The material about steel D2?

Question

This steel is Cr12MOV,it's before heat treatment,may by the

magnet adsorption,and treatment after can not,and then to

anneal,magnet also adsorption,THAT'S WHY ??

Answer 1

To harden steel it is heated above the "transformation point", a low red or just above where the steel becomes "non-magnetic".

Then it is quenched in brine, water, oil or even air. The steel becomes magnetic again.  

Afterwards it is tempered by reheating. This reduces the brittleness of the steel a lot and the hardness just a little.

HARDEN D2:

Heat Slowly. Preheat at 1500°F and austentize (NON-MAGNETIC) at 1800 to 1875°F. Hold at temperature for 15 minutes for small tools to 45 minutes for large tools. Quench in air and cool evenly on all sides. A block 3 by 6 in. will harden throughout to 62 to 64 HRC. When salt quenching, quench in salt bath at 1000°F, hold only long enough to equalize temperatures, cool in air.

TEMPERING D2:

Temper immediately at 400 to 1000°F after tool has cooled to 120 to 150°F. Double temper, allowing tool to cool to room temperature before second temper. range of hardness after tempering is 61 to 54 HRC.

IMPORTANT:

A2 and D2 are two common grades which may contain significant (20% or more) ***retained austenite*** (non-magnetic) after normal heat treating.

Retained austenite (non-magnetic) may be undesirable for a number of reasons.

By cooling the steel to cryogenic (sub-zero) temperatures, this retained austenite may be transformed to martensite (MAGNETIC again).

Annealing will also make the steel MAGNETIC again.

Answer 2

I looks like English is not your first language. It is difficult to understand what you are asking.

If you can get help from someone more experienced writing in English  you might get better answers.

Or maybe try to find somewhere to ask in your native language.