C# Windows Form การ Export Excel แต่พอเปิดไฟล์ดู HeadColumn ไม่มีแสดงให้ค่ะ

private void btExport_Click(object sender, EventArgs e)
        {
            string sql = @"SELECT id,Desc,SN,Type FROM tableAs";
            SqlCommand cmd = new SqlCommand(sql, Conn);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds, "data");
            DataTable dt = ds.Tables["data"];

            Excel.Application xlApp;
            Excel.Workbook xlWorkBook;
            Excel.Worksheet xlWorkSheet;
            object misValue = System.Reflection.Missing.Value;

            xlApp = new Excel.Application();
            xlWorkBook = xlApp.Workbooks.Add(misValue);
            xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
            int r = 0;
            int c = 0;

            // DGV To EXCLE ได้ แต่ HeadColumn ยังไม่เซฟเข้ามาในไฟล์ด้วย
            for (r = 0; r <= dataGridView1.RowCount - 1; r++)
            {
                for (c = 0; c <= dataGridView1.ColumnCount - 1; c++)
                {
                    DataGridViewCell cell = dataGridView1[c, r];
                    xlWorkSheet.Cells[r + 1, c + 1] = cell.Value;
                }
            }

            xlWorkBook.SaveAs(@"c:\details.xls", Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
            xlWorkBook.Close(true, misValue, misValue);
            xlApp.Quit();

            releaseObject(xlWorkSheet);
            releaseObject(xlWorkBook);
            releaseObject(xlApp);

            MessageBox.Show("Excel file created");
        }