US2388128A - Alloy steel - Google Patents

Description

Patented Oct. 30,

UNITED STATE.

s PATENT orrlcla'.

ALLOY STEEL Joseph C. Eckel, Ingram, Pa.

. No Drawing. ApplicatlonFebrnary 11, 1944.

' Serial No. 521,996

' 2 Claims. 01. 148-31) A continuous search for steels with increasing mechanical properties, mostly those combining a high yield strength with a sufficient elongation,

lack of such steels in the range of presently known low-carbon medium-alloy steels, most commonly employed for structural purposes. While both high strength and high elongation are frequently and conveniently produced in the highcarbon metals of this class by specific means, no.

' method or composition of the steel known heretofore permitted to combine them in low-carbon steels of this type without resortingto a greatly increased alloy content. It can be said without the danger of contradiction that only steels of the stainless group, more specifically those possessing conducted through years definitely indicated the an austenitic structure, typified by the analysis of 18. per cent chromium and. 8'per cent nickel, permitted the combination of these desired properties following. manufacturing processes suitable for industrial production.

The present invention relates to a group of substantially corrosion and heat resistant steels belonging to the low-carbon medium-alloy type, the properties of which, after commercial treatment show a combination of heretofore unavailable unheat resistance are combined, going hand in hand usually high yield point with an elongation assur-.

ang their value as an engineering material, and more particularly to steels containing about 0.10

, per cent carbon, about 5 percent nickel, about 2 of their carbon content; The alloying elements cannot be considered here as a direct cause of the properties of steel. On this account, in order to obtain the required mechanical properties following a predetermined heat treatment, the common practice for this group of alloys is toincrease their carbon content to the range adequate for producing the desired results, either by incorporating this element into the body of steel during the process of its manufacture, or' artificially building carbon content at the surface of articles v by carburizing or similar processes.

- Being amply capable of meeting mechanical requirements presented to thi group of alloys, these steels possessyhowever, a decided negative feature associated with pronounced metallurgical changes occurring on heating high carbon steels containing a comparatively high alloy percentage in the process of their final assembly into uning involved in the pelat1lres much higher than their upper critical ished products. These particularly pronounced in welding them. Heat latter brings the alloys to tempoint, and, unless proper precautions are exerted in order to prevent rapid cooling caused by the surrounding cold metal, there is always a possibility that the metal present in austenitic state might be transformed here into martensite or its a decomposition products associated with low duetility, and excessive hardness. A steel capable of meeting the severe erationshould have, therefore, a composition, in which carbon, usually considered as the most. prominent component from the standpoint of welding characteristics, is reduced to a minimum consistent with an adequate meclfanical performance of the alloy. The reduction of carbon content to the lowest possible percentage is,

therefore, one of the objects of my invention.

The steels of my invention are addressed particularly to applications in which a high mechanical strength, an adequate ductility, ood forming. characteristics, freedom from welding trouble, and-a reasonably good corrosion and with reasonably simple processes of steel making, comparatively low costs, and freedom from complicated heat treating methods to be applied to the finished products.

Aviation and automotive industries and building of mobile equipment appear to be the natural field for steels having these qualifications, particularly'when applied to parts of aircraft or automobiles, in which large surfaces possessing an elevated strength and resistance to atmospheric conditions must be produced. The steel of my invention are primarily suitable for the production of sheets; strip, and similar flat objects eventually fabricated either by forming or :welding, or a combination of the two, into structural members of the character described;

I have found that steels containing 0.05% to v 0.15%

carbon, 0.30% to 0.65% manganese, 0.050% maximum phosphorus, 0.050% maximum sulphur, 0.50% to 2.00% silicon, 0.20% maximum copp r, 4% to 6% nickel, and 2% to 6% chromium meet the above requirements in a particularly satisfactory manner. These steels respond to the commonly used heat treatment with ream:

' ness and completeness, permitting a wide range of properties, in which adequate yield point is combined with a sufilciently high elongation, and,

which show, furthermore, a very important prop-.

erty of being hardened to a very high extent by application of cold working operations such as cold forming, retaining after the latter a sufflcient degree of ductility to permit their application for structural purposes without incurring the danger of a. sudden failure in use. This feachanges of properties are treatment ofthe welding opture makes them particularly suitable for the a low temperature drawing. In this case, more manufacture of sheets and other fiat products, vigorous quenching in water resulted after a.

in which the degree of cold drawing can be regu- 700 draw in anelongation of 8%, while a. somelated at will and extended to the limit assuring what milder quenching, from the same temperathe desired strength. 5 ture in oil, resulted in a 6.5%. elongation. This In order to illustrate the mechanical characobservation shows that the steel has tendency to teristics of the steels constituting the present inremain austem'tic after a reasonably vigorous vention and their response both to hot rolling quenching, which serves as a contributing factor and cold rolling, the following tabulation is to the pronounced increase of its stren th by cold given in the way of an example, but by no means 10 rolling. Better properties can be expected in this limiting the scope of the present invention. Speccase, therefore, when a cold reduction operation imens represented in the tabulation, given below of a suflicient intensity is used either alone or in were made from a steel containing 0.08% carcombination with an appropriate stress relieving bon, 0.48% manganese, 0.008% phosphorus, heat treatment, such as a low-temperature an- 0.02 sulphur, 1.79% silicon, 0.02% copper, 5 nealing. 4.94% nickel and 2.92% chromium, cast and The above tabulation, illustrating the mechanrolled in a manner common to steel mill pracical properties of the steel constituting the subtices: ject of the present invention, indicates that they t? 211 T '1 El Hardness 8 eng ensie ong. Gen 0 Treatment 0.2 strength, roent g RmkweuB ($0553 lbs./in.= 312" lbs/in.

nor ROLLED SHEETS 0.087"--. Hot rolled"-.. 111 100,300 103,200 0 0.035-.-. Cold reduced... 115 242,750 251,000 3 nor ROLLED, PIOKLED AND COLD REDUCED snnn'rs 0.0s5-. Box annealed at 1250" 00 110, 000 110,300 10 Water quenched 110 163, 400 208, 500 6 on quenched 105 158, 000 100, 200 0. 0 Water quenched:

Drawn at 700 F 103 117, 000 105, 300 s Drawn at 900--- 105 104, 000 100, 200 4. a Drawn at 1000.. 103 107,100 113, 200 11 Drawn at 1100.- 98 120, 300 129, 400 14 Drawn at 04 100, 300 120, s00 15 Oil quenched:

rawn' at 700 F 103 170, 200 104, 000 c a town at 900.-. 103 156,400 168,000 6 0 Drawn at 1000-- 102 134, 100 130, 800 12 Drawn at 1100-- 07 ,e00 120,000 10 Drawn at 1200-.. 95 00, 200 129, 200 16 An examination of these figures clearly shows are much higher than the corresponding propthat the steel has a. very high yield strength toerties of the class of steels well known to the trade gether with an adequate elongation, even in a under the name of low-alloy, high tensilehot-rolled state, and that mill practices (parstrength steels. This difference seems to be ticularly heating for rolling, finishing temperamore of an average character than when specific ,tures and pilin or coiling temperatures) and treatments of selected steels are compared with finishing gauge have some eiiect on the finished certain values taken from the above tabulation. hot rolled product. A combination of hot rolling A further advantage of steels proposed by me,

hardness of steel, leads to a really remarkable, killed type, containing a comparatively high perincrease of the yield point, reaching 240,000 centage of nickel, is their marked resistance to pounds per square inch, while the elongation rethe notch eflfect, particularly at low temperatures. mains as high as 3%. The usual heat treatment This property commands the greatest interest in for uniform transverse and longitudinal propapplication of the steel to the aircraft construcoperation, leads to the results expected in the geatest demand .for this property. Furthermore, steels of this type, namely, a gradual reduction their elongation and mechanical properties other of yield and tensile strengths and an increase 6 than impact strength are but little afie'cted by in elongation. Among the above treatments, pan the lowering of temperature, as can be seen from ticularly interesting is water or oil quenching the following table of properties obtained with from above the critical temperature followed by 0.035" sheets: 1

Yield strength Tensile strength Elongation (0.2% oflset) nil-I111. percent 1112".

28 roar. 32 F. 28" 70F.

Normalized from 1600F 105,000 183,600 192,200 203,500 0 0 Water quenched and 11115555 with cold reduction, somewhat increasing the which belong preferably to the fine grain fullyerties, namely, quenching followed by a drawing tion, where the conditions are inducive to the structural members,

ance of the proposed steels isof a importance to their theproposedsteels have the corrosion I as some of the best known alloyslof .the above strength and ductility, reflective resistance to when it is recalled that welding characteristics of most steels are largely a function of their carbon content, and when it is realized that the carbon content or the proposed steel is well below the content of this element of all medium alloy structural'steels having the desired strength, better welding characteristics of the steels of my invention could be predicted in advance. This contention was amply supported by a comprehensive series of actual welding tests conducted principally with the use of the spot welding practice and which conclusively ability of the selected carbon range in combination withthe properly adjusted alloy content for welding applications.

of the welds or areas No pronounced hardening adjoining them could be noted in specimens examined and the welds were perfectly sound.

In applications involving high-strength thin such as used in construction of aircraft, any reduction of their thick trees by corrosion plays potential V very great potential users; It has been found that steels-of the type proposed in the demonstrated the suita very important role in the selectionof the material suitable for the On this account, the corrosion resisthardenin capacity, so that it may be subjected to the usual operations incident to hot and cold forming and welding with out suiiicient hardening and subsequent loss of ductility to heattreatment prior to structural application. I Though the steels of my invention are not intended for use as scaling-resistant material,-their capability to wlthstandheat under oxidizing conditions is-much greater than that of common carbon steels, in many occasions approaching that of-so-called stainless steels, particularly in the lower temperature ranges. It is particularly worthy of attention to note the character of the scale formed. when a common carbon steel. is

subjected to the eirect of temperature under a parallel set of conditions, the scale produced on it is oi a loose type poorly adhering to the base and capable of being easily dislodged even by such mild agents as a stream of air. The scale formed on the steel of the present invention does not develop any loosely adhering layers of oxide. The oxide in this. case issomewhat crystalline, tightly adherent, thin, and can be removed by mechanical means only with a considerable diinculty, of-

.fering a very adequate material for heat'screens and similar applications, in which scaling resistpresent invention have a practically seven-fold resistance than of plain carbon steel to the corrosion in industrial atmosphere taking place in the course of a five year exposure'The corrosion curve, expressing this property as a loss of weight per unit of area,

is free from any unusual deviation from the shape of the curve which might be considered-as a standard, diifering' from the latter only in the coemcient involved. Being f pronouncedly superior from the corrosion res'istant standpoint to the common carbonsteel,

have better corrosion properties than many proprietary alloys of low-alloy high-strength class sold at present, partially. on the corrosion-resistance basis. Both in industrial atmosphere and in a stream or fresh water, specimens of the steels made according to my' invention about twice as high group.

a The steel of the present invention has high high resistance to impact.

corroding media, and low ance of high-cost stainless steels is superfluous,

but the capability of resisting oxidation of common steels is not high enough to meet therequirements. I

The present invention is not limited to the proportions set forth in the illustrative embodiments, but may be otherwise modified'within the scope of the following claims.

I claim: l. A severely 'cold worked to 0.65% manganese, 0.05% maximum phosphorus, 0.05% maximum sul hur, 0.50% to 2.00% silicon, 0.20% 2% to 6% chromium, the balance being substantially all iron.

2. A severely cold worked shape of analloy steel composed of 0.05% to 0.10% carbon, 0.35%

to 0.50% manganese, 0.03% maximum phosphorus, v

silicon, 0.10% maximum c'opper,4% to 0% nickel,

2% to 3% chromium, the balance being substantially all iron. g

' JOSEPH 0. mm.

shape of an alloy steel composed of 0.05% to 0.15% carbon. 0.30%

maximum cop r, 4% to ni ke 0.05% maximum sulphur, 1.75% to 2.00%