Smoothed Line Chart
Customizable line tension
Line series has two very easy settings that can control how line smoothing algorithm works: tensionX and tensionY.
This allows tailoring smoothed line to suit your needs and data.
Axis ranges
Axis ranges is another powerful feature of amCharts 4. Besides other uses, it allows defining a range on any axis. Any visual property of the series, that falls within this specific range, will be overridden with specific values.
Demo source