High-strength weld toughness decreased with the strength reduction
The size of the columnar crystals in the three heat input conditions occurred change significantly, the width of the columnar crystals of the welding condition for 70fzm, the width of the columnar crystals of the welding condition reached 150pm. As can be seen from the microstructure, are not the grain boundary ferrite are acicular ferrite microstructure, but, with 4/5 of the increase, the weld organizations gradually coarsening 3 under the conditions of the welding conditions acicular ferrite appears granular observed massive ferrite. Acicular ferrite and a transmission electron microscope structure, can be seen between the ferrite and ferrite was a large inclination intersect, which is the basic characteristics of the acicular ferrite. The black islands is the MA group it Nuisance extremely high dislocation density.

For high-strength weld mainly refers to the tensile strength of theWelding Wire780MPa level, it is martensite, but also some lower bainite or lower bainite and mixed organization's, these organizations Nuisance effective grain size fine grain products do not belong to the organization, so as to increase the strength of its toughness decreased. However, for tensile strength of weld metal at the level of 400-780MPa. With strength increase its toughness curve changes, this change and the tissue is closely related to the change of. Low weld strength of their organization ferrite + pearlite low intensity, toughness is good.
However, because of its alloy content is less, the use of a large heat input welding, ferritic appreciate coarsening also decreased, decrease in the strength while toughness. For weld strength in the 490-590MPa class increased alloy content, hardened improve Ah, generate bainite. Because the upper bainite coarse grains are likely to form the junction of the W's body lath martensite islands, also called MA element. This element as the second phase exists, while strength mention Xie, but also the toughness is significant decline in the performance curve for the next Picheng. When the weld strength is further increased, due to the higher alloy content. Decline in the phase change point of the weld after the phase change may generate lower bainite, such lower bainite characterized in that the fine carbides in the bainitic internal precipitation of lath, compared with the upper bainite, effective grain size can be refined toughness again, showed dagger slope curve.

When the intensity exceeds 780MPa, tissue appeared martensite, i.e. generate the lower bainite and martensite mixed structure of this case the Welding Electrode Manufacturer乂 To reduce, downhill curve presented in Wen 6-51; When strength close to or more than 980MPa. their organizations into a single martensite and lower toughness. To sum up, the different levels of strength weld metal. Their organization is not the same, there under the Nuisance curve toughness.