Steels_ Metallurgy and Applications, Third Edition

Low-carbon structural steels 171

Table 2.11

grades

Mechanical properties of Lloyd's higher strength shipbuilding

Grade YieM Tensile Elongation

Stress Strength on 3.65~/So

N/ram 2 N/ram 2 % min.

rain. (see Note 2)

Charpy V-notch impact tests

Thickness Test Average energy

mm tempera- J minimum

(see Note 1) ture

*C Longitudinai Transverse

AH 32

DH 32

EH 32

FH 32

AH 36

DH 36

EH 36

FH 36

AH 40

DH 40

EH 40

FH 40

<100 0

315 440-590 22 <100 -20 31 22

._<100 -40

_<50 -60

< 100 0 34 24

355 490-620 21 -< 100 -20 34 24

-<50 -40 34 24

> 50 _< 70 -40 41 27

> 70 < 100 -40 50 34

-<50 -60 34 24

0

390 510-650 20 <50 -20 41 27

-40

-60

Notes

1. The requirements for products thicker than those detailed in the table are subject to agreement
   (see 3.1.4).


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

Thickness mm <5 >5 > 10 > 15 >20 >25 >35 >50

< 10 < 15 <20 <25 <35 <50

Strength level

32 14 16 17 18 19 20 21

Elongation Strength level

% 36 13 15 16 17 18 19 20

Strength level

40 12 14 15 16 17 18 19

"lobe

specially

agreed

After Lloyd's Register of Shipping, Rules and Regulations for the Classification of Ships (1995). t9

for the construction of submarines. These can be considered as pressure vessels

which have to withstand high hydrostatic pressures and the steels concerned have

minimum yield strength values of 550 N/mm 2 (Navy Q 1) and 690 N/mm 2 (Navy

Q2), coupled with high levels of toughness.

Design considerations

For design purposes, naval architects regard the hull of a ship as a beam or girder

in which the deck and bottom form the flanges and the sides constitute the web.

Lloyd's and the other classification societies specify the minimum thicknesses of

plate or scantlings that shall be used in various parts of a ship which, when acting