Analysis of room temperature after vacuum heat treatment and stripping analysis. Samples of 65 steel heated to 1100e for 5 min were cooled down to 900e at a cooling rate of 33e/min and held for 15 min, and then lowered to 2o/min to 680e during slow cooling. No formation of proeutectoid ferrite and pearlite (eutectoid) structures was observed. The metallographic structure of the specimen after not cooling to room temperature is shown in FIG. 3 . Due to the difference in texture and crystal surface, the surface oxidation coloring changes during the vacuum heating and cooling.

The average area of ​​austenite grains and the difference in Lm2 structure are not etched. It reflects the grain boundary of coarse austenite at high temperature and precipitates proeutectoid ferrite along the austenite grain boundary (or along grain boundaries). (Precipitation), in the form of massive or network-like distributions; followed by the precipitation of lamellar pearlite, which clearly shows the prior austenite grain boundaries and twin boundaries. The black block is pre-eutectoid ferrite. The body, which precipitates and grows from both sides or sides of the austenite grain boundary, and the white block in the middle and lower part is also ferrite. Most of the area in the field of view is a product of eutectoid transformation, ie, lamellar pearlite, whose color is different in different regions. The middle right portion is in a bright white stripe shape, and the upper left portion is in a different shade of black.

It appears that lamellar pearlite nucleation sites are generally located at the prior austenite grain boundaries or at the intersections thereof, and can also be nucleated at the edge of precipitated ferrite or pearlite, and then grown to the austenite grains. It seems that pearlite does not generally cross the prior austenite grain boundaries when it grows. For 65 steel, the leading phase of pearlite formation is ferrite. If the sample of the above tissue is lightly ground (or polished) to 7Lm and then etched with a nitric acid alcohol solution, the microstructure is shown in Fig. 4a, and Fig. 4b is after grinding away 35Lm. Three microhardness indentations can be seen in the field of view. The black structure is lamellar pearlite and the hardness is HV201. The white structure is proeutectoid ferrite. The left side of the field of view is massive ferrite. From the center to the right, it gradually changes from massive to reticular ferrite.

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