Research On Hydrogen Embrittlement Mechanism And Residual Stress Of Heavy Forging

Heavy forgings are the main basic components of all kinds of necessary, heavy, keyequipment and installations. It is the necessities during the national economic construction,national defense industry and modern science development. If there are the white flakes inthe heavy forgings, it not only causes the heavy forgings’mechanical properties fellsharply, but also makes the stress highly concentrated which would make the workcracking during the quenching heat treatment and the working process. And it would causesignificant accidents and loss. So, the white flake is a fatal flaw of the heavy forgings. Theheavy forgings with the white flakes must be scrapped.Hydrogen embrittlement is commonly known as the white flakes. It is thephenomenon that the hydrogen in steel makes the plastic and toughness of the steelreduced. In heavy forgings, hydrogen embrittlement is finally shown as the white flakes.The exist of the white flakes is due to the hydrogen pressure produced by the hydrogengathering in the steel and the residual stress formed during the cooling process of theheavy forgings’forming. So, this paper mainly studies in the high strength internal stressdistribution including the thermal stress, the organization stress and the forming stressduring the heavy forgings’forming and cooling to room temperature conditions processes.First, the hydrogen embrittlement mechanism of the heavy forgings was analyzed andthe mathematical model was set up. Then through the way of the test and calculationcombined, the thermal physical parameters of the Cr5 steel of the simulation werecalculated by the JMatPro materials software. And through the way of the test andsimulation verified, and through the comparison of the cooling curve, the accuracy of theheat transfer coefficient and the feasibility of finite element simulation were verified.Under the basis of the various parameters which were needed by the simulation, theheavy forgings model was set up. And the distribution of stress field of the heavy forgingswas simulated under the upsetting, dehydrogenation annealing, quenching and temperingprocesses. The residual stress generated at the internal area of the heavy forgings wasanalysed in the condition of these processes. Then, the micro-pore model in the heavy forgings was established. And the distribution of stress field of the heavy forgingsmicro-pore was simulated under the common function of the hydrogen pressure and theresidual stress which was generated during the upsetting, dehydrogenation annealing,quenching and tempering processes. The changes of stress field were analyzed andcompared under the three kinds of heat treatment process. And at last, we had predictedthat which area of the heavy forgings would be easy to generate the white flakes, whichprocess would be easy to generate the white flakes and what shape of the white flakeswould be probably generated under the three kinds of heat treatment process.