Satyabrata,
The JSFiddle that you have shared initially seems to have secondary axisY with dataSeries attached to it and toggling dataSeries through legend. To disable toggling (hide / show), you can remove toggleDataSeries function attached on click of legend and you can remove axisY2 by not attaching any dataSeries to it as shown in this updated JSFiddle.
my Secondary Y axis curve (axisY2) is always hidden
It would help us understand your scenario better and help you accordingly if you can create JSFiddle reproducing the issue you are facing or a pictorial representation of your requirements and share it with us.
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Vishwas R
Team CanvasJS