SH-CCT diagram and cold cracking sensitivity of a 1300 MPa grade high strength low alloy steel
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摘要: 采用Formastor-FⅡ全自动相变仪测定了1300 MPa级低合金高强钢的奥氏体化相变温度，结合光学显微镜与维氏硬度计等设备研究了800 ~ 500 ℃冷却时间(t8/5)对1300 MPa级低合金高强钢粗晶热影响区组织和硬度变化的影响规律. 结果表明，当t8/5为3 ~ 60 s时，1300 MPa级低合金高强钢粗晶热影响区组织均由板条马氏体组成，硬度值为438 ~ 454 HV5；随着冷却时间延长，粗晶区出现贝氏体类组织，当t8/5为150 s时，粗晶区为板条马氏体/贝氏体混合组织，硬度平均值为413 HV5；当t8/5为300 ~ 600 s时，粗晶区为板条贝氏体和粒状贝氏体混合组织，硬度值为341 ~ 381 HV5；当t8/5＞600 s时，粗晶区组织主要为粒状贝氏体，硬度值为269 ~ 322 HV5. 冷裂敏感性评价结果表明，该试验钢碳当量CE(IIW)和CEN均大于0.5%，具有一定的冷裂倾向，需焊前预热，焊后热处理或保温缓冷等措施，避免焊接冷裂纹的形成.
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关键词:
- 1300 MPa级低合金高强钢 /
- SH-CCT曲线 /
- 焊接热影响区 /
- 微观组织 /
- 冷裂敏感性
Abstract: Austenitization temperature of a 1300 MPa grade high strength low alloy steel was measured by the Formastor-FⅡ thermal expansion measurement, and the effect of cooling time from 800 to 500 ℃(t8/5) on the microstructure transformation and hardness change of the coarse grained heat affected zone was investigated by using Formastor-FⅡ, optical microscope, vickers hardness tester. The experimental results indicated that the microstructure of coarse grained heat affected zone (CGHAZ) was composed of lath martensite with hardness ranging from 438 to 454 HV5, when the t8/5 was 3 ~ 60 s. Along with the extension of cooling time, bainite began to form. When t8/5 was 150 s, the microstructure was mixtures of bainite and martensite with an average hardness of 413 HV5. The microstructure was mixtures of lath bainite and granular bainite with hardness ranging from 341 to 381 HV5 as t8/5 was 300 ~ 600 s. When t8/5 was longer than 600 s, the microstructure mainly consisted of granular bainite with hardness ranging from 269 to 322 HV5. The cold cracking sensitivity evaluation results show that the carbon equivalent CE (IIW) and CEN of the test steel are both greater than 0.5%, which has a certain tendency of cold cracking. Therefore, it is necessary to preheat welding, heat treatment after welding or heat preservation and slow cooling measures to avoid the formation of welding cold cracking. -
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图 3 试验钢近似平衡态奥氏体化相变温度
Figure 3. Austenite transformation temperature of the experimental steel
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图 4 试验钢不同冷速下HAZ粗晶区金相微观组织(t8/5：3 ~ 60 s)
Figure 4. OM images of the experimental steel at different cooling rate (t8/5: 3 ~ 60 s). (a)t8/5 = 3 s; (b)t8/5 = 6 s; (c) t8/5 = 10 s; (d) t8/5 = 15 s; (e) t8/5 = 30 s; (f) t8/5 = 60 s
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图 5 试验钢不同冷速下HAZ粗晶区金相微观组织(t8/5：150 ~ 3 000 s)
Figure 5. OM images of the experimental steel at different cooling rate (t8/5: 150 ~ 3 000 s). (a)t8/5 = 150 s; (b) t8/5 = 300 s; (c) t8/5 = 600 s; (d)t8/5 = 1 000 s; (e) t8/5 = 2 000 s; (f) t8/5 = 3 000 s
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图 6 不同t8/5条件试验钢CGHAZ不同组织占比
Figure 6. Microstructure proportion of CGHAZ of experimental steel at different t8/5
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图 7 不同t8/5条件下试验钢热模拟试样硬度
Figure 7. Hardness of experimental steel thermal simulated samples at different t8/5
表 1 试验钢的化学成分(质量分数，%)
Table 1 Chemical compositions of the experimental steel
C Si Mn P S Cr Ni Mo Fe 0.20 0.25 0.89 0.0070 0.0030 0.40 1.21 0.55 余量 
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表 2 试验钢的基本力学性能
Table 2 Mechanical properties of the experimental steel
屈服强度
Rp0.2/MPa抗拉强度
Rm/MPa断后伸长率
A(%)冲击吸收能量
(−40 ℃)AKV/J1320 1540 10.0 82
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