DE1947950C - Process for hardening rails - Google Patents

Description

The invention relates to the hardening of Siahlia rails in a fluidized bed.

It is known that the hardening of steel rails in a powdery fluid whirled up by a gas Solid can be carried out. It is also known. this fluidized bed to a certain temperature to be heated in order to achieve the hardening required in each case. Serve as powder solids refractory oxides such. B. Corundum. Silica. Zircon, silica and silicoaluminate. As a gas iq Lormiges vortexing agent is always used to make the hardening process less expensive. the Media formed by the fluidization are known to have a high thermal conductivity, which is a ensures good temperature uniformity. Fs is also known that the heat transfer coefficient at the interface between the steel and the swirled powdery! Medium relative is high.

It was searched for. on all parameters of the medium jin to act. around this heat coefficient: transition number further to improve. Fs are e.g. B. so diverse powder media such as glass. Bronze and copper suggested and it has been found that the optimal values of the heat transfer coefficient have the same order of magnitude for all these media, while the aluminum or the lead had lower values. In practice only the clay is considered Hardening medium is used and, as a variant, corundum swirled around by air this hardening medium between that of the des' (ils and the air.

From LSA. patent specification 3,053,704 are vortex media from metal powder: · !, such as B. Chromium. Fisen. Nickel. Molybdenum. Tungsten and ferrosilicon are used. However, when the rails cool down due to insufficient thermal conductivity, none for one rapid production process satisfactory cooling abilities provide.

Another peculiarity of powder media consists in the fact that, when at rest and before, they follow in a non-compressed state Termination of the whirling process, insulating properties have, namely low thermal conductivity and low heat transfer coefficient at the limit. »s surface solid steel powdery medium at rest. It follows that the powdery Media by a very large difference in these two thermal properties «Lcr vortex and the position of rest are marked. The result is. that in the case of a complicated shape of the parts to be hardened or in the case of large surfaces, their contact surfaces are inclined to the horizontal, the puKcr-shaped product will rest on these pieces can settle u.nl at these points the heat ss exchange considerably reduced. This results in these powdery media are generally dangerous an uneven cooling with all its consequences.

However, it is shown in the French patent specification I 458 175 that this property in the case of payment Can be used by rails by inserting the rail horizontally and rotated around ISO will be like this. that the head is down and the Ftil. 1 forms a horizontal plane on which the powdery material at rest in a pointed cone fi < form settles. These conditions try to balance the heat dissipation from the head and foot so that daft distortions are avoided. With a swirled powdery medium made of corundum and air, however, it was determined that the desired result is exceeded, because the head: In contrast to the cooling process, it cools down faster than the foot under normal conditions It is thus the embossing after a medium with Intermediate properties with which it is achieved that equality is achieved at every point in the cooling process between the mean temperature of the foot and that of the head, so that the splint without distortion is hardened and after the treatment its straightness is still so good that it can be straightened is not required.

It was at the current state; Knowledge and in comparison to the medium corundum-air none powdery vortex hardening medium known for steel, both a greater cooling rate and less deformation of the Rails guaranteed by hardening. This task is especially difficult because of these two properties usually contradict each other, because the faster cooling increases the anisothermia de * to be hardened and, as a result, the risk of deformation increases.

Through lengthy and costly research it has been possible to solve these problems with the help of a? To solve the hardening process in the powdery fluidized bed of steel rails. The procedure is characterized by that the rails in a fluidized bed set at a temperature of 100 to 500 C. are cooled, whose powdery metal particles are whirled up with steam.

Metal powders made from chrome are primarily used as powder media. Iron. Nickel and or the alloys of these metals, such as ferrochrome. Ferrosilicon. Ferronickel. Iron-aluminum and chromium-nickel alloys in question.

The advantages of the invention are shown in the following comparative tests: The metal powder used was corundum with a grain size of about 0.1 mm on the one hand and chromium powder with a grain size of 0.08 to 0.18 mm on the other. The fluidization took place in the first case by means of air and in the second case by means of steam. The fluidized bed is set to a temperature of 175 ° C. and operated under favorable conditions .

T, cr container to hold the fluid to be whirled up The medium has a circular cylindrical shape and the following dimensions: 6 (K) mm diameter (Inner diameter), 4 (X) mm height of the wire.

The steel gaps are round bars of 60 mm Diameter and 300 mm length. They consist of culektoidcm. carbon steel C = 0.85%. Mn - 0.3 "o. Si ~ 0.3%. Two thermocouples are used in such a way that the weld is in half Diameter, measured at the end face, is; one is in the axial direction, the other near the Surface attached. The test pieces are either in a vertical or in a horizontal position hardened, (in the latter case this is on the surface attached thermocouple near the point with vertical contact surface.

JaU * steel piece is aiistcnitized at 900 ¹ . The heating time in the muffle furnace is 45 minutes and the time in which the temperature is kept constant. 30 minutes (total time 75 minutes). The test piece is then placed in a whirled powdery Mc-

dium hardened at 175 C, and the temperatures recorded as a function of time.

The cool down times are either based on the pressing time (90 (TC)) or from the point in time calculated in which the thermocouple shows 800 C. The cool down times are different for the Temperatures inside the test piece (650, 600, 500, 400 C) were determined. Those from 800C onwards Times are more accurate.

The character r, which specifies this time in minutes, is assigned a code 1 or 2, depending on whether the hardening takes place in the medium corundum-air or in the medium chromium-steam. It will be the Differences and relative success numbers calculated in percent. The results are given in Tables I, Jl. III and IV reproduced. They concern the horizontal arranged test pieces with thermocouple in the middle, the vertically arranged test pieces with thermocouple inside and the vertically arranged test pieces with thermocouple on the (Surface of the test pieces.

Table I.

up to 650 C. Corundum- W ; t> scr- t'hroin- Ί "'■ HHl '■'—'--
Ί 600 air d.unpf, 500 C. __ί_ l _: steam 32 from 900 400 C. 4.4 3 '■ /
- 28 up to 650 C. 5 3.6 1.4 26th 600 C. 6.5 4.8 17 ': 500 C. 7.4 6.1 3.H 34 »In the SOO 400 C. 3.2 2.1 4.4 30 ' 3.8 2.7 0.6 26th 5.3 3.9 1.4 16 6.2 5.2 \ .4 Table II 3.8 .4 .7 up to 650 C. graining .3 KK) '- 6 (K) C. I uil .1 500 C. /, .1 17 ': 1 on 9 (X) 400 ( 1.7 .4 21 up to 650 C. 2.8 25th 600 C. 5.1 27 500 C. 6.1 50 From SOO 400 C. 1.2 39 ¹ ; 2.3 I, i, 35 4.6 32 5.6 0.3 0.6 1.3 1.7 0.6 0.9 1.6 .S

35

Corundum-
1-iifi
I ₁ Chrome-
Knowledgeable
ilampl
I, Γ T chrome Γ 1.5 Ί-'2 im '' - ^h 39 25th 3.3 2 3.4 steam
I, 2.3 1.3 ι, 44 32 from SOU to 650 C 3.9 5.1 3.4 1.7 38 33 600 C 4.7 -i 9 6.9 4.4 1.8 39 36 500 C 6.5 4th 1.5 0.9 2.5 40 400 C Table IV 2.9 1.7 52 Corundum- 4.6 2.8 HXl '"~ ^h 39 air
/, 6.4 1 τ, '. -H Ί 40 '', 0.5 1.1 from 900 to 650 C. 1.7 600 C 2.5 500 C 0.6 400 C 1.2 \ on SOO to 650 C 1.8 600 C 3.1 500 C 400 "C

As the test pieces are heated in the muffle furnace and with a rather long heating time follows, the oxidation on the surface is not inconsiderable, so that the heat transfer coefficient and the relative differences between the individual cooling media are reduced the success remains very pronounced and proves the advantage of the medium chromium vapor.

The relative successes in percent are

100

f. - h

40 at the transition from the medium corundum air to the medium chromium water vapor in Table V.

Table V

The values of

100

are calculated from a temperature of 800 C.

Alignment of the / jlinders ι

wiiaticrcchl j perpendicular I Position of the thermocouple

inside! surface inside j < Reference to the preceding tables

Table IfI

from 900 to 650 ° C
600 C
5 (K) "C.
4 (X) C

Konind-I.MM

3.8
4.4

5.2
7.0

Chrome water dull

2.8
3

3.7
4.8

1.4

1.5

2.2

26th
32
29
31 Optimal value ..
Average value

34
26.5

50 39

Ul

44 40

52 45.4

Λ S You can see that the success is quite considerable. at For steels with C = 0.85% and Mn = 1.85%, the transition from the medium corundum-air to the medium extends Chrome water vapor off. to go from a 70% pearlitic structure to a fully hardened one martensitic structure (as desired

according to the immersion time before the final cooling down to ambient temperature).

As an example it should be mentioned that round bars with the same dimensions as above, but with 2 steel hardening of alloy steel A and B at 900 C with a total heating time of 75 minutes were austenitized. They were swirled vertically in the powdery medium of chrome-water vapor Hardened at 170 "C, immersed for 4 minutes and then cooled in calm air. After a Cut in the middle of a round bar, the hardnesses were measured along the cross-section. This will Expressed in rock wave units (J? i - cone). The results are given in Table VI.

Table VI
Rockwell hardness Rc after hardening of the steel

to

inu.icriict / unii

* Si; thK

C.
Mn
Cr
W.
Si ..

i, os

1.80

ftc hardness on the top!

area: 55 to 51

Rc-Hiinc inside. . i 57

i .05
0.35

0.35

55 to 53

55 '/,

It can be seen that the hardness fluctuations along the radius are very small and correspond to those that one normally taking into account random fluctuations in a mold steel or bar steel can reach.

The same steels A and B. which are austenitized under the same conditions and then in a medium Corundum air were immersed at 170 C, do not accept the hardening. The 7? R-hardness remains between chains 28 and 36 on the inside and 30 and 40 on the surface.

Tests have been carried out with self-hardening steel in order to be able to operate in the relevant temperature range to have no "closeouts". It was placed in test pieces of the same size with a thermocouple worked inside, and the test pieces were hardened in a vertical position. Austenitization took place in each case at 900 C, and during curing, the temperature is recorded and the Wait until a temperature of either 700 or 800 C is reached. The following are lost: hardening with air and with oil in both - all at ambient temperature - as well as hardening In a powdery medium, chromium water vapor at 140C. The results are given in Table VII :

Table VII

medium ArI Tcmpcralur transition from 9 (10 at 500 C 1 060 air ("C) 900 to 700 C Chrome- 28 'Zeil (in minutes) Water* 340 120 steam ... 100 oil 140 28 60 50

It can be seen that the cooling rate of the powdery medium that is swirled with water vapor at a temperature of 140 C, the one Oil bath at ambient temperature is very close, which is a remarkable result.

Furthermore, the invention not only enables the cooling capacity of the medium to be improved and thereby the hardness properties of the steel, but also avoidance of anisotherm and the deformations that occur during the hardening of rails, which according to French patent 1,458,157 have been treated.

When a splint cools down under the usual conditions in the open air, the foot, whose upper part

i.s area is twice as large as that of the head, considerable faster. Between the head and the foot, this anisotherm has differences in both the thermal contractions during cooling as well as expansion during transformation to Consequence. Since the various parts are rigidly connected to one another, this results in tensions that by flowing in the range of the upper temperatures give themselves more or less, which however at lower ones Temperatures at which the metal is rigid.

2s result in permanent deformation. As is well known cools the rail when it leaves the roller on a grate and takes on the deformation that takes place the shape of a saber blade. To counter the formation of the curve, the rail is during

.ίο this cooling bracketed in such a way that it is kept straight. The thermal contractions are the same in the area of high temperatures by flowing to other areas. while towards the end of the cooling process the

.15 Steel "solidifies", so that the direction of the remaining tensions through the last moments of cooling given is. Since the head is the last to cool down, it tends to contract, and since it does not can do, he becomes the seat of tension.

When after the cooler, the brackets are removed the head contracts and deforms the splint elastically until it reaches inner equilibrium of tensions. The running surface of the head becomes concave and the supporting surface of the foot becomes convex.

4.S Is the splint hardened and not in calm air When cooled down, the anisothermal energy in the material naturally grows, as does the deformations stronger In order to ensure both the hardening and the spatial anisotherm during the cooling process To eliminate it, the following experiments were made which underscored the importance of the invention underline.

30 cm long pieces of rail made of Thomasstahl de :, type SNCF Vignole (French State Railways) with a weight of 50 kg / m were selected. A thermocouple was attached to each part by hot soldering and another inside the foot. These parts were ^{austenitized at 900 °} C. at the same time and hardened in different media. With one exception, the rails were ^{hardened horizontally in a position rotated by 180 °} C. The taxiway on the lower part and the foot form a horizontal plane. The only exception was the vertical immersion of the rail. The cooling curves were recorded. These curves record the time after which the mean temperature between the two thermocouples has reached 500 ⁰ C, the 'temneritturunit> r * r>Uir> A "around".! ""

the two thermocouples and the most heated side. The results are shown on Table VIII sviedcrgegcben.

Table VIII

.agc ilcr
rail

horizontal
horizontal
horizontal
horizontal

horizontal

perpendicular

! Tem K ^c "'| Ι'·»> | * ·· < BeschalTcn- I pem-i ^m ! T »r <lt" * eren-

hcit

door

calm air | 25th
Corundum air j 25
Corundum air j 175
Chrorti water vapor
Chrome water
steam
Chrome water
steam

(C)

75
170

6.51 110

5.5 6th 175 5 7th 140 2.5 155 175

strengthened
crhii / te
Ropes · "!

4 -

Copr

FuD
foot

FuD

! FuD

head

* l / eil. according to which the average of the temperature of both thermocouples is W> C
**) Difference / between the two I hcrmoclemcnlcn near this

Time. ···) After this / cn

xo

The following conclusions can be drawn from the preceding explanations and the table:

- On average, the powdery one cools. swirled medium chromium water vapor at the same Temperature of 175 C faster than that Medium corundum air.

- On average, the medium chromium water vapor cools just as quickly at 140 C as the medium Corundum air at ambient temperature.

- The head of the rail, that of a mass of the same The size of the foot, which has an area roughly half the size, cools less rapidly than the foot when it naturally cools in the open air (the same observation applies to the rail when leaving the roller) and in the case of a vertical position in the powdery. With Water vapor at 175 "C swirled chrome medium. The difference is greatest at this latter medium, because it cools in the shortest possible time and carries that which goes back to the professionals' Asymmetry bill.

-If the rail is horizontal and around ISO C cturned is hardened in a powdery medium, is the direction of the temperature difference reverse '. This is due to the slope of the retired powder that settles on the horizontal upper surface of the foot. _

- In this position of the rail, the I env f *> temperature difference with the medium chromium-steam is far lower than with the medium corundum-air, regardless of the temperature of these media.

-In this position, the rail is the tem- (>> peraturunterschied in the medium corundum air at 175 ⁼ C lower than in the medium corundum air at ambient temperature.

In this position of the rail and when using the medium Chmm water vapor the temperature difference remains small, regardless of whether the medium is at 175 or 140 "C is heated.

So I can say that with an ISO From the turned rail in a horizontal position, learn the medium of chromium steam at 140 ° C Pcratururschiede eliminated and thereby ensures a very strong cooling. Not a known one Medium exhibits this remarkable quality.

The previous tests concern rails from the current production with C 0.45 ¹ V Mn 1.5%. so do not let the steel harden with these media. The thermal anomaly or the smoothing attributable to the pearlitic deformation can be seen from the cooling curves. It goes without saying that it disappears completely in steels with higher carbide content and higher alloys such as those in Table VI.

F. * it should also be noted that every time a Anisolhcrmic is present, a deformation of the rails and that only the ί intaiichen in the new ge swirled powdery medium chrome-steam in the horizontal position of the rails rotated by ISO a straight, deformation-free rail after it has completely cooled down to ambient temperature results if the temperature was homogeneous at the beginning of immersion of the splint

In summary it can be said that the ge swirled powdery medium chrome-water vapor possesses this twofold property, which at the same time is paradoxical and appears to be contradictory and that consists of a faster cooling of the immersed Effecting parts and avoiding deformation with properly aligned rails.

In other words, this medium has / wc F. properties. namely a much higher hardness level kcit. and it avoids deformations like them occur when hardening rails. In addition, it has sufficient hardness for the those steel alloys that cannot be hardened in a Ko round air medium, whereby Verfor There is no need for hardening.

Further attempts, which are not discussed at this point is directed, since the results correspond to those de «pu! Deforming medium chromium-water vapor cover have shown that the chromium is prepared by one of the metals mentioned at the outset can be replaced.

In the context of the invention, the water vapor by an ent from the reaction of niethane, natural gas or coke oven gas by means of excess steam standing gas must be replaced, which in addition to W ^ sserdam production-related contamination of hydrogen and carbon dioxide and possibly nitrogen and or contains traces of carbon monoxide. Whom namely, a small amount of methane in the steam ζ. Β added in the form of natural gas or coke oven gas λ in: and if according to the following formulas the conversion of the methane takes place in the hot state goes, with reaction 1 differing from ImVs to right developed.

CH ₁ - ^ - 2H ₂ O ^ = CO ₂ + 4H ₂ di

and finally these products as follows with W ^: asse

209 622/24;

standing with balance:

CO ₂ f U ₁ ■■ - ■ (O 'H ₂ O (21

If a large amount of water vapor is present, the prevailing reaction then runs to the right, so that only traces of carbon are present Gas heat exchanger provided the heat balance. The conversion can be carried out in a catalytic, whirled powdery medium made of nickel and by heating via tubes immersed in this medium, as is also known. There is no need to separate the reaction products, so that the process runs smoothly and can be carried out in very simple devices. The addition of small amounts of methane, natural gas or coke oven gas is sufficient to obtain a gas mixture rich in water vapor with little effort and which has greatly improved cooling properties. Concerning the question of the temperature of the fluidized bed, it should be noted in conclusion that all temperatures between 100 and 500 ^° C. aimed for the metallurgical treatment can be considered for the process. It can do this e.g. B. be a temperature that is only a few '^ above the temperature Mx at the beginning of the martensitic transformation of the steel in question, if a graded martensitic hardening is to be carried out with a minimum of deformation and residual stresses. A slightly lower temperature can also be used if the critical hardening speed requires it. If isothermal conversion is intended, the temperature may be about 420 ° C, e.g. B. corresponds to the maximum conversion speed. <which, however, can be changed slightly depending on the steel composition, mine temperature between 420 and 5CXVC 'can also be used if a lower hardness than in the previous case is to be achieved.

Claims (3)

Patent claims: 1. Procedure for hardening the rails rs quenching them in a metal powder existing fluidized bed, characterized in that the rails are cooled in a fluidized bed adjusted to a temperature of ICX) to 5 (X) ⁰ C, the powdery metal particles of which are whirled up with steam. 2. The method according to claim I. characterized in that the metal powder is made of chromium. Iron, nickel and / or the alloys of these metals, such as ferrochrome. Ferrosilicon, ferro- J5 nickel, iron-aluminum and chromium-nickel alloys are used. 3. The method according to claim I and 2, characterized in that one from the reaction of Methane, natural gas or coke oven gas by means of VJ schüssigem water vapor produced gas is used, which in addition to water vapor production-related impurities of hydrogen and Contains carbon dioxide and possibly nitrogen and / or traces of carbon dioxide.