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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, 10:25 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, 09:48 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

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