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Study on the Process Optimization and Performance of Electro-superplastic Welding of Cr12MoV/40Cr

Author: WuZhiWei
Tutor: ZhangKeKe；ZhangZhanLing
School: Henan University of Science and Technology
Course: Materials Processing Engineering
Keywords: Cr12MoV Steel Electroluminescent superplastic Welding Microstructure Mechanical Properties
CLC: TG406
Type: Master's thesis
Year: 2011
Downloads: 31
Quote: 1
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Abstract


The electroluminescent superplastic welding is a combination of superplastic welding and electrical plastic in one special connection method. In this paper in order to improve the superplastic welding quality, the study of the theory of solid-state welding process a large volume fraction of carbide steel electroluminescent superplastic welding, enrich and develop materials for such a large volume fraction of carbide steel difficult to weld materials high quality connection to provide a new way. 40Cr steel steel Cr12MoV and by salt bath circulation quenching ultrafine processing a large volume fraction of carbide as the object to study the feasibility of two electroluminescent superplastic welding. First the hot rolled annealed Cr12MoV steel Electro mechanical properties of superplastic compression, electroluminescence analysis of the steel the superplasticity compression the carbide process parameters affect the laws of the evolution of behavior and the fine organizations based Cr12MoV/40Cr steel electric caused superplastic welding the orthogonal experimental and optimization of process parameters study on the electric field strength and the main welding parameters on the microstructure and properties of the Cr12MoV/40Cr superplastic welded joints, on this basis, proposed Cr12MoV/40Cr steel electric superplastic welded joints formation mechanism model. Experimental results show that: 800 ℃, initial strain rate of 1.5 × 10-4s-1, the electric field strength under conditions -2kV/cm compression, of Cr12MoV and 40Cr steel stress-strain curves both showed typical superplastic features, steady flow varying stress than conventional superplastic compression reduced to varying degrees; electroluminescent Cr12MoV Steel Superplastic compression compared with conventional superplastic compression to impose -2kV/cm electric field can make the strain rate sensitivity index increased from 0.21 to 0.24, the strain activation energy The reduced to 224kJ/mol, the Cr12MoV steel and the cycle quenching effect of 40Cr steel superplastic compressive deformation conditions, the electric field can be increased by 241kJ/mol. Cr12MoV/40Cr electroluminescent superplastic welding orthogonal test and optimize the test results show that the optimal welding parameters: welding temperature of 800 ° C, electric field strength 3kV/cm, welding time 10min, the initial strain rate of 1.5 × 10 -4s-1, corresponding to the welded joint strength (667MPa) reached 95% of the strength of the 40Cr base material the same thermal cycle state, and increased by 8% than the conventional superplastic welding joints on both sides, the radial deformation were less than 5% and Cr12MoV side of a small amount of deformation. Important role in the electroluminescence of Cr12MoV the superplasticity effect in Cr12MoV/40Cr electric induced formation of superplastic welded joints. The electroluminescent superplastic welded joints Cr12MoV/40Cr interface area can be divided into the transition zone and the base metal. Interface region by a discontinuous distribution, the Fe-Cr nano-particles of the size less than 100nm, local dynamic recrystallization, and the particle interphase was random distribution of ferrite and ferrite (α / α), ferrite and carbides (K / α), and carbides (K / K) connection region. Transition the area Cr12MoV side grain was equiaxed Intragranular Dislocations less dislocation around the grain boundary carbides grain boundary was wide phenomenon, showing obvious superplastic deformation characteristics; 40Cr side for coarse the ferrite grains, to unevenly distributed depleted carbon region. Promote dislocation motion electric field enhanced superplasticity effect of the interfacial region of grain boundary sliding and grain rotation, is conducive to the diffusion of the elements and promote increased 40Cr-side width of the carbon-poor areas. Electroluminescent superplastic welding tensile fracture surface can be divided into: class original interface and the metallurgical bonding. Joint fracture mainly to the interface region of the ferrite substrate and the carbide (α / K) fracture. Electric superplastic welded joints welding defects: the mechanical bonds area, interface MICROVOID, and inclusions. The electric field enhances the interface on both sides of the rotation as the representative of the grain boundary sliding and grain superplastic effect, to accelerate the diffusion of elements, promoting the formation of a metallurgical bonding zone, thereby to obtain a good welded joint.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Metal welding and test methods
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