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| 焊接热循环对P460NL1高强正火容器钢微观组织及低温冲击韧性的影响 |
| Effects of welding thermal cycle on microstructure and low-temperature impact toughness of P460NL1 high-strength normalized container steel |
| 投稿时间：2020-03-09 |
| DOI： |
| 中文关键词: 焊接热循环 压力容器钢 V(C,N) 热影响区 微观组织 低温冲击韧性 |
| 英文关键词: welding thermal cycle pressure container steel V(C,N) heat affected zone microstructure low-temperature impact toughness |
| 基金项目:国家自然科学基金资助项目(51971165). |
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| 中文摘要: |
| 采用焊接热模拟技术,结合OM、SEM、TEM及-40 ℃低温冲击韧性实验,研究了焊接热循环(不同峰值温度和t8/5参数)对P460NL1高强正火容器钢热影响区组织和低温韧性的影响,重点分析了不同焊接热循环中强化相V(C,N)粒子的演变。结果显示,当t8/5同为45 s时,P460NL1钢模拟热影响区的低温冲击韧性随峰值温度的升高大致呈降低趋势,且温度超过1200 ℃后冲击韧性急剧降低。峰值温度为1350、1200 ℃且t8/5在15~100 s范围时,模拟的是P460NL1钢焊接热影响区粗晶区,组织主要为铁素体和贝氏体混合组织,此条件下P460NL1钢的低温冲击韧性较低且基本不随t8/5的变化而变化；t8/5为45 s时,峰值温度1100、950 ℃对应的是焊接热影响区细晶区,此时组织为铁素体+贝氏体+珠光体混合组织,峰值温度870 ℃模拟的是两相区,主要为铁素体和珠光体组织。利用Thermal-Calc软件计算得到P460NL1钢中V(C,N)溶解温度为1160 ℃,故当峰值温度超过1200 ℃时,V(C,N)粒子完全溶解且未再析出,基体中存在的游离N会降低P460NL1钢的低温冲击韧性,且当峰值温度为1350 ℃时,随着t8/5增加,晶粒尺寸逐渐增大,但冲击韧性却没有因此而降低,表明游离氮是热影响区粗晶区冲击韧性的关键因素。 |
| 英文摘要: |
| By using welding thermal simulation approach, combined with OM, SEM, TEM and low-temperature (-40 ℃) impact toughness test, the effects of welding thermal cycle (different peak temperatures and t8/5) on the microstructure and low-temperature toughness of the heat-affected zone of P460NL1 high-strength normalized container steel were studied with the emphasis on the evolution of strengthening phase V(C,N) particles in different welding thermal cycles. The results show that when t8/5 is 45 s, the low-temperature impact toughness of the simulated heat-affected zone of P460NL1 steel generally decreases with the increase of peak temperature, and the impact toughness decreases sharply when the temperature exceeds 1200 ℃. When the peak temperature is 1350,1200 ℃ and t8/5 is in the range of 15~100 s, what is simulated is the coarse-grained heat affected zone of P460NL1 steel, and the microstructure is mainly a mixture of ferrite and bainite. Under this condition, the low-temperature impact toughness of P460NL1 steel remains low and basically does not change with the change of t8/5. When t8/5 is 45 s, the fine-grain heat affected zone is obtained after welding thermal test at the peak temperature of 1100 ℃ and 950 ℃, and the microstructure is the mix of ferrite, bainite and pearlite; the intercritically heat affected zone is obtained after simulating at the peak temperature of 870 ℃, and the microstructure composes of ferrite and pearlite. Moreover, by using Thermal-Calc software, the dissolution temperature of V(C,N) particles in P460NL1 steel is calculated to be 1160 ℃. Therefore, when the peak temperature exceeds 1200 ℃, V(C,N) particles are completely dissolved without re-precipitation. The presence of free nitrogen will reduce the low-temperature impact toughness of P460NL1 steel. When the peak temperature is 1350 ℃, with the increase of t8/5, the grain size gradually increases, but the impact toughness does not decrease as a result, indicating that the free nitrogen is the key factor affecting the impact toughness of the coarse-grained heat affected zone. |
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