Take a look at the following widgets:
- http://qwt.sourceforge.net/
- http://kde-apps.org/content/show.php?content=14017
- http://www.qcustomplot.com/
Also charts might be a good choice (easy to implement with QML)
https://www.qt.io/blog/2013/11/07/qt-data-visualization-technology-preview-and-charts-1-3-1-release
or implement one by yourself with
https://doc.qt.io/qt-5/qtwidgets-graphicsview-diagramscene-example.html