Influence of Tempering Process on the Strength and Toughness of E690 Ultra-high Strength Ship Plate

The metallographic analysis, tensile test and impact test were carried out on the ultra-high strength ship plate E690 developed by Hunan Iron and Steel Co., Ltd. using TMCP process and TMCP+550°C tempering process . The results show that the yield strength of the E690 steel plate produced by this process reaches 700 MPa, and the impact energy at -40C reaches more than 200 J , which has a good matching of strength and toughness . After tempering, the strength increased slightly, the proportion of impact crack propagation work to the total work decreased, and the fracture mode changed from ductile fracture to ductile-brittle mixed fracture mode .

With the development of China's shipbuilding technology, high-strength ship plates have been widely used , and various steel mills have started the development and certification of ultra-high-strength ship plates . Ultra-high-strength ship plates not only require high strength and high toughness , but also require good welding performance .
Therefore, in terms of composition and process route design, Hunan Iron and Steel adopts low-carbon components, adds MoNi Cu and other alloying elements and Nb V , Ti microalloying elements, reduces carbon equivalent and welding cold crack sensitivity index, and adopts TMCP+ tempering process route . Compared with quenching and tempering , the heat treatment process is simple , the process time is short , and it has advantages in cost , delivery time , and energy consumption , and is suitable for mass production in factories . In this paper, TMCP and TMCP +

E690 Test Method for Ultra-High Strength Ship Plates
High-strength E690 ship plate , using molten iron - 120 t top-bottom combined blown converter f LF furnace refining ~ VD furnace vacuum treatment * continuous casting production process to obtain good purity of molten steel .
test E690 ship plate was carried out on the 3800 mm four-high rolling mill of Hunan Iron and Steel Co., Ltd. It can realize rough rolling and large reduction , Main control parameters : heating temperature 1200C , rolling temperature 800-1100C , reddening temperature 380 ~ 550C . Roller hearth tempering furnace process parameters: tempering temperature The mechanical properties and fracture of the ultra-high strength ship plate E690 developed by the tempering process were analyzed .
Table 2 Tensile properties of E690 ship plate after tempering at 550°C

Production Process	Specification /nm	ReL(Rp0- 2) /MPa	Rm/MPa	A%	Remark
Before tempering	20	752	876	17 . 85	No Yield Platform
		756	866	18 . twenty three
Tempered at 550C	20	762	880	19 . 61	With Yield Platform
		757	871	19 . 25

1. with Mo — Ni — Cu — Nb series composition, ultra-high strength ship plate produced by TMCP +550C tempering process , Yield strength reaches 700 MPa - 40C impact energy reaches more than 200 j .
2. test steel was tempered at 550 C , the strength did not decrease but increased slightly, which was mainly attributed to the precipitation strengthening of e - Cu .
3. The toughness of the test steel decreased to a certain extent after tempering . In the impact test, the proportion of crack propagation work decreases , and the fracture mode changes from ductile fracture to ductile-brittle mixed fracture mode . It is mainly due to the damage caused by the decomposition of fine and dispersed MA components and the large amount of e - Cu precipitation on the toughness .

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