US3508911A - Low carbon steel with titanium aluminum and boron - Google Patents

Description

United States Patent O 3,508,911 LOW CARBON STEEL WITH TITANIUM ALUMINUM AND BORON John Y. Riedel, Bethlehem, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware No Drawing. Filed May 11, 1967, Ser. No. 637,617 Int. Cl. C22c 39/02 U.S. Cl. 75-124 7 Claims ABSTRACT OF THE DISCLOSURE A hypoeutectoid boron steel containing small amounts of aluminum, titanium and, optionally, columbium, which is readily weldable and which can be heat treated to provide a combination of high yield strength and low V-Notch Charpy impact transition temperature and in heavier sections than prior art steels.

BACKGROUND OF THE INVENTION 3,508,91 l Patented Apr. 28, 1970 ice known hardenability improving constituents from the group consisting of manganese, silicon, nickel, and molybdenum and will fall within the limits shown on Table I. The alloys of this invention do not contain significant amounts of either chromium or vanadium.

TABLE I Broad Narrow Carbon 10/. 30 12/. 21 Manganese 20/1. 45/. 75 Phosphorous. 1 00 Sulphur 05 i 05 'licon 75 Nickel 3. 00 3. 00 ChlomiunL. 1 20 1 20 Molybdenum 3. 00 3. 00 Aluminum. .02]. 20 05/. 10 Titanium .01]. 04 01/. 03 Columbium 01/. 13 02/. 0 Boron 0005/. 005 001/. 005 Vanadium 05 1 Maximum. 2 Optional.

The balance being essentially iron. All compositions are shown as percentages based on weight.

Table II shows a summary of the yield strength and V15 transverse Charpy transition temperature determinations made on specimens of various thicknesses of plate steel having compositions within the broad ranges of compositions of Table I. All of the steel plates were heat treated by water quenching from 1650 F. and tempering at 1200 P. so as to provide a microstructure which was predominately tempered martensite.

TABLE II Yield Transition Thicknes strength, temp Specimen No. (111.) 0 Mn p.s.i. F.

1 M 18 003 107, 000 2 .20 58 003 109,000 l25 .18 59 .004 117,000 4 16 82 002 112, 700 A 16 82 002 113,000 155 16 82 002 110, 400 95 16 82 002 106, 300 85 19 68 002 116, 350 -70 M 18 55 003 122, 000 -12 5 M 18 58 003 113,700 50 M 18 60 004 115, 000 110 1 10 67 003 135, 800 110 2 19 .67 003 109,000 2% 19 67 003 101,700 150 2 20 .67 006 106, 300 150 ficial elfect on the hardenability of hypoeutectoid boron steels. It is also known that when these steels have a microstructure which is predominately tempered martensite they will provide a minimum yield strength of approximately 90,000 p.s.i. in sections up to approximately 1" in thickness.

SUMMARY OF THE INVENTION It has now been discovered that the addition of small amounts of aluminum and titanium to hypoeutectoid boron steel improves the yield strength and V15 Charpy transition temperature when the microstructure is predominately tempered martensite. These aluminum and titanium additions do not affect the as-quenched hardenability as measured by an end quench test, but the improved properties of the steel of this invention are apparent in heavier sections, e.g. 1%" thick over similar steels which do not contain aluminum and titanium. It has also been discovered that the addition of a small amount of columbium to the above hypoeutectoid aluminum, titanium, boron steel will provide either an additional increase in yield strength without adversely affecting the V15 Charpy transition temperature or an equivalent yield strength and transition temperature in even greater thicknesses, e.g. 2 /2" thick.

The hypoeutectoid steel of this invention may contain as much as several percent of one or more of the well Specimens 1-7 illustrate the properties obtained with the heat treated hypoeutectoid aluminum-titanium-boron steels of this invention. Specimens 8-15 illustrate the properties obtained with the heat treated hypoeutectoid aluminum-titanium-columbium-boron steels of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT position was produced in the usual manner.

C .12 Si .002 Mn .13 Ni .02 P .012 Cr .04 S .032 M0 .56

2. The melt was blocked by adding spiegeleisen and silicomanganese to the metal in the furnace.

3. The heat was tapped from the furnace at a temperature of 2890 F. into a ladle containing sufiicient 50% ferrosilicon to recover approximately .25% silicon.

4. As the heat was being tapped into the ladle addi tions of carbon (coke), aluminum, titanium and ferroboron (13% boron) were made to the ladle in that se- The ladle was teemed into ingot molds equipped with hot tops. The ingots were stripped five hours after being poured and heated to 2440-2460 F. for rolling into slabs. The slabs were reheated to 2350-2400 F. and rolled into plates. Finishing temperatures varied between 1870 and 1480 F. Sample No. 8 on Table II shows the composition and properties of a sample heat treated plate from this heat.

In another specific example a 190 ton heat of steel was produced in the same manner as the previous example except that the base steel contained approximately 1.35% nickel and ferrocolumbium was added to the ladle after the titanium addition and before the ferroboron addition. Specimens 12-15 of Table II illustrate the composition and properties of sample heat treated plates made from this steel.

The novel steel compositions of this invention can be heat treated to a microstructure which is predominately tempered martensite in sections up to at least 2 /2" thick so as to provide a weldable steel having minimum yield strength of 100,000 p.s.i. in combination with a V15 Charpy transition temperature not higher than 50 F. in a direction transverse to the major direction of rolling.

In the specific examples the details of methods and the compositions are only intended as illustrations of this invention which is defined in the following claims.

1. A steel consisting of:

Percent Carbon .10/.30 Manganese .20 1.00 Silicon 10/ .7 Aluminum .02/ .20 Titanium .01 .04 Boron .0005 .005

the balance being essentially iron.

2. The steel of claim '1 which also contains .01/ 13% columbium.

3. A hypoeutectoid steel having a microstructure which is predominately tempered martensite and consisting of:

Percent Carbon (minimum) .10 Manganese .20/ 1.00 Silicon .75 Aluminum .02/ .20 Titanium .O1/.04 Boron .0005/.005

balance essentially iron.

4. The steel of claim 3 which also contains .01/.13% columbium.

5. A steel article having a microstructure which is predominately tempered martensite characterized by a yield strength of at least 100,000 p.s.i. in combination with a V15 transverse Charpy transition temperature not higher than 50 F., the said steel consisting of:

Percent Carbon .l2/.2l Manganese .45 .70 Phosphorus (maximum) .035 Sulphur do .040 Silicon .20/ .35 Nickel (maximum) 3.00 Chromium do .20 Molybdenum do 3.00 Aluminum .05 10 Titanium .01/ .03 Vanadium "(maximum)" .05 Boron .001/ .005

the balance being essentially iron.

6. The steel of claim 5 which also contains .02/ .05

columbium.

7. A steel article having a microstructure which is predominately tempered martensite characterized by a yield strength of at least 110,000 p.s.i. in combination with a V15 transverse Charpy transition temperature not higher than 50 F. in sections up to 2 /2" in thickness, said steel consisting of:

Percent Carbon .12/.21 Manganese .45/ .70 Silicon .20/.35 Nickel (maximum). 3.00 Chromium do .20 Molybdenum do 3.00 Aluminum .05/.10 Titanium .01/ .03

Vanadium (maximum) .05 Columbium .02/.05 Boron .001/.005

the balance being essentially iron.

References Cited UNITED STATES PATENTS 2,853,379 9/1958 Althouse 124 2,858,206 10/1958 Boyce 75126 3,198,630 8/1965 Tarwater 75--124 3,288,600 11/1966 Johnser 75126 3,418,110 12/1968 Goda 75-124 HYLAND BIZOT, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,508,911 Dated April 28, 1970 Inventor(s) John Riedel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, Table I, 1ine 10, under the column "Narrow" "phosphorous" should read .05 maximum and not ".00 maximum".

Signed and sealed this 1st day of September 1970.

(SEAL) ATTEST:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents F ORM PO-IOSO (10-69)