Development of 110 mm Thick High Tenacity Ship Plate FH32

Based on the premise of composition design, this paper studies the composition, normalizing process, structure and performance of >100 mm thick FH32 ship plate . The quality of the developed ship plate products fully complies with the requirements of the DNV Classification Society, and has passed the third-party witness of the DNV Classification Society, which provides ideas for the trial production and development of higher-level and larger-thickness ship plates .
Key words high toughness large thickness ship plate normalizing process mechanical properties

The maximum allowable thickness of F32 ship plate in DNV specification is 150mm , and the highest quality grade is F grade ( -60°C ). Before 2008 , the maximum thickness of Wugang's 32 kg ship plate certification production was 100 mm, and the highest quality grade was E ( -40C ) , which was still somewhat different from the maximum thickness and highest grade of 32 kg ship plate in DNV specifications. distance. In March 2009 , from the perspective of meeting the market demand for large-thickness, high-strength and toughness ship plates, realizing variety benefits, and improving the overall competitiveness of the enterprise, Wuyang Iron and Steel Co., Ltd. started with the research and development of large-thickness FH3 2 ship plates, and began to carry out large - thickness And the trial production and certification of high-quality grade ship plates. At present , the development of 110 mm thick FH 32 ship plate of Wugang has been successfully completed, and it is planned to further develop the research and development of ship plate with higher quality and greater thickness.

1 The target and idea of the trial production of high toughness ship plate FH 32
the goal and idea of trial production of high toughness ship plate FH32 are determined : (1) Large thickness (>100 mm ) ; (2) low cost ( reducing the amount of precious alloys ); ( 3 ) good matching of strength and toughness; ( 4 ) excellent weldability. In order to achieve the above goals, the design ideas must be clarified: firstly, a reasonable component design is required, and secondly, an appropriate production process must be matched with it. Composition design is the foundation, reasonable composition design and good internal quality provide guarantee for the development of technological level; production technology is the means, suitable production technology can give full play to the potential of alloying elements and meet the technical requirements of steel plates.
2- ingredient design
FH3 2 belongs to ferritic pearlitic steel, its main feature is excellent low temperature toughness and weldability , Therefore, the following two approaches are mainly considered in the composition design :

1. Low carbon and high manganese content , Control the carbon content at 0 . 10 % In the following , on the one hand, the loss of toughness due to the solid solution strengthening of carbon can be reduced, and on the other hand, the weldability of steel can be greatly improved.
2. Make full use of the effect of fine grain strengthening , It not only meets certain strength requirements, but also ensures good low-temperature impact toughness of the steel plate. To this end, it is necessary to add a small amount of Ni (W0. 30%) and microalloying element Nb (=C 0.025 %) , use Ni to narrow the pearlite lamellar spacing, reduce the ductile-brittle transition temperature to achieve the effect of toughening the matrix, and

And Nb prevents grain growth during heating and fine precipitation during rolling. Considering the above factors and controlling the content of harmful elements
Carbonitride grain refinement and precipitation strengthening to achieve fine grain strengthening. Under the premise, determine the internal control components of FH32 as shown in Table 1 .
Table 1 Internal control composition of >70 ~ 150 mm thick FH32 steel

C	Si	mn	P	S	Al	Ni	Nb	Ceq
0. 08 ~ 0 10	0 . 20 ~ 0 . 30	1 . 40 ~ 1 . 50	C0.012	C 0.005	C0 060	Appropriate amount	trace	C0 40

Ceq(% ) =C+Mn/6 + (Cr+Mo + v) /5 + (Ni+ Cu) /15

3 Rolling and heat treatment process design
3.1 Rolling process In the rolling process, reasonable control of process parameters such as heating temperature, rolling temperature and reduction system is the key, so that deformation and phase transformation are closely matched to obtain fine grain structure and good comprehensive mechanical properties . In order to make the performance of the steel plate thickness direction uniform, the reduction amount and rolling speed of each pass should be reasonably controlled during the rolling process: on the one hand, when rolling in the austenite recrystallization zone, a low-speed and high-reduction system is adopted to make the deformation in the The thickness direction fully penetrates to the central part, so that the austenite recrystallization can be fully carried out, and the grains are refined ; To ensure a certain deformation rate, the nucleation core for the transformation from austenite to ferrite is effectively increased by using the enlarged grain boundary area and the deformation zone introduced in the grain. After the steel plate is rolled , ACC water cooling is carried out to further control the phase transformation conditions, microstructure state and carbide precipitation behavior.
The main process parameters are set as follows : the highest heating temperature is 1250 °C , the soaking temperature is 1220 °C ; the air-dried steel rolling , the pass reduction rate of the first stage is > 10%, the thickness of the air-dried steel is 1.5 times the plate thickness, H Stage start rolling temperature W 920° C , finish rolling temperature > 800° C ; steel plate enters ACC rapid cooling after rolling.
3.2 A large number of heat treatment process test results show that the maximum nucleation rate of various microalloyed carbonitrides in ferrite precipitation is at 600 C , and the precipitation start and completion time under the maximum nucleation rate are 2 000 s and 20 s respectively . After the steel plate is normalized and quickly cooled to the temperature of the maximum nucleation rate of precipitation , To ensure that there is a certain amount of time to achieve the effect of precipitation strengthening , Around this temperature , it generally takes about 1 h of precipitation time to basically complete the uniform nucleation precipitation reaction . It is necessary to slowly cool the steel plate within this temperature range. Combining the above factors, according to the Acs point temperature of FH3 2 steel and the actual production capacity of the Wuyang Iron and Steel Normalizing Furnace , a suitable normalizing process was adopted in the production. Room temperature , so that the microalloy carbonitride has enough precipitation time , not only in the crystal defects such as dislocation lines , It also precipitates in large quantities on the ferrite matrix.
4 Trial production results and design ideas for 355 MPa large thickness ship plate in the next step
of the trial-produced 110 mm thick FH3 2 is mainly ferrite + pearlite . There is a certain number of segregation bands in the center , . The grain size of the whole cross-section is 8 . Except for level 0 , the rest can reach 9 . level 0 , For the 110 mm thick steel plate, the grain size can reach such a level, indicating that the process control is ideal.

Tables 2 to 4 are respectively the technical requirements of > 70 to 150 mm thick FH3 2 steel plates and the laboratory and production performance of the H0 mm thick FH3 2 steel plates that were trial-produced this time . It can be seen from the table that the strength of the steel plates is moderate, and the strength of the steel plate is moderate at -60° C Longitudinal and transverse impact energy both reach more than 200 J , good low-temperature impact toughness and small longitudinal and transverse differences , excellent lamellar tear resistance (> 35%) , and various performance indicators are relatively uniform , All meet the standard requirements and have a large margin.
Table 2 Technical requirements for >70 ~ 150 mm thick FH 32 steel plates

>

RH MPa	Rm / MPa	A / %	—60C Longitudinal A kv J
>315	440-590	>22	>46

Table 3 Laboratory performance of 110 mm thick FH 32 steel plate

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batch number	Rrn / Rm / A5 / Temperature /				direction	a kv / J	code/ %
	MPa	MPa	%	C
HA905281	365	495	29 . 0	—60	vertical	227252234
				—60	horizontal	219283 207	61
				—80	vertical	218296 290	63
				—80	horizontal	291 202297	65
HA905282	375	500	27 . 0	—60	vertical	272299244	65
				—60	horizontal	218234299	61
				—80	vertical	293 213 238	58
				—80	horizontal	299292287

   

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