metallography log
Zone 1: weld metal zone
The weld metal zone is where the parent metal and filler metal are heated together to the melting point and then cooled. There are two main microstructural features that can be observed in this zone: they are the Widmanstatten patterns and columnar grains. These patterns are observed to have random directions. The Widmanstatten patterns appear due to large austentite (gamma-Fe) grains being cooled rapidly, as steel is a good conductor of heat. The rapid cooling also resulted in the columnar grains.
Zone 2: grain growth zone
In the grain growth zone, it is observed that grains are just starting to form and grow, and that there are many open grain boundaries. This is because during welding, this zone is subjected to temperature slightly less than its melting point. The exposure to this temperature caused austenite grains to grow significantly. During the cooling to room temperature, this effect is retained as a region of coarse alpha-ferrite grains and Widmanstatten ferrite and pearlite.
Zone 3: grain refinement zone
In the grain refinement zone, the grain boundaries are closed and many small grains can be seen forming. This is because when the metal is cooled to room temperature, the austenite grains will start to nucleate at many points to form smaller austenite grains, and when it is cooled, it will result in fine ferrite and pearlite grains.
Zone 4: transition zone
In the transition zone, both small and large alpha-ferrite and pearlite grains can be observed. This is due to the parent metal being heated to the region where ferrite and austenite coexist, that is, only the pearlite grains have transformed to small austenite grains. When the metal is cooled, the formation of fine pearlite grains with ragged looking boundaries can be observed among the mostly untransformed original ferrite grains.
Zone 5: unaffected zone
In the unaffected zone, there are mostly large grains of alpha-ferrite. This zone represents the region of
The weld metal zone is where the parent metal and filler metal are heated together to the melting point and then cooled. There are two main microstructural features that can be observed in this zone: they are the Widmanstatten patterns and columnar grains. These patterns are observed to have random directions. The Widmanstatten patterns appear due to large austentite (gamma-Fe) grains being cooled rapidly, as steel is a good conductor of heat. The rapid cooling also resulted in the columnar grains.
Zone 2: grain growth zone
In the grain growth zone, it is observed that grains are just starting to form and grow, and that there are many open grain boundaries. This is because during welding, this zone is subjected to temperature slightly less than its melting point. The exposure to this temperature caused austenite grains to grow significantly. During the cooling to room temperature, this effect is retained as a region of coarse alpha-ferrite grains and Widmanstatten ferrite and pearlite.
Zone 3: grain refinement zone
In the grain refinement zone, the grain boundaries are closed and many small grains can be seen forming. This is because when the metal is cooled to room temperature, the austenite grains will start to nucleate at many points to form smaller austenite grains, and when it is cooled, it will result in fine ferrite and pearlite grains.
Zone 4: transition zone
In the transition zone, both small and large alpha-ferrite and pearlite grains can be observed. This is due to the parent metal being heated to the region where ferrite and austenite coexist, that is, only the pearlite grains have transformed to small austenite grains. When the metal is cooled, the formation of fine pearlite grains with ragged looking boundaries can be observed among the mostly untransformed original ferrite grains.
Zone 5: unaffected zone
In the unaffected zone, there are mostly large grains of alpha-ferrite. This zone represents the region of