Cracks with Induction heat treating of 1144 steel

[BeginnerHeattreater]

I have started with a company that uses induction heat treating on a part made from 1144 steel. The part is an adapter with the OD .73", ID .5" and .46" length with external threads. The requirements of the customer are HRC 59 min with a case depth of 0.01" - .100". We are experiencing circular cracks and melted threads periodically. The operators can only adjust the amount of water used when quenching and the voltage. There are no set variables for these. I am looking for any kind of advice of temperatures and time at heat treatment and after quenching. These parts are not tempered. They claim that they have never had this problem in the past 11 years.

 

[Steve898]

Rule #1: Don't induction harden 1144!
Reality #1: Everybody does it.

The cracking and melted teeth sound to me like the operator has turned the power up to get the hardness (or slowed down the scan rate).
The operator may have done this because the parts are not getting hard. This may be due to plugged quench ring, wrong polymer concentration, or even poor lot of material. You may also see if the operator is double hardening them (running them twice).
59 HRC is pretty high for this material.

 

[BeginnerHeattreater]

Thanks for the quick reply. We have been using the same lot of material for over a month and the certs are similar. The operator had not double hardened the first batch of cracked parts, but since then everything is being hardened twice to supposely help see the cracks.? The operator has told me that he starts his process by melting the first part and then turn down the voltage until the hardness is reached. When I ask about the quenching of the part, they have no clue of time and temperature that it should be. As long as the hardness is there, they run it. The temperature of the part after quench has been anywhere from 70°F to 130°F. This is where I need help.

 

[Steve898]

How are these quenched, spray or dunk?
What is the quenchant?
What is the temperature of the quenchant?
What is overall length of the part?
What type and brand of induction machine?
How much space between the coil and the part?
Do the cracks run along the length of the part?
Can the cracks be seen while heating in the coil?

Please don't double harden without annealing between. The risk of cracking gets very bad.

 

[BeginnerHeattreater]

Parts are sprayed with deionized water at 70°-75° degrees and the length of the part is 0.45". The machine is from Ameritherm model XP-30. There is 0.125" space between the part and the coil. The crack is circular mainly in the id about 0.050" from the top of the part, but some of the cracks will go through to the od of the part. The cracks come periodically therefore no one has ever been able to recreate the cracking. The cracks were found when someone picked the parts up to inspect them dimensionally.

 

[redpicker]

As far as the melting goes, don't get it so hot. ;^) No need to go over 1800 deg F.

Consider using a water-based polymer such as aqua quench 364. It may help the cracking. Also, you may want to monitor the temp of the part after quenching. There is no need to quench below around 400degF (that is, it can air cool from 400). Maintaining a minimum hardness of 59 HRC is unrealistic. 1144 has a minimum carbon content of 0.40% which will only develop a maximum hardness on quenching of 56 HRC. I would not want to use these parts without any temper; even a 400 deg F temper is better than nothing.

Nearly every problem I run into I get told that they never have had this problem before. Almost always, it's the same old problems, just a new day.

 

[Steve898]

Add the 364 to the water and promptly temper them at 300F for 1 hour.
I believe this is a crack due to the severe water quench.
As the parts set for a while, and the shop is quiet, you may even hear them crack. They may even crack while in use. Untempered water quenched 1144 overheated in an induction coil is not a good story to tell a customer.

Redpicker is right. I get that "never had the problem before" reply all the time.

 

[BeginnerHeattreater]

I am printing this off and holding a meeting this morning to share the information. Thanks again.

 

[BeginnerHeattreater]

Where can I buy the 364? I looked on the website and didn't see where I could purchase any.

 

[EdStainless]

One other rule, "We didn't change a thing" really means, 'We never checked that before.'

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[TVP]

Aqua-Quench products are sold by Houghton International. I HIGHLY recommend you contact D. Scott Mackenzie at Houghton to discuss the exact nature of your situation. A variable that has not been discussed yet is distortion, and it can become a huge problem even when everything else is tightly controlled. Use the following link for more information:

http://www.houghtonintl.com/

 

[Steve898]

http://www.houghtonintl.com/index.html

Houghton International

 

[gearman1234]

A few factors need to be considered.

Water quenching is not recommended for 1144. Oil quenching would not result in a thermal shock and the possibility of cracks will reduce with oil quenching.

The safe hardness for 1144 with my experience is about 45-50 HRc.

Having said that it is also important to note that circular cracks are a result of unveen cooling due to water. There may be some contamination in the heta treat tooling or formation of bubbles in water etc.

Secondly threads are inherently prone to cracking. Is it possible for the heat treater to mask it to prevent hardening?

 

[inductionexpert]

ASM Heat Treat Book says max hardness 52-55 RC, so you are pushing the limits f the steel.

The cracking could be caused by overheating, the word melting indicates you may be overheating. Overheating will cause cracking. Depending on how much sulfer is in the bar, and if it has any stringers of sulfur and how close the stringers are to each other can cause cracking in 1144.

Can you vary the scan speed?

Fred Specht
847-606-9462