Deep small bore boring tool advice

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A component with following bore & bore profile dimension needs to be machined on a NITRONIC STEEL. Profile & bore dimension description [{[ BORE DIA 9.80/9.88 , at the end of the 9.8 bore a 30 degree angle for a length of 0.15/0.2 followed by 35degree angle connecting to a bore of diameter 12.6/12.7 . The distance from face of the component to start of 9.80/9.88 bore is 72mm ]}] . We tried to finish the bore using a 10mm diameter insert type carbide boring bar . Boring bar holder is made of carbide at the front end where the insert seats an tool steel is fused or brazed to the carbide holder. When we followed the described boring bar we are facing chattering & an incorrect profile on the angle profile area. The part is machined on Mazak CNC Turning center & it is programmed according to drawing. Could you please advice us to achive our requirement.