Investigation On Impact Toughness And Step Cooling Embrittlement Law For 2.25 Cr1Mo Steel Electrode Deposited Metal

Hydrogenation reactor is the key equipment of oil refining and coal chemical industry. Although some progress has been made in Hydrogenation reactor manufacture area, such as the localization of 2.25Cr1 Mo steel sheets, forgings and inwall surfacing materials, the main body welding materials of the reactor which depending on import has becoming the major obstacle. In this thesis, the optimization design of core wire and coated powder, phosphorus, tempering parameter and heat input’s influence on the impact toughness of deposited metal and the effect of different phosphorus content on the step cooling embrittlement has been systematically studied.Various experiments such as Curing covering slag system, controlling the phosphorus content in the core wire have been proposed for selecting deposited metal of different phosphorus content. Microstructure analysis showed that Phosphorus content in the deposited metal has major influence on the low temperature impact toughness, in the temperature range of-30℃~-60℃, the impact energy of deposited metals significantly reduced with the P content increased, above 0℃ and below-80℃, the effect of P content on the impact energy is reduced. As the P content increased, the brittle transition temperature gradually increased, and the morphology of impact fracture of deposited metals at-30 ℃ changed from dimples + quasi-cleavage fracture to cleavage + quasi-cleavage fracture.Different tempering parameter and heat input test of deposited metal with lowest phosphorus level showed that with tempering parameter in 19.84~20.71, deposited metal impact toughness is more higher and stable, while tempering parameter was above 20.97, strength and impact toughness are decrease as the “Ferrite+Carbides” microstructure appear in deposited metal. Therefore the best temper parameter of R407 C electrode is between 19.84 to 20.71. As heat input is increased, strength and toughness are decreased. When heat input was belowing 18.68 k J/cm, as fine bainite and ferrite homogeneously distribute in the deposited metal, strength and impact toughness are improved. However, when heat input was above 24 k J/cm, strength and impact toughness of deposited metal are deteriorated by massive bainite and ferrite.Step cooling embrittlement tests showed that after step cooling tests, low-temperature impact toughness of deposited metals reduces, and embrittlement appears. The amount of temper embrittlement of deposited metals with different phosphorus content also changes, the amount of embrittlement increases with phosphorus content increases.At the same time,the morphology of impact fracture changed into intergranular fracture and the proportion gradually increases.The distribute of impurity elements on impact fractures has been studied by using Auger electron spectroscopy, The higher phosphorus content level in deposited metal, the more phosphorus elements segregates at the grain boundary which is in consistent with the results of analysis on the morphology of impact fractures. The main reason why R407 C welding rod has temper embrittlement after step cooling is that the impurity element phosphorus segregates at the grain boundary.