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| Analysis of reasons for the unqualified[z-direction] properties of Nb-bearing high strength ship plate steels |
| WANG Xiao-yong， DI Guo-biao，YANG Yong-da，WANG Yan-feng，MA Qing-shen |
| Plate Technology Department， Shougang Research Institute of Technology，Beijing 100043，China |
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Abstract The reason for the unqualified[z-direction]properties of the Nb-bearing high strength ship plate steels was analyzed. The microstructures and[z-direction]tensile fracture samples were observed by optical microscope (OM) and scanning electron microscope (SEM) and the solid dissolved temperature of NbC in the steel was calculated according to the Thermo-Calc software and the solubility expression of NbC in austenite. The results showed that gathered precipitates with Nb and trip-liked sulfide inclusions (MnS) were the main reason for the unqualified[z-direction]properties of the tested steels. While the increase of heating temperature is advantageous to dissolve the precipitates with Nb， the conventional rolling heating is hard to eliminate the adverse effects of large precipitates on the[z-direction]properties of the steel.
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Received: 11 March 2015
Published: 12 October 2015
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2015, Vol. 50 
