hardening and tempering 8

[aansssa]

Hi sir ,
i want to ask that how to controlled ferrite % in hardening and quench tempered steel.
after hard and tempered structure observed tempered martensite with 25% ferrite plz tell how to control ferrite level

 

[weldstan]

atibha,
Finally, have you confirmed the chemistry? It is not inconceivable that you could have a mixed steel.

 

[aansssa]

arunmrao no delay of quench quench delay time only 20-25 sec.
and furnace is not sealed quench its continuous furnace.7 tray area in furnace and each tray come out after 20 min

 

[aansssa]

corypad hardness come after hardening 229-255 BHN and
required hardness is 201-255 BHN after tempering
and after tempering hardness come is 207-241 BHN

 

[CoryPad]

Where on the part was the hardness measured? How thick is the part? If low surface hardness is detected after quenching, it suggests that the temperature was not high enough and you were in the austenite + ferrite field instead of in the austenite field. If the low hardness is in the center of a thick part, then it could mean inadequate quenching.

 

[aansssa]

THANKS TO REPLY ALL

 

[aansssa]

MAGBEN U WANT TO SAY THAT hardness of quench too low it should be higher side

 

[aansssa]

TVP how much quench tank time should be for sufficient duration.
how much quench hardness should be.it should be higher side for less ferrite
how much quench oil temperature and how much quench delay should be

 

[aansssa]

sir plz tell acidity of oil is also affected.
oil acidity is 0.40

 

[CoryPad]

Steel with carbon concentration of 0.43 % (and no Ni, Cr and Mo) should quench to > 500 HBW if the section size is not too large (~ 10 mm). Your as-quenched hardness plus microstructure suggest either the part was too cold prior to quenching or your part is thick and you cannot quench the core to achieve a high hardness.

 

[arunmrao]

They need to recheck the chemistry of steel ,their hardness measurement and calibration of thermocouple used.
It baffles me, that for a thin sectioned medium carbon steel material, low hardness is a issue.i would have expected discussions, regarding cracking or methods to lower hardness.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[aansssa]

TVP how much quench tank time should be for sufficient duration.
how much quench hardness should be.it should be higher side for less ferrite
how much quench oil temperature and how much quench delay should be

 

[redpicker]

how much quench oil temperature and how much quench delay should be

This depends on the specific oil you are using. The chemistry you quoted is not very hardenable, so you will need the temperature recommended by the oil manufacturer that will give the fastest quenching rate. The people who sold you the oil should be able to help here.

The other questions can be determined by looking at a CCT diagram. Referring to the CCT diagram referenced to from my post on 7 Jan:

how much quench tank time should be for sufficient duration

A cooling rate that would produce 50% ferrite, 50% pearlite with an as-quenched hardness of 95 HRB (215 DPH) will get your from 845C to 100C in two minutes. Since this is unacceptable, two minutes in the quench should be sufficient. I like overkill on quenching, so you could consider 10 minutes in the oil. It wouldn't hurt and would make sure the quench time is not your problem. If you need to shorten it to maintain the cycle time for furnace, that should be OK, but I wouldn't want to go less than 5 minutes.

how much quench hardness should be.it should be higher side for less ferrite

From the diagram, a mixture of 10% ferrite 90% pearlite would give you an an-quenched hardness of 21 HRC (242 DPH). 10% ferrite and the other 90% a mixture of bainite and pearlite would be 28 HRC (284 DPH). I'd assume DPH is 10KG Vickers. This tells me that you should be aiming for around 28 HRC as-quenched.

Now, understand that the diagram is not for your exact chemistry. You have a bit more C and a bit more Mn. Both of these will affect the results toward higher hardensses and longer transformation times. This is why I;d use 10 minutes in the quench. The higher carbon and manganese will increase your hardness targets, too, so you could consider an as-quenched hardness range of 28-32 HRC; that is if you are below 28 HRC, you probably will have too much ferrite and you should be closer to the 32 to make sure your process stays in control.

rp

 

[TVP]

I agree with redpicker, at least 10 minutes in the quench. I have been assuming that the goal was quenching the parts to 90+% martensite in the core, and then tempering them to reduce hardness/increase toughness. When quenching to > 90% martensite, the core should be > 50 HRC (>500 HB or HV). In general, the quench temperature should be high enough to prevent distortion and cracking, but low enough to produce the desired cooling rate (quench rate). If you intend to quench so that the core is hardened to martensite, then the temperature will need to be relatively low, say 30-80 C, depending on the exact oil being used. The quench delay should be as low as possible, and is typically in the range of 10-40 seconds. You want to be closer to 10 seconds than 40 seconds.

 

[arunmrao]

RP, always a pleasure reading your posts, though at times contrarian to generally held opinions. Cheers, keep it up. and a well deserved star.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[aansssa]

yes always appriciate all posts RP ,arun and other thanks

 

[redpicker]

Thanks for the kind words, arunmrao.

As for being a contrarian, I was taught long ago that generally held opinions are great for understanding things, generally. But, when you start dealing with specific problems, general opinions often can be misleading.

rp

 

[aansssa]

how to increase UTS in part Grade EN 8D with hard and tempered

 

[aansssa]

IN SKT 609 used material EN 8D C% 0.41, Mn% 0.82,raw material hardness 217,207
As quench 863degree,as quench hardness 255-302BHN ,oil temperature 39-52 degree.
Tempering Temperature 620 degree hardness achived 207-241 BHN specified hardness 201-255 BHN
customer told that 730 N/mm2 UTS Pc break and 830 N/mm2 pc not break.
plz tell me how can be analysed.
when hardness increase UTS all most will increase than should change material S45C against EN8D or other option.

 

[CoryPad]

This is the same problem discussed in the previous 35 replies. Either the part is not hot enough to be fully austenitized, or you are not quenching the part enough. The as-quenched hardness should be much higher. Where are you measuring hardness? What is the part shape?

 

[redpicker]

What does this mean?

customer told that 730 N/mm2 UTS Pc break and 830 N/mm2 pc not break.

Does it mean the customer requirement for UTS is 830 N/mm2 but you only achieve 730 N/mm2 for UTS?

What are the requirements you are trying to satisfy?