A Study On Cghaz Microstructure And Properties Of High Strength Copper Bearing Steel

Simulation HAZ Continuos Transformation of Copper-bearing Age hardening steels were studied by Formast-Digital in this Dissertation. Thermal simulating test of Copper-bearing steels were also studied through Gleeble-3500. Observe and test Microstructure and properties of Copper-bearing Steels. Compare with traditional shipbuilding steel and Copper-bearing steels. The result shows:Copper bearing steels transformation Variety of bainite in all cooling rate at CGHAZ(Coarse Grain HAZ).The cooling rate plays a very important role in the microstructure of HAZ. The morphology of bainite changed from Granular bainite and crude lath bainite to fine bainite with the increase of the cooling rate. The M-A island structure began to appear when t8/5≥200s, and with the increase of the t8/5, M-A island structure gradually form the strip into the block. In the welding thermal simulation test, the copper bearing steel shows a good low temperature impact toughness when t8/5 in wide range(6.7s-1000s), Impact energy of -40℃higher than 200J when t8/5= 100s. Compare of traditional 10Ni3CrMoV steel and 12Ni3CrMoV steel, copper bearing steels has low carbon content, lower preheat temperature and the lowest hardness in Heat Affected Zone, cold cracking sensitivity significantly reduced. t8/5 was relative low(≤20s), the copper bearing steel CGHAZ maximum hardness is 327 HV, which hardness far lower than the 10Ni3CrMoV steel(355 HV), microstructure is lath bainite, residual austenite between lath strip which shows good low temperature toughness. When t8/5was relatively high, the copper bearing steel CGHAZ microstructure was lath bainite also, However, the size of a single lath was coarse, coarse grain HAZ can still maintain a good low temperature toughness. After Secondary thermal cycle the HAZ of copper bearing steel has a higher low temperature toughness, which Coarse Grain HAZ+ Fine Grain HAZ shows highest impact toughness, after the secondary thermal cycle, the coarse grain HAZ and two-phase region hardness significantly reduce at CGHAZ.