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,
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??

 

[aansssa]

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.

 

[aansssa]

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

 

[aansssa]

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

 

[redpicker]

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

 

[aansssa]

thanks
rp ji

 

[aansssa]

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.

 

[aansssa]

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

 

[CoryPad]

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?

 

[aansssa]

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

 

[Lyrl]

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.

 

[aansssa]

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

 

[redpicker]

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

 

[aansssa]

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

 

[redpicker]

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

 

[aansssa]

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

 

[aansssa]

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.

 

[aansssa]

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

 

[aansssa]

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 .

 

[CoryPad]

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.