Effects of Si content on microstructure and toughness of the 800 MPa grade high-strength low-alloy deposited metals
The influence of silicon(Si)on the microstructure and toughness of 800 MPa grade high-strength low-alloy(HSLA)deposited metals was investigated using scanning elec-tron microscopy(SEM),transmission electron microscopy(TEM),and electron backscatter diffraction(EBSD).Experi-mental findings revealed that the yield strength of the depos-ited metal(0.035C-0.45Si-1.47Mn-2.56Ni-0.68Cr-0.62Mo)increased from 850 MPa to 895 MPa,and the tensile strength rose from 917 MPa to 954 MPa,while the impact energy ab-sorption at-50℃decreased from 115 J to 73 J,as the Si con-tent increased from 0.45%to 0.66%.The microstructure of the deposited metal with 0.45%Si primarily comprised lath bainite,with a smaller proportion of granular bainite and lath martensite.However,with an increase in Si content to 0.66%,the microstructure predominantly featured slender lath-shaped martensite,accompanied by some lath bainite.This increase in Si content from 0.45%to 0.66%led to a reduction in the trans-formation temperature of austenite → bainite/martensite mixed structure.As the Si content increased,the lath substructure and block substructure changed from interlaced distribution to par-allel distribution,and both become slender.However,the size of packet substructure increased significantly,which reduces the proportion of the large angle grain boundary of the depos-ited metal,leading to a decrease in its impact toughness.
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