Hello WeldAddict,
What you would like to perform is a great challenge - congratulations on your forthcoming efforts. I suppose there have to be expected some...
I guess you have already explored the Internet for finding adequate filler-metals for joining the steel grade you want to join, isn't it? And? Have you found them? No? What do you guess is the reason for not finding filler-materials for the steel you have mentioned?
And furthermore. Although you have the luck to find the most experienced people on the forum, why do you personally think that it appears that no one is making a definite and straight recommendation for what you would like to perform - joining Ck 60 to Ck 60 for creating a later dynamical loaded component? I truly would not have not expected another reaction, because I strongly believe in the forums people expertise and directly coupled with that, their responsibility in any advise they are providing via the forum. I am also certain that there are some experts who would like to advise but not finding the time to reply.
Well, from my subordinate point of view, the main reason for that is, that what you want to carry out is a slight tricky welding operation. Simply because you can't separate by using the principle "First things first" both, "filler metal" and "heat treatment". Both belongs together.
Due to your information in regard to the component made of Ck 60 I would like to explain basically and strongly simplified what happens when choosing the first named combination "Ck 60 / Ck 60".
Ck 60 (by the way C 60E is the new standardizations description of W.-Nr. 1.1221 but the composition has remained the same) is a typical "high-grade-steel". We use the technical term "Vergütungsstahl" in Germany, which could probably be translated best by "Anneal-Steel"(?). The problem - just as already mentioned by "Fredspoppy" - with these materials is that they are indeed "weldable" but only under strong restrictions and special measures due to their problematical composition. Ck 60 has a Carbon-content of ~ 0.6% mean, which is high, isn't it? I'd say: "Yes it is", when considering that the natural limit of steel materials "weldability" (without additional measures) is approx. at 0.2% C. The materials Carbon-content shows that it is roughly temperable when cooling down from the field of austenitic microstructure (> A3 - temperature, see Iron-Carbon-Diagram for further information). This means, the material forms strongly the hardness-microstructure of (well known) "Martensite" which can cause cracking and many other undesired effects, which I do not treat herein further, for not additionally extending the matter.
Nonetheless also steel-materials of those "exotic" compositions have to be welded in some cases. Therefore - as mentioned above - both has to be considered the filler material on the one + the welding-sequence or -procedure on the other hand.
Resume?
Normally temperable steels, e.g. containing higher but moderate amounts of Carbon are weldable by using simple ways of preheating the material to extend the cooling-rate and thus to preventing a larger formation of Martensite. These procedures - I suppose - are already well known as you have already mentioned the preheat-temperature by calculating the C-Equivalent. And furthermore, by giving us the information that you have carried out some trials on scrap parts of the material and having preheated the parts up to 250°C, checked it afterwards and found no kinds of cracks etc. Well, in my opinion you will never find any cracks in the joint or HAZ when performing like mentioned. Since it does not reflect the conditions to be expected after welding and u s i n g the gear-wheel! Please don't hit me, I would like to explain what I mean immediately...
But these explanations are being based on a more or less theoretical fundament for clarifying the "nature" of what happens when welding the steel.
For the case you are not interested, in what I would like to describe, here is my honest recommendation for your welding operation:
· Contact the steel supplier or the steel mill for receiving specific information about the materials condition (hardened and tempered? etc.). I suppose the material you want to use may have the condition "Normalized". This is only an assumption but it means that the part should has to be normalized again after welding, or annealed after welding or whatever to achieve the same mechanical properties as before welding.
· Try to get also specific information about the welding-procedure being recommended by your steel-supplier, or the steel mill the material has been produced by. Believe me, in such critical welding-operations the most comprehensive and adequate information about the ways the material has to be handled, may come from those people who are earning their money by producing the materials.
Steel materials like the mentioned Ck 60, are basically used to be welded in a quite different way, since here it might not be sufficient to extend the cooling-time alone for preventing hardness-microstructure but also to use a combination of preheating- increased welding- or working-temperature and finally extended cooling-rate (+ in some cases annealing after welding). Therefore it is hard to recommend some specific in regard to your welding-application, since it is unknown what kind of mechanical properties the welding joint- or better the welded component has to fulfil after welding in particular. Since I suppose that the large gear-wheel (how large is "large"?) has to withstand the full load of the subsequent exertion I guess that the welding-joint - as a part of the entire construction - has to fulfil at least the same mechanical properties as the base-material itself. And when these base-material properties have been achieved by a specific heat-treatment before welding, they have also to be achieved again after welding, but therefore - of course - the weld must have a similar material-composition as the base-material itself. This means, the deposited weld-metal (based on the used filler-metal) must have the similar ability to be annealed after welding, like the base-material. But due to you likely will not find a filler-metal absolutely similar to the base material composition it is hard to say what kind of filler you should use for welding Ck 60.
Subsequently I would like to deal with only two different ways of procedures for welding your material and I request your understanding when not dealing with the - indeed interesting - but partial intricate mechanisms of sequences being observable when welding materials like Ck 60. I suppose it should be practically comprehensible for you what we are talking about now.
The procedures mentioned above are combinations of preheat-conditioning (before welding) - heat-conditioning while welding and post-heat-conditioning (after welding). In Germany we call it "Stufenhärtungsschweißen or "Isothermes Schweißen" which is likely translated best by using the terms "step-temper-welding" or "Isothermal Welding". I guess there is also an American English term for these procedures but I beg your pardon for not knowing it. I would like to use the term "Isothermal Welding" subsequently. These procedures again can be separated into three different ways of "Isothermal Welding":
1. "Simple" Isothermal Welding
2. "Pure" Isothermal Welding and
3. "Modified" Isothermal Welding
Two of these should be explained in a more detailed way afterwards. The "Simple" and the "Pure" Isothermal Welding. The latter one - I request your understanding - should not be dealt with herein since this one is the most intricate one (from the metallurgical side) and it would take more than this short reply on the forum to explain it in a way it would have deserved.
"Simple" Isothermal Welding:
This kind of welding-procedure combines a preheat-conditioning (prior to welding) with a heat-conditioning while the entire welding-sequence is performed. Just comparable with what you have already executed when welding the "scrap-parts" of the steel to find out how the materials reaction may be. It is used in cases where the base-material needs no high amounts of hardness after welding (which might assumable be also the case in your Ck 60 welding-application) but only has to meet a high amount of avoiding cracks. A large benefit of using this kind of welding-sequence is the fact, that a high-quality and "severe" temperature control is not stringently necessary. You can use simple high Carbon containing hardfacing-electrodes for this kind of welding they "only" need to have a high inertia of their austenite-transformation, i.e. the transformation from the field of austenite in a temperature range between 250°C ... 550°C has to occur strongly delayed, please ask your consumables supplier for adequate materials. Or just as you have already mentioned you can also use a pure austenitic filler-metal, e.g. 18 Chromium - 8 Nickel - 6 Manganese (~ 307) or 29 Chromium - 9 Nickel (~ 312) being stable austenitic and having no kind of transformation into Martensite. Combined with the way of welding-procedure (simple isothermal welding) I guess that you may succeed when manufacturing your gear wheel. For a better understanding or visualization of what "Simple Isothermal Welding" means, I have drawn a sketch which I would like to attach to this reply, see also Simple_Isothermal_Welding.pdf. Herein one can see how to carry out the welding-procedure. The part is being warmed up above the Martensite Start Temperature which is above 300°C (I attach the continuously time-temperature-transformation-diagram of the Ck60 (C60E) for a better understanding, see also TTT-Diagram.pdf). I do not want to deal with the explanation of this type of diagram, but what you can see is, the longer the time for cooling down the material from temperature levels above A3, the lower the materials hardness (circled numbers in Hardness Vickers) after cooling down to room temperature. This effect has its origin in a lower amount of Martensite which is being formed - as well known - as a function of the materials analysis (e.g. high Carbon content) and the cooling rate. By the way, this diagram is the fundamental basis for welding the Ck 60 material. As you can see the Martensite Start temperature (Ms) for this specific material Ck 60 lying at ~ 300°C and thus the preheat temperature of the component has of course to be lying above 300°C in order to avoid the formation of hardness-microstructure Martensite. Therefore I guess the preheat-temperature you have used for welding the "scrap-parts" (~ 250°C) was a bit too low and when you are going to carry out the real welding-operation under using this level of preheating-temperature you might get problems after welding, due to hard and brittle areas. Well, when having a look onto the sketch (Simple_Isothermal_Welding.pdf) you can see that one has to:
· Preheat the part above the field of austenite (A3-temperature) into the field of its hardening temperature which is ~ 800... 840°C for Ck 60, see also the sketch Simple_Isothermal_Welding.pdf, and hold the material for a while, subsequently
· Cooling down the material to the Isothermal Welding Temperature which must be lying assured above the Martensite Start Temperature to avoid any formation of hard microstructure
· Welding the part and holding the isothermal temperature constant while welding
· Holding the isothermal temperature after welding for a good while to be certain that the welded joint (and Heat Affected Zone) has experienced no transformation into Martensite but into softer microstructures (Ferrite, Bainite etc.)
· Cooling slowly down the part to room temperature, by storing it under ashes, mica or comparable substances
"Pure" Isothermal-Welding:
This kind of welding-procedure is commonly used for welding steel-materials having a high inertia or delay of transformation in regard to austenite microstructure. Tool-steels like W.-Nr. 1.2601 (X165CrMoV12) - having a Carbon content of ~ 1.5% mean and a Chromium content of 12 % mean (!) belong - for example - to the group of those materials. Materials like the mentioned one are able to temper only by being cooled down in air. For welding these materials the "Simple Isothermal Welding" is insufficient, since the material properties are more intricate to achieve. Therefore "Pure" Isothermal-Welding is necessary to be conducted and thus likewise here it is necessary to get knowledge of their specific time-temperature-transformation diagram. These are, I must repeat, normally available from the base-material supplier (steel mill etc.). The base-material is then warmed up to its hardening-temperature (> A3 to be recognized from the respective specific diagram) which is also the field of austenitic microstructure (Carbon is completely dissolved). After holding the material on that temperature for a while it is being cooled down to the Isothermal-temperature lying approx. at 500... 550°C (for the mentioned steel). Once again on this temperature level the entire welding sequence is performed. For this kind of welding procedure high-alloyed austenitic filler-materials are being used for securing a high cracking resistance of the weld deposit. While cooling down the weld on air or in hot oil, its temperature passes the martensite-start temperature and the austenite is being transformed into martensite, and that again means, that the welded area can be annealed again in the same way as the base material itself and thus having the same mechanical properties like the base material, although this has partially been affected by high temperatures, i.e. welding.
Likewise for that kind of welding procedure I have drawn a .doc-sketch and have converted it into a Portable Document File (Pure_Isothermal_Welding.pdf). I attach also this small sketch for enabling a better understanding of what I have written although you can see it is a bit more intricate than the Simple Isothermal Welding sketch (but however, easier than the "Modified Isothermal Welding" one).
May the Almighty God give now that I have found the right words for my short explanations. I truly hope that you could use a bit of what I have written, for performing a sound and proper weld!
I personally guess it may be hard to fail, when using pure austenitic filler materials like the mentioned "307" or "312" for joining the high Carbon-containing steel, but I have also welded - no pure C-steel - but higher alloyed "Anneal-Steels" under preheating them in an appropriate way and using low-hydrogen, gas shielded basic flux-cored wires, comparable to AWS E 70T-5J H4. The joints had to be loaded highly dynamical and no failure of the components had to be reported.
Last but not least and as always, I am looking forward for any kind of correction, for the case that I have explained or stated something wrong and I am inquisitive for any further information in regard to your topic coming from the experts on the forum.
Regards,
Stephan
P.S. The greatest "Thank You" I have ever expressed to J. and C. (I hope they understand who is meant when they are reading this) who have given me their honest and extraordinary support when I have needed it most! You are wonderful people!
