Microstructure And Mechanical Properties Of CLAM Steel In TIG Weld

As is well-known,reduced activation ferritic/martensitic steels(RAFM) are commonly considered as the primary structural materials for the DEMO fusion plant and the first fusion power reactors because of their excellent thermophysical properties and mechanical properties and their relative mature technical foundation.,for example the low irradiation swelling and thermal expansion coefficient,high thermal conductivity etc..China Low Activation Martensitic steel(CLAM) is the RAFM which have independent intellectual property rights with Chinese and optimized chemical composition and properties.CLAM is considered as the primary structural materials for the China designed ITER test blanket module.As others RAFMs,W,Ta and V etc in CLAM were used to replace Mo,Nb and Ni etc.in common ferritic/martensitic steels,because of the low activation requirement.Welding technology and process is one of the key technologies for CLAM using in project.In this paper,we referenced some research methods of the others foreign RAFMs and the common ferritic/martensitic steels to make the experiment and research scheme.The preheated and non preheated 4mm CLAM plates were welded by TIG,then they were post-weld heat treated.Microstructure and carbide distribution of weld joint were observed by metalloscope and SEM.Hardness and mechanical properties were detected respectively in hardness test and tensile test experiments.According to the results of observed and tested,metallurgical principles and related theories were used to research and analysis welding thermal cycle,microstructure, carbide precipitation,the mechanical properties and hardness of welded joints.As shown in results,grain coarsening lath martensite and high-density dislocations were observed in welding seams and HAZ close to welding seam, and a large number of fine rod-like carbides were precipitated in grain boundaries and martensitic laths' boundaries.High dislocation density is conducive to improving the mechanical properties of weld.Fine carbides play a role of dispersion strengthened,and impede dislocation movement.This makes welding seams showed better tensile properties and slightly higher hardness than the base metal.Noticeable hardening phenomenon was not seen in welding seams because lattice were distortion caused by Carbide precipitation.Most area of the impact fracture is fibre zone,and dimples can be clearly observed in the zone.The fine tempered martensite was observed in HAZ closed to base metal.In the process of welding thermal cycle,this zone equivalent to has undergone a tempering process,the decomposition of martensite and spheroidizing carbides were appeared.The tensile properties of this zone degenerated because the large granular carbides can no longer impede the dislocation movement.Tensile specimens fractured here in the tensile test,and the hardness of this zone is lower than base metal.A soften narrower strip was detected in this zone.