Steels_ Metallurgy and Applications, Third Edition

Low-carbon structural steels 169

basic types of steel:

9 Grade A- ordinary shipbuilding steel
9 Grade B - intermediate grade based on the ABS approach
9 Grade C - highest grade based on the ABS approach
9 Grade D - intermediate grade based on specified impact strength at 0C (Euro-
pean approach)
9 Grade E- highest grade based on specified impact strength at -10C (Euro-
pean approach)

Since that time, further rationalization has taken place and Lloyd's 19 now
specifies four grades of steel with increasing impact strength requirement at the
standard minimum yield strength of 235 N/mm 2. Details of the composition and
mechanical properties of these steels are given in Tables 2.9 and 2.10. Whereas
normalizing was mandatory at one time for the higher toughness grades, these

Table 2,9 Chemical composition and deoxidation practice for Lloyd's standard
strength shipbuilding grades

• , ..... , ................... - - , .......
  Grade A B D E

Deoxidation

Chemical composition %
Carbon

Manganese

Silicon

Sulphur

Phosphorus

Aluminium

(acid soluble)

Any method Any method Killed and Killed and

(for rimmed except fine grain fine grain

steel see rimmed steel treated with treated with

Note 1) aluminium aluminium

(see Note 2)

0.21 max.

(see Note 3)

2.5 • min.

0.50 max.

0.040 max.

0.040 max.

0,21 max. 0.21 max. 0.18 max.

0.80 rain. 0.60 min. 0.70 min.

(see Note 4)

0.35 max. 0.10-0.35 0.10-0.35

0.040 max. 0.040 max. 0.040 max.

0.040 max. 0.040 max. 0.040 max.

• 0.015 rain. 0.015 min.
  (see Note 5) (see Note 5)

Carbon + ~ of the manganese content is not to exceed 0.40%

Notes

1. For Grade A, rimmed steel may be accepted up to 12.5 mm thick inclusive, provided that it is
   stated on the test certificates or shipping statements to be rimmed steel and is not excluded by
   the purchaser's order.


2. Up to 25 mm in thickness, Grade D steel may be supplied in the semi-killed condition and without
   grain refinement, in which case the requirements for minimum silicon and aluminium contents
   do not apply.


3. The maximum carbon content for Grade A steel may be increased to 0.23% for sections.


4. For Grade B, when the silicon content is 0.10% or more (killed steel), the minimum manganese
   content may be reduced to 0.60%.


5. The total aluminium content may be determined instead of the acid soluble content. In such cases
   the total aluminium content is to be not less than, 0.020%.

After Lloyd's Register of Shipping, Rules and Regulations for the Classification of Ships (1995). 19