Steels_ Metallurgy and Applications, Third Edition

Engineering steels 275

operation is the cold sawing of the rail ends on high-speed machines with carbide-
tipped blades. Rails are generally supplied in lengths up to 36 m.

Rail steel spec~ications

Historically, high-volume rail steels have been based on fully pearlitic microstruc-

tures which are characterized by high resistance to wear and plastic flow, both

of which are major property requirements for good rail performance. Although

the potential of martensitic structures has been evaluated, they proved to be

unsuitable, possessing inadequate toughness and ductility. Therefore rail steels

continue to be based on pearlitic microstructures which are generated through

various combinations of carbon, manganese and other elements.

Rail steel specifications can be classified into three types, based on tensile

strength:

1. Normal grades, ~700 N/mm 2 min. TS


2. Wear-resisting grades, 880 N/mm 2 min. TS


3. High-strength grades, 1080-1200 N/ram 2 TS

Normal grades

Typical examples of normal grades are BS 11" 1985 Normal and UIC 860-
O Grade 70 (Table 3.23). These are the high-tonnage grades which are used
in normal service conditions in conventional railways, including high-speed
passenger traffic (200 km/h), and medium-speed (100 km/h) relatively heavy axle
load (25 tonne) freight. The majority of London Transport underground track is
also laid in BS 11 Normal grade.

Wear-resistant grades

The hardness and wear resistance of pearlitic steels are increased by refining

the pearlite lamellae. This is achieved by increasing the c~bon and manganese

contents as illustrated in the specifications for wear-resisting grades given in

Tables 3.24 and 3.25.

Thus similar levels of tensile strength can be obtained from various

combinations of carbon and manganese, both of which depress the temperature of

transformation from austenite to pearlite and thereby refine the pearlite lamellae.

These wear-resisting grades are used for heavy axle loads, high-density traffic

routes or tightly curved track. However, the use of wear-resisting rails on

conventional railways can also show economic advantages.

Table 3.23 BS 11 Normal grade UIC 860-0 Grade 70

............ - _. .....

Grade C% Si% Mn% TS min. Elong. min.

(N/mm 2) 5.65~/So

BS 11 Normal 0.45-0.6 0.05-0.35 0.95-1.25

UIC 860-0 Grade 70 0.4-0.6 0.05-0.35 0.8-1.25

710 9

680 14