Railroad Wheel Information

8/9/2019 Railroad Wheel Information

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Graphite molds may be used as short-run permanent molds since they are

easier to machine to shape and can be used for higher-melting point alloys,

e.g., steel. The molds are softer, however, and more susceptible to erosive

damage. Steel railroad wheels may be made in these molds and can be cast

by filling the mold by low-pressure casting methods.

B. Technological Background

To make cast steel railway wheels, a manufacturer needs molten steel to pour

into wheel molds.2 Solid steel is normally converted to a liquid state in electricarc furnaces. In this industry, such furnaces usually have a capacity of2 to 2!

tons. There are different ways of making the wheel molds that will receive the

liquid steel. "leeschulte Tr. #!#-#!$.

%ne way to make a mold is to use graphite that is specially contoured with a

pattern so that it is shaped like the plate and hub of a wheel.

&fforts were made at 'ahwah in the late ($)s to use graphite molds and

pressure pouring to make cast steel railway wheels.

'-(#('-2* is the ++ general specification for railway wheels, and is

entitled heels, /arbon Steel.


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Steels used for the manufacture of railway wheels are classified as carbon steels.

/arbon steels can contain up to (.0!1 manganese, .01 silicon and .01

copper with all other elements at residual levels.

ailway wheel materials within the carbon steel3 group are generally classed as

medium carbon steel with some wheel steels classed as high carbon. Themicrostructure as manufactured is referred to as pearlitic. 4owever the

lower5medium carbon steels also contain a ferrite phase which is more ductile, and

adds a more resilient, impact resistant and more ductile element to the hard pearlitic

structure. 'ost alternative wheel microstructures have been investigated, but in

spite of this and lack of alternatives it appears that pearlitic steels offer the best

performance, are ine6pensive and are well understood.

The choice of a particular grade of steel is

dependent upon its application, design,

braking mechanism, and previous

e6posure of the grades within that

operating railway. The intendedapplications for some grades from various

international railway networks are quoted in

+ppendi6 I7.


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Effect of Elements in wheel steels:

Carbon is the most important single element in wheel steels, as e6plained later. It is

so important that in carbon steels, most other significant elements in the steel can

be measured on their metallurgical effect they have in terms of a theoretical carbonlevel termed the carbon equivalent3 8/eq9. This is calculated using the following

formula.

Increasing the carbon content raises the hardness of the wheel and makes it more

wear and /: resistant. This is well demonstrated, and moving from grade ; to / in

the ++ standard, for e6ample, can reduce /: failures by

of a wheel to /: and shelling depends largely on the wheel hardness, so that

increasing the carbon content also reduces the chances of shelling. =nfortunately,

high carbon content makes the wheel much more susceptible to the thermal effects

of braking and slip, because it is easier to produce brittle martensite in high carbonsteel, and this phase of a railway steel is more liable to thermal cracking when the

wheel is braked on the tread. The resistance of the wheel to brittle fracture is

reduced as the carbon content increases, and it is therefore undesirable to use a

high carbon wheel in a service where tread braking or slip is at its most severe. The

effect of carbon on the susceptibility of a wheel to thermal damage is comple6 and is

difficult to predict.


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>ower carbon wheel steels are prevalent in continental &urope, where the focus

has been to avoid catastrophic failure on tread braked wheels during heavy braking

such as that e6perienced in mountainous regions. It is the e6perience in &urope

that lower carbon wheel steels have a higher martensite formation temperature and

decreased brittleness. This factor assists in the reduction of martensite formation,and its effect once formed, and therefore leads to reduced thermal damage on

wheel treads. There is evidence that lower carbon steels reduce the quench

sensitivity and therefore further reduce the amount of martensite formed. This

e6perience has meant that for similar applications, the &uropeans have adopted

lower carbon grade steels 0 or #, whereas =" and other railway bodies have

kept higher grades such as *. This is represented in +ppendi6 I7.

Manganese has a similar effect to carbon in increasing the strength. 'anganese

also improves toughness, but it also makes the wheel more prone to thermal

cracking. ?iffering from carbon, however, it does not have such a detrimental

effect on the resistance to brittle fracture. 'anganese also improves the depth ofhardening, important in wheels throughout their service life, through many

reprofilings. 'anganese also increases high temperature strength.


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Silicon is normally added during steel making, acting as a deo6idant to the steel to

reduce the o6ygen level by reacting to form silicate inclusions, which are preferred

to the iron o6ide 8:e%5:e2%


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Aluminium is added to wheel steels to develop an inherently fine grained structure

and this is generally found to be advantageous. :ine grained steels have improved

strength, toughness and fatigue resistance. The typical range of aluminium is

.(*5.!1, but can be controlled to tighter limits if required. The lower limit

.(*1 is the guide taken from ;S$#, and the higher limit based upon economicalsteelmaking practice, and the need to ensure alumina inclusions are not an issue in

the end product. The aluminium content is not a requirement of any of the national

specifications, but is quoted by manufacturers and steelmakers alike to ensure fine

grained steel. :ine grained wheels to the same analysis and strength as coarse

grained wheels are much more resistant to thermal cracking and have better

mechanical properties. +luminium can also have a slight effect on the hardening ofthe wheel during heat treatment, which is not always beneficial, and as mentioned

earlier, may also give rise to undesirable alumina inclusions.

Chromium and Molybdenum are added to improve wear resistance and form very

hard wear resistant stable carbides in the steel. heels with chromium A.


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Vanadium promotes the formation of stable carbides, fine grained structure,

toughness, ductility and mechanical strength.

'ost specifications limit the residual elements 8nickel, copper, tin, chromium,molybdenum and vanadium9, but if not, these are controlled by the steelmaker to

ensure that they are not so high as to detrimentally affect the properties of the

steel. Some residual elements are added deliberately in carbon steels, as

e6plained, to confer certain improved properties on the wheel, but their use as

alloys adds to the cost of the steel, especially nickel. /opper and tin are usually

regarded as undesirable due to their influence on the manufacturing process withregards to hot cracking.

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Railroad Wheel Information