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采用热膨胀法结合显微金相与硬度检测,在热模拟试验机上测定了1 000MPa级低碳微合金高强钢焊接过程中的临界点Ac1和Ac3,绘制出该钢在不同冷却速率下的焊接连续冷却转变曲线(SH-CCT曲线),研究了冷却速率对焊接热影响区粗晶区(CGHAZ)组织和硬度的影响规律,揭示了不同冷却速率下焊接热影响区的相变过程及组织特征,同时获得了奥氏体晶粒平均尺寸随t8/5的变化关系。研究结果表明,在焊接条件下,该钢的奥氏体化温度要比平衡状态下的奥氏体化温度显著升高;该钢在相当宽的冷却速率范围内发生中温转变,获得贝氏体组织;在较快的冷却速率(≥40℃/s)下,焊接热影响区组织以马氏体为主;随着冷却时间t8/5的增加,硬度逐渐下降,最高硬度HV10为425。在试验条件下,奥氏体晶粒粗化程度并不显著。
The critical point Ac1 and Ac3 in the welding process of 1 000 MPa grade low-carbon micro-alloyed high-strength steel were measured by thermal expansion method combined with microstructure and hardness measurement. The welding of the steel under different cooling rates was drawn (SH-CCT curve) was used to study the influence of cooling rate on the microstructure and hardness of CGHAZ. The phase transformation process and microstructure characteristics of heat affected zone (HAZ) under different cooling rates were revealed. At the same time, the relationship between the average size of austenite grains and t8 / 5 was obtained. The results show that under the conditions of welding, the austenitizing temperature of the steel is significantly higher than the austenitizing temperature at equilibrium; the steel undergoes a moderate temperature transformation within a fairly wide range of cooling rates to obtain bainite The microstructure of the HAZ was dominated by martensite at higher cooling rate (≥40 ℃ / s). With the increase of cooling time t8 / 5, the hardness gradually decreased and the maximum hardness HV10 was 425. Under the experimental conditions, the degree of austenite grain coarsening is not significant.