4130 machining, welding, heat treat- What comes first??

[AZsuspension]

We curently process a raw 4130 tube Rc22 as follows; Machine internal and external threads, weld 4130 plates and ears to the partial length of the tube, rebore ID, final hone ID.

Can we heat treat the raw tube to a Rc 30-35 to make it easier for initial and rebore machining?

What does this do to the weld strenght and overall strength of the tube? We are TIG Welding using 70s or 80s filler material.


Thanks,
AZ

 

[metengr]

AZsuspension;
I have several question/comments for you to ponder after reading your post;

1). If you currently process 4130 tube supplied with no specified heat treatment for minimum mechanical properties why would you increase cost of the product by introducing an added heat treatment step? Yes, I understand increased machinability but this cost needs to be compared to introducing another fabrication step.

2) If you introduce a heat treatment step prior to welding be aware that welding will locally affect the mechanical properties of the 4130 steel adjacent to the weld regions. You can weld first and perform the heat treatment operation. However, since you have been producing these components with no requirement or need for a minimum strength level above what 4130 is being supplied at 22 HRc, what is the cost benefit?

 

[AZsuspension]

Thank you for your help. I appreciate it very much. I hope to give you as much information as possible so that we can figure out what is best for our product.

As a an owner / engineer I am always striving to improve our product while looking at the cost. The cost of heat treatment is minimal on the front end and looks like it could be a benefit, but we are worried about the strength / brittleness / toughness of our welded area, if we choose to try this method (method ii).(our current method works very well)

--Our goal is to improve our product, without incurring massive costs, or compimise strength.(maybe even save money, or processing time... a small dream)

Do to our material properties we can not rebore to a good size and finish and therefore incur a very large honing cost due to the amount of material we end up having to remove. The reboring and honing shops "dislike" our soft gummy material.

so...

1) No problem on the cost of heat treatment (minimal lot charge to do raw tubes)

2)
a) What is the difference in locally affected weld zone from our current method;

i) raw non heat treated tube, machine, weld, rebore, final hone.

and our proposed method;
ii) heat treat tube blank, machine, weld, rebore, final hone.

Do we gain, do we lose; strength, brittleness, toughness ?? Does the the weld area become more brittle or less compared to the origianal method?

We have a third procedure that we feel is the best however the machineing cost goes throught the roof. Most shops will not even look at the job, the welded plates make the tube near impossible to machine. iii) descale od, weld plates, heat treat, Machine threads ID, Od both ends, rebore, hone. (we may neer to add a benchining / straightening procedure in there after heat treat)


Hope the information provided gives you a better picture.


Let me know what you think,


Thanks

AZ

 

[metengr]

Re;Welding
4130 material has acceptable weldability with local preheat. What I would do is the following;

1. Have several 4130 tubes heat treated - quenched and tempered at 1000 deg F. This tempering temperature should put you at a hardness of 315 BHN.

2. Conduct the welding using a 300 deg F local preheat. Keep the interpass temperature below 600 deg F. I would use the following weld rod composition for this - E8010 B2 or ER80S-B2

3. After welding, have one tube sent to a local metallurgical lab to conduct a destructive examination of the weld region (one or two bend tests) and determine hardness of the weld/heat affected zone and base metal surrounding the weld region. Going this qualification route will allow you to verify process steps and the effect of welding after heat treatment. The cost for the destructive examination by a metallurgical lab with a report will be less than $2k USD. Cheap insurance.

 

[AZsuspension]

You are on the same page as us.

We are in the planning phase and are awaitng out next production run. We can not run samples this week and are a month away or more and we are getting anxious. We might even start an inter office pool, or dart board.

1.Do you have a guess on wether or not it will be better or worse than the original procedure, as far as strength, brittleness, toughness?

2. Do you have a specific heat treat spec or procedure that you like to follow? we are consulting with the Lab and Heat treat shop in the next week or so.

3. How do you come up with the pre heat and inter pass temps? what is the reasoning? (this is where I lack the knowledge and experience) I will pass the word on to the welders.

I noticed the preferance of filler ER80S-B2 or ER8012. Reasoning? Is it more appropriat for the BHN315 condition?

Sorry for the questions but as you may understand or see from my questions, I still want to learn, love my job and profession.

Thank You,

AZ

 

[metengr]

1.Do you have a guess on wether or not it will be better or worse than the original procedure, as far as strength, brittleness, toughness?

The bulk properties of the heat treated 4130 will not be affected by welding if you follow what I suggested for welding. As far as the weld regions - I would expect some loss of ductility and increase in hardness along the fusion zone of the welds. Away from the fusion zone there will also be a localized region where you have a loss in strength related to the heat from welding - this is unavoidable.

Is this a problem? Only bend tests will determine the outcome - I believe you should be able to pass the bend tests.[/quote]

2. Do you have a specific heat treat spec or procedure that you like to follow? we are consulting with the Lab and Heat treat shop in the next week or so.

If you in consultation with a heat treater, they will provide this information. All you need is to specify the hardness range.

3. How do you come up with the pre heat and inter pass temps? what is the reasoning? (this is where I lack the knowledge and experience) I will pass the word on to the welders.

The preheat requirements are found in literature. If you search around you will find the requirements. Interpass temperature is selected based on the alloy composition and heat treatment condition. The objective is to avoid too much heat input in the base material during welding.

I noticed the preferance of filler ER80S-B2 or ER8012. Reasoning? Is it more appropriat for the BHN315 condition?

Yes. It will be a closer match. The prefix 70 or 80 in the weld metal designation refers to minimum ultimate tensile strength.

 

[AZsuspension]

Fantastic,

We asuumed that this would work as far as strength / brittleness / toughness and be our best methodology with cost factored in.

We were pre heating to 400F but not looking at our interpass temps. This was done to control warpage. We will have to look at that more closely when we change procedures.

Should we concider any post weld stress relieving, slow cooling. etc.

What happens to a welded joints strength if you want to post heat treat the finished product but use ER80s as a filler material instead of 4130.
Obviously the welded joint will not be as stong. Most people say that the alloy mixing of a small joint (under 1/4") is sufficient and usually produces negligable strength differances. Is this true?


Woderfull information thank you.

AZ

 

[metengr]

Should we concider any post weld stress relieving, slow cooling. etc.

I don't believe PWHT would be required for your weld joint configuration with preheat applied. I would wait until the lab results.

What happens to a welded joints strength if you want to post heat treat the finished product but use ER80s as a filler material instead of 4130.

The purpose of PWHT is to reduce residual stress from weld shrinkage and to temper or soften the region of the base metal adjacent to the fusion zone of the weld, and in some cases the weld metal itself. So, the weld metal strength and portion of the base metal heat affected zone on PWHT will tend to decrease in hardness.

Obviously the welded joint will not be as stong. Most people say that the alloy mixing of a small joint (under 1/4") is sufficient and usually produces negligable strength differances. Is this true?

Not true. I will keep the explanation as simple as I can….You have a choice of various filler metals each with different chemical compositions when compared to the base metal that upon melting with the base metal will result in either under- or over-matching strength in comparison to the base metal strength. The performance of a weld joint really boils down to how the joint will be loaded in service and selection of a suitable filler metal. Case in point, an under matched filler metal strength may be desirable to enhance weldability and because of the location of this weld and anticipated service load, it performs acceptable in service.