Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a rail wheel with wheel rim,
wheel disc and wheel hub.
Rail wheels are predominantly prod~ced from unalloyed
carbon steels. They are used in the naturally hard, normali~ed ~ `
heat-treated and trea~-heat-treated state. The rail wheel as
a solid wheel can consist of one and the same steel or in the
form of a composite material it may have a high-carbon material
-at the periphery (wheel rim) and a softer carbon steel in the
interior (wheel disc and wheel hub~. Such a composite rail wheel
is for example described in UAS. Patent Specification 1,149,267.
The high carbon wheel rim has a structure of`mor~ or less c
finely laminated pearlite. This structure and the chemical compo-
sition of the wheel rim impair the tenacity of the steel. To this
is added the fact that when abrasion occurs by block braking or by
slipping and sliding and martensite is formed because of the high
carbon content, high martensite hardnesses are attained which can
lead to an acute danger of cracking. In order to raise the tenacity
in the wheel rim or in the whole rail wheel alloye~ steels have
been used. With these alloyed steels a heat treated structure is `
developed in order to attain high tenacities by a heat treatment ;~
consisting of hardening and tempering. Even if a bainitic structure
is produced by carefully adjusting the analysis and taking into
~ account the given shape of the rail wheel and this is tempered in
order to improve tenacity properties the susceptibility to damage
to the outer surface by abrasion martensite is not removed.
When stress is very high, e.g. in high velocity traffic,
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considerable risks remain as the resistance to rupture is not
sufficient because of insufficient tenacity and the danger of the
formation of abrasion martensite exists.
~n object of the present invention is to ~evelop a rail
wheel which ha$ a tensile strength in the rim of at least 900 N/mm2
without necessarily involvin~ expensive heat treatment and a yield ;;
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~;nt of at least 650 N/mm2, having a high resistance to rupture,
a good abrasion resistance and in spite of this not susceptible
to the formation of abrasion martensite.
According to the present invention there is provided
a rail wheel in which at least the wheel rim consists of a
steel having the following composition:-
0.04 to 0.12 % carbon
0.20 to 0.70 % silicon
3.5 to 5.0 % managanese
0.005 to 0.025 % nitrogen
0 to 0.4 % niobium
0 to 0.4 % vanadium, but
0.002 to 0.4 % niobium + vanadium P
0 to 2.0 % copper
0 to 0.5 ~ molybdenum
0 to 0.2 % zirconium
0 to 0.01 % boron
0 to 0.3 % titanium
0 to 0.1 % metallic aluminium
remainder being iron and the normal low impurities.
It is possible, but noL preferred, to replace (substitute)
1 to 1.5% of the manganese by chromium.
~ A preferred composition contains a minimum proportion
of molybdenum of 0.05%, zirconium of 0.02~, boron of 0.002~ and
titanium of 0.01%.
Very good results are attained by a composition having
0.07 to 0.12 ~ carbon
0.20 to 0.50 % silicon
4.0 to 5O0 % manganese
0.04 to 0.12 % niobium
0.007 to 0.012 % nitrogen and
0.005 to 0.025 % metallic aluminium. ;
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,~thermore it is preferred to provide a minimum proportion of
carbon of 0.09% and/or manganese of 4.5%. A minimum proportion
of 0.3% molybdenum may be useful.
In a particularly preferred embodiment not only the - ~ -
wheel rim consists of such a steel, but the whole wheel (solid
wheel) is made of such a steel.
Surprisingly it has been shown that a rail wheel of -
a steel as defined above can have a tensile strength of up to
or over 1.000 N/mm2 with a yield point of 750 - 1.000 N/mm2 and
with a high yield point ratio. Despite this the rail wheel has
tenacity against rupture and shows no tendency towards the forma-
tion of abrasion martensite in use. -~
~n production it is expedient to ensure a low hydrogen
content in the steel, for which various treatments are possible.
The steel can he melted low in hydrogen and/or the hydrogen content
can be reduced by one of the known steel degassing treatments.
Another measure c.onsists in precipitating the heat- _
formed wheels or wheel rims for the purpose of the removal of '~
hydrogen at room temperature or elevated temperature, preferably
in the region between 300 to ~00C. Such measures for the removal
of hydrogen are known in the art.
The wheels or wheel rims are preferably heat formed in `
- a heat from the raw ingot to the finished section. Cooling of
the finished wheel or wheel rim can normally take p-lace in air.
In order to permit removal of hydrogen a delayed cooling in air
is possible. During cooling in air a structure of bainite and
ferrite results. ~
According to a preferred process the wheels or wheel x
rims are quenched in water or in another quenching medium after
heat forming. This accelerated cooling results in a pure
bainite structure which surprisingly has a better resistance to !'~'. '
rupture than the structure resulting from slower air cooling.
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A particular advantage is seen in that the whole rail
wheel can be prepared from one material, this material being
abrasion-resistant, resistant to rupture and not inclined to
form abrasion martensite. This can be explained by reference to
Tables 1 and 2.
In both Tables are given eight steels, numbers 1 and 2
showing previously known steels used for the wheel rims, numbers
3 to 8 being within the present invention. Table 1 gives the
chemical composition whereas Table 2 gives the essential
mechanical properties of the material.
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The previously known high-carbon steels 1 and 2 have
a good tensile stxength, but poor values for tenacity (toughness).
The impact value ls low so that these steels are inclined to
rupture, especially at high traffic velocities and low temperatures.
They are also inclined to form abrasion martensite.
On the other hand the rail wheel steels 3 to 8 within the
present invention have good technological properties for use as
rail wheels. The reduction of area is considerably more than 50%
and the impact value according to the DVMF test known in Germany
or according to the internationally known ISO-V test show especiallY
good values at temperatures of -30C and room temperature, respect-
ively. Moreover the fatigue strength (bending change strength) is
clearly above 400 N/mm , as steel numbers 3 and 4 show.
Column 2 of Table 1 gives the treatment after heat
forming. Cooling in air is labelled with (L) and quenching in
water with (W). It is surprising that the impact values of the
samples 5(W), 6(W), 7(W) and 8(W) quenched in water are higher than
the same samples in the air-coole~ state. Therefore, with regard to
increased resistance to rupture, quenching in water is preferred.
The properties of the rail wheel steels 3 to 8 are so good that the '
whole rail wheel may consist of a single steel composition so as to
overcome the difficulties initially mentioned.
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