US2771651A - Method of preparing non-aging steels - Google Patents

Description

2,771,651 METHOD OF PREPARING NON-AGING STEELS Eric R. Morgan, Dearbormand John C. Shync, Belleville, Mich assignors to Ford Motor Company, Dearborn, Mich a corporation of Delaware 1 No Drawing. Application October 28, 1955,

- Serial No. 543,611

3 Claims. (Cl. 212-215 This invention is specifically directed to a process for the manufacture of rimmed chemically capped steel suitable for the production of deep drawn parts. The specific virtue of this process is that it enables steels of this type to be consistently and economically produced in a nonaging condition.

A large percentage of the sheet steel produced in this country is manufactured by the classical rimming process described on page 444 of Francis and Camp entitled Making, Shaping and Treating 'of Steel. As ordinarily produced this steel is highly satisfactory for deep drawing operations provided such operations are conducted U promptly after the steel is given the final temper or skin pass. However, if this steel is permitted to age appreciably as by storage for a few days at average summer temperatures it develops a yield point and increases in hardness and loses ductility to a point-where commercially satisfactory deep drawing operationsmay not be conducted. United States Letters. Patent 2,356,450, issued August 22, 1944, to Epstein demonstrates an understanding of this problem and'suggests a solution by the addition of small quantities of vanadium. The use of vanadium has been retarded by its scarcity, cost and general critical nature. A further solution has been taught by Morgan and Shyne in copending application Serial No. 497,462, filed March 28, '1955, and assigned to the assignee of this invention.

The present invention is predicated upon the use of the combination of a boron addition and chemical capping to give a very economical and commercially dependable non-aging deep drawing steel.

In the execution of this invention a two hundred-ton "ice open hearth heat was prepared with the following analysis:

Percent Carbon 0.055 Manganese 0.27 Phosphorus 0.010 Sulphur 0.025 Nickel 0.05 Chromium 0.01 Copper 0.05 Molybdenum 0.01 Tin 0.01

This heat was teemed into commercial thirteen ton ingot molds. Into one of these ingots during teeming was added eight pounds of ferro-boron containing 17.5% boron. This addition was made as the metal was poured into the ingot mold. While boron is admittedly a deoxidizer, the amount added in this instance was insutficient to do more than to slightly inhibit the usual vigorous rimming action associated with this type of metal. This vigorous rimming action was allowed to proceed for two or three minutes, or until a satisfactory skin had been built up on the exterior of the ingot. At this time the ingot was chemically capped by the addition of aluminum as is customary in the steel industry. This aluminum addition took the form of three pounds of aluminum shot. The top of the ingot was thoroughly stirred after the addition of the aluminum. This treatment resulted in an ingot having a boron content of 0.0045 This boron containing a chemically capped ingot was then permitted to solidify and take its normal course in its conversion into sheet steel.

A similar ingot was prepared except that 16 lbs. of 136% ferro-boron was added to the mold during the teeming of the thirteen ton ingot. This ingot was permitted to rim and then was chemically capped with aluminum. The final analysis indicated a boron content of 0.0065

Chemical capping as used herein is defined in Basic Open Hearth Steel Making, Revised Edition, 1951, pages 364, 3.65 and 369.

The physical properties obtained from these ingots are summarized in the following tables:

Properties of ingot containing 0.0045 B Increase Ultimate Yield Total In Yield Tensile Olsen I Rockwell Point Elonga- Condition Strength stren th Cup 3" Elongation, Per- During (p s Test Hardness tion, Percent in 2 Aging cen inches As Annealed 43, 200 8. 0 41. 4 Prestralned 10 o In Tension and Ag 0 43, 470 0 42. 0 Temper Rolled 0.5" 399 40. 5 Temper Rolled 0.5% and Aged 40. 9

1 Aged 7 days at room temperature. Aged 10 minutes in boiling water. I Sheet thickness 0.036 inch.

Properties of mgot containing 0.0065 B Increase Ultimate Total In Yield Tensile Olsen Rockwell Yield Point Elonga- Oonclltion Strength Strength Cup "13 Elongation,

I 1 During (p. s. i.) Test Hardness tion, Percent in Aging Percent 2 Inches As Anneal 42, 660 7. 4 42. 1 Prestreined 10% lnTenslon and Aged 1 0 42, 700 0 43. 4 Temper Rolled 0.5% 398 39. o Temper Rolled 0.5% and ged P 40. 0

Shoe

tthlok'nellmln Particular attention is invited to the fact thatthe'standard boiling water aging treatment failed to appreciablyharden the metal.

The exact procedure for obtaining the requisite boron content in the steel is immaterial as long as the rimming action is not detrimentally affected. For example, a portion of the boron may be added in the ladle if more economical. The total boron content carried in the metal leaving the ladle should not substantially exceed 0.005 if proper rimming action is to be had. The remainder of the boron should be added in the ingot after the desired amount of rimming has taken place and while a substantial portion of the steel is still molten. This boron should be added prior to the addition of the aluminum so that the aluminum will be available to reduce back into the steel oxidized boron compounds in the slag floating on the molten portion of the ingot. However, if one is willing to forego this matter of economy, the boron may be added after the aluminum as long as it actually alloys with the steel. The preferred practice is to add a portion of the boron to the ingot mold as it is being teemed with molten metal, and to complete the addition of boron at the time the ingot is chemically capped. Boron should be added to give a boron content in the steel of from 0.002% to 0.02% with a value of about 0.008% preferred. The preferred range is 0.005% to 0.01% boron.

While aluminum is the preferred material for accomplishing the chemical capping, any strong deoxidizer not harmful to steel may be substituted in its stead. For example, zirconium and titanium have been so employed.

Finished sheet steel from the boron treated ingot described in detail above was stored for five weeks during the hottest part of the summer just passed immediately adjacent to finished sheet steel from the same heat which was not boron treated. The boron treated material when pressed into automotive door panels made a product completely satisfactory from every standpoint. The corresponding untreated metal was quite unusable and had to be returned for roller leveling.

We claim as our invention:

1. The process of producing a rimmed steel which is substantially non-aging under usual conditions of commercial storage comprising establishing in a mold a mass of molten steel of rimming composition and having a boron content insufficient to detrimentally affect the rimmingaction, permitting the rimming action to proceed until a skin has been formed and after said skin has been formed chemically capping the steel, said process being further characterized by the alloying of the steel with sufiicient boron to yield a final boron content of 0.002% to 0.02%.

2. The process of producing a rimmed steel which is substantially non-aging under usual conditions of commercial storage comprising establishing in a mold amass of molten steel of rimming composition and having a boron content insufficient to detrimentally affect the rim ming action, permitting the rimming action to proceed until a skin has been formed and after said skin has been formed chemically capping the steel, said process being further characterized by the alloying of the steel with sufficient boron to yield a final boron content of 0.005% to 0.01%.

3. The process of producing a rimmed steel which is substantially non-aging under usual conditions of commercial storage comprising establishing in a mold a mass of molten steel of rimming composition and having a boron content insufiic'ient to detrimentally afiect the rimming action, permitting the rimming action to proceed until a skin has been formed and after said skin has been formed chemically capping the steel, said process being further characterized by the alloying of the steel with sufficient boron to yield a final boron content of about 0.008%.

Claims (1)

1. THE PROCESS OF PRODUCING A RIMMED STEEL WHICH IS SUBSTANTIALLY NON-AGING UNDER USUAL CONDITIONS OF COMMERCIAL STORAGE COMPRISING ESTABLISHING IN A MOLD A MASS OF MOLTEN STEEL OF RIMMING COMPOSITION AND HAVING A BORON CONTENT INSUFFICIENT TO DETRIMENTALLY AFFECT THE RIMMING ACTION, PERMITTING THE RIMMING ACTION TO PROCEED UNTIL A SKIN HAS BEEN FORMED AND AFTER SAID SKIN HAS BEEN FORMED CHEMICALLY CAPPING THE STEEL, SAID PROCESS BEING FURTHER CHARACTERIZED BY THE ALLOYING OF THE STEEL WITH SUFFICIENT BORON TO YIELD A FINAL BORON CONTENT OF 0.002% TO 0.02%.