Bar Chart Group By

I have the simple FACT table "Piece" with the columns "Piece Key" and "Duration". A piece key may occur multiple times (as seen in the left table below). Yet, I want to group by "Piece Key" to get the summed duration per piece (as seen in the right table below; 407436 is summed to 60)

This works fine so far.

The DAX code I use for grouping by "Piece Key" is the following:

Duration SUM = 
CALCULATE(
    SUMX(
        SUMMARIZE('Piece', 'Piece'[Piece Key], "SumDuration", SUM('Piece'[Duration])),
        [SumDuration]
    )
)

Yet, I want to show the distribution in the sense of frequency per summed duration in a bar chart. But it does not work, I cannot drag & drop my measure with the summed duration by piece key into the x-axis field. How can I do this?

I can only use duration for each row, so it counts the value "30" twice, instead of summing it up to "60" and then counting "1".