US1827616A - Manufacture of railway and tramway rails - Google Patents

Description

Oct. 13, 1931.

c. vP. sANDBERG ET AL MANUFACTURE OF RAILWAY AND TRAMWAY RAILS Original Filed May 29, 1929 Fig. 1.

Patented Oct. 13, 1931 UNITED STATES PATENT OFFICE CHRISTER PETER SANDBERG, OSCAR FRIDOLF ALEXANDER SANDBTRG, AND NILS PERGY PATRICK SANDBERG, OF LONDON, ENGLAND, ASSIGNOR-S TO THE FIRM 0F MESSRS. SANDBERG, 0F LONDON, ENGLAND l MANUFACTURE OF RAILWAY AND TRAMWAY RAILS Continuation of application Serial No. 367,082, filed May 29,1929, and in Great Britain September 29, 1928.

This application filed June 10, 1931.

A rail problem which of recent years has greatly exercised the minds of railway engineers and rail manufacturers hasbeen the defect known as internal fissures which may be either transverse or longitudinal: These fissures develop under service by fatigue, and may ultimatel result in complete and, sudden fracture o the rails without warning.4 .A rail containing these fissures is sometimes described as having a shattered Zone.

We have found that one of the chief causes of these fissures or rupturing of the steel originates in a serious dierence of temperature during cooling between the outside metal and the interior metal, more particularly of the big mass in the head of the rail, while the rail is cooling through a range which occurs between 500 C. and 350 C.

We have found that if substantial differences in temperature are avoided between the various parts of the rail, particularly between the inner and outer portions of the rail head, while the rail is cooling through this range, the danger of such defects is largely obviated.

The object of the invention is to prevent or check loss of heat by radiation at a temperature whenthe whole section of the rail is still above 500 C. but after it has passed through the critical range, so that the temperature of the whole section becomes substantially uniform and that therefore as it subsequently cools through the ran e 500- 350 C., the difference of temperature etween any parts of the section shall be a minimum:

so avoiding the settin up of internal strains when the strength o different parts of the section is not uniform.

Accordingly our invention comprises the idea of so controlling the cooling of the rail between 500 C. and 350 C. that no consequential differences in temperature are present while the rail is cooling through this range.

More specifically our invention comprises the step of submitting the rail to equalizing conditions, before the maj or mass of the rail metal, or at least the head of the rail, khas dropped as low as 500 C. Preferably this Serial No. 543,478.

iietal of the head has cooled as low as 500` Our invention also includes the idea of effecting a cooling following equalization of such a character that temperature differences of a consequential degree cannot develop while the rail is cooling between 500 C. and 350 C.

Preliminary to setting forth the invention in greater detail it may be well to first indicate the changes which occur in certain mechanical properties of rail steels, as they cool, special consideration being given to those changes which take place in the range between 500 C. and 350 C.

Therefore, referring to the drawings:

Fig. l shows curves representing the tensile strength and ductility of two steels, .91% and .55% carbon respectively which were obtained by Dupuy and published in the Journal of thelron and Steel Institute 1921 No. 2. v

The tensile strength curves show that the strength of both steels on heating tends to increase up to a temperature of about 320- 350 C. and then falls very rapidly.

The ductility curves show that the elongation after a slight fall at about 250 C. rises rapidly up to 430 C. and then falls to about 550-580 C. and again rises.

The reverse series of changes occurs upon cooling from a high temperature.

Fig. 2 shows some results obtained during the course of the investigation which led to this invention, and were obtained by the slow bending of notched bars in the Humfrey notched bar test machine, the steel contain.-

ing 0.82% C. and 0.71% manganese. The curves represent the maximum bending motemperature at which tests were made. The J angle `bent through a very similar curve, but after falling rapidly from 400 C. to 500 C. rises again as the temperature increases. Letk us consider, byA way of example, the rail head of a cooling rail which has cooled to such` a stage thatthe head temperaturesa` are'within the range 500 to 350 C. Wheth"'"' er this rail has cooled from the mill heat on the hot bed in the usual way or whether the cooling has been ,accelerated through the critical range to produce a sorbitic microstructure, inA either case there will be a subf stantial difference'between the interior and exterior temperatures of the head.

From the diagrams of the drawings,.it will be apparent that the tensile strength of the cooler outer portions of the head have a greater strength than the hotter interior portions. As the rail cools the metal contracts. We believe that in such a rail the hotter interior 4contracts more rapidly than the exterior, at least under certain conditions. Now this greaterV contraction of the interior portions occurring while the metal of the interior is considerably weaker than the exterior furnishes just the condition to favor the production of stresses and strains in the Y metal which may lead to fissures and'other defects` of metal structure.

' Curves C and D of Fig. 1 clearly indicate how the elongation of steels may vary as the temperatures change. As the temperature' rises there is a falling off in the elongation to a relatively low 'value between 200 and 300 C'. As the temperature continues to rise the elongation increases in value until the 'temperature has risen to from 425 to 450 C. Further rise in temperature is accompanied by a fallin off in the elongation until atemperature o from 550 to 580 C. is reached after which further rise of temrature is accompanied by increase in the elongation..

It, will be readily apparent from `these curves that there are two ranges of temperature within which steels on heating dimmish in theirductilit first, the range 200 to 300 C., commonl known as the bluev heat or the blue britt e range; and, second, the range 430 to 580 C., which latter range may be conveniently deslgnated the seconda brittle range to distinguish from the primar or b ue brittle range. Upon cooling atee s these changes in ductility will be the reverse of those 'ust outlined. As the rail cools from 580 .the ductility will increase' until a temperature of from 450 to 430 C. is reached. Obviously the secondary brittle -range varies somewhat with different conditions such as steel composition particular conditions of the heats and thelike. Curves C and D show the variations of this secondary brittle range with varyin carbon contents, curve C being for astee having .91% carbon land curve D for a steel having .55%

bodiments thereof.

carbon. With rails which are cooled without observing the precautions of. our invention and which, therefore, have substantial differences between the inner and outer 'regions of the rail head, relatively large portions of the inner hotter metal of the rail will, at certain 'stages of the cooling, be in a brittle state and of a relatively low tensile strength while the cooler outer regions have greater tensile strength. These conditions will greatly increase the likelihood of the development of dangerous stresses and strains. The equalization of the temperature of the rail, in accordance with our invention, before any consequential portion of the head has cooled to 500 C. will be elfective to remove stresses before the Vmajor mass of the hotter interior metal of the head has dropped below this secondary brittle Zone.

In addition to the stresses caused by temperature diderences between inner and outer portions of the railstresses are also produced as a result of temperature dierences between different parts of the r'ail as it is obvious that normally the thinner portions such as the flanges and web will 'dro to relatively lower temperatures than the ead.

But we do not wish to be limited in anyway by a particular theoryas to what occurs. The essential thing is thatwe find it to bel possible to avoid serious danger of fissures and like defects by seeing to it that the rail, particularly the rail head, cools from 500 to 350 C. with but inconsequential temperature differences between the different parts of the rail, particularly the inner and outer portions.

To more fully indicate the invention, we shall now describe several illustrative em- Our invention is especially useful in the production of the so-called heat treated?? rail. Rails leave the mill with temperatures between 800 C. and l1000 C. They are allowed to cool somewhat but while still above the critical range'the rail is subjected to a cooling medium to effect an accelerated cooling of at least a portion of the rail head through the critical range. Preferably We employ as the cooling medium an elastic fluid as set forth in Patent No. 1,178,352; that is to say, air, atomized wateror the like.

`In practice we have found the following to be an effective procedure: The rail from 'the mill is allowed to cool, the edge of a flange bein tested from time to time with a magnet. ust as soon as the edge of the flange is found to be magnetic thehead of the rail is subjected to an .accelerated cooling by theapplication thereto of atomized water,

preferably atomized to such an extent as to treatment the desired sorbitic microstructure can be secured. The eXtent of sorbitization of the rail head can be easily varied by Varying the length of time of application.

This treatment produces very substantial temperature differentials between the inner and outer portions of the rail head. If the rail in this non-uniform temperature condition were now to cool through this zone, .500 C. to 350 C., there would be asubstantial chance that the stresses induced in the metal would give rise to those conditions which develop into fissures and other defective meta-l structure. f

Therefore, immediately following the accelerated cooling through the critical range, we substantially equalize the temperature of the rail and -then allow the rail to cool through at least the greater part of this range of temperature, (500-350 (l), withoutpermitting consequential differences of temperature. to occur.

It is important that the rail be submitted to equalizing conditions before the temperature of the major mass of metal in the head of the rail has dropped below 500 C. Preferably the equalizing operations should be begun before a substantial part of the rail head has dropped below 500 C. Accordingly, the treatment with the cooling medium should not be too drastic. In the particular example of accelerated cooling here given, the atomized water is a much less drastic quench than water in its ordinary state. The length of time of application is also a. factor. The more drastic the action of the cooling medium chosen, the shorter the time, both factors being chosen so that the rail may be rapidly cooled yet without lowering the temperature of a substantial amount of metal of the rail head below 500 C.. l/Ve moderate, in other words, the accelerated cooling. Of course, in `any heat treatment operation the exterior surface may be cooled to a relatively low temperature but the point which we make here is that the quench should not be sufficiently drastic nor so long continued as to lower the temperature below 500 C. to a consequential depth.

The equalization may be effected in various ways. For example, the rail, immediately following the sorbitizing treatment, may be introduced into a furnace in which a uniform temperature is maintained. This uniform temperature may be 500 C. oreven somewhat higher, but we have found that it is frequently not essential, and, in many cases, not desirable for the temperature of the furnace to be so high. `We have found that furnace temperatures of 425 to 450 C. may be successfully employed. l/V hen introducing the rails into a furnace having a temperature of let us say, A450" C., the rate of cooling of the rail will immediately be greatly reduced, and the conduction of heat from the hotter interiors will quickly bring about a condition of substantial equalization. As the temperature of no substantial part of the metal is below 500 C. upon being put in the furnace, and as the interior portions are at considerably higher temperatures substantialA or approximate equalization will be effected at rail temperatures not substantially less than 500 C.; actually, in most cases at temperatures somewhat abovel Following equalization the rail is allowed to cool. The cooling operation should be under control to prevent consequential temperature differentials'developing before the temperature has dropped to 350 C. This controlled cooling may be eEected in various ways. The rails may cool under shelters of one sort or another to protect them from draights and from too rapid radiation of heat from the rails, or unduly rapid losses of heat by convetion or conduction. These shelters maybe of more or less varied character. They may take the form of hoods which are adapted to move over the rail on the hot bed; or stationary hoods ou the hot bed beneath which the rails may be moved. They may be mere lean tos over the hot bed.

ln some circumstances special shelters may be entirely dispensed with. By stacking or bunching the rails cooling maybe sulticiently retarded to prevent damaging differentials of temperature being produced during the temperature drop to 350 C. Under certain conditions the equalized rail may cool on the hot bed without special protection or manipulation. Tf the situation is free fi am draughts and weather exposure, and weather conditions are favorable, the unprotected rail may cool down to 350 C. without consequential temperature differentials. The important thing is that the rail be freed from substantial di'crentials of temperature and that the cooling rail be not allowed to develop consequential difi'erences during the cooling to 350 C.

iVhile our invention is especially useful in connection with the heat treatment of rails because of the fact that the accelerated cooling of the rail necessarily introduces more or less marked differentials of temperature vet our invention is of definite utility in the manufacture of ordinary rails. ln cooling rails in the usual way on the hot bed we have found very decided vtemperature differences to occur between the thicker and thinner parts of the rali, and between the inner and outer portions especially of the head. in this case, as with the heat treated rail., there is the same tendency to produce defective metal structure because of the stresses which are produced as a result of substantial differentials of temperature while the rail is cooling from 500 C. to 3500 C.

The rail is allowed to cool in the normal way onthe hot bed until the metal has cooled l effected while the rail metal is not lower than 500 C., the temperature of the rail metal should not be above the critical range as retarded cooling through such range will produce undue softness of the metal.

` y Equalization and control of cooling may be accomplished in the manner already outlined with a heat treated rail.` We havev found the following to be especially effective and convenient in the handling of the rail not heat treated. The rail after having cooled through the critical range but while still at 500 C. or higher is placed under a hood of a material which is a poor' conductor of heat. This retards the cooling sufficiently so that a condition of approximate equalization is soon reached. The rails may be allowed to remain under this hood until they have cooled to 350 C. after which they are removed therefrom and allowed to cool in the ordinary way on the hot bed.

A variation of this method of treatment may beto employ a hood over the rails, which hood may be furnished With means for supplying heat in addition to that received from the rails and the rails allowed to remain within its protection until substantial equalization of temperature is effected after which the rails may be removed therefrom and allowedto cool in the regular way on the hot bed with or without a shelter protection of some sort to prevent the appearance of substantial temperature differentials before the rail has reached 350 C. Methods such as here indicated for the ordinary rail may also be applied to the heat treated rail.

Obviously when shelters or equivalent protective means are used to retard the cooling through the range 500-350 C. the rails may be rempved therefrom after they have cooled to 350 C., or the rails may be left within them until the rails have cooled to still lower temperatures, or cooledA completely.v

Where we use the expressionsv equaliza- \tion or substantial equalization of temper- `ature in the claims, we do not intend to limit the process to obtaining an absolute uniformity of temperature of the rail. We( may attain such a uniformity. We may, for exam ple, put therail'in an equalizing furnace maintainedata constant temperature, and keep the rail there until the temperature has become uniform. On the other hand, how.

ever, we may merely reduce the rate of cooltype of cooling-in which the rate of cooling is greater than would take place exceptby the use of means or media for increasing such rate. By the expression accelerated cooling we intend to cover that increased cooling rate through the critical range of sufficient to substantially modify the microstructure of the metal, and in particular that type of cooling which We employ' for the purpose of securing a micro-structure ultimately sorbitic in character.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is l. In a process for treating a rail, the steps of subjecting'at least 'a portion of the rail to an accelerated cooling through the critical range and then before any consequential portion of the metal of the rail head has cooled to 500 G. subjecting the rail to temperature equalizing conditions. L

2. In a process for treating a rail, the step of subjecting a cooling rail.to temperature equalizing conditions before any'consequential portion of the metal of the rail head has cooled to 500 C. but after the rail has cooled below the critical range.

3. In a process for treating a rail, the step of gradually cooling the iail between 500 C. and 350 C. to avoid consequential differences in temperature in the rail after the rail has lcooled through the critical range.

4. In. a process for treating a rail, the steps I -ofx subjecting atleast a portion of the rail to an accelerated cooling through the critical range and then subjecting the rail to temperature equalizing conditions before the major` mass of the head of the rail has dropped to` 5. In a process for treating a rail, the step of subjecting a cooling rail to temperature equalizing conditions after the rail has cooled through the critical range but before the major mass of the head has cooled to 500 C.

6. In a process for treating a rail, the steps of subjectingv at least a portion of the rail to an accelerated cooling through the critical range but moderated to avoid cooling the major mass of the head of the rail below 500 C. and immediately subjecting the rail to teinperature equalizing conditions.

7. In a process of cooling a rail from the mill heat, the steps of subjecting the rail to temperature equalizing conditions before any Y S1 consequential portion of the metal of'the rail head has cooled to 500o C. but after atleast a substantial part of the metal of the head has dropped below the critical range and then gradually cooling the rail under conditions to prevent any consequential temperature differenc-es therein between *500 C. and 350 C.

8. In a process for treating a rail, the steps of accelerating the cooling through the critical range and retarding the cooling through the range of temperature 500 C. to 350 C.

9. In a process for cooling a rail, the steps of cooling the rail in the normal way through the critical range and retarding the cooling through the range of temperature 500 C. to 350 C.

10. In a process for treating a rail, the steps of accelerating the cooling of at least a portion of the head metal through the critical range, and then subjecting the rail to temperature -equalizing conditions before the major mass of the head of the rail has cooled below the secondary brittle range.

Signed at London, England, this 29th day of May, 1931.

CHRISTER PETER SANDBERG. OSCAR FRIDOLF ALEXANDER SANDBERG. i

NlLS PERCY PATRICK SANDBERG.

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