US2375953A - Alloy steel - Google Patents

Description

Patented May 15, 1945 ALLOY STEEL Luciano G. Selmi, Detroit, and Clarence L. Altenburger, Dearborn, Mich., assignors to National Steel Corporation, a corporation of Delaware No Drawing. Application September 30, 1942, Serial No. 460,274

4 Claims. (Cl. 75-126) This invention relates to improvements in low alloy steels. More particularly, the invention relates to steels of the type disclosed and claimed in applicants Patent No. 2,234,130 issued March 4, 1941.

In the steels described in the foregoing patent, zirconium is incorporated as a constituent to deoxidize the steel and attain an inherently fine grain. In the present invention, by substituting titanium for the zirconium in similar steels the many advantages of the steels of the patent have been retained while eliminating certain disadvantages inherent in the use of zirconium. These disadvantages in the use of zirconium in no way affect the characteristics of the patented steels but appear only during the manufacture. By the present invention a similar steel incorporating the same characteristics as those of the patented steels can be more easily produced, the substitution of titanium for the zirconium eliminating many of the pouring and casting troubles encountered With the use of zirconium. On the other hand, incorporation of the titanium in place of the zirconium does not deleteriously affeet the physical characteristics of the specific steel involved. Thus the steel of the present invention has substantially the same physical characteristics as the steels disclosed in Patent No. 2,234,130.

Objects of the invention include the provision of an improved high tensile steel; the provision of an improved high tensile steel having a maximum of 0.25% molybdenum and 0.20% titanium; and. the provision of an improved high tensile steel having a maximum of 0.25% carbon.

Other objects of the invention include a provision for a steel whose composition shall be variable within definite ranges in accordance with the size and shape of the finished steel; the provision of an improved high tensile steel capable of being heat treated to predetermined but narrow ranges of hardness distribution or other physical properties dependent thereon.

The above being among the objects of the present invention, the same consists in a certain new and useful alloy steel and particularly to one of new and novel analysis as well as to articles formed therefrom whereby to impart to the same certain desirable characteristics, to be hereinafter described and then claimed, having the above and other objects in view.

As is well known, many compositions of steel produced with laboratory facilities can be balanced chemically so as to produce physical properties within a given range. Such compositions may or may not be capable of yielding these same desired properties when subjected to the conditions prevailing in actual commercial steel manufacturing. Rolling temperatures, rate of cooling after rolling together with the size and shape to the finished material are the main variables aflecting this condition.

In the specific case of those steels which have become known to the trade as low-alloy high tensile steels, in general they are required to possess tensile properties approximately as follows:

Yield point 50,000 psi. min. Tensile strength 70,000 p.s.i. min. Per cent elongation in 2 25% min.

Many comparatively simple analyses are capable of producing tensile properties in the aforesaid range when rolled hot to comparatively thin gauges, by controlling finishing temperatures and by the use of copious application of water to the steel on the run out table or cooling bed after the steel has passed through the last stand of rolls. When the gauge or thickness of strip or plate, for example, increases, such procedures become rapidly less effective and tensile properties lower than the above minima are obtained from the steel in its rolled condition.

In the past few years the requirements of low alloy high tensile steels have increased swiftly. They were originally intended for relatively simple fabrication methods. Today such steels must weld by all commercial welding processes as easily as mild carbon steels; they must be equal to or better than mild carbon steels in the matter of deep drawing objects therefrom; they must be capable of responding to the ordinary methods of heat treatment and case hardening; they must possess good notched bar resistance at both normal and sub-normal temperatures, high fatigue resistance, especially fatigue resistance at notches or other stress-raisers which may reside within the body of the steel itself. The steel should have all contained nitrogen fixed in inactive forms and be free from strain or quench aging. The steel must not be air hardening at any carbon content and should possess no precipitable elements capable of impairing its physical properties upon stress relieving after Welding or normalizing. This imposing list of properties demanded by modern steel users is due in part to the increasing precision of modern manufacturing and partly to the increased use of technical testing of fabricated structures.

A steel, which Will hereinafter be referred to as steel A, of the following analysis has been found partly to fulfill the above:

Per cent Carbon .05-.25 Manganese .50-.75 Silicon .70-.90 Chromium .45-.75 Titanium .05-.15 Phosphorus .03 max. Sulphur .03 max.

Moreover, hardness distributions across heat treated sections cannot be controlled to predetermined but narrow ranges except on small or thin shapes.

It has been found in accordance with the present invention that a steel, hereinafter referred to as steel B, of materially better characteristics than the above mentioned steel, adapting it to the same and also to wider and different fields of use, can be obtained by producing a steel incorporating the same alloying agents as in the steel above mentioned but containing, in addition thereto, small amounts of molybdenum. In other words a steel according to the present invention will have the following composition:

Per cent Carbon .05-.25 Manganese .50-1.00 Silicon .50-.90 Chromium .25-.75 Titanium .015-.35 Molybdenum .02-.25 Phosphorus .03 max? Sulphur .03 max,

It is to be understood that although steel A does not equal the performance of steel B under the conditions set out herein, there are many conditions under which steel A meets all requirements for a highly desirable low alloy steel.

Nickel and copper may be present as residual 5 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 present in amounts up to approximately 0.10% and copper in amounts up to approximately 0.14%. Amounts of nickel up to 0.6% and copper up to 0.3% may occur in the alloy of the present invention without materially affecting the properties thereof, the nickel in the higher amounts perhaps adding some toughness, enhancing the heat treatment and reduction of area to a slight extent, and adding somewhat to the corrosion resisting properties of the alloy.

In the matter of carburizing, it has been found that the case strength after heat treating of both steel A and steel B to compare with the highest types of alloy steels for carburizing known to the trade. The core hardness is too low for 70 many purposes in steel A but steel B, due to its greater hardenability, corrects this condition.

In the specific case of armor plate applications, this is a matter of paramount importance. In

such applications, one face of the steel plate to be fabricated into armor plate is carburized. Thereafter, the plate is heat treated. It is required that the face not carburized be not too hard for in that event a bullet striking the car- 5 burized side may efiect cracking on the other side and throw splinters or particles off therefrom defeating the purpose of such armor. On the other hand, if the material of the plate in regions not carburized be too soft the case will spall off when struck by a bullet and hence render that area liable to penetration upon being struck by a second bullet thus defeating the purpose of the armor.

When utilizing steel B in heat treated plates, various optimum percentages of the constituents have been found to exist. The following table shows these preferred compositions:

'lliicknws of plate, inches Under it to l 2 and up Per cent carbon 15-. 15-. 25 15- 25 Per cent manganese. 50-. 75 .85-. 05 90-1. 00

25 Per cent silicon .50-.00 .50-.00 .50- .90 Per cent chromiuim. 50-. 75 60. 70 .60- 70 Per cent molybdenum. 10-. 2O 10-. 20 l0- 20 Per cent titanium 015-. 10 015-. 10 .015- 10 The steel of the present invention is inherently ne grained and substantially deoxidized.

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 accomplishing the objects set forth is provided.

Having thus described our invention, the nature and scope thereof are defined in the ap- 40 pended claims, it being understood that the particular relationships and ranges specified may be subject to slight or reasonable variation without departing from the spirit of our invention.

We claim:

1. A low alloy high tensile steel having deep drawing properties, high fatigue resistance and freedom from strain and quench aging, consisting of carbon .05 to 25%; manganese .50 to 1.00%;

silicon .50 to .90%; chromium .25 to 375%; titanium .015 ,to .20%; molybdenum .02 to 25%; the

balance being iron and incidental impurities.

2. A low alloy high tensile steel having deep drawing properties, high fatigue resistance and freedom from strain and quench aging, consisting of carbon .05 to .25%; manganese .50 to 1.00%; silicon .50 to .90% chromium .25 to .75%; titanium .015 to .l0%; molybdenum .02 to 25%; the balance bein iron and incidental impurities.

3. A low alloy high tensile steel having deep 60 drawing properties, high fatigue resistance and freedom from strain and quench aging, consisting of carbon .15 to 25%; manganese .50 to 1.00%;

silicon .50 to .90%; chromium .25 to .75%; titanium .015 to .l0%; molybdenum .02 to 25%; the balance being iron and incidental impurities.

4. A low alloy high tensile steel having deep drawing properties, high fatigue resistance and freedom from strain and quench aging, consisting of carbon .15 to 25%; manganese .85 to 1.00%; silicon .50 to .90%; chromium .60 to .70%; titanium .015 to .10%; molybdenum .02 to 25%; the balance being iron and incidental impurities.

LUCIANO G. SELMI.