US3251215A

US3251215A - Process for making rails

Info

Publication number: US3251215A
Application number: US221160A
Authority: US
Inventors: Graef Rudolf
Original assignee: Huettenwerk Oberhausen AG
Current assignee: Huettenwerk Oberhausen AG
Priority date: 1961-10-21
Filing date: 1962-09-04
Publication date: 1966-05-17
Anticipated expiration: 1983-05-17
Also published as: GB935814A; LU41843A1; DE1178880B

Description

May 17, 1966 R. GRAEF 3,251,215

PROCESS FOR MAKING RAILS Filed Sept. 4, 1962 FIG2 AGENT RUDOLF GRAEF I United States Patent 9 Claims. 61. 72-364) My present invention relates to a method of making rails for railroad installations and the like.

Railroad rails, which are generally produced in many sizes according to the requirements of each country, must have a relatively high Wear resistance, tensile strength and hardness in order to withstand the rigors of such applications. It is usually desirable that such rails have, over their entire cross-section, an ultimate tensile strength of at least 90 kg./mm. and a hardness of at least 250 B.H.N. (e.g. as measured with conventional Brinell hardness-testing apparatus). Heretofore, it was necessary to increase the hardness of the head of the rail by means of localized rolling, coating or alloying of the steel with significant quantities of chromium, vanadium, manganese or the like. Such alloying, however, has generally played an insignificant role since it affects other desirable properties of the steel. Customarily, the manufacture of rails in such manner as to make use of their natural hardness, thereby avoiding special hardening treat- ;ment, was carried out by rolling of cast ingots in a single heat. Thus, the ingot was removed from the soaking pit in which it was brought to a substantially uniform rolling temperature and progressively reduced in crosssection to the size of the requisite rail.

A major disadvantage of these naturally hard rails, which were composed of a single substance (i.e. iron with only the usual auxiliary elements carbon, silicon and manganese, as opposed to alloy steels containing substantial quantities of other metals, was that they were susceptible to internal stress which led to severe dislocations in the formof nodular fracture or flaking. The formation of kidney-shaped dislocations of the type generally termed granular fracture. reduced substantially the ultimate strength of these rails. It has been found that, to a large extent, the internal dislocations previously mentioned were caused by the dissolution of substantial quantities of hydrogen in the steel. Heretofore, it was proposed that hydrogen could be removed or excluded from the steel by casting it in vacuo to form the ingots or by smelting it in an electric-arc furnace. Other techniques required prolonged cooling of the finished product. All these methods were relatively costly and of only limited effectiveness. The prolonged gradual cooling of thefinished rails was particularly disadvantageous since expansive installations were necessary.

It is an object of the present invention to provide a method of producing rolled-steel bodies having a high natural hardness, tensile strength and wear resistance while being substantially free from internal fracture and dislocations.

Another object of the invention is to provide a method of making railroad rails having improved mechanical characteristics while obviating the disadvantages of hitherto existing techniques.

These objects are achieved, according to the invention, in a process which comprises the steps of rolling a steel ingot in a plurality of heats and controlledly cooling a billet formed in a rolling step prior to the final rolling over a prolonged period toa temperature of substantially 200 C. in order to effect substantially complete evolution of the hydrogen contained therein. The resulting rails have been found to have an ultimate tensile strength 3,25 1,2 15 Patented May 17, 1966 of at least kg./mm. and are composed entirely of steel, without substantial amounts of alloying constituents, free from internal fractures or dislocations. More particularly, the cast-steel ingot is brought to rolling temperature (e.g. approximately 1000 or somewhat higher) and rolled into a billet of reduced cross-section which is cooled in the above-rnentioned manner for a period on the order of one day. The billet is thereafter again heated to the rolling temperature, which may, in this case, be less than the rollingtemperature previously indicated.

. After the post-cooling rolling step, the billet may be descaled or cleaned, again heated and, finally, rolled into the finished rail. It has been found, surprisingly, that by carrying out controlled cooling of the intermediate rolled body, i.e. the billet, the formation of internal nodular fractures can be almost entirely eliminated and that any flaking which may occur takes place in the intermediate stage. The subsequent rolling steps completely eliminate any trace of the original flaking so that the finished product is free of these imperfections. In contradistinction, known treatment techniques cool the finished product so that the imperfections mentioned remain in the finished rail. Moreover, the intermediate body has a larger cross-section than the finished product so that control of the cooling process is much easier to effect.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following detailed example thereof,

reference being made to the accompanying drawing in a which:

FIG. 1 is a diagrammatic view of a rolling mill schematically illustrating the process of this invention; and

FIGS. 2 (A), (B), (C), (D) are cross-sectional views taken along the lines IIA to IID, respectively, showing successive cross-sectional areas of the rolled bodies.

In FIG. 1, I schematically show a rolling mill for an ingot 10 composed of steel having substantially the following composition: carbon from 0.45 to 0.75% by weight of the steel, silicon from 0.07 to 0.50% by weight, manganese from 0.8 to 2.1%, phosphorus from trace amounts up to 0.05%, sulphur from trace amounts up to 0.05%, the remainder being substantially iron. The ingot, also shown in FIG. 2(A-), is passed in a first rolling heat at a temperature ranging upwardly of about 1050 C. between

rolls

11 and 12 which represents successive passes between the usual rolls of the blooming mill. In the first heat the transverse cross-section of the ingot, which may have a length of 1880 mm., awidth of 820 mm. and a depth of 622 mm, is rolled into a billet 20 whose cross-section is between one quarter and one sixth that of the cast-steel ingot. Thus the intermediate billet' may have a length of 7400 mm., a width of 250 mm. and a depth of 350 mm. as indicated in FIG. 2(B). The billet 20 is then disposed in a controlled cooling chamber 13, e.g. a heat-retaining or heated furnace wherein its temperature is reduced from about 1050 C. to 500 C. in a period of about 6 hours. Again it is pointed out that the chamber 13 is merely representative of any controlled cooling unit and may be of the soaking-pit type or of the continuous type as shown in the drawing wherein the billet 20 is continuously displaced on, say, conveying rollers 14 through the unit for the requsite rolling period.

After the initial cooling step the billet 20 is cooled at a progressively decreasing rate for a period on the orretaining chamber 13 previously described, it is also possible to employ a second chamber 17 for this purpose. This chamber is provided with a conduit 18 by means of which a reduced pressure can be sustained within the chamber in order to facilitate de-hydrogenation of the billet 20. A hydrogen-free atmosphere or one deficient in hydrogen may be introduced if desired via a further conduit 19. The billet 30, which is rolled from the cooled billet 20 after the latter has been reheated and, prior to such reheating cleaned, descaled or smoothened, .may be approximately 7500 mm. in length and have a cross-section whose width and depth range from 170 mm. to 205 mm. and from 270 mm. to 225 mm., respectively. I have found that highly effective results are obtained if the cooling process is carried out so that the temperature of the intermediate billet-20 drops from about 800 C. to 200 C. in approximately 38 hours. It is particularly important that the temperature drop between 450 C. and 200 C. be carried out over a prolonged period on the order of about 24 hours since sudden cooling, even in this temperature range, will cause flaking. This may appear to be surprising in view of the fact that the hydrogen evolution in this temperature range is relatively slow. It should be noted, however, that significant quantities of hydrogen are still released. The following table illustrates the preferred cooling rates for a billet having the approximate dimensions 250x 350x 7400 mm.

TABLE I the resulting rolled-steel body has a tensile strength upwards of 90 kg./mm. and a hardness of at least 250 on the Brinell scale. The wear resistance of the body is comparable to that of rails which have been locally hardened by specialized case-hardening and metal-working techniques. The rails are free from internal dislocations and fracture as well as from the flaking characterizing other types of rolled-steel bodies.

The present process also permits ready inspection and descaling of the intermediate billet 20 or the subsequent billet so that defects may be detected before these billets are converted into thefinished rails.

The invention as described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art. All such modifications are deemed included within the spirit and scope of the invention as claimed.

I claim:

1. A method of making a rolled-steel body comprising the steps of hot-rolling a steel ingot into an intermediate billet having a cross-sectional area between substantially one-quarter and one-sixth that of said ingot; controlledly cooling said billet to a temperature of substantially 200 C. for a period on the order of a day with relatively rapid cooling to a temperature of about 500 C. followed by relatively .slow cooling to a temperature of substantially 200 C. in at least 24 hours; reheating said billet to rolling temperature; and hot-rolling said billet to form sa d body, said ingot having substantially the following com- 30 position: carbon from about 0.45 to about 0.75% by Minimum time required to reach T weight of said steel; silicon from about 0.07 to about Cooling Stages in a 0.50% by weight of said steel; manganese from about 0.8 Time (t) in min. to about 2.1% by weight of said steel; phosphorus from From T2 t0 Total cooling 381 6? $2 trace amounts up to about 0.05% by weight of said steel; timeto reach end p u e and sulphur from trace amounts up to about 0.05% by temvpmture T1 weight of said steel, the remainder being substantially iron. 238 $8 $88: Q8 %8 2. A method according to claim 1 wherein said billet 600 to 500 0 is cooled in an atmosphere deficient in hydrogen. 500 to 400 n 160 120 40 3. A method according to claim 2 wherein said billet 400 to 300.-.. 760 600 is cooled under reduced pressure. 300 to 200 2,260 1,500 4. A method according to cla m 1 wherein said cooling of said billet is carried out at a progressively reduced rate as the temperature of said billet falls from about 500 C. to about 200 C.

5. A method according to claim 4 wherein said billet is cooled from a temperature of about 800 C. to said temperature of about 200 C. in approx mately 38 hours.

6. A method according to claim 5 wherein said billet is cooled from about 800 C. to about 600 C. at a rate of about 10 C./minute; from about 600 C. to about 500 C. at a rate of about 5 C./minute; from about 500 C. to about 400 C. at a rate of about 08 C./minute; from about 400 C. to about 300 C. at a rate of about While this table also pertains to the billet 20 whose dimensions have been given heretofore, it should be noted that similar results are obtained with other billets whose volumes differ from that of the billet referred to. The process described above has the principal advantage that 0,16 C./minute; and from about 300 C. to about 200 C. at a rate of about 0.07 C./ minute.

7. A method of making a rolled-steel body comprising the steps of hot-rolling a steel ingot having substantially the following composition: carbon from about 0.45 to about 0.75% by weight of said steel; silicon from about 0.07 to about 0.50% by weight of said steel; manganese from about 0.8 to about 2.1% by weight of said steel; phosphorus from trace amounts up to about 0.5% by weight of said steel; and sulphur from trace amounts up to about 0.05% by weight of said steel, the remainder being substantially iron, into an intermediate billet having a cross-sectional area between substantially one-quarter and one-sixth that of said ingot at a rolling temperature upwards of substantially 1050 C.; controlledly cooling said billet from said rolling temperature to a temperature of substantially 500 C. in a period of about 6 hours and thereafter cooling said billet at progressively decreasing rates to substantially 200 C. for a period on the order of a day; reheating said billet to rolling temperature; and hot-rolling said billet to form said body.

8. A method of making a rolled-steel body comprising the steps of hot-rolling a steel ingot carbon from about 0.45 to about 0.75% by weight of said steel; silicon from about 0.07 to about 0.50% by weight of said steel; manganese from about 0.8 to about 2.1% by we ght of said steel; phosphorus from trace amounts up to about 0.05 by weight of said steel; and sulphur from trace amounts up to about 0.05 by weight of said steel, the remainder being substantially iron, into an intermediate billet having a cross-sectional area between substantially one quarter and one-sixth that of said ingot; controlledly cooling said billet to a temperature of substantially 200 C. for a period on the order of a day with relatively rapid cooling,

to a temperature of about 500 C. following by a relatively slow cooling to a temperature of substantially 200 C. in at least 24 hours; reheating said billet to rolling temperature; and hot rolling said billet to a further billet whose cross-sectional area is less than that of the firstnamed billet; descaling said further billet; and hot-r0lling said further billet to form said body.

9. A method of making a rolled-steel body, comprising the steps of hot-rolling an ingot composed of steel of the following composition: carbon from about 0.45 to about 0.75% by weight of said steel, silicon from about 0.07 to about 0.50% by weight of said steel, manganese from about 0.8 to about 2.1% by weight of said steel, phosphorus from trace amounts up to about 0.05% by weight of said steel, and sulphur from trace amounts up to about 0.05 by weight of said steel, the remainder being substantially iron, into an intermediate billet having a cross-sectional area between substantially one-quarter and one-sixth that of said ingot at a roll ng temperature upwards of substantially 1050 C.; controlledly cooling said billet from said rolling temperature to a temperature of substantially 500 C. in a period of about 6 hours and thereafter cooling said billet to substantially 200 C. for a period on the order of a day; reheating said billet to rolling temperature; hot-rolling said billet to a further billet whose cross-sectional area is less than that of the first-named billet; descaling said further billet; and hot-rolling said further billet to form said body.

References Cited by the Examiner UNITED STATES PATENTS 2,067,293 1/1937 Spooner 148--12.4 2,101,047 12/1937 Brunner et a1 148-l2.4

' FOREIGN PATENTS 422,954 l/1935 Great Br tain.

OTHER REFERENCES The Making, Shaping and Treating of Steel: U.S. Steel, 1957, pp. 501, 502, 527-529 and 825.

Prevention of Flakes in Steel Forging Billets: Metal Progress, April 1955, Kingsley, 6 pages.

CHARLES W. LANHAM, Primary Examiner. WHITMORE A. WILTZ, Examiner.

L. A. LARSON, Assistant Examiner.

Claims

1. A METHOD OF MAKING A ROLLED-STEEL BODY COMPRISING THE STEPS OF HOT-ROLLING A STEEL INGOT INTO AN INTERMEDIATE BILLET HAVING A CROSS-SECTIONAL AREA BETWEEN SUBSTANTIALLY ONE-QUARTER AND ONE-SIXTH THAT OF SAID INGOT; CONTROLLEDLY COOLING SAID BILLET TO A TEMPERATURE OF SUBSTANTIALLY 200* C. FOR A PERIOD ON THE ORDER OF A DAY WITH RELATIVELY RAPID COOLING TO A TEMPERATURE OF ABOUT 500*C. FOLLOWED BY RELATIVELY SLOW COOLING TO A TEMPERATURE OF SUBSTANTIALLY 200*C. IN AT LEAST 24 HOURS; REHEATING SAID BILLET TO ROLLING TEMPERATURE; AND HOT-ROLLING SAID BILLET TO FORM SAID BODY, SAID INGOT HAVING SUBSTANTIALLY THE FOLLOWING COMPOSITION: CARBON FROM ABOUT 0.45 TO ABOUT 0.75% BY WEIGHT OF SAID STEEL; SILICON FROM ABOUT 0.07 TO ABOUT 0.50% BY WEIGHT OF SAID STEEL; MANGANESE FROM ABOUT 0.8 TO ABOUT 2.1% BY WEIGHT OF SAID STEEL; PHOSPHORUS FROM TRACE AMOUNTS UP TO ABOUT 0.05% BY WEIGHT OF SAID STEEL; AND SULPHUR FROM TRACE AMOUNTS UP TO ABOUT 0.05% BY WEIGHT OF SAID STEEL, THE REMAINDER BEING SUBSTANTIALLY IRON.