| Lager forgings usually used to significant carrier and large-scale structuralcomponents. With the rapid development of our country economy, electric powerconsumption growth with each passing day. Nuclear power as a kind of economic, clean,reliable substitute energy has been recognized in the world. Lager forgings assignificant structural components used in nuclear power equipment, the demand will begetting bigger and bigger. But many lager forgings used in nuclear power depend onimportation, for researches of lager forgings begin late in our country, the capacity ofequipment that manufacture lager forgings can’t meet the requirement. In this way, notonly the cost is very high, but also be controlled by foreigners, even terribly delayed thedevelopment of our country nuclear power. Therefore, improving manufacturingcapability of lager forgings will be one of very urgent and important missions to thedevelopment of our country nuclear power, which has important significance.In this paper, we investigated the flow stress curve of20MnNiMo at differentdeformation conditions, the steel used in lager nuclear power head. Combined withmethods of mathematical analysis, established flow stress models in high temperatureand microstructure evolution models, which can precisely indicate material’sthermoplastic deforming behavior. Meanwhile, the workability of20MnNiMo indifferent deformation areas is researched based on dynamic material model. On thebasis of research, we show the numerical simulation that combined lager nuclear powerhead forging deformation and microstructure evolution, which will provide referencevalue and spot guidance for practical production of lager nuclear power head.The true stress-strain curves of20MnNiMo steel samples at different deformationconditions have been obtained by high temperature compression tests on theGleeble-1500thermal simulation machine. Two different flow stress models have beenbuilt on the basis of Sellars model, the parameters variation Arrhenius and Laasraouiwith two segment flow stress models. Compared the models, we found that, the curvecalculated from the model with two segment agree well with those of experiments. Themaximum relative error is less than10%. That is to say, the model can truly reflect theflow stress of20MnNiMo at high temperature.Based on the processing map theory of the dynamic materials model, using20MnNiMo steel’s true stress-strain data as the basic material model to calculate the strain rate sensitivity (m-value), the energy dissipation efficiency (-value), theinstability criterion (-value). Finally, the thermal processing map including strain of20MnNiMo is drawed out. The results show that: with the strain increase, the thermalprocessing security region increase too. It illustrate that when the strain is large, thedeformation temperature and strain rate won’t occur flow instabilities in wide range. Sothe heating times decrease, the productivity improve.In the end, the DEFORM-3D numerical simulation software was used to renderlager nuclear power integrated head gradually rotating cycle forging forming process.The results show that: when using small deformation gradually rotating forming process,forgings deform uniformly during the whole cyclic process of forging, the innerspherical of the forgings is in a state of three-direction compressed stress, the region thatoccurs the full dynamic recrystallization can up to95.4%account for whole forgings.The average grain size belows10m at the inner spherical of the forgings, which canbasically reach the requirement of grain size of the product’s microstructure. Accordingto the actual production test, the integral forming condition of forgings is well, shapeand size can reach the basic drawing requirement, the surface crack or folding defect notbe appeared, uniform deformation within forgings, microstructure and property uniform,which can reach each technical indicators of lager nuclear power head. |
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