Effect of Cr content on the austenitization of 500 MPa class high-strength seismic rebars
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摘要: 应用光学显微镜、扫描电镜等手段观察显微组织，研究了不同Cr含量钢筋在不同铸坯再加热温度和保温时间下奥氏体晶粒的变化，探讨了Cr含量对500 MPa级高强抗震钢筋奥氏体化的影响。结果表明，不同再加热温度范围内，Cr含量对试验钢奥氏体晶粒的影响规律不同。在950～1050 ℃温度区间时，含Cr钢奥氏体晶粒的生长速率慢，随钢中Cr含量的增加，奥氏体晶粒尺寸减小；高于1050 ℃时，奥氏体晶粒生长速率加快，随钢中Cr含量的增加，奥氏体晶粒尺寸增大。相同再加热温度下，随保温时间的延长，奥氏体晶粒长大。当Cr含量较高时，随着再加热温度的升高或保温时间的延长，Cr元素在晶界处偏聚减弱，导致奥氏体晶粒更容易长大和粗化。在再加热温度为1050 ℃、保温时间为30 min条件下含Cr试验钢可得到细小均匀的奥氏体组织。Abstract: The microstructure was observed by means of optical microscope, scanning electron microscope, etc. The change of austenite grains of the steels with different Cr contents under different reheating temperature and holding time of the casting billet was studied. The effect of Cr content on austenitization of 500 MPa high-strength seismic-resistant rebar was discussed. The results show that the effect of Cr content on austenite grain is different in different reheating temperature range. In the temperature range of 950～1150 ℃, the growth rate of austenite grain in Cr-containing steel is slow when the reheating temperature is lower than 1050 ℃, and the size of austenite grain decreases with the increase of Cr content. When the temperature is higher than 1050 ℃, the growth rate of austenite grain increases, and the size of austenite grain increases with the increase of Cr content. At the same reheating temperature, austenite grains grow up with the extension of holding time. When the content of Cr is high, with the increase of the reheating temperature or the extension of the holding time, the segregation of Cr at the grain boundary is weakened, leading to the growth and coarsening of austenite grains more easily. Fine and uniform austenite structure can be obtained under the condition of 1050 ℃ and 30 min reheating temperature.
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Key words:
- Cr-containing rebars /
- austenitization /
- slab /
- reheating temperature /
- growth rate
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图 1 三种含Cr钢筋在不同铸坯再加热温度下的奥氏体晶界形貌
Figure 1. Austenitic grain boundary morphologies of different Cr-containing steels at different soaking temperatures
图 2 在1000、1100 ℃时保温时间为60 min和90 min的三种含Cr钢筋的奥氏体晶界形貌
Figure 2. Austenitic grain boundary morphology of different Cr-containing steel bars under different holding time at 1000 and 1100 ℃
图 3 在(a) 1000、(b) 1100 ℃下保温30、60、90 min时不同含Cr钢筋的奥氏体晶粒尺寸
Figure 3. Austenitic grain size of different Cr-containing steel bars at 1000, 1100 ℃ for 30, 60, 90 min
图 4 不同条件下试验钢中Cr元素分布的线扫描和能谱
Figure 4. Line scan and energy spectrum of Cr element distribution in the test steel under different conditions
图 5 奥氏体平均晶粒尺寸随铸坯再加热温度的变化规律
Figure 5. Variation of average austenitic grain size with reheating temperature of the slab
图 6 再加热温度为1050 ℃和1100 ℃下的三种不同含Cr钢的奥氏体晶粒尺寸正态分布
Figure 6. Austenitic grain size distribution of three Cr-containing steels at 1050 ℃ and 1100 ℃ reheating temperature
表 1 不同Cr含量试验钢的化学成分
Table 1. Compositions of experimental steels with different Cr contents
% 编号 C Si Mn S P Cr N V Fe 0.04Cr 0.22 0.53 1.57 0.044 0.021 0.043 0.015 0.091 余量 0.07Cr 0.24 0.42 1.50 0.035 0.021 0.069 0.015 0.090 余量 0.24Cr 0.21 0.44 1.35 0.025 0.015 0.238 0.018 0.089 余量 
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