Research on Controlled Cooling Technology of High Strength Ship Plate Steel DH36

The impact toughness and mechanical properties of ship plate steel DH36 are analyzed through different cooling control processes and different cooling rates, final rolling temperatures and final cooling temperatures . In order to obtain the best cooling process: 8 mm thick steel plate, the final cooling temperature is controlled at 660 ° C ~ 680 C , 0 mm thick steel plate, the final cooling temperature is controlled at 630 r ~ 670 r o so that the low temperature impact of ship plate steel Toughness meets standards and classification society requirements.

In recent years, my country's shipbuilding industry has developed rapidly, and the demand for ship plate steel is increasing day by day. At the same time, with the development of modern industry, the requirements for ship structure materials are getting higher and higher. This kind of steel not only requires high strength, but also requires low temperature toughness. .
Therefore, the development and research of DH36 high-strength ship plate steel has a broad market prospect . Ideal organization and performance, so as to realize the high-quality production of ship plate steel.

DH36 research method and process design
Research method of ship plate steel DH36
The experimental billet DH36 strictly controls the content of P , S and other elements when smelting the billet to ensure that the chemical composition of the experimental billet strictly complies with the national standard GB/712-2000, providing a guarantee for accurate experiments. See Table 1 .

Table 1 The chemical composition list of high-strength ship plate steel DH36 used in the experiment /wt%

C

Si

mn

P

S

als

Nb

V

Ti

Cu

Cr

Ni

Mo

W 0.18

W 0.50

0.90~1.60

W 0.035

W 0.035

M 0.015

0.02~0.05

0.05~0.10

W 0.02

W 0.35

W 0.02

W 0.40

W 0.08

Cut the hot-rolled test steel plate along the rolling direction and perpendicular to the rolling direction. The steel plate sample obtained in the experiment was ground with metallographic sandpaper, and after polishing, it was etched with 2% nitric acid alcohol solution, and its morphology was observed under an optical microscope.

Table 7 Evaluation of Pipe Body Collapse Resistance

Evaluation agency	Steel pipe number	Collapse value /psi
		design value	test value
TPCO Engineering Laboratory	1 #	17000 >	20000
TPCO Engineering Laboratory	2 #	17000 >	20000
China Petroleum Pipe Research Institute	3 #	17000	21000
China Petroleum Pipe Research Institute	4 #	17000	20500

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Rolling and cooling process specification set in Table 2

Finished product thickness /mm	Baking temperature /° c	Rough rolling start temperature plant c	Finish rolling start temperature plant c	Finishing temperature mill c	Final cooling temperature /° c	Cooling rate factory C /s
38	1 170 ~ 1 210	1 070 ~ 1 200	890 ~ 900	820 ~ 840	660 ~ 680	5~8
50	1 170 ~ 1 210	1 070 ~ 1 200	870 ~ 890	820 ~ 840	660 ~ 680	5~8

Result and analysis of high strength ship plate steel DH36 :
Effect of Cooling Rate on Impact Toughness of High Strength Ship Plate Steel DH36
impact of different cooling rates on the impact toughness of the general plate steel DH36 , different cooling rates after rolling have a significant effect on improving the strength of the material. For a ship plate steel with a finished thickness of 38 mm , the impact toughness value with a cooling rate of 6.2^/s is higher than that with a cooling rate of 6.7°C/s, while for a steel plate with a finished thickness of 50 mm , the cooling rate is 7.4^/ s The impact toughness value of s is 6.0^/s higher than the cooling rate . This is due to different thicknesses, different requirements for cooling rates, different cooling rates, and different room temperature structures. Because the faster the cooling rate, the finer the ferrite grain after phase transformation, so the impact toughness of the material is improved.

Research conclusion of ship plate steel DH36 :
1. The trial production of high-strength ship plate steel DH36 steel plate is carried out on the production line . The results show that the ship plate steel trial-produced by the controlled rolling and controlled cooling process meets the requirements of D -grade ship plate steel certified by the classification society, and can achieve good low temperature Resilience lays the foundation for the next step of industrial production.
2. Through the analysis of test data, it can be obtained that the best cooling parameters that can be realized in the current production site are that the finished steel plate with a thickness of 38 mm has a cooling rate of 6.5 . %, the finished steel plate with a thickness of 50 mm , the cooling rate reaches 7.0 ^ /s o
3. From the on-site test of the rolled piece temperature data, after analysis, the final cooling temperature corresponding to different finished product specifications and thicknesses can be obtained. For steel plates with a finished product thickness of 38 mm , the final cooling temperature is controlled at 660 °C . ~680 . , the finished steel plate with a thickness of 50 mm , and the final cooling temperature is controlled at 630 °C . ~670 . .
Through the sampling analysis of finished products, the results show that under the optimal final rolling temperature and the optimal final cooling temperature, the low-temperature impact toughness of the obtained steel plate not only meets the requirements of the classification society, but also the low-temperature toughness of -40 and -60 is much higher than standard.

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