US2395688A - Alloy steel - Google Patents

Description

Patented Feb. 26, 1946 I 2,395,688

UNl'lED STATES PATENT orr ce ALLpY STEEL No Drawing. Application April 10, 1944,

Serial No. 530,396

2 Claims. (Cl. 75-126) This invention relates to improvements in low its shear strength to make the steel resistant to alloysteels. More particularly, the invention rethe growth and propagation of cracks. It is delates to steels' of the type disclosed and claimed sirable that these steels have high degree or levels in our pa nts N 2,2 4,130 issued March 1, 1941 of hardness, variable hardenability, good ductility and No. 2,250,505 issued July 29, 1941. 6 and machinability.

The subject matter of the present application As is well known, many compositions of steel includes certain subject matter appearing in our produced with laboratory facilities can be balcopending applications, Serial Nos. 460,272 and I anced chemically so asto produce physical prop- 460,273, both filed on September 30, 1942,'and the erties within a given range. Such compositions present application is therefore in the nature of 10 may or may not be capable of yielding these same a consolidated continuation in part of the two desired properties when subjected to the condicopending cases. tions prevailing in actual commercial steel manu- In the steels described in the foregoing patents, facturing. Rolling temperatures, rate of cooling zircomum isincorporated as a constituent to deafter rolling together with the size and shape of oxidize the steel and attain an inherently fine the finished material are the main variables afgrain. In the present invention, by substituting fecting this condition. vanadium for the zirconium in similar steels the In the specific case of those steels which have many advantages of steels A of the patent have become known to the trade as low-alloy high tenbeen retained ,while eliminating certain disadsile steels, in general they are required to possess vantages inherent in the use of zirconium. These tensile properties approximately as follows: disadvantages in the use of zirconium in no way affect the characteristics of such steelsbut ap- $312 5: $22" pear only during the manufacture By the pres Per cent elongationdh 2 per cent min 25 cut invention similar steels incorporating the same characteristics as those of the steels A in 25 ny mp v y sim le analyse are capable the patents can be more easily produced, the subof producing tensile prope s i the afores id stitution of vanadium for the zirconium eliminata e w en ro e t to c mpa atively thin ing many of the pouring and casting troubles enau s. by n r l ingfinishing temperatures and countered with the use of zirconium. On the by the use of copious app i n f a r to'the other hand we have found that the incorporation steel on the run out table or cooling bed after the of thevanadium in place of the zirconium does steel has passed through the last stand of rolls.

not deleteriously affect the physical characteris- When the gauge or thickness of strip or plate, tics of the specific steel involved. Thus the steel for example, increases, such p res ecome of the present invention has substantially the rapidly less efiective and tensile properties lower same physical characteristics as steel "A di than the above minima are obtained from the closed in patents, No. 2,234,130 and No. 2,250,505. Steel in its rolled condition.

The general object of the present invention is In the past few years the, requirements of low to provide a -steel which may be easily and ecoalloy high tensile steels have increased swiftly. nomically manufactured and which shall have They were originally intended for relatively simimportant characteristics heretofore obtained 40 Die fabrication methods. Today such steels must only in steels using larger quantities of alloying weld by all commercial welding processes as easily metal as mild carbon steels; they must be equal to or More specifically referring to those alloys of better than mild carbon steels in the matter of the present invention wherein the carbonismaindeep drawing objects therefrom; they must be tained on the low side. the objects of the inyencapable of responding to the ordinary methods tion include provision for steels the compositions of heat treatment and case hardening; t y must 'of which shall be variable within definite ranges possess good notched bar resistance at both norin accordance with the size and shape of the mal and sub-normal temperatures, high fatigue finished steel; the provision of an improved high' resistance, especially fatigue resistance at notches tensile steelsfor use in the as rolled" condition or or other stress-raisers which may reside within capable of being heat treated to predetermined the body of the steel itself. The steel should have and narrow ranges ofhardness distribution or all contained nitrogen fixed in inactive forms and other physical properties dependent thereon. be free from strain or quench aging. The steel Referring more specifically to steels of the presmust not be air hardening at any carbon content ent invention wherethe carbon is maintained on and should possess no precipitable elements capathe high side. other objects of the invention inble of impairing its physical properties upon clude the provision of steels resistant to high vestress relieving after welding or normalizing.

locity impact, resistance to shock and fragmenta- This imposing list of properties demanded by tion, and which shall have permanent high comodern steel users is due in part to the increashesion strength, the latterbeing' in high ratio to ingprecision of modern manufacturing. and partelements and by small changes of out below:

. Per cent Carbon .05to .25 Manganese .50to1.00 Silicon .50to .90 Chromium .25 to .75 Vanadium .01to .20 Phosphorus, maximum .03 Sulphur, maximum .03

Balance iron and incidental impurities When rolling temperatures are properly maintained on the lighter gauges and with accelerated cooling on the heavier gauges, the desired tensile properties can be achieved in the finished material. In stock of relatively small cross section, heat treatment by quenching and drawing is effective to produce a satisfactory hardenability and in such stock hardness distributions across heat treated sections can be controlled to predetermined and narrow ranges.

In the matter of carburizing it has been found that the case strength of the above steels after heat treating compare favorably with the highest types of alloy steels for carburizing known to the trade and the core hardness is satisfactory where too high a value. is not required. In certain types of armor plate this is a matter of para- I mount importance. In such applications, one face of the steel plate to be fabricated into armor plate is carburized and the plate is treated. It is required that the face not carburized be not too hard so that a bullet striking a carburized side will not effect cracking on the other side and throw oil splinters or particles.

Steels of the present invention with the carbon maintained on the high side have characteristics and properties similar to high alloy steels which include appreciable amounts of nickel, for example. With the carbon on the high side the -steels of the present invention hardenability through unexpectedly wide ranges controllable by relatively small variations in the quenching temperatures. Such steels according to the present invention will have compositions within the following approximate ranges:

Per cent Carbon .15- .70 Manganese .50-1.00 Silicon .50- .90 Chromium .25. .75 Vanadium .01- .20 Phosphorus, maximum .03

Sulphur, maximum .03

Balance iron and incidental impurities A specific example of such steels with a carbon content of .48%, manganese 30%, silicon 35%, chromium 52%, vanadium .l%, phosphorus 09%, sulphur 021%, the remainder iron, will have a hardness in excess of 50 Rockwell C alon a flat end quench bar up to 3" from the quenching end when quenched from 1500? F. Such heat treatment includes holding an inch round bar at 1500 F. for an hour prior to quenching. The cooling rate is maintained at a rate in excess oi 21 F. per second at 1250 F.

the above dehave variable fine grained and then beat nese about .85 to about 1.00%,

, be varied materially by changes as small as The higher carbon steels of the present invention may have the levels or hardness varied through large ranges by slight variations in temperature. The degree or levels of hardness may 00 in quenching temperatures with shapes having comparatively thin or narrow cross sections. The steels may thus practically be treated to attain desired hardness 'levels throughout by variations of quenching temperatures through narrow ranges.

Throughout the range of carbon content in the present steels, nickel and copper may be present as residual elements. That is they may be present in the final steel because of forming an alloying element of the steel scrap employed in the production of the steel of the present invention. Where present as residuals, nickel may be in amounts up to approximately .10% and copper in amounts up to approximately .14%. Amounts of nickel up to .6% and copper up to 3% may occur in the Steels of the present invention without materially afiectin'gthe property thereof, the nickel in the higher amounts perhaps adding some toughness, enhancing the heat treatment and adding somewhat to the corrosion resisting properties.

The steel of the present invention is inherently substantially deoxidized.

We have found that in using the steel of the present invention for heat treated plates that certain optimum percentages of the constituents exist in accordance with the thickness of the plate. The following table shows some of these preferred compositions: Plate thicknessin inches Up to )6 l 2 and up Per cent carbon 0.154150 0.15-0.50 o. 15-0.!50 Per cent manganese 50- .75 .85- .95 .90-L00 Percentsilicon .50-.90 .50-.90 .50-.90 Percent chromium .50 .75 .60- .70 .60- .70 Per cent vanadium .01- 10 .01- i0 .01- .10

From the foregoing description it will be seen that the applicants have produced a low alloy high tensile steel having its alloy elements selected, combined and balanced within narrow, but specific and critical ranges, whereby the improved steel having the characteristics and accomplishin the objects set forth is provided.

We claim:

1. A low alloy steel adapted for use as a high tensile steel and case carburizing purposes in the low carbon ranges and having improved heat treating properties in the higher carbon ranges, consisting of carbon up to about .70%, manganese about .70 to about 1.00%, silicon about .50 to about .90%, chromium about .50 to about vanadium about 0.1 to 10%, the balance being iron and incidental impurities.

2. A low alloy-steel adapted tensile steel and case ca low carbon ranges and having improved heat treating properties in the higher carbon ranges, consisting of carbon up to about 50%. mangasilicon about .50 chromium about .60 to about 315%. the balance being to about .90%, vanadium about .01 to .10-%,

- iron and incidental impurities.

LUCIANO G. SELMI. CLARENCE L. AILITIE'IN'BIJRGER.-