Steels_ Metallurgy and Applications, Third Edition

170 Steels: Metallurgy and Applications

Table 2.10

grades

Mechanical properties of Lloyd's standard strength shipbuilding

Grade Yield stress

N/mm 2

minimum

Tensile Elongation Charpy V-notch impact test

strength on 5.65~'S'o (longitudinal)

N/mm 2 % minimum Test Thickness Average

temperature mm energy

*C J minimum

A

B 235

D

E

400-490 22

(see Note 2)

0 <50 27

(see Note 3)

-20 <50 27

-40 <50 27

50 < m 70 34

70< w 100 41

Notes

1. Requirements for products over 50 mm thick in Grades A, B and D and 100 mm thick in Grade
   E are subject to agreement. See 2.1.1.


2. For full thickness tensile test specimens with a width of 25 mm and gauge length of 200 mm
   (see Fig. 2.2.4 in Chapter 2), the minimum elongation is to be:

Thickness mm > 5 > 10 > 15 > 20 > 25 > 30 > 35

<5 < 1O < 15 <20 <25 <30 <35 <50

Elongation % 14 16 17 18 19 20 21 22

3. Impact tests are generally not required for Grade B steel of 25 mm or less in thickness provided
   that satisfactory results are obtained from occasional check tests selected by the Surveyor.

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

can now be supplied in the thermo-mechanically controlled processed condition,
provided the specified mechanical properties can be achieved.

Higher-strength steels

By the mid-196Os, the higher-strength steels, based on micro-alloy additions,
had become established and each of the classification societies introduced speci-
fications with yield stress values in the range 300-400 N/mm 2. Tile mechanical
properties of high-strength steels currently specified by Lloyd's are shown in
Table 2.11. The higher strengths are achieved by grain refinement and precipita-
tion strengthening and the steels can be supplied in the as-rolled, controlled-rolled
or normalized condition. The steels are normally made to a restricted carbon
equivalent (CE) of 0.41% max., based on the formula:
Mn Cr + Mo + V Ni + Cu
CE = C + --6- + 5 + 1----ff --Wt%

Lloyd's also specifies a range of quenched and tempered grades (grades 42-69)

with minimum yield strengths in the range 420-690 N/mm 2 which are used in

offshore construction. However, quenched and tempered grades are also used