Just a number of issues that need to be clarified: 1) Are you welding with the SMAW (Also called stick or MMA) process? This is what you indicated, but the the filler trade name you used (Inconel 625) is actually a bare rod typically used for the GTAW process. As GTAW is rarely used for overlays, I assume that you are talking about SMAW. In this case, the corresponding INCO trade name would be Inconel 112. (2)What material composition are you finally aiming for? You need to know this, to be able to calculate the number of layers of overlay to deposit. Once you have given this info, it will be easier to give further guidance.

Regards
Niekie Jooste

The whole issue of producing overlays with the required chemical composition does not lend itself to a quick, short answer. There are a number of basic issues that must be understood to really get a grasp of the problem. I think I will highlight these issues and give you a basic example. After this you should come right. The basic issues are the following:

1)With every layer of filler you deposit, you will naturally melt some of
the underlying material with it into the weld pool. This is called dilution
of the weld pool. Each process has typical values for dilution. For SMAW, it is between 25 and 40%. The 25% will be achieved when you use low dilution welding parameters and techniques. Conversely the 40% will be achieved when you use high dilution techniques.
2)The entire weld pool is assumed to have the same composition. In other words, if you deposit a run of weld metal, it is assumed that the
composition on the outermost "skin" of the run is the same as that right
against the underlying metal. This is essentially so because of the high
turbulence within the weld pool.
3)Certain compositional ranges are crack sensitive. Each layer of weld must therefore be checked to see what the potential problems are. Certain compositions give a hard, brittle microstructure that is sensitive to for example hydrogen (cold) cracking. Some microstructures that are fully austenitic will be prone to hot cracking. These microstructures can
generally be predicted using a Schaeffler diagram.
4)Certain fillers can only accommodate a certain maximum amount of certain alloying elements before "bad news" intermetallics are formed, or other problems arise leading to a poor weld deposit with potential cracking problems.

Let us look at your problem. Here I can make the following general comments:

1)Using a larger size elctrode will not generally lead to fewer layers of
weld deposit being required, if you are aiming at achieving a given weld
composition. It may however help if additional deposited thickness
requirements are specified. Typically, the customer may ask for a final weld deposit thickness of at least 10mm. Then using a thicker electrode may be helpfull, because you will achieve your desired composition before you have reached the 10mm, when using a thinner electrode.

2)If you want to achieve EXACTLY the minimum chemical composition for
Inconel 625, using Inconel 112 electrodes, you could potentially NEVER
achieve this no matter how many layers of weld you deposit. This is so
because the electrode specification lies outside that for the parent
material you are aiming at. (e.g. Inconel 625 min. Ni=58%. Inconel 112 min Ni = 55%. If you are unlucky with your filler, and you get a batch at the minimum Ni content, you will never achieve the required 58%)What we need to remember is that Inconel 625 is routinely welded with Inconel 112 electrodes, so that the welds will in any case be a little different from the parent material. Also, the filler will rarely be at the minimum of the specification limit.

It therefore becomes an issue to decide what is important with respect to the chemical composition, so that you can ensure that these important alloying elements are deposited at or above the minimum required. Here the important impurities should also be considered. In your case, the typical important element would be Ni. While you would want the other elements close, a half of a percentage point will not be a disaster. In terms of the impurities, the important one would typically be the Fe content. Here we see that the max Fe value for Inconel 625 is 5% while for Inconel 112 it is 7%. Keeping in mind that you will have a lot of Fe pickup from your A516 Gr 70, this could be a real problem.

To overcome the above problems, you may just make sure that when you order your electrodes, they are ordered with tighter chemical composition limits, or you could use another electrode for your first (or intermediate) layer. Typically here you could considder using a Nickel 141 electrode for your first layer. (Will probably be easier to order your filler with tighter chemical composition limits. e.g. Ni min 62% and Fe max 3% and Cr min 22% and Mo min 9%.)

3)Low dilution techniques are typically:
-Use current settings that are at the lower end of the range for the
particular electrode diameter.
-Weld with the parent metal at as low a temperature as possible. (Low
pre-heat and interpass temperatures.)
-Keep the electrode at a shallow angle to the workpiece. The closer to 90° it is to the workpiece, the better the penetration and therefore the higher the dilution.

Let us look at a sample calc:

1)Assume 30% dilution by using low dilution welding techniques.
2)Assume the following electrode chemistry: Ni=62%, Fe=3%, Cr=22% (Will not go further)
3)Ni composition of the layers are as follows:
-1st layer: 0%(Gr70 Ni cont.)*0.3(dilution) + 0.62(In112 Ni Content)*0.7 = 43.4%
-2nd layer: 0.434*0.3 + 0.62*0.7 = 56.4%
-3rd layer: 0.564*0.3 + 0.62*0.7 = 60.3%
4)Now do the same for the Fe:
-1st layer: 0.98(Gr70)*0.3 + 0.03*0.7 = 31.5%
-2nd layer: 0.315*0.3 + 0.03*0.7 = 11.6%
-3rd Layer: 0.116*0.3 + 0.03*0.7 = 5.6%
-4th layer: 0.056*0.3 + 0.03*0.7 = 3.8%
5)Now do the same for the Cr:
-1st layer: 0(Gr70)*0.3 + 0.22*0.7 = 15.4%
-2nd layer: 0.154*0.3 + 0.22*0.7 = 20%
-3rd layer: 0.20*0.3 + 0.22*0.7 = 21.4%
6)This must be dome for all the alloying elements and impurities of
interest.
7)From this we see that you will probably be close enough after the third
layer. The only real issue being the Fe content. Depending on the results of a chemical analysis, you may decide you are close enough, or you may go for the fourth layer.

What about the cracking tendancy? Having a quick look at the Ni and Cr
contents of the first layer shows that this material will be fully austenitic. It will naturally also be fully austenitic for all the
subsequent layers. We will therefore tend to get hot cracking problems. That means that all possible low melting point contaminants must be avoided. - WELD CLEAN. As the flux of the SMAW process will tend to clean the weld deposit, you should not have a problem as long as you do the basics right.

Will we get any funnies wrt. the dilution of the iron in the Inconel 112
deposit? Only above 50% will you get problems. The highest you are getting will be 31.5%, so you are OK here as well.

You will appreciate that the process described above is based on a lot of
assumptions. It is for this reason that you are required to do the test
plate, so that you can be sure that the assumptions are valid. You may find that your welder is welding at around 40% dilution. In this case, you will pick up all kinds of problems.

I hope this helps.
Regards

Niekie Jooste
Sasolburg
South Africa

We have been using the same application for years for the pulp and paper industry for recovery boiler applications.

Why are you using the E-NiCrMo-3 filler and what is the target chemistry
you want to achieve??

What are the service conditions?? elevated temps?? garbage burners??
what application do you have.

Some of your replies contain excellent guidance just need to know your application.

Dirk

I wrote such a long explanation on welding of overlays, that I decided to just turn it into an "official" paper. Anyone interested in this, can view it on the following website:

www.proknownet.com

From the home page, click on the "papers" link. Then click on "search for paper". Next place the keyword "cladding" in the search box and search.

I also loaded an associated spread sheet that helps with making the described calculations, and plots it on a Schaeffler diagram. This can be downloaded by following the "software" link from the home page, followed by "search for software". Enter "cladding" as a search term.

Regards
Niekie