Dear Qamar

The retained ferrite phase in the transformed martensitic phase of the AISI 1045 steel after quenching the steel in oil is due probably the temperature of the quenching liquid, Oil, or the temperature of the ferrite phase prior the quenching. Have you tried to lower the quenching temperature of the oil or lower the ferrite phase temperature than 90 C, if possible, prior quenching.

Dear Prof Khaled,

Thanks for responding my question.

Furnace temperature is 900C, the work-piece is soaked for 15 min at 900C, and then suddenly quenched in oil which is 40C (oil is also agitated for break vapor blanket phase of oil ), I also tried to change the temperature of oil from 30C to 80C, but the result is same, there is ferrite on grain boundaries of martensite that severely damages the machining tool due to long turning chips which entangles on tool causing damage to work-piece and breakage to corner of the turning insert.

Turning chips must be broken and it is related to microstructure, if there would be 95-100% martensite chips would break and if there is ferrite content on grain boundaries of maternsite, chips would not break and creat this problem.

I hope this explanation would help to give me your expert opinion.

Dear Qamar

The 1046 steel , with 0.45%C, can be solution annealed in a furnace at around 825 oC-830 oC to completely transform (Ferrite + Gama phases) to Gama phase, rather than at 900 oC, for an annealing duration of an hour or so . Then the annealed sample can be quenched in a 25 oC oil to get the complete martensitic phase.

Dear Prof Khalid,

Thanks for giving me this suggestion. I think annealing prior to quenching may help in homogenization of alloying element. Let me try this method.

Thanks again.

Regards

Qamar

No problem,

you are welcome

Dear Qamar:

1045 CS does not have much hardenability. How big is the cross-section that you are heat treating? With hardenability equations you can calculate the as-quenched hardness profile for different cross-section sizes and different quench media. As you say that you have ferrite in the prior-austenite grain boundaries, it seems obvious that the quench rate is too low. Water quenching will give you a faster quench and eliminate the ferrite in the grain boundaries. But, it is a faster quench and I do not know the cross section shape and whether or not your part may be susceptible to quench cracking. If it is a round bar, no big problem. If it has sharp corners, you have a stress concentration present and potential for quench cracking. In either case, you need to temper the part immediately after it gets below the martensite finish temperature.

George Vander Voort

Dear George,

Good Morning to you and really thanks for your response on my question. Yes, you are right weight and cross section have much to do with hardenability of a steel and we consider it while heat treating but i missed it in my question. Anyhow the weigh of the workpiece is about 5kg and its a motorbike crankshaft. I tried it in water quenching but it gets crack. So, I have only one option to quench it oil. But here I want ask you that does type of quenching oil also effects quenching rate, hardenability and ferrite content of grain boundaries. If so, what factors should I consider while choosing quenching oil.

Thanks

Qamar

Qamar:

That is a bit outside my area of expertise, as my main focus is on microstructural analysis and failure analysis. A polymer quenchant might give a quench rate in between water and oil. When you tried water quenching, did you remove the crankshaft as soon as possible and immediately temper it? Dan Herring, the Heat Treat Doctor, could probably help you with the quench process. You can probably find his e-mail by searching Google. He published articles regularly in Industrial Heating magazine.

George

Dear Mr. George,

Good Evening to you.

I shall try polymer quenchant.

Yes, I tempered the workpiece for 1 hr at 650C to obtain hardness of 20HRc. But water quenching produces cracks and workpeice also gets bend.

I shall also discuss this mater with Dr. Dan Herring.

Thanks again.

Regards

Qamar

Dear Qamar!

To you has ideally answered George Frederic Vander Voort. I can prompt: Try other steel with the smaller maintenance of carbon.

Dear Qamar:

Yes, you could switch to a steel with more hardenability. As you are tempering to only 20 HRC, you really do not need to use a 0.45% C steel. You could probably use a steel like 8620, with more hardenability, relative freedom from quench cracking and easily Q+T to 20 HRC.

George

Dear Prof George,

You are rightly saying that for 20 HRC steel with 0.45% C is not a good choice but its project from a third tier vendor and end user for the part is HONDA, I have seen original drawing which stats that material should be 1045 or alternately S48C.

May be I should try S48C which has little higher carbon content and its hardenability would also be little higher compared to AISI 1045.

Thanks again to you and Prof Tamaz Vasili Eterashvili.

Regards

Qamar

Dear Qamar

I have gone through the above interesting discussion. I agree with Dr. George Voort regarding the low hardenability of the mentioned steel. In this steel one can not get 95 to 100% martensite in oil quenching at any austenization temperature. You can conduct one trial at austenization temperature of 810 to 815C, soaking time 30minute than water quench, temer at 600C for two hours. Alternativelly go with fast quenching oil with austenization temperature of 850 to 860C, soaking time 30 minute. But in second case one can only get 80 to 85% martensite.

Hello Sanjeev,

I am really thankful to you for your suggestions. I will try both of them. But can you please let me know something about fast quenching oil. what factors should I consider while choosing quenching for Carbon steel.

Thanks

Qamar

sir,

In order to augment the hardenability of your steel you can increase the austenitizing temperature to increase the austenite grain size, try, if possible, 950°C or 1000°C. Furthermore, what is the holding time prior quenching?

Regards,

AG

Be careful how high you raise the austenitizing temperature, especially if you switch to a higher carbon steel, as suggested previously. 1000 C would dissolve at the carbon and depress the martensite start and finish temperatures resulting in retained austenite. If the 1045 is Al-killed, 1000 C will not cause substantial grain growth. Your best bet is to use a higher hardenability steel so that an oil quench will yield 100% martensite and avoid quench cracking.

George

Dear Alain Guilt,

Thank you for your suggestion.

Holding time is 15min at 900C.

You rightly said that Austanite grain size have profound effect of martensite transformation, Lager the grain size of Austanite, lesser would be the ferrite transformation in quenching and finer the grain size of Austanite (larger grain boundary area i.e transformation sites), very high pro- eutectoid ferrite content would be there on grain boundaries of martensite.

But unfortunately the steel which I am using is Al-killed so as Prof George said increasing the temperature would not cause substantial grain growth plus it will also produce de-carburization on surface.

What I concluded from this discussion is, best way is to use steel with high hardenability or to use some good quenchant may be polymeric.

Anyhow thank you Alain Guilt for your support.

Regards

Qamar

Qamar:

I agree with Dr. Vander Voort. And yes, a polymer quenchant would be optimal at a temperature of about 90F-95F. Also, if you are producing these large curly chips, have you tried using a better grade of carbide insert with a chip breaker?

Dear Qamar!

Try to temper (quenched ) in water