3%, carbon from as low as possible content up to 1%. Manganese may be present in amounts usually found in alloy steels, up to .7 5%, and the usual amounts of metalloids, such as phosphorus and sulphur may be present. The carbon content varies in all cases with the amount of nickel, and their approximate relative proportions are expressed by the equation :20 1.6+ .06 1, where m is the carbon content in per cent and y the nickel content in per cent.

l/Ve do not wish to be held exactly to the equation just given, but as near as we can determine it sets forth the limiting condition between the carbon and nickel content.

For best results, we have found that the silicon and the tantalum must always be used in approximately e a1 quantities; that is, if silicon is used in th amount of 1- it is desired to have talitalum in a nearly similar amount. i

As already stated, alloy steels made within this range of composition are particularly resistant to t e action of sulphuric acid, whether the acid is used cold or hot.

The following is a gpod example of a pre- Application filed November 26,1926. Serial No. 151,013.

ferred analysis which we wish to make in this range Carbon 0.8m Manganese 0.50 Nickel 18.00 Chromium 10.00 Silicon 2.00 Tantalum 2.00

The attack which occurs is most' pronounced during the first 24 hours. Thereupon the material becomes extremely passive and corrosion proceeds at a uniform, but almost negligible rate. The protecting film formed during the first exposure of approximately 2 k hours is of such a nature that it prevents, to all ntents and purposes, further corrosion. It 1s important to note that the protecting film does not alternately break down and rebuild with consequent loss of the acid resistant alloy steel.

The steel after attaining passivity is in a state of equilibrium with regard to acid attack, even if the degree of acid dilution is changed frequently; that is, the tank containing acid might be washed out with water and the passivity of the steel previously set up through acid attack would not be broken down.

The corrosion tests against sulphuric acid attack have shown that the loss in weight in all dilute sulphuric acid solutions below 20% is about equal. When the strength of the acid is increased from 20% to40%, the at tack on the alloy steel diminishes and after the strength of the acid solution is increased from 50%to 100%, the attack is again slightly increased, being equal in the latter case to the losses in the dilute acids below 20%. The acid attack, no matter what the dilution or condition of the acid, is'so small in amount as to be practically negligible for most commercial purposes of which we have any knowledge.

The corrosion resistance of our alloy steel against mixed acids, for instance, as sulphuric and nitric, is approximately as good as against sulphuric acid of different solutions.

In contra-distinction to most materials of which we have any knowledge as being good casts with a good surface and can be cast into any form or shape desired, such castings can be annealed by heating from 1400 to 1600 F. and slowly cooled and when so annealed can be easily machined. Rolled and forged products can be annealed with similar\ results.

The physical properties of this material are good. The alloy steel having the tensile strength of about 85,000 pounds in the annealed condition and good impact shock resistance. These properties can be modified by heat treatment.

a Essentially, the steel is not, however, a

steel which can attain tool steel hardness. By air cooling after heating to 2100, it will be possible to get a hardness of about 400 Brinnell which will be hard enough for many parts that must be hardened to resist wear; while at the same time resisting the attack of acids and acid fumes.

The alloy steel of our invention need not be cleaned of the hot scale of rolling or hammering or casting to makeit resistant to the acid attack. The scale that is formed is'very smooth and adherent. For many purposes it will be desirable to remove this scale and this may be done by the ordinary processes of machining and grinding. The clean metallic surface thus obtained will be equally resistant to acid attack.

established.

The thermal coefiicient of expansion of this allo steel, is not again broken down.

We find that the additions of tantalum are peculiarly effective in the alloy steel of our invention to maintain the passivity of the steel against acid attack once this has been We claim:

1.' As a new product, an alloy steel resistant to sulphuric and mixed acids, comprising nickel from 14% to 30%, chromium from 6% to 20%, silicon from 1% lum from 1% to 3%, and the balance iron.

2. An alloy steel resistant to sulphuric and mixed acids, comprising nickel from 14% to 30%, chromium from. 6% to 20%, silicon from 1% to 3%, tantalum from 1% to 3%, carbon in all percentages of the nickel range being substantially in accordance with the equation a=1.6.06y, where a: is the carbon and y the nickel content.

3. An alloy steel resistant to sulfuric acid, comprising nickel from 14% to 30%, chromium from 6% to 20%, silicon from 1% to 3%,,tantalum from 1% to 3%, carbon from 0% to 1%, and the balance iron, the lesser amounts of carbon being used with the greater amounts of nickel.

' RALPH P. DE VRIES.

HENRY A. DE FRIES.

carbon from 0% to 1% to-'3%, tanta-