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Our plant had a issue of surface anomaly as shown below.

I received the part for analysis. I cut the longitudinal sect of surface anomaly. and found the following phases. Although the root cause was the kerf process which was carried out in steel mill based on the lamination of soft layer (Ferrite) on base material (Fig.1).

My question to me is, if it was from steel mill then how come I see the pearlite formation on heat treated part? rest of the OD is free of decarburization (fig.2). Please explain.

Our plant had a issue of surface anomaly as shown below.

I received the part for analysis. I cut the longitudinal sect of surface anomaly. and found the following phases. Although the root cause was the kerf process which was carried out in steel mill based on the lamination of soft layer (Ferrite) on base material (Fig.1).

My question to me is, if it was from steel mill then how come I see the pearlite formation on heat treated part? rest of the OD is free of decarburization (fig.2). Please explain.

What is the base material?  What is the heat treatment?  Could be atmosphere in the furnace causing decarb on the surface, leading to a "slack quench" on the surface.  Please provide more details of the heat treat process.

Thank you 

Our plant had a issue of surface anomaly as shown below.

I received the part for analysis. I cut the longitudinal sect of surface anomaly. and found the following phases. Although the root cause was the kerf process which was carried out in steel mill based on the lamination of soft layer (Ferrite) on base material (Fig.1).

My question to me is, if it was from steel mill then how come I see the pearlite formation on heat treated part? rest of the OD is free of decarburization (fig.2). Please explain.