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  • Questions about welding 4140 steel and embrittlement

    I work in an engineering setting and have recently experienced a failure of a large pin that functions in the chassis of heavy machinery. In our machines, the pin is welded to a yoke that supports the wheels by one of our vendors. Unfortunately, this pin completely sheared in two during operation. I am not a welding expert and I wanted to research if there is any chance that improper welding practices could have led to the failure. I have done a bit of reading on welding 4140 and had a few questions:

    Why is welding on 4140HT not recommended and why does it cause cracking?

    Why does 4140 need to be preheated prior to welding?

    Any other additional information I should be aware of about welding 4140 that if done improperly could cause failure?


    Thank you for your assistance

  • #2
    If it wasn't preheated properly it would brake in a short time IMO I learned the hard way.

    Comment


    • #3
      Originally posted by 7055 View Post
      I work in an engineering setting and have recently experienced a failure of a large pin that functions in the chassis of heavy machinery. In our machines, the pin is welded to a yoke that supports the wheels by one of our vendors. Unfortunately, this pin completely sheared in two during operation. I am not a welding expert and I wanted to research if there is any chance that improper welding practices could have led to the failure. I have done a bit of reading on welding 4140 and had a few questions:

      Why is welding on 4140HT not recommended and why does it cause cracking?

      Why does 4140 need to be preheated prior to welding?

      Any other additional information I should be aware of about welding 4140 that if done improperly could cause failure?


      Thank you for your assistance
      There is no HELPFUL way to answer your questions with the information you gave.

      1)There are plenty of ways that "improper welding practices" could have resulted in the pin failure. See Hydrogen ,and other types of embrittlement.

      2) 4140 requires annealing, heat treating and stress relieving as a chrome-moly alloy steel, and preheating is part of the process.

      3) Any metallurgical text will supply much additional information regarding practices that could lead to failure.

      Comment


      • #4
        Originally posted by digr View Post
        If it wasn't preheated properly it would brake in a short time IMO I learned the hard way.
        Could you provide more information on what preheating is? Is it basically just heating the metal before performing the weld?

        Comment


        • #5
          Originally posted by Northweldor View Post

          There is no HELPFUL way to answer your questions with the information you gave.

          1)There are plenty of ways that "improper welding practices" could have resulted in the pin failure. See Hydrogen ,and other types of embrittlement.

          2) 4140 requires annealing, heat treating and stress relieving as a chrome-moly alloy steel, and preheating is part of the process.

          3) Any metallurgical text will supply much additional information regarding practices that could lead to failure.

          If you let me know what additional information you need, I can try to provide it for you. If you could expand on some of the common or likely ways that improper welding practices can result in failure with 4140HT that would be helpful in guiding me in the right direction.

          Comment


          • #6
            Originally posted by 7055 View Post


            If you let me know what additional information you need, I can try to provide it for you. If you could expand on some of the common or likely ways that improper welding practices can result in failure with 4140HT that would be helpful in guiding me in the right direction.
            Preheating is not a simple process, if done to code, especially if it involves strict control of inter-pass temps. and controlled cooling.
            Read the article below, and you will have some idea of what is involved. (4140 is a Q/T) steel.
            https://www.lincolnelectric.com/en-c...at-detail.aspx

            The weld you described should have had a WPS and an inspection, and this would be required, as well as a failure analysis on the failed pin. Was this done? If so, supply them.
            Last edited by Northweldor; 10-05-2018, 11:25 AM.

            Comment


            • #7
              Some useful info: http://weldinganswers.com/how-to-weld-4140-steel/

              Also:
              Welding of 4140 in the hardened and tempered condition (as normally supplied), is not recommended and should be avoided if at all possible, as the mechanical properties will be altered within the weld heat affected zone. It is preferred that welding be carried out on 4140 while in the annealed condition, and that the work piece, immediately on cooling to hand warm, is then stress relieved at 595 oC - 620 oC prior to hardening and tempering.If welding in the hardened and tempered condition is really necessary, then the work piece, immediately on cooling to hand warm, should be stress relieved at 15 oC below the original tempering temperature.
              --- RJL ----------------------------------------------

              Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
              -------------------------
              DialArc 250 (1974), Idealarc 250 (1971), SyncroWave 250 w/Coolmate 3, SP-175+, TA 161STL,
              Lincwelder AC180C (circa 1952), Victor & Smith's O/A, Dayton (Miller) spot welder, 1200 sq.ft. of garage filled with crap and a kid that can actually run the stuff +++

              Comment


              • #8
                Originally posted by usmcpop View Post
                Some useful info: http://weldinganswers.com/how-to-weld-4140-steel/

                Also:
                Welding of 4140 in the hardened and tempered condition (as normally supplied), is not recommended and should be avoided if at all possible, as the mechanical properties will be altered within the weld heat affected zone. It is preferred that welding be carried out on 4140 while in the annealed condition, and that the work piece, immediately on cooling to hand warm, is then stress relieved at 595 oC - 620 oC prior to hardening and tempering.If welding in the hardened and tempered condition is really necessary, then the work piece, immediately on cooling to hand warm, should be stress relieved at 15 oC below the original tempering temperature.
                7055:

                You may be in the process of the reading already recommended. But you should also know that your questions are even more complicated by the lack of info you supplied. The posting by usmcpop above, under "Also:..", is just one small part of Interlloy's spec. sheet for 4140. Here is the rest:

                http://www.interlloy.com.au/our-prod...tensile-steel/

                What you really need to answer your questions is a metallurgist, an experienced CWI, or a partial or complete failure analysis. Here is a sample of a complete failure analysis below:

                https://met-tech.com/welded-steering...ndle-assembly/
                Last edited by Northweldor; 10-06-2018, 10:48 PM.

                Comment


                • #9
                  Also my question would be is this a one time failure, or is it multiple failures over time of same part/assembly... A one time failure may be just random, if its multiple failures then it may be a design/engineering/fabrication fault....

                  Dale
                  Lives his life vicariously through his own self.

                  Comment


                  • #10
                    Originally posted by Dale M. View Post
                    Also my question would be is this a one time failure, or is it multiple failures over time of same part/assembly... A one time failure may be just random, if its multiple failures then it may be a design/engineering/fabrication fault....

                    Dale
                    Or, if it is fatigue embrittlement, it may be the first of many! Only analysis by qualified personnel can tell!

                    Comment


                    • #11
                      Click image for larger version  Name:	image_38812.jpg Views:	1 Size:	34.0 KB ID:	702441
                      Read up on "heat affected zone". It will drastically alter the properties of a hardened/hardenable material, set up stresses, can cause micro cracking and whatnot. What type filler did you use? Which welding process?

                      I'm assuming that the break occurred at or near the weld, not a foot or two beyond the yoke attachment point.

                      Incidentally, 4140 exhibits some odd behavior in the hardness vs toughness/impact curves depending on the tempering temperature. There's a sort of "no go" zone where the curve dips. There may well be such an area in the heat affected zone. See graph:

                      http://practicalmaintenance.net/wp-c...-tempering.jpg
                      Last edited by usmcpop; 11-05-2018, 12:19 PM.
                      --- RJL ----------------------------------------------

                      Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
                      -------------------------
                      DialArc 250 (1974), Idealarc 250 (1971), SyncroWave 250 w/Coolmate 3, SP-175+, TA 161STL,
                      Lincwelder AC180C (circa 1952), Victor & Smith's O/A, Dayton (Miller) spot welder, 1200 sq.ft. of garage filled with crap and a kid that can actually run the stuff +++

                      Comment


                      • #12
                        Originally posted by 7055 View Post
                        I work in an engineering setting and have recently experienced a failure of a large pin that functions in the chassis of heavy machinery. In our machines, the pin is welded to a yoke that supports the wheels by one of our vendors. Unfortunately, this pin completely sheared in two during operation. I am not a welding expert and I wanted to research if there is any chance that improper welding practices could have led to the failure. I have done a bit of reading on welding 4140 and had a few questions:

                        Why is welding on 4140HT not recommended and why does it cause cracking?

                        Why does 4140 need to be preheated prior to welding?

                        Any other additional information I should be aware of about welding 4140 that if done improperly could cause failure?


                        Thank you for your assistance
                        Well I'd like to see a picture of what broke? While I didn't do a word count, I'm thinking a picture could save a whole bunch of typing?

                        Having said that...and following along with some interest, you post a picture, I'll give you a thousand words. But to answer your question "
                        is any chance that improper welding practices could have led to the failure
                        ", yes, depending on the failure and where it broke? It could be in design as well? Hard to say?

                        Being a bit blunt, you mention you work in an engineering setting? I'm curious, what do they say about it? Was this blame the welder day?

                        Now you had other questions...much has been posted in reply for your consideration in response. I'm not sure how much of it made sense to you?
                        What I will offer up, if you provide a picture, is that thousand words of explanation. Because then I could see the weld, it's appearance for defect or guess by it's appearance to parameters used, where it broke, metallic surface structure of the break, as well it's in service usage.

                        https://met-tech.com/welded-steering...ndle-assembly/

                        Interesting...I'm not sure what everyone else got out of it but I think we are blaming the guy welding for this one? Him and the QC guy maybe? Just goes to show, fill in those craters.

                        Comment


                        • #13
                          Originally posted by oldguyfrom56 View Post

                          Well I'd like to see a picture of what broke? While I didn't do a word count, I'm thinking a picture could save a whole bunch of typing?

                          Having said that...and following along with some interest, you post a picture, I'll give you a thousand words. But to answer your question "
                          is any chance that improper welding practices could have led to the failure
                          ", yes, depending on the failure and where it broke? It could be in design as well? Hard to say?

                          Being a bit blunt, you mention you work in an engineering setting? I'm curious, what do they say about it? Was this blame the welder day?

                          Now you had other questions...much has been posted in reply for your consideration in response. I'm not sure how much of it made sense to you?
                          What I will offer up, if you provide a picture, is that thousand words of explanation. Because then I could see the weld, it's appearance for defect or guess by it's appearance to parameters used, where it broke, metallic surface structure of the break, as well it's in service usage.

                          https://met-tech.com/welded-steering...ndle-assembly/

                          Interesting...I'm not sure what everyone else got out of it but I think we are blaming the guy welding for this one? Him and the QC guy maybe? Just goes to show, fill in those craters.
                          We are all well aware of your ability to supply a thousand words or more, but how, exactly, do you have the skill to replace an SEM with an ordinary picture, when hot cracking is involved? Also, I think it is pretty obvious that the OP was not able to contact the engineering dept. of his firm, since he never came back with info. (I suspect fear of identification).
                          Anyway, tell us (briefly) about your remarkable NDT skills.

                          Comment


                          • #14
                            Originally posted by Northweldor View Post

                            We are all well aware of your ability to supply a thousand words or more, but how, exactly, do you have the skill to replace an SEM with an ordinary picture, when hot cracking is involved? Also, I think it is pretty obvious that the OP was not able to contact the engineering dept. of his firm, since he never came back with info. (I suspect fear of identification).
                            Anyway, tell us (briefly) about your remarkable NDT skills.
                            My ability to type a thousand words is called putting forth the effort. As far as getting away with looking at a picture and giving an opinion with out a SEM, assuming you mean Scanning Electron Microscope, that would be because of three reasons.

                            1) Visual clues.
                            Fractures surfaces give clues to edge deformation, previous existing surface appearance, metallic structure, and the fracture usually follows a path.
                            2) Out come predictability.
                            Visual defects, real or imagined can be expected to offer typical results. Welding craters shrink.
                            3) I read a lot. One of my interesting book sets is 11 volumes, 8th Edition, Metals Handbook. In particular, Volume 9, Fractography and Fractographs, and Volume 10, Failure Analysis and Prevention. Admittedly, sometime I just look at the pictures.

                            As far as my NDT (Non Destructive Testing) skills go, well... I'll say this. If you were leaving craters at the end of your weld, cold lumpy starts, over welding ,underfilling, under cutting, not following Weld Procedure Specification for preheating, inter-pass temperature controls, post welding heating... my skills are enough to have looked at that front end spindle, it's welds, and almost predicted in a worst case scenario the existing defects leading to a possible failure risk if the right conditions were met. Race car accident damage as was the case, or driving into a curb or careening off a wall maybe? A cold Alberta winter and a pot hole could have cause it to snap?

                            Would a "Hot crack" have been spotted? Probably no, followed by maybe, depending on size, location, and reason in development. A weld crater blister or pin hole, pretty obvious. Over fluid puddle and rapid quenching, not as obvious.
                            Depending on the material and weld appearance, it might have been suspect for conditions of, based on weld appearance alone especially on thicker materials.
                            Do you think other then a QC visual any other NDT was done on the part before it was boxed and shipped? I don't think so? They did however receive a stress relieving procedure?
                            "
                            confirming failure occurred due to overload and not fatigue."

                            But if you were asking pointedly if I'm a card holding member of that club who are ticketed/certified to perform such NDT as ultrasonic and radiographic examination, no, I'm not. But I hold my own in conversation.
                            Besides, the easy money is in welding. All a guy has to do is learn solid to liquid and back to solid. About four different ways is usually enough to earn a living. The rest comes with time, willingness to learn, asking questions, and circumstance.

                            But back to the topic at hand...you telling me that you couldn't/wouldn't looking at a weld in a picture, make some observations based on your experiences? Offer a greater opinion?
                            I'm going to give you enough credit to think you could. Depending on your experiences, more or less, but I'm not looking to see who has had more or what they were other then in passing interest? I reply based on my experiences, more or less.

                            Three initial questions.

                            -Why is welding on 4140HT not recommended and why does it cause cracking?

                            -Why does 4140 need to be preheated prior to welding?

                            -Any other additional information I should be aware of about welding 4140 that if done improperly could cause failure?

                            If I can't see a picture...what more is there to be said?
                            Case closed.







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