Z - direction tensile performance analysis of EH40 high-strength ship plate

EH40 fracture morphology and inclusions are analyzed by using scanning electron microscopy ( SEM ) and EDS． The results show that sulfide at the plate thickness direction greatly influence lamellar tearing resistance． To meet the requirements of through thickness property ， the sulfur content should be controlled in the process of smelting．
Key words:EH40; tensile properties of through thickness property; lamellar tearing

EH40 steel plates used for some important welded components such as shipbuilding, offshore oil production platforms , boilers and pressure vessels not only require certain mechanical properties along the width and length directions , but also require good lamellar tear resistance in the thickness direction.
The lamellar tear resistance of EH40 high-strength ship plate steel plate is evaluated by the reduction of area 0z in the thickness direction tensile test . For steel plates with performance in the thickness direction , the standard GB5313-85 stipulates the requirements for the sulfur content in the steel, the grade of the steel plate in the thickness direction and the average value and individual value of the reduction of area.

W 0.010	Z15	R5	$ 10
W 0.007	Z25	$ 25	$ 15
W 0.005	Z35	$ 35	$ 25

1. Test results and analysis
the statistical analysis of the fracture morphology of many Z -direction tensile specimens, it is found that the Z -direction tensile fracture of EH40 high-strength ship plate steel of different materials has roughly three fracture morphology , as shown in Fig. 1 ( a ) , ( b ) , ( c ) .
fracture morphology and the reduction of area 0z is shown in Table 2 . When 0 ” > 50% , the sample appears necking and the fracture is cup-shaped , which is a typical ductile fracture , as shown in figure 1 ( a ) , which is obviously expected by all large-scale welded structures such as offshore drilling platforms, ships, and bridges High-quality material; when 0 z is 30% ~ 50% , although the deformation of the sample is not obvious before fracture , there is no necking process , but the step shape is no longer obvious , The oblique fracture showing a shear shape is shown in figure 1 ( b ) ; when 0 z < 30 % , the fracture of the sample is obviously stepped , and it breaks almost without any deformation , as shown in figure 1 ( c ) . The performance cannot even meet the requirements of the national standard , and the reduction of area of EH40-3 is only 11.5% .

Table 2 Z - direction tensile fracture morphology of EH40 ship plate steel
type	Fracture morphology	The corresponding 0z / %	Fracture Morphology
I	plastic fracture	>50	The sample is fully plastic fracture, with large plastic deformation and obvious necking.
no	shear fracture	30 ~ 50	The fracture is oblique shear shape, with certain plastic deformation, and the necking is not obvious before fracture.
Sichuan	step fracture	<30	There are obvious steps in the fracture, almost no plastic deformation occurs, and there is no necking phenomenon before fracture.

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