How To Weld 4140 Steel

Let’s keep it simple. 4140 steel can be welded without problems as long as you follow some simple guidelines. This also applies to AISI 4140 and 4340.  We will not be discussing the metallurgical properties of 4140 or trying to explain what happens to its microstructure when it cools too rapidly, just remember that the key is to control our cooling rate. If the weld and heat affected zone cool too quickly we are in trouble.

AISI  4140 steel is alloyed with chromium and molybdenum, hence the term chromoly steel.  The addition of these alloying elements and its relatively high carbon content (around 0.40%) provide this low-alloy steel with excellent strength to weight ratio and make it a lot stronger and harder than standard 1018 and 1020 steels.  The disadvantage is the need to be more careful when welding 4140, or other medium to high carbon steels for that matter, as compared to low carbon steel.

When welding 4140 material it is absolutely necessary to preheat.

When welding 4140 material it is absolutely necessary to preheat.

4140 is typically supplied in either the hardened and tempered condition (referred to as 4140HT) or in the annealed condition.  For welding it is recommended that you use the latter.  Welding on 4140HT is not recommended due to the high susceptibility for cracking, even when using preheat.  If you must weld 4140HT it is absolutely necessary that you stress relieve the part at a temperature 60F [15C] below the original tempering temperature.  Typically, if you have to weld on 4140HT you are making a repair.  4140HT should never be used for standard fabrication if possible.

If you are manufacturing parts out of 4140 we can assume that it is in the annealed condition.  4140 will weld very similar to your low carbon steels.  The  difference is that its high carbon content can screw things up.  To avoid cracking you need to preheat 4140 prior to welding.  This is done to slow the cooling rate after we are done welding and avoid embrittlement (formation of martensite and hardening of the weld and HAZ), which can lead to cracking.

Steps to weld 4140:

1. Preheat

Per Table 6-13 in page 6.1-29 of The Procedure Handbook of Arc Welding we need to preheat as follows:

Up 1/2″ thickness   400-500F [205 – 260C]

1/2″ – 2″ thickness  600-700F [316 – 371C]

Other  publications recommend a preheat of only 350F [177C] up to 1/2″, 450F [232C] from 1/2″ to 1″, and 500F [260C] for 1″ to 2″.  Keep in mind that when a part is preheated over 500F [260C] it becomes extremely uncomfortable for the welder.  These lower preheat temperature are used with success, but go with the higher ones is you want to play it extra safe.  The higher temperatures will produce slower cooling rates.

It is important that the interpass temperature be kept at or above the preheat temperature.  If more than one pass is required make sure the part is above that minimum interpass temperature, if not, apply more heat to the part with oxyfuel or other means.

2. Use a low-hydrogen electrode (whether using GTAW, GMAW or SMAW)

The filler metal recommended for welding 4140 steel is ER80S-D2.  ER70S-2 can be used but you will be undermatching the base material.  Low-hydrogen electrodes minimize the amount of diffusible hydrogen in the weld.  With the elevated carbon content even low levels of hydrogen can wreck havoc. A common problem with medium to high carbon steels is their susceptibility to hydrogen-induced cracking.

3. Slow cool the part. Preheating  will take care of this most times; however, using heating blankets to assure a slow cooling rate is good practice.   As mentioned above, a slow cooling rate prevents or reduces embrittlement (crack sensitive area in the heat affected zone).  It also allows hydrogen more time to leave the weld, thus reducing the possibility of hydrogen-induced cracking.

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Do you typically weld 4140  or other high  carbon steel? Please include your thoughts and any tips in welding these materials.



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110 thoughts on “How To Weld 4140 Steel

    • 4140 will require preheat. Austenitic stainless steels such as 316 does not. You actually don’t want to preheat 316 because you can actually create a corrosion problem by increaseing the amount of time in the sensitization zone. See Sensitization in Welding Stainless Steel. You want to slow cool the 4140 and rapid cool the 316. It will be best to a weld test and determine whether the results can meet your acceptance criteria.

  1. Bonjour, es-ce que vous avez une procédure pour souder 4140 et acier inoxydable 316? Préchauffe? Électrode 309? Refroidissement lent?

  2. What is the best shielding gas for either GTAW or GMAW, filler metal and welding process to weld 414 to 1045 materials?

    • Hello Steve. GTAW of 4140 and 1045 should be done with 100% argon. For GMAW you have several options. A mix of argon and CO2 is preferred over argon-oxygen. Using and Argon/CO2 mix of 85-90% Argon with the balance being CO2 is recommened.

  3. Hallo Sir,
    I want to joining and weld:
    – Casing 20″ OD 0.625″ Wall-Tick, X56 material, 2ft length to
    – Circulating Sub 20″ OD 0.625″ Wall-Tick, 4140 material, 1 ft length

    can we do it?
    what is the recommended process: GMAW/ SMAW/ SAW?
    if so, please advise for pre heat temp, filler metals recommended?

    we have WPS for weld 4130 material to X56 material
    is it similar?

    • Yes, it can certainly be welded. Follow the preheat guidelines for the 4140 as it will have the higher preheat temperature. Any process is acceptable as long as you follow low hydrogen practices.

  4. I want to recondition excavator jack hammer points. The process involves re-machining the correct angle on the end, rebuilding the corners with welding and then hard facing. Would MIG welding be ok for this?

    • Hello Dave. Mig (GMAW) is not recommended since mig wire typically don’t have the alloying necessary to provide adequate wear resistance. However, there are plenty of flux-cored (FCAW) wires that can do the job if you are looking to use a wire process. If this is what you were looking for then you can look up the recommended filler metal for your given application in a flux-cored wire and use that. There are equivalents to SMAW and SAW consumables.

  5. Dear Sir,
    My query is about qualifying a procedure for the combination, EN19 (AISI 4140) to Weldox (S690QL)
    As you’ve stated in this article, qualifying 4140 in annealed condition is easier and S690QL properties will deteriorate on PWHT, What would be the heat treatment condition for the both materials then prior to qualifiaction to avoid PWHT
    Can I qualify Quenched and Tempered S690QL to annealed/normalized 4140 ?


  6. Dear Gents
    I am planning to weld Ø404mm dia AISI 4140 material to 100mm thickness HARDOX450 plate. Could you recommend that this operational is applicable or not? Normally we are manufacturing this parts as casting and planing to replace with 4140 and BHN450 friendship. With this thickness welding operation is applicable for AISI 4140 or not? If yes could you advise that related filler matierial and preheat temperature.


    • Hello. A lot depends on what properties you want out of the weld and the base metal. The heat input from welding can change the harndess and wear resistance of the Hardox and the 4140. IF this is acceptable then welding should not be an issue. Make sure you follow the instructions on how to properly weld 4140.

  7. Dear experts,
    When we compare AISI 4140 to SCM 440. It look the same? So, now, we need to weld SCM440 (round bar with O.D =90mm) to ASTM A570 Gr. 50 (plate 25mm thickness). It’s is fillet weld. I have some question as below. Can you help me?
    – Which is group according to ISO 15608. In case it’s was tempered and quenched. It is same group or change to another group.
    – Preheat and interpass temperature for this weld (both materials) is from 315 – 350 degree Celsius . Is it OK?
    – We use FCAW with E71T- 1C. Is it OK?.
    – The client required to test according ISO 15614-1 but in this standards, no showing fillet weld between round bar and plate. ( Just have T joint for plate to plate). How can I do? (We don’t have SCM440 plate type; just have round bar type).

    • Hello. Testing of materials not listed in the code requires qualification by testing and must be approved by the Engineer in charge. This is true of most codes. Not sure if ISO changes the group if A570 is quenched and tempered. However, Q&T increases tensile strength which may exceed the scope of the code. Regardless, Q&T steels can be problematic to weld as they are susceptible to cracking. It is sometimes recommended to first anneal the steel, then weld it and then do Q&T again.
      As far as testing ISO should provide guidelines. Qualification tests don’t necessarily mimic the exact joint details seen in production. The plate test (T-joint) should be OK. In AWS D1.1 running a test on plate (fillet welds) will qualify the procedure for tubular sections as well (fillet welds).

  8. I am concerned about welding 1/2 A36 hub to 2-3/8″ 4140 ANLD shaft. We are preheating the shaft and hub to 700 degrees but the shaft will spin at 2500RPM with substantial over hung load and am concerned about shaft breakage. A total of 4 hubs will be welded on 78″ long shaft.

        • If this is your concern you should pay very close attention to your preheating procedure to ensure that the right preheat is reached before welding and maintained during welding. Also, you will need to control your cooling rate. A slow cooling rate will help with increases ductility and reducing hardness. This will reduce susceptibility to hydrogen induced cracking and brittle fracture. However, keep in mind that this essential anneals the base material. So the hardness and high tensile strength of the 4140 may be affected.

  9. I need to repair a large Hydraulic cylinder by replacing the cylinder rod this repair will require the cylinders original cylinder rod end to be welded onto a new 4140/42 CrMo4 induction hardened and hard chrome cylinder rod the rod diameter is 220 mm length of 2500 mm the original rod end is a cast material with a tensile strength of 690 Mpa. the weld preparation will be a partial penetration butt weld. The intended filler material is AWS A 5.28 ER 110 S-G GMAW welding process with Ar CO2 shielding gas welded in a rotator in the 1G Position. Volts 34.5 Amps 300 T speed 400 mm/min.
    As the 4140 cylinder rod has been induction hardened to H1 condition and hard chromed can you recommend the pre-heat and Maximum inter-pass temperature

    • The preheat requirements remain the same as stated in the article in order to prevent or at least minimize susceptibility to cracking. However, the microstructural changes that will take place will yield a weld metal and HAZ with significantly different characteristics than the H1 condition.

  10. Kindly advice, i want to qualify a procedure for welding A36 to N80 Casing material likewise 4140 Modified (Quench &Temper) to N80 casing material, is this possible and which electrode is good for this.

    • It is possible to weld 4140 quenched and tempered but you have to be OK with at least some cracking. The best way to prevent cracking would be to anneal the 4140 part before welding. That is not always feasible. You can weld 4140 Q&T following the same guidelines as for regular 4140 on this post. However, you must know that you will lose the Q&T properties after welding. If these are critical they most be restored through PWHT. The electrode to be used depends on the application. You don’t have to use a matching (strength) filler metal unless you need the strength. If you are doing a fillet weld or partial joint penetration groove weld you may be better served by using an undermatching filler metal, something like an ER80S-D2 for GMAW. The 4140Q&T may be as high as 140Ksi or even higher, so finding a matching filler metal would be tough. What are the details of the joint and the application? Can you provide this information so we can help you further?

  11. I am trying to weld Liftting lug (50 mm thick pine -alloy 617 (inconel )) to clump (55 mm thick – SA240 TYPE 347H) AS HANGER DEVICE FOR HRSG BOILER for power plant , WELD TYPE IS FILLET , this welding is for installation harp system. welding as per AWS D1.1 .Pls advise preheat temp., weld process SMAW , type of ELECTROD to be used, PWHT required or not, if PWHT required than at what temp / soaking time / cooling process.please send me proc

    • These base metals are not governed by AWS D1.1 as this is the structural welding code for steel. Are you sure the requirement is to use D1.1? You would need to treat these materials as “unlisted” and develop your own procedure and qualify by testing. However, we suggest going back to the engineer in charge and asking if they really want to use D1.1

  12. Hi I am welding 41/40 1-1/2 shaft to 20mm bisalloy 400 plate joint is critical for strength the shaft is set into a hole in the plate and plug welded on the end what is the best procedure .

  13. When welding 4140 machined billet that is machined to approx 310 outside dia then tapered down to 273 outside dia 12.7 wall thickness to grade 350 273mm outside dia 12.7mm wall thickness would ER110s-g
    Or would ER80S-D2 be better

    • It depends on what you need out of the weld. Is this a complete joint penetration weld? If so you more than likely need to match the weakest of the two materials. If you are making a fillet weld or partial joint penetration weld using ER80S-D2 may be a better choice as undermatching will increase ductility.

  14. I am setting two procedures: 4140 to 4140 and 4140 to SA 516-70 I am using the FCAW process.
    I am using E101T1-K3C flux core wire with 100% CO2 gas shield. 500 degree preheat and maintained till complete. Any advice? Thanks, SB

    Will this procedure cover 4130 as well?

    • What criteria was used to select the E101T1-K3C flux cored filler metal? 4140 (depending on its condition – annealed, quenched and tempered, etc.) can have extremely high tensile strength. 4140 selected for welding would have a minimum tensile strength of about 90ksi. If this is the case you will be overmatching which is not necessarily good when we’re dealing with this type of material. The higher the tensile strength the lower the ductility. If the joint is highly restrained you may run into cracking issue. 4140 can be welded to 4140 with undermatching filler metals such as ER70S-6 or ER80S-D2 (or equivalent flux-cored wires) provide the application does not require full strength.
      If you require complete joint penetration welds then matching filler metal is suggested. But for partial joint penetration groove welds or fillet welds it is recommended to go with an undermatching filler metal and gain additional strength by increasing the size of the weld (this keeps your ductility high).
      Another point to keep in mind. Although SA 516-70 may not require preheat (it does after a certain thickness) you still have to preheat it. Since you are joining it to the 4140 it will act as a heat sink and will accelerate the cooling rate of the 4140 if its not preheated.

      One last thing. The SA516-70 has a minimum specified tensile strength of 70-90ksi. The E101T1 is overmatching this. When welding 4140 to a lower tensile strength steel it does not add any strength to the connection to match the higher strength metal (in cjp’s). It actually has a detrimental effect by having less ductility than if a lower tensile strength filler was used.

  15. I have an annealed block of 4140 that I want to use as a riser block Hardy on my anvil.
    The block is 2″ thick, 3″ x 3″ sq. I need to wire weld the 1018 dim. 1″ x 1″ x 4″ post which will enter the anvils Hardy hole. I don’t have a way to measure 650-700 deg. My plan is to build a coal fire in the forge. Place the assembled block of 4140/1018 hardy post in the fire and see the colors. When the block reaches gray, I will assume it is hot enough to weld. The assy. will be placed on a steel plate next to the fire. Then, using the wire welder, weld the 4 sides of the hardy post. To cool the welded assy. it will be located at the edge of the hot coals where it can slowly cool for an hour. Do you see any problems or a way it can be welded better.

    • Paul, this seems perfectly acceptable. It is a great benefit that the 4140 is annealed rather than hardened. The 600-700F is ideal but in practice, as in your case, it is not always feasible to heat to this temperature. It is advisable to measure the temperature just to make sure you don’t exceed the critical temperature. You can use temple sticks which will tell you if you go above a certain temperature. You can use an ER80S-D2 wire to make this weld. You can even go with an ER70S-6. Do not use a 4140 wire. The slow cooling as you describe is good. Let us know if you have any additional questions.

  16. Hello every couple of months I mig weld a threaded cap onto a cylinder tube made of 4140 Q&T i believe. The cap is made of the same material, the total diameter is around 8″, the thickness is around 1″. I weld a v-groove thats less then an inch wide, and a little less then an inch deep. I was told to use er100s-g, preheat, and slow cool with a blanket. Ive been having great luck with this setup, except for small pitting at times, which i am able to usually grind out and re-weld without many issues. Also these cylinders are lifting 150 tons around 10,000psi. I noticed you guys recommend er80s-d2. Any reason I should switch to that over the er100s-g if I’m having luck with it? Any additional info would be great, thanks!

    • Hello John. If the ER100S-G is working for you then stick with it. When we get into this high strength steels it is useful to consider the use of undermatching filler metals. One instance where you definitely want to match the strength is if you are making a complete joint penetration (CJP) weld and which will be loaded in tension. I believe what you are describing is groove weld which may or may not be CJP.
      One of the main reasons for undermatching is to reduce residual stresses, the 80S-D2 will have higher ductility than the 100S-G. You compensate for the lower strength (if necessary) by increasing the fillet weld size or by increasing the weld size in partial joint penetration (PJP) welds. If doing a CJP you cannot increase the size so you would use the matching filler metal.
      So keep using the ER100S-G!

      • hello, I am revisiting the site for a few extra questions on my same application I described above. Just trying to make the process as easy and painless for myself as possible so I started doing some research and noticed the er100s-g calls for either 95% ar/5% CO2, or 98% ar/2% O2 for spray. I haven’t welded with either before, just know that 90% ar/ 10% CO2 didn’t work that great for the application. As of now I’ve been using 75/25 for globular transfer, which has been working but the splatter is pretty bad. So just wondering which of the 2 between 95/5 and 98/2 would work best for the 4140. Thanks!

        • When welding 4140 we normally want to use an undermatching filler metal such as an ER80S or ER70S, however, when you need to match the strength as it appears the case for you things are a bit different. It isn’t the 4140 or the gas that makes it difficult. It’s the ER100S wire. The higher the alloy content the lower the weldability of the wire, meaning it doesn’t run great. Are you joining or doing some kind of repair/overlay? For joining I would go with 85-90% argon, balance Co2.

          • Yes I am welding a large threaded cap to a large cylinder tube, that’s joined together with a large v groove. I’d like to run spray instead of globular transfer to keep the splatter to a minimum, which tends to cause problems in later passes. The 90/10 didn’t seem to work for me, then noticed the other day that 95/5 and 98/2 is recommended for that wire for running spray. Just wasn’t sure if one would work better then the other for this application. I might just have to get a small bottle of one and try it out. Thanks

          • In the later passes it tends to get small pockets from time to time when its machined down, which hasn’t been a big problem, I do clean the weld in between passes with a wire cup on an electric grinder which helps a ton. But usually by the last half of the last pass the wire seems to start sticking to the tip at times, causing it to stutter almost, at times even causing the wire to stop coming out, I clean the tip every pass, and even started using a separate tip and nozzle already cleaned and sprayed with a heavy duty splatter protectant. That stuttering is one of the more annoying things on this application. Not sure if the wire is getting too hot at that point or I’m getting a small chunk of slag on the tip causing the wire to rub against it. But I’ve never had that problem on any other application, but also don’t weld anything with this high of heat.

          • John, if you are welding really hot and it the gun or torch overheat it is possible that the wire is also seeing some expansion. Typically this is only an issue with aluminum wire, but it can happen with steel. As you mentioned, you may be getting the nozzle clogged up with spatter. Make sure your diffuser is not getting blocked, sometimes the nozzle looks clean but the diffuser is shot. Have you checked your gas flow? Is it between 35-50 cfh? I see a lot of leaks at the back end of the gun because O-rings break down.
            The following link provides a few things to check for when getting porosity. Basic items, but take a look:

          • I was thinking that the wire could be getting hot as well and expanding, so good to know that’s possible. And that’s good to know about the diffuser, I will definitely make sure to keep an extra one on hand. I do run the gas around 32-35, but might bump it up a little more. I wouldn’t say I’m having a porosity problem like I was in the beginning, but its mainly just one weld not completely overlapping the previous weld I believe. But like I said it hasn’t been much of an issue. One last question, to keep the heat down a little on the last pass, is it possible to wrap it in a blanket after the second to last pass, let it cool overnight, then hit it with the torch and do the final pass that way or will that cause brittleness and more problems? My engineer/machinist didn’t think it would cause problems but I figured I would ask you guys. I really appreciate all of your help with this! Thanks

          • 4140 should be welded very carefully, this includes preheating and cooling properly. If you do as you said, as long as you cool it slowly (as you do when you are done), then preheated properly the next morning and finish the weld you should be OK. It is recommended that you do it all at once if possible though. But I completely understand why you want to do it this way. Have you tried running much lower amperage in the last pass? THis is similar to a weld test when everything is OK in the groove but if you keep running those hot passes for the cap everything spills over. Good luck.

  17. Hi
    first of all thanks lot for your detailed information on the 4140 welding, really helps lot!
    I am using AMSE IX spec to qualify the WPS on fillet weld on pipes, material is 4140. base metal -1: ID-3.38″ x OD-3.95, Base Metal-2: ID-3.61″ x OD-3.76″. As we need to maintain the hardness range below 22 HRC, could you please advise me further on the requirement of post weld and other essentials like tips to follow.

    • 4140 which has not been hardened usually has 13 HRC. To harden you must austenetize at 1570F [855C] followed quenching in oil. This will give you way more than the desired 22 HRC. You will then need to temper it after quenching to achieve 22 HRC. Tempering requires you reheat the structure. Reheating to 400F will provide almost full hardness. Heating to 1000F will get you close to 30HRC. The cooling rate is very important. You will need to consult with a metallurgist or review the ASM Heat Treater’s Guide for holding times and specific temperature to achiever 22HRC.

  18. I have an application where I might need to weld 4″ diameter round stock to a piece of 2-1/4″ thick ASTM 514 grade E. We have to do a CJP weld so the 514 plate will have the weld prep for welding the round into a slot cut in it. the preheat temp for the 4140 is actually higher than the allowable interpass temp for the A514. I wasn’t sure if there were any suggestion as how to accomplish this. Also there is a possibility that the 4140 is HT, it says it requires post weld heat treat but the 514 has a disclaimer on the cert. that recommends against any post weld heat treat. Thoughts?

    • Jason, this is a very tricky situation. Normally the answer to preheat is that the amount of preheat used is that required by the thickest member (or member that requires higher preheat). In this case the 4140 will a higher preheat required. However, A514 is a quenched and tempered steel. You will be affecting its properties. More preheat means slower cooling rate which may increase ductility but reduce hardness and strength. To properly answer this question we need to understand the service requirements of the A514 in terms of hardness, toughness, strength and ductility.
      Post weld heat treat is discouraged on A514 because you will be destroying its properties. Perhaps a better words is “change” its properties. If you PWHT you will end up changing the A514 as described above.

  19. hello guys
    I am welding a handle to a big mass steel block, print requierements only calls for SMAW .190
    both parts (handle and block) are 4140 but I am concern for the final process electroplating zinc
    is 7018 filler suitable for zincplating
    thanks a lot

    • Hello Joaco, 7018 is not the best option for welding over a zinc coating. The zinc coating produces gases that generate both internal and surface porosity. 7018 have a
      “soft” arc which does not dig very well. A better option would be a 6010 electrode. Of course, the best alternative is to grind off the zinc plating before welding. Welding will remove the corrosion resistant properties of the zinc coating anyway, so might as well get a good weld.

    • High preheat, around 650-700F, use a low-hydrogen filler metal (ER80S-D2 for GMAW is generally used unless you need to the match the exact characteristics of the 4140), slow cool. Since you will probably be doing multiple passes make sure your interpass temperature stays at a minimum of 650F. Is the 4140 in the annealed condition?

  20. Hello,
    I am making an attempt to weld 4140 prehard material. I’m experiencing some cracking. What I did was groove it out. Did a per heat of 500 degrees, and let it soak in the oven for about 3 hours. I was told to use stainless rod. As soon as I do a small pass, I can hear it crack. Any advice would be helpful thanks.


    • Hello Scott, could you provide a bit more detail? Are you welding the 4140 to repair an area that is worn or are you joining two pieces together? How thick is the material you are welding? Also, you mentioned you soak in the oven for 3 hours, this is after welding, correct? What is the purpose of using stainless filler rather than a mild still filler such as ER80S-D2?
      It appears you are following the correct guidelines. Assuming the preheat is to the right temperature and you are slow cooling properly the issue could be with the 4140. You mentioned it is prehard – we’re assuming this means it is quenched and tempered. This makes 4140 extremely susceptible to cracking even when following adequate procedures. The recommendation here would be to first anneal the part, then run your welding procedure (preheat, weld, slow cool) and then do post weld heat treatment to attain the desired results.

  21. how do the blankets lower the cooling rate? heat transfer is through radiation, conduction and convection. How does the blanket interact with this processes

    • The blankets wrap around the part that has been welded trapping heat that would be lost. Instead of the part cooling in ambient air (say 70F) it is now cooling in air that has been trapped by the blanket, which is at a significantly higher temperature. The heating blanket acts as insulation.
      As you stated, heat from the weldment is lost by conduction (transfer of heat between substances in contact – metal and air). The rate of heat transfer depends on the temperature of both substances. If the part is at 500F and the air is at 70F the cooling rate of the part will be higher than if the air was at 150F. The blanket traps the air that originally may have been at 70F and because air cannot escape easily the air surrounding the part increases in temperature, thus reducing the cooling rate.

  22. hi

    if i wish to weld a used AISI 4140 shaft, whereby the journal has been worn down by approx 1 mm.
    what should my welding procedure be ? undercut how many mm down, pre heat and weld with ER80s as per the steps above to welding of AISI 4140?

    • Yes, follow the recommendations on this post for preheat, interpass and PWHT. The main difference is that in this case you will want to match the mechanical properties of the shaft with your choice of wire. Is the 4140 in the annealed condition? Is it quenched and tempered? Welding on it will change its properties. You may need specific PWHT to bring those back to the desired state.

  23. Hi guys I’m planning on making a set of dies for my power hammer. My idea is to weld 1 1/2″ 4140 annealed solid round bar to 3/8″ 1018 flat bar. I have an inverter type welder and was planning on making several passes with e7018 1/8″. Preheat to 400 and stress relieve at 1150 for 30 minutes and then heat treat. I was wondering about 7024 because it’s supposed to lay down material quickly or maybe 8018 or whatever you suggest I’m just concerned with the impact it will be exposed to.
    Thank you Gilbert

    • We would advice against using the 7024 as it is not a low hydrogen electrode. Increased hydrogen in the deposited weld metal can lead to cracking (hydrogen induced cracking). Using an E8018 does no provide additional benefits compared to E7018 since you only need to match the 1018 steel. There is nothing wrong running the E8018, it’s just not necessary.
      In your case where you are concerned about resistance to cracking due to impact you need toughness rather than strength (tensile strength). Keeping harness levels down will help. Your post weld heat treatment should take care of that.

  24. Can a 4140 HT pipe test be successful if preheated to 400 degrees F with 17 to 19 volts for the root and 17 to 21 for the balance using GMAW .035 ER80SD2 wire. Interpass temperature 600 degrees F and 1 hour post heat of 1125 degrees F? Pipe is 1 inch thick with backing. 60 degrees V groove.

    • Hello Victor. Welding 4140HT is not recommended by the manufacturers of this steel and by many who have done it in the field. There are a few things to consider. When you weld on 4140HT you will be annealing the the material near the weld (HAZ), so your end product will not be what the base material is (different microstructure). You will have a significant variation in harndess and ductility. If you absolutely have to weld on 4140HT you need to do post weld heat treatment of the weldment to relieve the stresses as you mentioned in your comment along with the recommended preheat and interpass temperature based on material thickiness. Check with the manufacturer of the steel regarding the actual temperature range needed for stress relieving. Also, the cooling rate must be controlled. Keep in mind that if you have the ability to PWHT then there should be no reason why you can’t anneal the part prior to welding, and then PWHT to bring back to the hardened condition. Thus avoiding the high susceptibility to cracking when welding in the hardened condition.
      Like anything else, our recommendation is to qualify your welding procedure. You can weld and PWHT exactly as you describe. Perform tensile and harndess tests in weld metal, HAZ and beyond the HAZ as well as any other tests required by the code or standard you are following. Make sure the properties you require can be achieved with your procedure.

  25. Hello,

    Great information!

    I am looking to create a strong and cosmetically attractive weld joining a forged hammer head to a forged handle. The material is 4140. I will ultimately want to automate the weld process, but for the first articles I am planning to hand weld in order to fully understand the process that creates the best weld result. I will be post heat treating the assemblies to eliminate stresses from forging and to force a RC40-45 hardness. Question is, given the post heat treatment, must I pre-heat the components prior to welding? If so, do you have any recommendations for the best way to achieve this? I am thinking a hand torch with temp indicating chalk until the process is measured, and then using timed torch application when automated.

    Also, would yo uall recommend MIG or TIG? I feel that MIG will be most straightforward for automating and easier for a novice like me to achieve a cosmetic result.

    Sorry for long winded question! I appreciate any and all replies.

    • Hi Ben, good question. Regardless of whether you will be doing any postweld heat treatement you will need to preheat the material. We preheat 4140 and other medium to high carbon steels to slow down the cooling rate. This in turn reduces the formation of martensite with which is very hard and brittle. The slow cooling rate also helps in reducing susceptibility ot hydrogen cracking.
      You can use different methods to preheat – put parts in an oven or furnace, use induction heating or use as torch as you describe (oxygen with propane or acetylen works great). We always want to measure the temperature at least 1 inche away from the joint in ALL directions. If the thickness of the material is over 1 inch then take the temperature reading at a distance equal to the thickness of the material. If you are welding on a small hammer it shouldn’t take long to preheat the entire part – this will certainly give you a very slow cooling rate and eliminate a lot of issues.

      Both MIG and TIG are good processes to use. TIG welding usually has a higher overall heat input due to how slow it is compared to MIG. Higher heat input means slower cooling rate. However, since you’ll be preheating this is not a concern. TIG will have a better cosmetic appearnce but you can certainly make great looking welds with MIG, especially if you end up automating the process. Hope this helps and good luck!

    • Both Hardox 500 and ASTM A514 will require preheat. You need to know what the weld requirements are. If you do not need to match the strength of the base metals then don’t. Both of these base metals are prone to hydrogen induced cracking. Reduce this risk by:

      * Minimizing the hydrogen content in and around
      the prepared joint
      * Use the right preheat and interpass temperature (this will depend on the thickness of the material and could also be affected by the the requirements of the A514 in terms of harndness)
      * Use welding consumables with a low hydrogen content
      * Keep impurities out of the weld area

      For additional information on hydrogen induced cracking read: Factors Influencing Hydrogen Induced Cracking and Preventing Hydrogen Induced Cracking.

    • What is the thickness of each of these materials? What welding process will you be using (GMAW,GTAW,SMAW,etc.)? 1045 and 4140 will definitely need preheat and slow cooling, but the actual temperature depends on material thickness.

  26. hi dear please advise about PWHT, We are going conducting PQR 4145 X4140 PIPE, 4145X A36 AND 4140X A36 its all required pwht on the test coupon waht si temp.
    please advise.

    • When performing the Procedure Qualification Record you should use preheat and PWHT if that is what the base material needs. In this case you do need to preheat and PWHT according to what you expect to run in production. Remember that the qualification process is making sure that what will be done in production works, so your WPS must be based on the procedure used for your PQR. 4140 and 4145 typically don’t require PWHT other than simply slow cooling, but this may depend on the final properties you want out of your welded material.
      The Procedure Handbook for Arc Welding suggests using a preheat of 400-500F for thickness up to 1/2 inch and 600-700F for thickness of 1/2 inch to 2 inches.
      If this weld requires multiple passes make sure your interpass temperature is the same (minimum) as your preheat.

    E10018 OR E12018-H is Possible Please advise.
    thanks u

    • What are the requirements of the weld in terms of mechanical properties (tensile/yield strength, elongation, etc)? This affects filler metal selection. AISI 4145 has a tensile strength ranging from 94 to 128 Ksi (650 – 880 MPa). In most cases you don’t need to match the strength. If you are welding 4145 to 4145 and needed to match the strength of the base material then E12018-H would be a good choice. Remember to preheat and slow cool adequately to avoid cracking.

      When joining to metals with lower tensile strength (like 4140 and A36) you only need to match the strength of the weaker base metal. So welding A36 to 4140 can be done with a E7018. For 4145 to 4140 you can use E12018, but keep in mind 4140 may have a tensile strength as low 94 Ksi, in which case E10018 would suffice. You need to know if the material is cold drawn or if it has been heat treated.

  28. I need to arc weld a piece of 4140 that has 4″x 4″x1/8″ deep hammered marks in it that needs welded and machined flat , should I preheat this piece its 4″ thick by 36″ in dia. I was just going to use a machineable rod for this 7018MR

    • You definitely need to preheat. For 4″ thick material go at least 650-700F if possible. Make sure your interpass temperature is at least 650F as well. If you cannot get it that hot try to slow the cooling rate down by throwing a heat blanket or bury in sand. Fast cooling rates may cause cracking. Even though this is for build up and not joining the same rules still apply. Low-hydrogen electrodes are necessary so 7018MR should work. Are there any other specific requirements for this deposit?

  29. Hi, I am welding AISI4140 block to a 6mm thickness ASTM A588 rectangular hollow. May I know what kind of electrode shall I use? And is that OK if I preheat it to 500F?

    Thank you.

    • ASTM A588 is a Group II base metal according to AWS D1.1. Filler metal for matching strength would be any low hydrogen stick electrode (E7015, E7016, E7018, E7028), any F7XX flux-cored electrode. For GMAW use ER70S-X (ER70S-3 or -6) electrode. GTAW use ER70S-2. 500F preheat should be plenty. Recommended preheat is 400-500F for AISI 4140 up to 12mm in thickness. Are there any special requirement? What is the application? Answers to these questions may allows us to be more specific with process and filler metal.

  30. I’m making an angle plate for machine shop use. I’d like to add a brace, as most angle plates have them. I’m using 4140 as I have some around, and the hardness is helpful for wear resistance. The strength isn’t particularly important.

    It’ll be around 7/8″ thick when welded. I’m not sure what I’ll use for the brace, maybe more 4140, maybe 1018 or similar, not sure on thickness either – 1/2″ minimum, but I might go thicker.

    This is all being done in a home shop, and I don’t have a torch big enough to reasonably preheat. The best option that I can think of is to tack it up, throw it in my oven (which I think is good for a little over 500F) for a while, run a single 7018 bead down each side using 1/8″ rod (I don’t have a machine that’ll run bigger), and bury it in dry sand.

    After welding I’ll machine it to final dimensions (3/4″ thick for the L shape part).

    If I get it up to 500F, how likely is it to crack?

    How about if I just weld it at room temperature, is cracking likely in that case?

    Thanks for any advice.

    • Hello Daniel, the process you are describing sounds good. It’s better than how it is being welded in some shops we visit. Preheating to 400-500F with your oven, welding with 7018 then slow cooling by burying in sand should take care of problems associated with cracking due to embrittlement in the HAZ. The reason we preheat is to have a very slow cooling rate which avoids, or minimizes, the formation of martensite. See the post on hydrogen induced cracking for more information: Preventing Hydrogen Induced Cracking and Factors Influencing Hydrogen Induced Cracking.
      We do not recommend welding without preheat, but it is theoretically possible if you use an extremely high heat input when welding, typically this can only be achieved with submerged arc welding. You would be nowhere near with a 1/8″stick electrode.
      The E7018 is a good choice for filler in this case. We would suggest using A1018 for the braces as you mentioned. Good luck.

  31. dear Gentlemen,

    kindly i am asking about what is the best welding electrode to weld Hardox600 with steel 4140

    • Mohamed, I will email you a guide to the eamil address you provided. This is a welding guide published by SSAB which is the manufacturer of Hardox wear plate. Selection of the right filler metal is important. Equally as important is strictly obeying the minimum and maximum preheat and interpass temperature. Welding Hardox can be done without any issues. If the weld does not need to match the tensile properties you can weld with the GMAW process using an ER70S-6 filler metal. This is true for both 4140 and Hardox 600. You can also us an ER80S-D2 wire. This guide should point you in the right direction. If you do not receive it by email you can find it on SSAB’s site at:!accordion=workshop
      under Workshop and Design Information.

  32. Hi,

    I am trying to plug a 6mm (0.236 inches) dia hole in a tool (to repair the tool) that will be used in oil and gas application and will experience pressures upto 1378 bar (20 000 psi) at high temperatures of about 100 degree celsius. I was wondering if welding the hole will seal is off effectively and plug the hole permanently. Thanks in advance.

    • Properly welding the hole can definitely provide a good seal. However, care must be taken. How deep is the hole? If it is too deep it may be difficult to achieve good side wall fusion. In some cases,if too deep, you may need to open up the how a bit. Also, what is the base material and how thick? Depending on the amount of carbon and thickness you may need to preheat in order to avoid excessive hardening in the heat affected zone. Also, make sure the surfaces are very clean as contaminants such as mill scale can prevent good side wall fusion.

      • Hi welding Guru,

        I would like to run a PQR for AISI 4145 to AISI 4145. kindly advise me which electrode can be used to weld this PQR so that it meets the minimum tensile strength requirement and Bend test requirement as per ASME Sec IX. This material is being used as per API 5D for drilling tools. The actual scenario is that weld build up / buttering to be done after the removal of existing hard banding on a drill tool.

        • AISI 4145 is considered an unlisted material so it has not group number assigned. Qualification will need to be done by testing. The UTS of AISI is 135ksi. The question is: do you need to match the tensile strength of the base metal for this application or are you using this material for its hardness. This is typically the case for tools that have to resist abrasion. AISI 4145 is used extensively on down hole drilling tools such as drill collars due to its high carbon content which in turns provides excellent hardenability.
          Since you will have to qualify by testing it is important to understand the requirements. In many cases similar materials are welded with 110Ksi filler and with dilution the test results creep into the 120’s.

  33. I am trying to weld Lift lug (25 mm thick plate -AS3678 Gr350) to clump weight (725 mm dia x 725 mm height – AISI 4130 / AISI 4140). Pls advise preheat temp., weld process, type of filler to be used, PWHT reqd or not, if PWHT required than at what temp / soaking time / cooling process.

    Thanking you

    • Hi Rusty, to provide a more complete recommendation we need a lot more information (application/intended purpose, service conditions, joint type, etc). For now here are a few tips. First, do you need to match the strength of the 4140 casting with the weld? Otherwise you can use an ER70S-6 GMAW wire. Preheat 600-700F and slow cool. The need for PWHT depends on the final mechanical properties you need.

  34. If I weld AISI 4140 with AS 3678 Gr350, what consumable I have to use for this combination and what is the preheat nad postheat temperature?

    • Vijai, AS3678 has 22 points of carbon max, 4140 has approximately 4140,so definitely need to consider preheat. However, this depends on the the thickness of the material. Can you please provide more details? Material thickness, joint type. ER80S-D2 is typically OK, but may not be optimal depending on the application.