Proper Material Selection for Welded Assembly & Heat Treat 2

[Pirate2719]

I have a weldment that we are working on bringing to market. Customers are asking for a more durable welded assembly for longevity. I am trying to achieve a 50-60 Rc Hardness throughout the part. I initially was suggested a 1045 material to machine to size, weld, and heat treat (stress relief of the assemblies prior to case hardening). The price of machining bar stock is driving up the cost tremendously going this route.

I have link showing the picture of the subject weldment sample I just received from my customer.

I have tested the hardness on it and results were Rc 55. Customer has no idea of material other than carbon steel. I have had a PMI done and have attached the snapshot I took from the analyzer.

I have measured its size and material seems to be of standard pipe size, but I have not ruled out tubing either. The larger section has a barely visible seam (seamless pipe or tube) and smaller seam has a visible weld seam. All ends are tapped to there respective pipe sizes of 2 NPT & 1-1/4 NPT

I have had a heat-treat facility tell me to stay away from Alloy Steels?? A machine shop is telling me to staying away from structural pipe?? I am confused at this point of what direction to take on material selection and was looking to some pro's to give some advice.

Thanks in advance.

Ben

 

[EdStainless]

You want to case harden it, then there are alloys that are great for that. Surely you don't need that core hardness.
What is the application?
These pieces are both welded pipe. Common welded pipe is very poor quality (alloy variations, welds, and size control) but you can get material made to pipe sizes that is to higher quality.

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P.E. Metallurgy, Plymouth Tube

 

[Pirate2719]

The application is for media blasting using steel shot & grit. Surface hardness is what we are after for durability and wear. Also, measurements taken show 2.375" OD x .226" Wall Thk.; 1.665" OD x .189" Wall Thk. These numbers directly correspond with Schedule 80 pipe.

Would pressure vessel quality pipe SA106GrB/C Seamless pipe be a viable option to fabricate this weldment from? Would it be receptive to the case hardening heat treatment process?

 

[CoryPad]

You don't want to use 1045, that is not easily welded. You do not want 60 HRC (or really anything higher than40 HRC) in the threads if there will be any sustained tension because that can lead to hydrogen embrittlement.

Low carbon steel tubing or pipe (like SA106) can be surface hardened via case carburizing.

 

[ornerynorsk]

Why not go the other route and just make them so easy and cheap to manufacture that they are considered a disposable. The best material isn't always the best solution, cost-wise.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Pirate2719]

All hoses and accessories connected to this weldment and cost our customers time and money disassemble and reassemble. Some have (8) weldments on (1) large blasting unit. I sure would cuss and spit fire if this part didn't last. Some customers know they can get through a season and automatically schedule PM's to replace them.

 

[Pirate2719]

CoryPad -
Through discussions with our welder, I have found the process of preheat and slow cooling for the 1045 material to be more costly also.

As far as the embrittlement of the threads, our heat treat facility has advised a suggestion to mask the threads before case hardening to prevent them from becoming unduly brittle. They seemed quite confident about this. There is no extreme tension on either threaded connection.

The case depth would be specified as .060” minimum total case depth. The case will penetrate the walls of the pipe from both the O.D. and I.D. This will ensure that .120” of the wall thickness will be RC 50+ minimum.

 

[metengr]

Case hardening for abrasive/impact wear may not be very effective. Too many times individuals believe higher hardness equates to abrasion/erosion resistance. This is simply not true. A thin rubber lined carbon steel pipe may be all you need.

 

[mrfailure]

If you go the case hardening route, have you considered using 8620? You can order it in tube form per ASTM A519. I do not know how well this (or any) steel will do for you if you weld after case hardening.

 

[ornerynorsk]

Have you thought about a carbide or other eutectic coating for the inside? How many of these parts do you go through in a year?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Pirate2719]

ornerynorsk-
We are looking to bring this to market as extreme duty solution. Our anticipated 1st year usage is 100-200 after product release.

 

[ornerynorsk]

With that volume range, it might be worthwhile to look at a custom casting in an abrasion resistant alloy. Think mining application parts. Titus Steel castings come to mind, there are others, as well. Good luck on the project!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[tbuelna]

As others noted, making this fitting from welded pipe is probably not the best approach. It would be better to cast the fitting from a suitable material (like HSLA steel) using rapid prototyping, heat treat the casting, machine the threads, then apply masking and case harden the internal flow surfaces using a process like liquid salt bath nitro-carburize.

The combination of a very hard, corrosion resistant flow surface with smooth, rounded edges would likely last longer than the welded pipe manifold with sharp corners.