1144 Steel Hardness Problem

[mtnz]

Hi Guys!

I am currently doing heat treatment of cylindrical shape-1144 Steel. I am trying to harden them from RC40-45 to RC50-52. I set up the furnace on 1575 degrees. Based on the smallest cross section, soak time is about an hour. The outcome is always harder than we expect (around 60ish). What can I do to solve that problem?

Thanks!

 

[weldstan]

What is your quench medium?

 

[bobjustbob]

What temper temperature are you using?

 

[EdStainless]

RC60 is the as quenched hardness, right?
And you don't have any sections thicker than about 1/4", right?
Bob is right, what temper temperature are you using?


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P.E. Metallurgy, Plymouth Tube

 

[AidanMc]

I looked at the Heat Treater's Guide and it only quote 52-55 HRC as-quenched hardness. What type of atmosphere are you using for heat treating?

And to echo everyone else, it looks like it should be about a 300°F tempering temperature (though I suppose that could have to be adjusted for the higher as-quenched hardness).

Aidan McAllister
Metallurgical Engineer

 

[mtnz]

Hi Guys!

Thanks for following up on the issue. Let me explain the process then I can hopefully get your thoughts.

The material is 1144 Steel.The hardness before quenching is RC40-45. The furnace is set up 1575 degrees. (I tried 1550 and it was harder than before..). The smallest cross section on the part is 3/4" that is why soaking time is 50-55 minutes (cylindrical shape part ). As soon as it is done, oil quenching is taking place. They stay in there for like a minute then we put it in another mixture to get the grease out. Then we test the hardness, it comes up always harder than expected. we expect RC50-52 but it is around RC60. So we have to temper it on 500 degrees for 2 hours to be able to get the desired hardness.

This whole process takes about 3-4 hours which is more than we want. So let me ask you couple questions if you don't mind;

1)Is there a way to get RC50-52 without tempering with 3/4" cross section thickness part?
2)Do we have to temper it if it is bigger or smaller than a certain thickness? Is there such a rule about tempering after oil quenching?
3)What degree is the oil supposed to be at? Does it possibly affect the process a lot?
4)Do you see anything wrong in the process that I explained?

I am actually new in heat treatment so please don't mind me. I appreciate your help!

Thanks

 

[bobjustbob]

What properties do you want the final part to have? Is hardness the only acceptance criteria?

1. Maybe, forced air cool. I would not recommend leaving a part in the un-tempered condition.

2. You temper to relieve stress and temper back to your final properties. The section size really does not matter beyond soaking time.

3. Consult your quench oil supplier. Oils are designed to work at a certain temperature range.

4. The only critique I would have is the time in the quench. 1 minute seems too short of a time to fully remove the heat out of the center of your section thickness. Are you using a batch process or a continuous belt type reheat furnace? I am assuming that you are going from the quench directly into a water based washer, is this correct? What temperature are the parts at when going from the quench into the washer?

 

[mtnz]

Hi Bob,

We want them to have RC50-52 hardness. Yes, That seems like the only acceptance criteria. Before quench and temper, they are in RC40-45 range hardness.

So, as you say "The section size really does not matter beyond soaking time", Does it mean that even if the part more than an inch or smaller than 1/8" , they can both stay in the furnace let's say an hour. How do we decide how long those parts will stay in the furnace? I mean what is our criteria beyond deciding soaking time?

We are using batch process. And yes, we are going from the quench directly into a water based washer. I will check the temperature of the parts today and let you know. I didn't have a chance to go very deep yet.

 

[EdStainless]

It sounds like the material in normalized to start with.
The only way to get it harder is to quench and for martensite.
The only way to keep that martensite from being extremely brittle is to temper it.
Your process time is very normal. That is all that there is to it.
The only other option is to change materials and go to lower C content.
But that is a bad idea if it means leaving out the temper.
You will have no toughness without some temper step after quench.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bobjustbob]

I agree with Ed. You are probably getting the material in in the as normalized condition. Check your incoming material certs for confirmation. If so the only way to harden the parts with with a faster cooling. With that should go a temper.

If you want shorten your cycle down to a normalize only, you will need to adjust chemistry. I would ask your supplier for a normalized material with the hardness that you want. Your material is not going to have much impact toughness but if that is not a concern.

 

[dbooker630]

You could change to a higher carbon steel such as 1060 or 1065 and send to an outside heat treater for austempering. This process quenches the part in salt directly to the desired hardness range with no additional tempering required. Toughness will be better than if using 1144 in the as-quenched condition.

 

[mtnz]

Thanks for the answers!! I am now trying to see if we are wrong in timing so I have couple more questions...

1)How long should I temper it at the beginning of the process? (500 degrees for 1144 steel)
2)What would be the ideal oil temperature and how long should I quench ?
3)What would be the ideal part temperature before they go in water based washer?
4)I would like to measure the temperature of the oil and the parts. What kind of a thermometer can I buy?

Thanks!