Our apology for not explaining clearly and in details.
Let me explain our concern; and we are not delaying payment (our reputation is also important).
We have orders Q&T bars which I believed that you also understand that all mills do the same way.
If the mill has offer us induction hardening, then it should state so and it is update t us to accept.
All along, my question is why the mill uses induction hardening and not full hardening (Q&T).
I have explained in my previous mail that I am also concern with the microstructure and uniformity
of strength.
I have also concern about how long is the crack and how to confirm how much to cut to remove
the crack.
May I refer to our metallurgist comment, which I believed that the mill will agreed. I can read from
his comment that he is neutral and fair; without taking side with us.
QUOTE:
1. The main purpose for induction hardening is for surface hardened, may be 1-2 mm deep.
2. The case depth may be deeper, or may be through section (for small OD), depends on the
machine capacity (kHz, and kW), heating speed, speed of the bar moving through the coil, etc.
3. For normal NQT process, the soaking time must be sufficient. But in case of induction
hardening, the soaking time may not sufficient, the transformation may be not completed,
especially for the big OD bars.
4. The microstructure and hardness throughout the section and the whole length may be
non-uniform.
5. The crack may be not only the ends, but also other parts. Must check carefully.
6. The reason for the mill to used induction hardening method instead of normal NQT
processes, may be because the want to avoid the distortion.
7. For the small OD it may be possible to NQT by induction machine, but for the bigger OD,
I don’t think it is the proper method.
8. In my opinion, for the bar, the uniform property is required, the normal NQT processes
is much better. UNQUOTE.
I hope that now you have a better understanding of our concern.