Deformation behaviour analysis of dual phase steels

In this thesis, DP600 (Dual Phase) steel sheet which has commercial purity was used to obtain tensile testing samples in 0-45-90 degree according to rolling direction.Via using these tensile testing samples, tensile testing was done by tensile speed of 2 mm/min in the Istanbul Technical University Mechanical Testing Laboratory. Moreover, engineering and true stress-strain curves were specified for DP600 steel by using tensile testing results.Thus, the first step to determine the mechanical properties of the DP600 steel that we have has been completed. After that, DP600 steel sample was taken out and grinding, polishing and etching operations were applied respectively to determine the microstructure and phase morphology of DP600 steel. The best microstructure image has been obtained in SEM (Scanning Electron Microscope) at 5000 enlargement level by using % 4 Nital and %10 Sodium metabisulfite etchants during 30 seconds. The best microstructure image of DP600 has been imported to Autocad 2012 drawing and design programme to draw the grain boundaries of martensite that looks like islands and have bright colour and ferrite that have dark colour if we compare with martensite phase in terms of detecting the percent areas of the both phases in DP600 steel. Besides, the drawn 2d objects in Autocad which represent the martensite and ferrite phases in related steel were used to create the model for the finite element method analysis. In order to reveal the relationship between deformation behavior in macro dimension and microstructure, 3 different finite element analysis were performed. At the first one, the model was encastre supported from the one node at left side of the model and displacement of the other nodes along this edge were allowed in only y and z direction. Besides, 500 MPa pressure was applied to right side of the model in positive x direction. In the second model, it is encastre supported from the one node at down side of the model and displacement of the other nodes along this edge were allowed in only x and z direction. Beside, 500 MPa pressure was applied to up side of the model in positive y direction. In the third model, the model was same with first and second model without boundary conditions. The same model was embedded into a new model which has 5 times bigger than the initial model and from the one node at down side of the model was encastre supported and other nodes along this edge were allowed in only x and z direction. Besides, 450 MPa pressure was applied to up side of the model in positive y direction. All the models which have been analyzed were constrained by their nodes along the edges without the edge that has some boundary conditions like encastre or etc. Details of the models can be seen in the fourt part in the thesis. Furthermore, material data of the phases (ferrite and martensite) is obtained from 3.1 and 3.2 equation. For all materials, the value of modulus of elasticity is 210 000 MPa, the value of poisson ratio is 0.3 are applied in Abaqus programme. In conclusion, three different 2d models have been analyzed in Abaqus finite element analysis programme to specify and have the answer of how the load and stress get shared between phases during the analysis. Thus, many details about the microstructure of DP600 steel and mechanical performance of the material have been examined.