Analysis of reheat embrittlement and softening of coarse-grained zone of Q960E welding joint
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摘要: 为了精确获得不同温度梯度条件下焊接热影响区的组织和性能，采用焊接热模拟的方式对一种低碳当量Q960E及其对比钢进行了两次模拟热循环试验，并获得了一次热模拟后的CGHAZ，以及二次热模拟后的未变粗晶热影响区(UA CGHAZ)、过临界粗晶热影响区(SCR CGHAZ)、临界粗晶热影响区(ICR CGHAZ)和亚临界粗晶热影响区(SR CGHAZ)的显微组织，开展了组织分析、冲击韧性测试和硬度表征.结果表明，低碳当量Q960E和高碳当量对比钢的ICR CGHAZ和SR CGHAZ均有再热脆化敏感性，在−40 ℃下对比钢的SR CGHAZ的冲击韧性低至9 J，其晶界点状和条状碳化物分布是再热脆化的主要原因；低碳当量Q960E的SR CGHAZ软化最为严重，其原因是细晶强化、位错强化和析出强化联合丧失造成的.Abstract: In order to accurately obtain the microstructure and properties of the welding heat affected zone under different temperature gradient conditions, two simulated thermal cycle tests were carried out on a low carbon equivalent Q960E and its comparative steel by using the welding thermal simulation method. And the microstructures of CGHAZ after the first thermal simulation, and UA CGHAZ, SCR CGHAZ, ICR CGHAZ and SR CGHAZ after the second thermal simulation were obtained. Microstructures were analyzed, impact toughness test and hardness characterization were carried out in this paper. Results showed that both ICR CGHAZ and SR CGHAZ of Q960E and comparative steel had reheat embrittlement sensitivity. The impact toughness of SR CGHAZ of comparative steel was as low as 9 J at −40 ℃. And the distribution of point-type and strip-type carbides formed at the grain boundary was the main reason for reheating embrittlement. The softening of SR CGHAZ with low carbon equivalent Q960E is the most serious, which is caused by the combined loss of fine-grain strengthening, dislocation strengthening and precipitation strengthening.
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Keywords:
- CGHAZ /
- reheat embrittlement /
- softening /
- thermal simulation
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图 1 不同tp2温度下再热CGHAZ的SEM像
Figure 1. SEM images of reheated CGHAZ under different tp2 temperatures. (a) UA CGHAZ of Q960E; (b) UA CGHAZ of comparative steel; (c) SCR CGHAZ of Q960E; (d) SCR CGHAZ of comparative steel; (e) ICR CGHAZ of Q960E; (f) ICR CGHAZ of comparative steel; (g) SR CGHAZ of Q960E; (h) SR CGHAZ of comparative steel
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图 2 不同tp2温度两种试验钢冲击吸收能量和硬度分布
Figure 2. Impact absorption energy and hardness distribution of two test steels at different tp2 temperatures. (a) impact absorption energy; (b) hardness distribution
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图 3 Q960E大梁钢ICR CGHAZ的TEM像
Figure 3. TEM images of ICR CGHAZ of Q960E. (a) bright field image; (b) dark field image; (c) diffraction pattern of retained austenite
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图 4 两种试验钢的CGHAZ和SR CGHAZ的TEM像
Figure 4. TEM images of CGHAZ and SR CGHAZ of two test steels. (a) CGHAZ of Q960E; (b) SR CGHAZ of Q960E; (c) CGHAZ of comparative steel; (d) SR CGHAZ of comparative steel
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图 5 低碳当量Q960E母材及其模拟CGHAZ金相组织
Figure 5. Microstructure of low carbon equivalent Q960E and its simulated CGHAZ. (a) Q960E; (b) CGHAZ
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图 6 透射电镜下的位错密度变化
Figure 6. Dislocation density change under TEM. (a) Q960E; (b) CGHAZ; (c) SR CGHAZ
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图 7 透射电镜下的第二相粒子形貌变化
Figure 7. Morphology change of second phase particles under TEM. (a) Q960E; (b) CGHAZ; (c) SR CGHAZ
表 1 Q960E和对比钢的化学成分(质量分数，%)
Table 1 Chemical composition of Q960E and its comparative steel
材料 C Si Mn P S Cu Ni Cr Mo B V Ceq Q960E 0.12 0.23 1.30 ≤0.02 ≤0.002 — — 0.50 0.50 0.001 2 0.1 0.395 对比钢 0.14 0.40 1.0 ≤0.02 ≤0.002 0.1 2.2 0.50 0.50 0.001 1 — 0.546 注：Ceq= C + ( Mn + Si )/6 + ( Ni + Cu )/15 + ( Cr + Mo + V )/50 
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表 2 Q960E和对比钢的典型力学性能
Table 2 Typical mechanical properties of Q960E and its comparative steel
材料 屈服强度ReL/MPa 抗拉强度Rm/MPa 断后伸长率A50(%) −40 ℃冲击吸收能量AKV(%) Q960E 990 1 020 13.5 43, 40, 49 对比钢 1 000 1 080 13.0 45, 47, 43
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表 3 CGHAZ热模拟工艺
Table 3 Thermal simulation process of CGHAZ
工艺
编号一次热循环 二次热循环 预热温度
T0/℃升温速率
v /(℃·s−1)峰值温度
Tc/℃保温时间
ts/s热循环时间
t8/5/ s升温速率
v /(℃·s−1)峰值温度
Tc/℃保温时间
ts/s热循环时间
t8/5/s1 25 150 1 250 2 7 — — — — 1A 25 150 1 250 2 7 150 1 250 2 7 1B 25 150 1 250 2 7 150 950 2 10 1C 25 150 1 250 2 7 150 750 2 12 1D 25 150 1 250 2 7 150 600 2 15
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