Discussion on the Factors Influencing the NDT Temperature of Hull Structural Steel Plates of Grade E
The main difficulty of hull structural steel plates of Grade E series is that it is difficult to ensure the conformity of NDT temperature,which leads to the complete waste of steel produced.The chemical composition,metallographic struc-ture and inclusions of the samples are analyzed after NDT test in order to find out the factors affecting the NDT temperature,optimize the process,and get the products with qualified NDT temperature.After experimental analysis,the following measures should be taken to obtain that the NDT temperature is lower than-40 ℃:use Δ=0.5(V+Al)+Nb+Ti val-ue,(Cu+As)value to control alloy elements,the value of Δ is in the range of 0.065％～0.090％,and the value of Cu+As is in the range of＜0.060％,which is a necessary condition;The inclusions are controlled below grade 1.5,the ban-ded structure is controlled above grade 3.0,the grain size is controlled above grade 9.0,and the ferrite content is con-trolled between 60％and 80％;Normalizing process shall be adopted as far as possible in the production process.The final rolling temperature of hull structural steel plates of Grade E series shall be controlled at 790±20 ℃,and the starting roll-ing temperature of steel plate shall be ensured at 1 070～1 120 ℃,and the specific control target shall be controlled at 1080±10 ℃.
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