Why select max partitioned column is much slower than indexed one?
Think I mis-understood/mis-read the question initially.


  The table is partitioned on column K1. However the following query
  takes a half minute and the scan count is 170 and logical read is
  603K.


To satisfy the MAX(k1) query in this case requires a clustered index scan of each of the 70 partitions.


  However the similar query on on non-partitioned table with index on K1
  takes no time and scan count is 1 and logical read is 5.


With an index defined on K1, an ORDERED BACKWARD scan of the index is chosen, which probably translates to 4 pages read from the non-leaf index pages plus 1 for the leaf level.