Research and development of E36-Z35 ship plate
With the development of the shipbuilding industry, my country has become one of the major shipbuilding countries, and the demand for ship plates is increasing year by year. Combined with the technological equipment advantages of its own medium and thick plate production line, according to the classification societies of nine countries, it independently developed high-strength ship plate E36-Z35 with a thickness of 50 mm and delivered in normalized state . The product quality has been approved by the United States, China, Japan, South Korea, Germany, Italy, the United Kingdom, Norway, and France are certified by the classification societies of nine countries.
Trial-manufacturing process of E36-Z35 ship plate
Trial production process route: hot metal pretreatment- 120 t converter smelting - 120 t LF refining -120 t RH refining-slab continuous casting-slab heating- 3 500 mm four-high reversing mill rolling-controlled cooling-steel plate straightening- Air cooling-flaw detection-normalizing-marking-delivery.
E36-Z35 ship plate composition design :
strength ship plate E36-Z35 requires pure steel, high strength, good toughness, excellent lamellar tear resistance and welding performance. Therefore, the idea of composition design is mainly based on the regulations of classification societies of nine countries and the normalized delivery status.
In order to ensure good low-temperature toughness and excellent welding performance, the composition design should appropriately reduce the carbon equivalent; considering the impact on strength after normalizing, the carbon equivalent should not be too low. Therefore, the design choice of E36-Z35 carbon equivalent > 0.42% 0 adding an appropriate amount of microalloying element Nb is beneficial to obtain fine ferrite grains to improve strength and toughness; appropriate addition of Ni element can ensure good low temperature toughness. In order to ensure that the steel plate has excellent lamellar tear resistance, the S content must be strictly controlled.
E36-Z35 ship plate smelting process :
E36-Z35 converter smelting adopts low-sulfur molten iron top-bottom combined blowing; adopts ferrosilicon manganese, medium carbon ferromanganese, aluminum, and ferro-niobium for deoxidation alloying; LF feeds aluminum wire to make white slag for refining, and the refining time is more than 30 minutes; RH uses this Treatment mode , pure degassing time > 5 min, ensure sufficient net argon blowing time after calcium treatment, and avoid naked leakage of molten steel surface during net blowing. Continuous casting adopts protective pouring, and the casting speed is controlled at 0.90 ~1.10m/min .
- Rolling and normalizing process
2.3.1 Heating process control
The size of the austenite grains in the slab heated will affect the size of the steel plate grains after rolling, and the austenite grains grow up with the increase of the heating temperature. In order to prevent grain coarsening caused by excessive heating temperature, the heating temperature of E36-Z35 is controlled at 1 180-1 250 and the heating time is controlled at 3-3.5 h under the premise of ensuring that the microalloying elements carbon and nitride are fully dissolved .
2.3.2 Rolling process control
E36-Z35 adopts two-stage controlled rolling , and the rolling temperature of the slab is 1050~1100t . In the complete recrystallization zone, a larger reduction is used as much as possible to refine the austenite grains, and the reduction rate of each pass is controlled at 10% to 20% . When it is rolled to 2~3 times of the thickness of the finished steel plate , it starts to wait for the temperature. According to the characteristics that Nb can increase the recrystallization temperature of austenite , the starting rolling temperature of E36-Z35 non-recrystallized zone should not be higher than 950 °C, the pass reduction rate should be more than 15%, and the final rolling temperature should not be higher than 880 °C.
- Cooling Process Control
During the controlled rolling process, the grains can be refined through repeated deformation-recrystallization, but the deformation process induces phase transformation, which increases the temperature of Ar3 , resulting in the precipitation of ferrite at a higher temperature. Slow cooling after rolling is easy to make the grains The grain grows up. After E36-Z35 rolling, the steel plate enters the ACC device for cooling, and the final cooling temperature of the steel plate is > 720°C .
- Normalizing process control
normalizing temperature of E36-Z35 is designed to be 880 ~ 910 °C, and the heating time is 1.6 ~ 1.9 min/mm to effectively eliminate structural defects , improve the quality of the core of the steel plate, fully refine the grains, and finally obtain excellent comprehensive mechanical properties.
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