US1837189A

US1837189A - Rail heat treatment

Info

Publication number: US1837189A
Application number: US533791A
Authority: US
Inventors: Edward F Kenney
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1931-04-29
Filing date: 1931-04-29
Publication date: 1931-12-22
Anticipated expiration: 1948-12-22

Description

Patented Dec. 22, 1931 UNITED STTES PATENT OFFICE EDWABD I. IENNEY, 01' PMSYLVANA, ASSIGNOE '1'0 :mam

' STEEL COMPANY, .A. OOBPOBATION 01' PENNSYLVANIA.

nan. mur 'rammm Application filed April 29, 1931. Serial Io. 583391.

My invention relates to the heat treatment of rails and other massive bodies. This a plication is a continuation in part of app cation Serial No. 377 ,7 filed July 12, 1929.

An important object of my invention is the 5 revention of permanent strains in the metal of rail or other massive body which tend to be produced therein during cooling, particularly during such rapid cooling as occurs during quenching.

When a rail is sub'ected toa rapid cooling operation, marke temperature difl'erentials are produced between different portions of the rail metal. These diflerentials of temperature, particularly those between the interior and exterior portions of the head, produce more or less severe strains in the metal, which may result in permanent weaknesses or other defects in the rail, if the rail is allowed to cool in the usual way. It is an important purpose of my invention to prevent these strains 'from resulting in permanent defects in the metal. Accordingly, a significant feature of my invention is the elimination of these strains while the rail is still hot. This I accomplish by subjecting the rail, while in its condition of having marked temperature difl'erentials, to a rapid heating operation to quickly reduce the temperature 30 diflerentials.

To illustrate my invention a specific embodiment thereof will now be described. The drawing gives a cross section, full sized, of a rail to which this specific description applies.

35 This rail weighs about 130 lbs. per yard, is

Manga- Phoe- Carbon ne Dhoma Sulphur Silicon A rail'of the cross section shown is produced in the rail mill in the usual way. The rail is allowed to cool from the mill heat un- 0 til an 'edge of one of the flanges becomes magnetic. Obviously, at this stage, by 'far the greater mass of the rail is still above the critical range. In this state the rail is immersed in a water bath for 30 seconds and is then removed and immediately transerred u to and immersed in a bath of molten lead having a temperature of about 1000 F. It is kept in this lead bath a eriod of from 4 to 5 minutes. From the lea bath it'is immediately transfer-'red to a closed furnace which go althou h it may be kept in this furnace a na somew at greater len h of time, sa up to three hours. The ral is then wit drawn from the furnace and allowed to cool in the air.

The treatment of the rail just outlined qo comprises first, rapidly cooling the greater part of the rail metal through the critical range; second, the ra id reduction of temperature difierentials n the rail in the lead bath, which difl'erentials have been produced 15 by the rapid cooling operation; third, drawing the metal of the rail in the furnace, that is to say, producing a sorbitic or troostite-sorbitic micro-structure in the hardened metal;

and fourth, cooling the rail to atmospheric 00 temperatures.

The rapid cooling of the rail metal occurs not only while the rail is actually in the aqueous quenching bath but continues through the interval which elapses between 85 the removal from the water bath and the immersion in the lead bath; While the immersion in the lead bath "immediately follows the removal from the water bath `it will be obvious that in handling an ob ect such as a rail the time interval between the two steps must necessarily be of appreciable duration. In treating full sized rails of the section shown I have ordinarily kept this time interval at twenty seconds or less. It is well to bear in mind, however, that the rapid cooling operation continues for a short interval after the removal from the actual quenching bath.

'This step of rapidly cooling the rail producea very marked difierences of temperature in diflerent parts of the raiL The thinner as the web andflanges, will be at subtantally lower temper'atures than the head;

- the exterior portions of the rail will be at When the rail is immersed in the lead bath I a goodl proportion of the rail mass is still above e blue heat zone. Particularly is this true of the head. While the rapid cooling operation has been suflicient to lower the temperature of the entire mass of rail metal to temperatures below the critical range, the interior of the head is still above the blue heat zone. This is important as the elimination or substantial reduction of temperature differentials in the head while a considerable mass thereof is still above the blue heat zone tly diminishes the chances of permanent efects from the strains produced by temrature diflerentials. Four to five minutes n the lead bath for thisparticular section of rail, cooled as above, is suflicient to subtatially equalize the temperatures of the As above indicated, the rail is next taken from the lead bath to a furnace maintained at about 1000 F. for drawing the metal of the rail which has passed rapidly through the critical range, with the resulting transformation of the micro-structure of this metal to the sorbitic or troostite-sorbitic state. Following this the rail is allowed to cool in the air.

A modification of the process just outlined has n very successful. Following a quench in water for seconds, as in the previous example, the rail is immersed in a lead bath having a temperature of 850 to 875 F. for three minutes, and then immediately 'transferred to the drawing furnace having a temperature of 850 to 875 F. in which it is held for 1 hours. By using lower temperatures than in the previous example substantially higher mechanical properties such as tensile strength and elastic limit are secured.

In these two illustrations of the invention the temperatures employed for the lead bath and the durations of immersion therein are suflicientto efl'ect substantial equalization of the temperatures of the rail. While sub- 66 etantial equalization is desired, successful results may also be obtained where complete uniformty of temperatureis not secured.

For example, following the uench, 'the rail precia le diflerences of temperature between ortions of the rail but they will be so reuced that equalization of temperature will be quickly accomplished when the rail is placed in the drawing furnace. The imary function of the lead bath is to %uiuy reduce the temperature diflerences in t e whether such reduction of temperature differences is carried to a condition of temperature uniformity or not.

The process ust described may be modified by efiecting the drawing operation in the lead bath instead of in the furnace. Instead of keeping the rail in a lead bath just long enough to reduce temperature dfierentials, as in the process just described, the immersion in the lead bath is prolonged sufliciently to eflect the drawing operation. Instead of an immersion in the lead bath for a period of from four to five minutes, the immersion will be maintained for one hour or longer. After withdrawal from the lead bath the rail is allowed to cool in the air.

Obviously the time periods given for rapid cooling, lead bath treatment, and drawing will va somew-hat with the particular section an weights of metal treated. The figures given have been found to be effective with the particular section shown.

The best results have been obtained when the entire mass of the rail head has been rapidly cooled through the critical range but obviously m process is not limited to such treatment. or example, the rapid cooling operation may be so limited in duration that `a substantial portion of the 'interier of the rail head is not rapidly cooled through the critical range, and only a portion of the head metal therefore being hardened.

Obviously the process may be altered in various wa s. For example, instead of cooling from the mill heat until an edge of the flange becomes magnetic and then quenching, as above given, the rail may be equalized at a definite temperature above the critical range and then quenched.

Although it is advantageous to quench from the mill heat, whether or not an equalizing operation is employed prior to the quench, it may be desirable at times to reheat and treat rails which have already been cooled to atmospheric temperaturesl Obviously in such case the rail may be heated above the critical range and then treated in accordance with the methods already outlined.

In several of the claims which follow reference is made to the head only of the rail, the other parts of the rail not being mentioned. Obviousl such claims arenot in-' tendedto be limited to methods in which the head alone is treated. These specify the head because of the fact that this portion of the railis the most important as regardsmy ,treat-ment and the process is eficetive 'whether or not the other s of the rail are treated. Obviousl it s correct to refer to the 'head having' subjected to the steps of my process whether or not the remaimng of the rail .have been also subjected ereto. Instead of a lead bath for quickly reducing temperature diflerences other li uid baths ma be successfully employed. or example have found certain salt baths to be successful. As au illustration mention may be made of a salt bath made of equalbefore it is placed in t e drawing furnace and when the temperature of the salt bath is 875 F. about five to six minutes is sufficient.

As is evident from the illustrative embodiments of the invention given above the temperatures of the li uid bath may vary considerably. Prefera l the tem eratures of such bath should not e below t e blue heat zone.

What 'I desire to emphasize in this connection is that the important thing is to rapidly transfer heat to the rail to quickly reduce temperature difierences and ths may be eifected in a metal bath, 'as lead', or in some other'fluid material as for example various salt mixtures. i v

What I mean by the blue-heat zone, as this expression is used in this disclosure, is that range of temperatures, below the critical range where steels in heatin increase in tensile strength and the elastic limit, and also decrease in ductility. At temperatures, within this range, most steels when exposed to air take on a blue color, due to oxidation,

but since, with some steels, this color is not' readily apparent, I do not wish to be limited to the color as a means of determining or definng this zone. V

By the expression critical range I mean that temperature range through which the steel must be cooled to eflect a. hardening thereof.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

. 1. In'a process for the treatment of rails, the steps of rapidly cooling arail to cause a substantial portion of at least the head of the -rail to pass rapidly through the critical and then immer-sing the rail while still hot in a liquid bath maintained at a temperature not lower than the blue heat zone tials n e rail.

2. In a process for the heat treatment of f rails, the steps of immersing a rail, the major 'and then before the innermost portions of the head have reached the blue heat zone iners-'` ing the rail in a liquid bath maintained at a temperature not lower than the blue heat zorie to quickly reduce temperature differentia s.

3. In a process for the treatment of rails, the step: of rapidly cooling a rail and then, while t e innermost portions of the head of the rail are still above the blueheat zone, subjectin the rail to-'a hot liquid metal'of high speci c gravity to quickly reducethe temperature diflerentials.

4. In a process for the treatment of rails, the steps of rapidly cooling the rail, a substantial proportion of at least the head of the rail being passed rapidly through the critical range, immersing the rail while still hot in a liquid bath maintained at a temperature not lower than the blue heat zone to rapidly reduce the temperature difl'erentials in the rail and then subjecting the rails to a drawing operation in a furnace.

5. In a process for the treatment of rails, the steps of rapidly cooling a'rail whereby marked temperature diflerentials are produced and then immersing the rail while still hot in a liquid bath maintained at a temperature not lower than the blue heat zone to quickly reduce the temperature diflerentials.

6. In a process for the treatment of ferrous metal bodies, the steps of rapidly cooling the object whereby marked temperature diflerentials are produced between portions of the body and then immersing the object while sti-ll hot in a liquid bath having a temperature not lower than the blue heat zone to quickly reduce the temperature diiferentials.

7. In a process for the treatment of ferrous metal bodies, the steps of rapidly cool-a ing the bodies in an aqueous medium whereby 'a marked temperature differential is proat least a portion of the body through the to rapidl reduce the temperature difierencritical range and thereby roducing marked temperature difl'erentals %etween difierent portions of the body, and then immersing while the .body while still hot in a salt bath having a temperature notlower than the'bhe heat zone to quickly reduoe *the temperature differentials.

9. In a process for the treatment of rails. the* ste 'of rspidly cooling a rail and then, e innermost portions of the head of the rail are still above the blue hoat zone, immersing the' rail in a, molten bath of lead to quickly reduce the temperature dfierenti'als.

In testimony whereof I hereunto aflix my signature.

EDWARD F. KENNEY.