使用Gleeble-3800热模拟试验机模拟单道次焊接条件下大厚度(50 mm)F460钢板热影响区(HAZ)热循环过程, 通过OM, SEM, EBSD和TEM研究了HAZ的显微组织随热输入($E$)的演化规律. 测试了不同E下HAZ的室温硬度(HV),在-40和-60 ℃下进行了Charpy冲击示波实验(CVN). 当E=15 kJ/cm时,显微组织为高位错密度板条马氏体(LM), 板条间呈现出大取向差,板条间存在细小片状马氏体/奥氏体(M/A)组元. 当E=30 kJ/cm时, 板条贝氏体(LB)形成,随着E提高至50 kJ/cm, 板条宽度增大, 且有粒状贝氏体(GB)形成,大角度晶界减少, M/A组元粗化. 当E为100-300 kJ/cm时, HAZ的显微组织由GB+上贝氏体(UB)+准多边形铁素体(QPF)构成, 组织均匀性恶化.HAZ的硬度、CVN最大载荷(Pm)、脆性断裂止裂载荷(Pa)、脆性断裂裂纹扩展速率、CVN载荷降至0时的位移(d0)等均随着E的增加而降低.脆断单元解理面尺寸随$E$的提高而逐渐增大, 从而揭示HAZ铁素体等效晶粒尺寸随E的提高而增大、低温韧性随E的提高而降低的规律. E不高于30 kJ/cm时,在-60 ℃下的HAZ与母材的韧性相匹配.
Thermal cycles of the heat–affected zone (HAZ) of an advanced F460 steel plate used as offshore structure and ship–building in the future were simulated by employing a Gleeble 3800 thermomechanical simulator. The microstructures of the HAZ formed at different heat input energies (E) were characterized by means of OM, SEM, EBSD and TEM, and mechanical properties were measured. When E is equal to 15 kJ/cm, the microstructures consist of mainly lath–like martensite (LM) with high density dislocations and large misorientations, between the laths exist fine martensite/austenite (M/A) constituents. When E is equal to 30 kJ/cm, lath–like bainite (LB) is formed. The lath grains and M/A constituents will coarsen and the amount of high angle (≥15?) boundaries will decrease with the increase of E to 50 kJ/cm. When E is in a range of 100—300 kJ/cm, the microstructures consist of granular bainite (GB)+upper bainite (UB)+quasi–polygonal ferrite (QPF). The hardness of the HAZ (HV), the maximum Charpy V notch (CVN) impact load (Pm), the brittle fracture arrested load (Pa), the crack propagation rate, and the entire displacement (d0) of the CVN impact course decrease with the increase of E. The size of cleavage facets increases with the increase of E, which can be used to explain the effective grain size of the HAZ increases with the increase of E, as a result, the hardness decreases and low temperature toughness deteriorates as E increases. The upper limit of the simulated heat input E for the F460 steel is 30 kJ/cm which makes the toughness of the HAZ equivalent to that of the mother plate at −60 ℃.
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