Ti/N control of precipitates and toughness in welded Mg-treated shipbuilding steel plate
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摘要: 通过400 kJ/cm焊接热模拟试验探究了Ti/N比对Mg处理船板钢-20 ℃焊接热影响区低温冲击韧性的影响。当Ti/N比从3.00（TN30）增加到5.67（TN57）时，钢中的析出粒子均为TiN粒子，纳米析出粒子的平均尺寸从150 nm增加到205 nm，且TN57钢中粒子的数量密度约为TN30钢中的2.5倍。TN30钢中尺寸约为3 μm的Mg-Ti-O-MnS复合夹杂物能够有效诱导IAF的形核，铁素体板条和位错塞积的出现有利于提高其韧性；在TN57钢中观察到形状规则、棱角分明的尺寸约为5 μm的含Ti(C, N)复合夹杂物，这种粗大的碳氮化物不利于钢材的韧性。当钢中的Ti/N比由3.00增加到5.67，钢材在-20 ℃低温冲击韧性由183 J降至49 J。Abstract: In this study, the effect of the Ti/N ratio on the impact toughness at -20 ℃ of Mg-treated shipbuilding steel plates after high heat input welding of 400 kJ/cm had been investigated. When the Ti/N ratio is increased from 3.00 (TN30) to 5.67 (TN57), the main precipitated particles are TiN particles. The average size of nano secondary phase particles increases from approximately 150 nm to 205 nm, with the particle number density in TN57 being approximately 2.5 times than that in TN30. In TN30 steel, Mg-Ti-O-MnS composite inclusions with a size about 3 μm can effectively induce IAF nucleation. The ferrite laths and dislocation pile-ups significantly enhance its toughness. TN57 steel contains Ti(C, N) composite inclusions which are regular in shape, sharply angular and approximately 5 μm in size. These coarse carbonitrides are detrimental to the toughness of the steel. As the Ti/N ratio is increased from 3.00 to 5.67, the low-temperature impact toughness at -20 ℃ decreases from 183 J to 49 J.
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图 1 TiN平衡溶解度与实际溶解度比较
(a) 液相; (b) 两相区; (c)γ-Fe相
Figure 1. Comparison of equilibrium solubility products with actual solubility products of TiN
图 2 纳米粒子的典型形态和组成
Figure 2. Typical morphologies and compositions of nanoparticles
(a)(b) TN30; (c)(d) TN57
图 3 粒子尺寸分布对比
(a) 尺寸分布; (b) 平均尺寸和数量密度
Figure 3. Comparison of particle size distributions
图 4 TN30钢Mg-Ti-O-N-MnS复合夹杂物形貌及EDS面扫描分析
(a)夹杂物1；(b)夹杂物2；(c)夹杂物3；(d)夹杂物4
Figure 4. Morphologies and EDS-mapping of Mg-Ti-O-N-MnS composite inclusions in TN30 steel
图 5 TN57钢夹杂物形貌及EDS面扫描分析
(a)(b)(c) Mg-Ti-O-N-MnS复合夹杂物; (d)以Ti(C, N)为主的复合夹杂物
Figure 5. Morphologies and EDS-mapping of inclusions in TN57 steel
图 8 钢中第二相粒子、原奥氏晶粒和微观组织关系的示意
Figure 8. Schematic diagram of the relationship among the second phase particles, PAGs and microstructures
(a) TN30; (b) TN57
表 1 试验钢的化学成分
Table 1. Chemical compositions of the steel samples
Steels Chemical composition/% Ti/N C Si Mn P S Mg Ti N TN30 0.076 0.22 1.55 0.007 0.004 0.0027 0.012 0.004 3.00 TN57 0.081 0.22 1.56 0.007 0.004 0.0026 0.017 0.003 5.67 
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表 2 焊接热模拟试验条件
Table 2. Experimental conditions of simulation welding
Plate
thickness/mmWelding heat
input/(kJ·cm-1)Peak
temperature/℃Peak holding
time/st8/5/s 50 400 1400 3 385
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