US2378994A - Cold rolled manganese steels - Google Patents

Description

Patented June 26,

COLD ROLLED MANGANESE STEELS Russell Franks, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Original application July 22, 1942,

Serial No. 451,893. Divided and this application November 28, 1944, Serial No. 565,579

6 Claims.

There is a large and increasing demand for structural materials having very high strengths per unit of weight and per unit of volume, and a great toughness and ductility. The principal demand has been by the makers of aircraft and other vehicles, but the advantages of highstrength, light-Weight structures are gaining recognition is other fields.

Plastic-bonded non-metallic materials, aluminum-base alloys, and magnesium-base alloys are widely used to obtain a combination of great strength with light weight, but for many purposes the structures built of such materials are undesirably bulky, thus oil'setting to a degree the advantage gained by a high ratio of strength to weight.

Austenitic-type chromium-nickel stainless steels, cold-rolled to a high tensile strength, have also gained considerable favor for the manufacture of airplanes, railway cars, and other structures. These steels are very tough and ductile,

and offer the advantage not only of a high ratio of strnegth to weight but also of a high ratio of strength to volume. They are, moreover, very resistant to corrosion and ordinarily do not require surface-protection against the weather.

Several special alloy steels, containing but a few per cent of alloying ingredients, and submitted to strengthening heat treatments, have been used for a limited number of purposes, for instance, airplane tubing and railway trucks, wherein a high ratio of strength to weight is important; but such steels when welded and not specially annealed have not had enough toughness and ductility at very high strength levels to adapt them to all uses in the field of highstrength, light-weight structures.

An object of this invention is to provide a new material having a very high strength per unit of weight and per unit of volume, and great toughness and ductility. This application is a division of my application Ser. No. 451,893, filed July 22,1942.

Another object is to provide a new steel for use in cold drawing, cold rolling, and other cold forming operations.

Another object is to provide novel cold drawn, cold rolled, and otherwise cold formed steel articles; and a. further object is to provide such steels and articles which are also resistant to progressive rusting.

In a search for steels which would achieve the objects of the invention, the so-called Hadfield manganese steels containing 10% to 14% manganese were investigated. The results were disappointing throughout the composition range, because the material cracked after relatively light cold rolling. Raising the manganese content to 16%, 17.5%, and 18% did not obviate this difilculty. When the manganese content rose to 20% to 30%, the material was dimcult to hot roll.

I have discovered, however, that a manganese steel which is readily hot rolled, and is readily cold rolled or otherwise cold worked, and which has when sufiiciently cold worked a. very high strength and excellent ductility and toughness. can be obtained if the manganese content is maintained within certain narrow, critical limits, and if copper or both copper and nickel are added in certain small, critical proportions. I have also discovered that these steels have a substantial resistance to progressive rusting, which resistance can be considerably enhanced, without ill effect on the physical properties, by the addition of a small proportion of chromium.

The invention comprises steel articles in the condition produced by cold drawing, cold rolling, and other similar cold forming operations, containing manganese betweeon 15.5% and 20%, preferably between 16% and 18%, and 0.25% to 1.75% copper, and preferably also containing chromium, remainder substantially iron.

In a preferred embodiment of the invention, the steel contains 0.5% to 1.75% copper. To enhence the resistance of these steels to progressive rusting, chromium is added in a proportion between 0.25% and 7%, preferably 1% to 4%.

By remainder iron and remainder substantially iron as used herein and in the appended claims, I mean to include not only chemically pure iron but also iron containing the common impurities and incidental ingredients found in ordinary steels. For instance, carbon may be present in a proportion from 0.01% to 1% or somewhat higher without greatly altering the characteristics of the steel, although it is preferred that the carbon content be less than 0.35%. Nitrogen in a proportion up to about 0.15%, phosphorus up to about 0.2%, sulfur up to about 0.05%, silicon up to about 1%, and residual deoxidizers, scavengers, and grain refiners,.such as calcium, may also be present.

The steels described above can be hot forged and hot rolled readily, without checking, cracking, or tearing, and can be cold worked, without intermediate or subsequent annealing at high temperatures, to obtain a very high strength while retaining great toughness and high ductility.

The strength and ductility of the steel arti cles oi the invention are illustrated by the tensile test data in Table A, obtained on a typical steel within the composition limits described herein.

The test data were obtained on standard coupon samples of cold-rolled strips, the amount of cold-rolling being indicated in the table. The coupon samples were each 0.035 inch thick, and were given no heat treatment during or following cold-rolling. The yield strengths at 0.2% ofiset were determined in accordance with the U. S. Navy Department specification No. 47821.

In the foregoing table, percent red.-indicates the percentage reduction in thickness of section effected by cold rolling before testing; E" indicates the initial tangent modulus of elasticity in millions of pounds per square inch; yield strength p. s. i. represents the yield and the as rolled and heat treated condition. Data are listed for physical tests in both tension and compression. The tabular headings correspond to those of Table A. Buckling stress in p. s. i. represents the load in pounds per square inch at which the test specimens buckled under compressive loading.

It will be noted from Table C that, the as rolled and heat treated specimens, marked "3" under the column headed "condition," show a higher yield strength in both tension and compression than corresponding specimens cold rolled but not heat treated, marked A in the same column. This effect is particularly pronounced in the specimens tested under compression. These specimens show an increase in yield strength of from 30,000 to 50,000 pounds per square inch over the untreated specimens.

The materials of this invention may be welded by the common welding methods, including the various spot electrical resistance weldin methods, electric arc welding, and oxyacetylene torch welding. This characteristic is of particular value, because welding is usually faster and cheaper than riveting. The material need not be annealed after welding.

Table B strength in tension, measured at 0.2% perma- C in we (em memo nent set, in pounds per square inch; tensile n r a n strength p. s. i." represents ultimate tensile Steel No.

u Per cent Per cent Per cent strength in pounds per square inch, and per- Mn 0 cent e1." represents percentage elongation of the tensile test specimen to rupture, in an initial 1 10. 1.13 0.10 gauge length of two inches. 2

Although the steels of the present invention TableC Tension Compression Steel 53;; Condi- No. ted tion Yield Tensile Per- Yield Buckling E strength, strength, cent E strength, stress, p. s.'i. p. s. i. e1. p. s. i. p. s. i.

35 A as 130,000 195,500 18 27 100,000 175,200 35 B 20.7 140,200 187,000 10 29 150,200 100,000 25 A 20 114,000 100,000 13 21 86,000 143,200 25 B 28 130,000 180,000 22 35 A 23 148,500 103,200 3 28 112,000 178,300 35 13 30 158,800 214,000 11 20 100,500 205,200

A-As cold rolled. B-As cold rolled plus 24 hours at 200 C. followed by air cooling.

ar suitable for lightweight high strength members in the cold rolled condition, still further improvement in certain physical properties may be effected by subjecting the cold rolled steel to a low temperature heat treatment between 100 C. and 250 C. A suitable treatment is at 200 C. for 24 hours. At the lower end of the temperature range a somewhat longer time is required to eiiect the. desired result, whereas the time may be lessened at the higher temperatures of the range. At the higher temperatures of the range, some benefit may be derived from heating for as short a period as 30 minutes. In other instances, particularly at the lower temperatures of the range, it may be desirable to heat for as long as 100 hours. Date, illustrative of the marked improvement of the low temperature heat treatment on the stress-strain characteristics of the steels are given in Tables 13 and C.

Table B lists typical steels of the present in- I claim:

1. Steel article of manufacture in the condition produced by cold drawing, cold rolling, or similar cold forming operations, comprising manganese between 15.5% and 20%, copper 0.25% to 1.75%, remainder substantially iron.

2. Steel article of manufacture in the condition produced by cold drawing, cold rolling, or similar cold forming operations, comprising manganese between 16% and 18%, copper between 0.5% and 1.25%, remainder iron.

3. Steel article of manufacture, resistant to progressive rusting, in the condition produced by "cold drawing, cold rolling, or similar cold forming operations, comprising manganese between 15.5% and 20%, copper between 0.25% and 1.75%, chromium between 0.25% and 7%. remainder iron.

4. Steel article of manufacture, resistant to progressive rusting, in the condition produced by cold drawing, cold rolling, or similar cold forming operations, comprising manganese between 16% and 18%, copper between 0.5% and 1.25%, chromium between 1% and 4%, remainderiron.

5. A cold formed, high strength article comor a steel containing manganese between 15.5% and 20%, copper between 025% and 1.75%, remainder substantially iron, said article being in the condition resulting from heating within the e of 100 C. to 250 C. for a time between 30 minutes and 100 hours.

minutes and 100 hours.

RUSSELL FRANKS.