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hardening and tempering
8

hardening and tempering

hardening and tempering

(OP)
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

RE: hardening and tempering

Increase the quench severity (quenchant type, temperature, flow rate), insure steel hardenability via composition, decrease the ratio of part mass to quenchant mass.

RE: hardening and tempering

2
What is the steel composition/steel grade?

What is the section size?

What time/temperature are you using for hardening?

What time/temperature are you using for tempering?

Without knowing these, all we can do is guess at your problem.

rp

RE: hardening and tempering

Can you find the relevant CCT Diagram which may help you understand what is happening.

RE: hardening and tempering

(OP)
sir,
steel composition is C%-0.43,Mn%-0.82,Si%-0.23,S%-0.014,P%-0.032 EN8D grade,
Socket 831 Pc Wt is 1kg200gm,loading per tray was 60 pc in hardening(continues furnace 7 tray)(4back and 3front in soaking area)
time 2hr 20min (including soaking time 1 hr) temperature-860 degree oil temperature-46 degree hardneing hardness-229-255 BHN
tempering temperature 580 degree/ time soaking 1hr 20 min,hardness achived 207-241 BHN

RE: hardening and tempering

Use a faster quenching oil, and reduce the temperature of oil . 46Degrees Celsius is a bit too high, under 40C, will be better.


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

Mahatma Gandhi.

RE: hardening and tempering

Check the delay of the batch before immersion to the quenching bath. Increasing of austenitizing temperature to 870 - 880C should be more effective than lower oil temperature in this case.

RE: hardening and tempering

How thick are the parts? Your material has limited hardenability for thick parts and may never through harden. I disagree with Martinos, changing the austenitizing temperature by 10 degrees C is not likely to be more effective than reducing quenchant temperature or increasing the quenchant flow rate.

RE: hardening and tempering

I am thinking more along the lines of Martinos. I suspect you are seeing the free ferrite/tempered martensite mixture in the microstructure because the parts are cooling to below 800C before hitting the oil. I've seen this in carburizing plain carbon steels, particularly in thin sections.

rp

RE: hardening and tempering

I agree with Cory and Arun. This grade has very low hardenability, and you are trying to quench large loads in a continuous furnace with a relatively high oil temperature. At the very least, you need to experiment with quench parameters:
  • decrease quench temperature--> depending on the oil, you may want to go even lower than the 40 C suggested by Arun
  • increase quench agitation--> Use the maximum agitation/impeller rpm possible within the quench tank
  • increase the time in the quench tank--> it is possible that the parts are not in the quench tank for a sufficient duration
Have you tried a smaller load with the current furnace settings and quench parameters? I would not increase the austenitizing temperature above 860 C. The standard range is 800-860 C for this type of steel (SAE 1045, C45E EN 10083-2, S45C JIS G4051), and since there is likely not a long quench delay with a continuous furnace, this is unlikely to be helpful, and may lead to cracking problems if a more aggressive quench is used.

RE: hardening and tempering

How many parts are quenched simultaneously? Too many together will adversely affect quench rate. Depending on part configuration, I wouldn't be too concerned about cracking if using an agitated water quench.
How long does it take to move from the furnace to the quench tank?

RE: hardening and tempering

60 pieces and about 72 kgs of charge . This is a normal charge weight and I assume it to be a Seal Quench furnace. Thus there is no delay in quenching the parts.


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

Mahatma Gandhi.

RE: hardening and tempering

I agree with TVP, decreasing the load size may help. If the load is too heavy the parts in the middle may be undersoaked.

RE: hardening and tempering

I may have misunderstood the OP: (continues furnace 7 tray)(4back and 3front in soaking area)

If this is a sealed quench furnace, then there is a quench delay when the parts are moved from the heating chamber into the vestibule prior to quenching. However, I doubt that the delay is so significant that the temperature is dropping below 800 C if the full load has been properly soaked to achieve 860 C. If there is a significant delay, say more than 20 seconds, then this should be investigated together with the quench details.

RE: hardening and tempering

Very low hardness after quenching and flat (no much) change after temper indicated that you didnot get a full martensitic structure, in stead, you most probably got lots of ferrite to make the hardness low. This alloy has the capability to hit over 500BHN hardness!

RE: hardening and tempering

Quote:

Can you find the relevant CCT Diagram which may help you understand what is happening.
This is close
http://www.pearson-studium.de/books/3827370597/cd0...
While the composition for the steel in the diagram is slightly lower in Carbon and Manganese, it is close (0.39C and 0.72Mn vs 0.43C and 0.82Mn, which would shift the curves to the right). If you are seeing an as-quenched hardness of 229-255 HBW, this diagram would suggest the microstructure is ferrite and pearlite. No martensite would be expected. The pearlite would be very fine and difficult to resolve with an optical microscope. Are you sure you are looking at 25% ferrite 75% tempered martensite?

rp

RE: hardening and tempering

I suggest doing a metallography exam, section off and polish up some test pieces, etch with nital and hit the martensite spots with a vickers or knoop hardness tests to verify it's martensite and not pearlite. You'll be looking for some high numbers on that.

RE: hardening and tempering

Assuming that a furnace TC is used to monitor the austenitizimg temperature, place a TC on the part to see if you are actually achieving the temp. While it should be OK, it doesn't have to be.

RE: hardening and tempering

Is 229-255 HBW the required hardness or the hardness achieved after quenching?

RE: hardening and tempering

I do not suppose that cooling rate in oil was so low to reach as low hardness as was reached. In my opinion bad austenitization (low temperature, check the sensors) or big delay before immersion can be responsible for that.
I met the problem like this in the past (steel C35).


Metallography should be very helpful. I suppose that there is a mixture of pearlite and ferrite, no martensite.

RE: hardening and tempering

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

RE: hardening and tempering

(OP)
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

RE: hardening and tempering

(OP)
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

RE: hardening and tempering

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.

RE: hardening and tempering

(OP)
THANKS TO REPLY ALL

RE: hardening and tempering

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

RE: hardening and tempering

(OP)
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

RE: hardening and tempering

(OP)
sir plz tell acidity of oil is also affected.
oil acidity is 0.40

RE: hardening and tempering

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.

RE: hardening and tempering

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.

RE: hardening and tempering

(OP)
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

RE: hardening and tempering

Quote:

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:

Quote:

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.

Quote:

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

RE: hardening and tempering

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.

RE: hardening and tempering

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.

RE: hardening and tempering

(OP)
yes always appriciate all posts RP ,arun and other thanks

RE: hardening and tempering

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

RE: hardening and tempering

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

RE: hardening and tempering

(OP)
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.

RE: hardening and tempering

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?

RE: hardening and tempering

What does this mean?

Quote:

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?

RE: hardening and tempering

atibha,
Similar to redpicker comments: The hardness range achieved (207-241) is within the hardness range required (201-255) and thereby meets the specs. What's the problem??

RE: hardening and tempering

(OP)
corypad we are measuring hardness in Brinell hardness tester with 3000kg load and part quench 12-13 min and hot proper
actually customer told that part is break our process is ok everything hardness to micro.but he want to asked if part break and heat treatment is ok hardness is ok micro is ok than should increase hardness specification and or change grade for increase UTS becoz 800N/mm2 UTS part is not break and 730N/mm2 part was break.
so i want to suggestion from ur side what can i do.

RE: hardening and tempering

(OP)
No rp ji i was saying specification of hardness is 201-255 BHN than convert in UTS 650-850 N/mm2
he told that 730 N/mm2 pc break and 830 N/mm2 pc was not break means he asked to her what can change process or material or other that improved UTS or part are not break

RE: hardening and tempering

(OP)
rp will u suggest me how much carbon and Mn should be presnt in material

RE: hardening and tempering

OK. If I understand you correctly, your process is running correctly, but your customer is saying that parts at 217 BHN break in service while parts at 241 BHN do not.

So, you want to change the material so that minimum hardness is 235 (UTS 800N/mm2), correct?

You will need a range of hardness. If you were 201-255 BHN, let's say now 235-285 BHN.

With your process, you will drop about 50 BHN during tempering. So, you will want your as-quenched hardness to be around 285-341 (or higher).

You can probably get there with just increasing C and Mn. If you try to raise the C very much, however, you can risk cracking. I don't know what steels are available to you. You will probably want to limit the carbon to around 0.47 max. I'd try to find something around 0.45 C and 1.00-1.25 Mn.

Good Luck

rp



RE: hardening and tempering

(OP)
thanks
rp ji

RE: hardening and tempering

(OP)
I want to disscuse very simple issues but it is happend 2-3 parts in our heat treatment process.
part name Socket 304 wt per pc 0.520kg,material used EN8D C%-0.42, Mn%-0.85 and Raw material hardness is 179-187 BHN
loading per tray is 180 pcs
normalising temperature is set 860 degree and time 1hr 20min soaking ,7 tray furnace
part hardness required 162-210 BHN and hardness observed 156-170 BHN only proper fan cooling
than increase temperature 10 degree than little bit hardness achived 163 BHN
so plz suggest to me what can i do to improved hardness.

RE: hardening and tempering

(OP)
will u tell be if Skt 220 we will increase tempreature 880°C against 860°C and time 25min against 20 mins /tray soaking than pc will burn.
and pc wt is 0.320kg loading 300 pc per tray.becoz specification is 175-220 BHN .material used EN8D C% 0.42,Mn%-0.86,Si%-0.25

RE: hardening and tempering

For socket 304 if you are normalizing and have low hardness, then you need to cool more rapidly to increase pearlite and decrease ferrite. Can you increase fan speed? Can you decrease number of pieces produced per unit time to allow for faster cooling?

For socket 220, what do you mean by burn?

RE: hardening and tempering

(OP)
sir plz tell me if i have set the temperature of furnace 860 degree and furnace temperature observed 860-861-862-863-864-865 degree .
so plz tell me its ok or not .
and how much degree temperature can varies.and how much permisible deviation should be

RE: hardening and tempering

Permissible deviation is determined by your customer. Some customers require very tight tolerance of ±5°C, while other customers allow tolerance of ±25°C. For a small non-aerospace customer that doesn't specify a tolerance, I'd suggest ±13°C as a common default.

RE: hardening and tempering

(OP)
As quench hardness we achived in EN 18D and SAE4140 is BHN than can u tell me for low hardness we will go higher side tempering temperature 680degree than hardness should low but structure will also affected ferrite % will increase or not .
example:-SKT 609 Specified hardness 241-295 BHN
1-hardening temperature -862°C (Spec.860±10°C) & socking time 1 Hr.
2-Micro structure –Tempered Martensite with % of Ferrite 10
3-As Quench hardness – 514-601 BHN
4-TemperingTime(Socking) – 1 Hr. 20 Mints. & Temperature-680°C (Spec. 450-680°C)
5-As Tempered hardness-269-285 BHN
structure will affected or not in tempering in 680 degree

RE: hardening and tempering

Increasing your tempering temperature to the high end of the range (680C) will not increase the amount of (free) ferrite seen in the microstructure.

As your hardness is within range, I am not sure why you want to increase tempering temperature.

rp

RE: hardening and tempering

(OP)
rp ji quench hardness is too high that why tempering temperature going to higher side plz see i have written my privious mail
and i want to just ask to u plz tell me can i do tempering at higher temperature and what effect in structure

RE: hardening and tempering

Yes, it is possible to temper at a higher temperature than 680C to lower the hardness after temper without causing bad affects on the microstructure. You could probably go up to 690C and be OK. However, most furnaces have a tolerance on the temperature uniformity, +/- 13C is common. If the temperature of the steel starts to go above 700C, you can ruin the microstructure and have to start all over.

How much do you have to lower the hardness? Have you tried to increase the tempering time at 680C? You might find that doubling the tempering time at 680C will solve your problems and you will not have to worry about harm to the microstructure.

rp

RE: hardening and tempering

(OP)
SKT 609 Specified hardness 241-295 BHN
As Quench hardness – 514-601 BHN than lower hardness have range with in spec 241-295 BHN in temered.
yes i hv done at 680 degree temperature to lower the hardness
after tempering hardness come 255-269-285 BHN
means there is no bad effect in micro structure and no ferrite increase if we will go upto 690 degree in tempering
thanks rp ji

RE: hardening and tempering

(OP)
hi sir,
plz tell me how to fix tempering temperature for diff part and different grade becoz tempering temperature depend on as quench hardness and as quench hardness depend upon carbon percent and other alloying element.
so plz tell me how to fixed temperature of tempering.

RE: hardening and tempering

(OP)
hi frds and sirs...
sorry to come very late..
how r all of u..
anyway sir i want one simple question if i will tempered part in temperature 450°C and 400°C than what effect on structure and other properties.
and can i tempered my part at this temperature
what should be range of tempering temperature.

thanks,
atibha

RE: hardening and tempering

(OP)
Sir plz suggest me how to down ferrite % of hardening.
can i increase soaking time than effect in ferrite %
and oil temp. we can same kept 50°C .

RE: hardening and tempering

If you temper 4140 steel at 400 °C to 450 °C, then the structure will be lightly tempered martensite. The properties will be high strength and low elongation and low impact energy.

To decrease ferrite, you need to have high quench severity (high austenitizing temperature, low quenchant temperature, high quenchant agitation). Increasing the soak time will not affect ferrite in the final structure.

RE: hardening and tempering

(OP)
that means if we done with 400-450°C than not much more effect in structure and structure not fully tempered martensite.only stress relief in this temperature for better structure should i go above 500°C tempered.and material is 35C8 grade

RE: hardening and tempering

What strength/hardness do you need? If it is 241-295 HBW, then 500 °C to 550 °C should work.

RE: hardening and tempering

(OP)
sir hardness required 180-220 BHN after tempering and observed after hardening max 255BHN

RE: hardening and tempering

Why are you quench hardening to achieve 180 HBW? Other options seems better (as rolled, normalized).

RE: hardening and tempering

(OP)
hi sir,

please suggest to me for reduce decarburization.
actually new development item i have hard n tempered.
but in final micro observed fully decarb.
its socket Wt. 800gm Spec hardness 201-255 BHN

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