Steels_ Metallurgy and Applications, Third Edition

Low.carbon structural steels 191

i ill

I Dlscon,nuousl

l ...... stress-strain

I _

significant loss of

strength from

plate to pipe

As-rolled

ferdto-

pearlite

O. 15-0.2% C

Controlled

rolled

poarllte

reduced steel

0.08-0.12% C

X60

Normalized

ferrlto-

peadlte

O. 15-0.2% C

X60

X65

X60 i _

[:::l

X65

X70

I I

l ii I i

........ i

Type (b):

minimum loss of

strength from

plato to plpe

...... i

Controlled I

rolled I

pearlito I

reduced steel +l

transformation

product

0.08-0.12% C I

.... ='"_ I

X70

r

..... I

.i.

Cold-worked

ferdte

steel

(peadite

reduced)

"'' ~1 ,

Continuous

stress-strain

strength from

plate to pipe

ii

1

Controlled

rolled

two-phase

steel

0.06% C

a. , ,

":]

X70-80

IMo-Nbl stool /

steel

X70

Figure 2.24 Summary of steel pipes in production for high-strength steel pipelines in
Europe, the Americas and Japan (After Sage 33)

in either case, the hot-working operations are not conducive to the generation
or preservation of the fine-grained structure, characteristic of controUed-rolled
linepipe. Pipeline fittings are therefore supplied mainly in the normalized or
quenched and tempered condition. However, by limiting the hot-working temper-
ature to about 750~ fittings can be produced from controUed-rolled plate with
little loss in properties.