一種Fe-Cr-Ni-Mo高強高韌合金鋼焊接接頭的組織和力學性能

一種Fe-Cr-Ni-Mo高強高韌合金鋼焊接接頭的組織和力學性能MICROSTRUCTURE AND MECHANICAL PROPERTIES OF WELDED JOINT OF A Fe-Cr-Ni-Mo STEEL WITH HIGH-STRENGTH AND HIGH-TOUGHNESS

采用熔化極活性氣體保護焊（MAG焊）對一種Fe-Cr-Ni-Mo高強高韌合金鋼板進行多道次焊接，利用SEM、EPMA、TEM以及拉伸、沖擊等實驗研究了焊接接頭的組織和力學性能。結(jié)果表明，焊縫金屬由柱狀晶和等軸晶組成，其中上部焊縫以柱狀晶為主，而下部焊縫的等軸晶含量增加。焊縫上部因冷速較快形成回火馬氏體組織；下部因合金元素含量較高，淬硬傾向較強，形成了粒狀貝氏體組織?？拷缚p的熱影響區(qū)為較粗大的馬氏體組織，其硬度最大（620HV），明顯高于母材（410HV）。上部焊縫金屬的硬度為365HV，低于母材，而下部焊縫的硬度高于焊縫上部和母材，為450HV。因此，焊接接頭上部拉伸試樣在焊縫處發(fā)生斷裂，斷裂強度為1109 MPa，而焊縫的下部拉伸樣在母材處發(fā)生斷裂，斷裂強度為1183 MPa。本實驗用Fe-Cr-Ni-Mo合金鋼的焊接接頭強度較高，焊接強度系數(shù)不小于0.93，焊縫金屬的沖擊功為53 J。

High-strength steel has the advantages of high strength, low cost and good hot and cold workability, etc., which is widely used in various fields of national economy as engineering steel, such as bridge, vehicle, ship, pressure vessel and so on. As increasing strength, the plasticity and toughness of high strength steel have not meet the demand in some industrial areas, especially the low temperature impact toughness. Recently, a Fe-Cr-Ni-Mo steel with high-strength and high-toughness has been developed and has been successfully prepared high pressure vessels. In this work, MAG welding (Metal active gas welding) with multi-pass welding was used to join a Fe-Cr-Ni-Mo high-strength and high-toughness steel. The microstructure and fracture morphologies of welded joint are investigated by SEM, EPMA and TEM and the micro-hardness, tensile strength and Charpy impact energy are tested as well. The results show that the morphologies of welded metal (WM) consists of columnar crystal (CC) and equiaxed crystal (EC), where the upper WM is predominantly CC and the proportion of EC increases in the lower WM. The microstructure of upper WM is tempered martensite for the faster cooling rate. Because the higher content of alloying elements in lower WM improves the hardening tendencies, the lower WM is granular bainite. The heat affected zone near WM is coarsen martensite and has the highest hardness (621 HV), which is significantly higher than that of the base metal (BM) (410 HV). The hardness of the upper WM is 365 HV, which is lower than that of BM and the lower WM has higher hardness (450 HV). Therefore, the upper tensile sample of welded joint was broken in the WM and the fracture strength is 1109 MPa and lower than that of BM (1190 MPa). While the fracture position of lower tensile sample is in the BM and the strength is about 1183 MPa. The welded joint of experimental Fe-Cr-Ni-Mo steel has higher strength and the welding factor is not lower than 0.93. Moreover, the impact energy of WM is 53 J.

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