There are two ways to achieve this.
The first one is to hide the whole coordinate system:
m_view.chart.cartesianSystem.visible = NO;
The second one is to hide lines only by altering properties of axes and grid lines.
For example, to hide the line of X-axis, do the following:
m_view.chart.cartesianSystem.xAxis.lineVisible = NO;
To alter the appearance of grid lines, you can use properties of the class NChartAxisGrid. To access the grid lines, you can use getters of cartesianSystem like xAlongY and similar. For example, to hide grid lines that are perpendicular to X-axis and stroke along Y-Axis, do the following:
m_view.chart.cartesianSystem.xAlongY.visible = NO;
However after that the border of plot area will still be visible. To hide it too, do the following:
m_view.chart.cartesianSystem.borderVisible = NO;