Low Impact properties of 4130 Steel 2

[jimsan]

Does anyone have experience of improving the Charpy impact properties of 4130 steel @ -101C in the hardened and tempered condition?
Although general structures and tensile properties are good, Charpy Impact results are as low as 10 to 15 Joules despite good control of heat treatment and testing methods

 

[metengr]

What was your heat treatment? Tempering temperature?

 

[jimsan]

water quenched & tempered @ 700 C

 

[metengr]

I just noticed that your impact test temperature is -101 deg C? Is this value correct or should it be -10 deg C?

 

[metengr]

At this point I am going to assume your impact test temperature was -10 deg C for the stated values.


The carbon content has the biggest effect on impact values for low alloy steels. The next biggest driver is prior austenite grain size - a course grain size prior to transformation will lower impact values.

If I had to guess, I would suspect your prior austenite grain size was larger than desirable to drive the impact values to being lower than expected.

 

[jimsan]

Thanks guys but -101 C is correct!
Our customer is looking for minimum 27 joules

 

[arunmrao]

Can you consider double tempering. How much was the retained austenite after tempering.

 

[TVP]

The impact toughness of almost any martensitic steel is going to be quite low when tested at - 101 C. If you must use 4130, then you will need to have an extremely fine prior austenite grain size in order to achieve good toughness. This means an ASTM number of 8 or higher, preferably 10 or higher. In order to achieve this, the hot-rolled material (bar, rod, plate, etc.) should be thermomechanically rolled, also called controlled rolling, with a lower rolling temperature. Then the heat treating process must use as low an austenitizing temperature as possible, meaning 845 C rather than 870-900 C. Also, the steel must be extremely clean, meaning S ~ 0.005 or less, little O & N, inclusion modification using Ca, with ASTM E 45 levels of 1/2 or less. Unless you have a close working relationship with your steel suppliers, then I doubt you will be able to obtain 4130 that meets all of these parameters.

 

[jimsan]

This part is a forging made from steel bar of grain size of about 6/7. Forgot to mention that!
Hot forged, then quenched & tempered.
Would agree fully about cleanliness & grain size but will be very unlikely to get GS of higher than 7.

 

[TVP]

Then in my opinion, you will not achieve the requirement of 27 J at - 101 C.

 

[jbeckhou]

Can you use other material such as A350 LF3 Class 2. That material will meet your charpy requirements.

Petrotrim Services

 

[metengr]

Agreed, you will need to change material to meet 27 J at -101 deg C. At this point, you need nickel as an alloy element.

 

[redpicker]

This part is a forging made from steel bar of grain size of about 6/7. Forgot to mention that!
Hot forged, then quenched & tempered.
Would agree fully about cleanliness & grain size but will be very unlikely to get GS of higher than 7.

You will get improved results if you add a normalizing treatment before the Q & T. Section size and surface condition as well as the quenching process can also be very important, since 4130 can be somewhat shallow hardening.

There are steel producers that market modified 4130 chemistries (increased Mn, Cr, and Mo, with improved cleanliness) that will get you there.

rp

 

[MetalGuy10]

I agree with met engr that you should consider a nickle alloy.

A nickle alloy is not cheap, but after all that special processing you may still fall short on impact properties for such a low temperature. The higher cost may also be ofset by avoiding a service failure.

I reviewed a few Nickle 718 alloy test reports that a for an API type application,the charpy test was performed at -75 F(-59.4C) with impact values that range from 40 ft/lb(54 J) to 50 Ft/lb(67.8J). The yield strenght averages 130 KSI (896 MPA).

Obviously, 718 is not the only option.

 

[Guest102023]

I agree with comments about prior austenite grain size, and the doubts about 4130 having any possibility of meeting requirements at that low temperature (-101°C).

I think metengr is suggesting nickel alloy steel, as opposed to a nickel alloy. I concur with that also.

 

[deadrange]

TVP,
I'm a little confused by your statement about prior austenite grain size. The austenitic grain size is not going to change due to thermo-mechanical work. It is established during the casting/solidification of the material. I think you are looking at the ferritic grain size which can be controlled by thermo-mechanical work.
In all of the above statements noone has asked yet how the material is being quenched. Induction versus a longer hold austenitize. This along with the austentize temperature will change how much carbon goes completely in solution. I would assume that the heat treater is austentizing at a temperature sufficient to get the carbon in solution, but it doesn't hurt to ask.

I agree that nickel should help the Charpy impact toughness of the material. And I have heard from a few suppliers of mine that a small additional of titanium will also help improve the Charpy impact toughness as it binds with some of the excess Nitrogen.

 

[metengr]

In all of the above statements noone has asked yet how the material is being quenched.

It was provided by the poster -

water quenched & tempered @ 700 C

 

[deadrange]

metengr,
I think I phrased my statement incorrectly. What I was trying to find out was the austentizing procedure. A induction heated and quench and tempered product vs. a continuous/box furnace heat will produce different Charpy results.

 

[TVP]

deadrange,

The austenite grain size is very much affected by the temperature at which hot working is performed. I suggest you review some references on the subject. Here is one:

http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=EN&NM=267