what is relationship bet.HRA & HV ( hardness nos.)

There really is not a relationship between the hardness values of the Rockwell A scale and the Vickers hardness scale. Both methods measure the amount of plastic deformation caused by loading an indenter. Attached is a table that you could load into a spreadsheet the values and plot them to see what the result is. There may exist a coincidental relationship.

http://www.carbidedepot.com/formulas-hardness.htm

One reason you can not legitimately convert between hardness scales is because the act of making the measurement changes the apparent hardness of the part you are trying to measure. This is known as work hardening. Different materials work harden at different rates when they are deformed. This is why hardeness measurements are usually relative, or superficial.

Hi Son Pavan,

To my knowledge there no simple conversion formula. ASTM A370 has tables of "Approximate Hardness Conversion Numbers for Nonaustenitic steels" which includes Rockwell A and Vickers.

The notes on the table state the data should not be used for austenitic stainles steels, but are applicable to ferritic and martensitic stainless steels.

It also notes "Where more precis conversions are required, they should be developed specially for each steel composition, heat treatment and part."

If you have access to a copy of ASTM A370, there is some interesting information in there about the different hardness tests that are used.

(Perhaps I should get a life.......)