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I have a hardox #10mm plate that needs to be tested on Rockwell hardness.

As hardox is sensible to heat I would like to avoid any heat treatment before the testing.

The plate has been water cut.

The rust from the metal plate should be removed, but I do not have an idea how to prepare the surface without causing heat.

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    $\begingroup$ could do it by hand tools. a person with a file can only go so fast which means metal will dissipate most of it instead of increasing in temperature by much. If it is too fast and getting warm, slow down. $\endgroup$
    – Abel
    Feb 22, 2022 at 12:30
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    $\begingroup$ Scrub it with Scotch Brite 7447 or coarser by hand. Your hands can't be that powerful. There's also rust removal chemicals. $\endgroup$
    – DKNguyen
    Feb 22, 2022 at 15:21

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Sand with silicon carbide paper. Pits will not affect the test, unless the indenter goes into one. You only need to clean the bottom to provide a solid base. If it is structural steel (not quenched and tempered), temperatures below 600 F won't do much. Do you mean ( "hardox") it in weld hardfacing ?

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  • $\begingroup$ Thanks. Nice advice to pay attention to the bottom side. I am using Hardox 450 and the manufacturer says that temperatures above 250°C change the properties. mtladv.com/wp-content/uploads/2016/01/… $\endgroup$
    – elano7
    Feb 22, 2022 at 20:34
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    $\begingroup$ It is quenched and tempered so above 250 C might possible do some softening You probably know that you need a diamond indenter and Rockwell C scale. . And you likely know you only test each location once then move to a new area about 10 mm away. $\endgroup$
    – blacksmith37
    Feb 22, 2022 at 21:15
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    $\begingroup$ The brochure says the steel is only sold in the hardened condition , so it should be HRC 41 to 46, approximately. $\endgroup$
    – blacksmith37
    Feb 22, 2022 at 21:55
  • $\begingroup$ Yes, you are right about the Brochure hardness. I have a task to test the hardness and after that do some welding, gas cutting, milling and test the hardness again. $\endgroup$
    – elano7
    Feb 23, 2022 at 5:52
  • $\begingroup$ This steel has relatively high hardenability and so will be a challenge to weld. I would start with very high preheat, above 400 F and contact a welding consultant. $\endgroup$
    – blacksmith37
    Feb 23, 2022 at 15:17
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Immerse overnight in phosphoric acid, then scrub clean and rinse. The grade of phosphoric to use is that which is sold as concrete prep or concrete etch at Home Depot or hardware stores; it is used to prepare broken concrete before patching and happens to be the right strength to remove oxides from steel. No heat is required unless you are in a hurry and have protective clothing, as hot phosphoric eats iron oxides really fast.

An additional bonus: you can sharpen a dull metal file by soaking it overnight in concrete etch solution. The phosphoric acid is an undercutting etch which means it attacks the valleys between the teeth and leaves the teeth tips sharp enough to cut the skin on your hand.

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