best heat treatment to improve impact toughness at -40 ¦C 2

[stanislasdz]

Hi everybody

A friend who work on casting part with this composition (according to the ASTM A 148) want to improve the impact toughness at -40 °C ?

Can anyone give us best practices in heat treatment to improve the impact toughness at -40°C

- What is the austenization temperature AC3 + ????

- Can a homogenization before the austenization improve the mechanical properties?
- Can a normalizing before the austenization may be improve the mechanical properties?
- What is the temperature of the tempering ?
- Is a second tempering may improve the impact toughness ?
- How can we adjust the chemical composition to improve the impact toughness at -40 °C


C 0.13
SI 0.52
Mn 1.31
S 0.005
P 0.011
Cr 0.165
Ni 0.70
Mo 0.06
Al 0.05
Cu 0.08
Nb 0.004
V 0.001
Ti 0.003
Sn 0.004
B 0.0005

Thanks in advance

 

[metengr]

stanislasdz;
The ASTM A 148 specification requires either normalization, normalization and temper or quench and temper heat treatment. Several questions are below based on a review of A 148;

Questions
What heat treatment has your friend performed thus far and what are the impact test results at -40 deg C?

What size casting?

What minimum strength level is necessary for the casting?

What minimum impact value are you looking to achieve at -40 deg C?

Basically, for austenization you need to keep grain size under control. Coarse austenitic grains will result in lower
notch toughness. The quench and temper heat treatment should be the best for notch toughness.

Regarding chemical composition the low carbon content, which you have shown below, is good because this is the main element that affects notch toughness behavior.

 

[stanislasdz]

Thanks metenger !

What heat treatment has your friend performed thus far and what are the impact test results at -40 deg C?

Autenization at 940 °C and tempering at 630-650°C

What size casting?

3250 * 325 * 325 mm bloc test

What minimum strength level is necessary for the casting?

90 Ksi

What minimum impact value are you looking to achieve at -40 deg C?

27 Joules

 

[arunmrao]

LCB grade castings will be more suitable than ASTM 148,which are high strength cast steels.

A comparison of the two indicates that your carbon is low 0.13% and Mn high 1.31%. Did your friend achieve R.T mechanical properties with 0.13% C?(90ksi)

Normally even for 148 grades, carbon is maintained at around 0.25-0.28% and Mn around 1-1.1%. Your Ni addition is good,add some Mo 0.2%(it helps,don't ask how or why?)

Once you have adjusted the chemistry, Normalise and double temper the castings,you will get the -40C impact values. Just forgot add some grain refiners like CaSi,mischmetal,ferro silicon zirconium in the melt just before pouring.


If you think education is expensive, try Ignorance.
- Andy McIntyre


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[stanislasdz]

Hi arunmrao (the casting master)

The data given by my friend indicated that he tried several compositions

here some examples

 

[arunmrao]

I will suggest 0.23% C ,also lower Si around 0.25%, Ni 0.5% and Mo 0.2% atleast for him to get the desired properties. I am still surprised that with 0.13% C,he could record 524MPA. Was the casting water quenched?


If you think education is expensive, try Ignorance.
- Andy McIntyre


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[stanislasdz]

Yes water quenched
Thanks but what about the quenching and tempering temperatures ?

 

[arunmrao]

Why adopt such a risky process. Might as well take the safe route. If you need faster cooling as you have 325mm thick casting,perhaps could have considered fast air cooling by using blowers.

My experience with heavy section castings is limited,perhaps others might come in soon and share their experience.

Good Night!


If you think education is expensive, try Ignorance.
- Andy McIntyre


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[stanislasdz]

You too thanks bro

 

[metengr]

I agree with arunmaro on the proposed chemistry change - increase carbon for strength and offset the strength increase with Ni, for increased toughness. In addition, I would quench and temper for this casting thickness. Austenitize at 870-890 deg C, quench and temper at 595 deg C. You may need to fine tune the tempering temperature based on strength properties achieved based on mechanical testing (tensile and impact).

 

[arunmrao]

Double tempering the casting is essential. The second tempering will have to be done at a lower temperature than the first,say 525-530C.


If you think education is expensive, try Ignorance.
- Andy McIntyre


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