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

 

[CoryPad]

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

 

[redpicker]

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

 

[FennLane]

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

 

[aansssa]

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

 

[arunmrao]

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.

 

[Martinos]

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.

 

[CoryPad]

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.

 

[redpicker]

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

 

[TVP]

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:
[ul]
[li]decrease quench temperature--> depending on the oil, you may want to go even lower than the 40 C suggested by Arun[/li]
[li]increase quench agitation--> Use the maximum agitation/impeller rpm possible within the quench tank[/li]
[li]increase the time in the quench tank--> it is possible that the parts are not in the quench tank for a sufficient duration[/li]
[/ul]

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.

 

[weldstan]

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?

 

[arunmrao]

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.

 

[dbooker630]

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

 

[TVP]

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.

 

[MagBen]

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!

 

[redpicker]

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/cd01/Articles/ASM/1040.pdf

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

 

[DeleteriousPhases]

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.

 

[weldstan]

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.

 

[CoryPad]

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

 

[Martinos]

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.