Technical Details of Welding Normalized 4130 are Presented Here; for Other Information:

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Selecting the proper welding filler metal and techniques requires an understanding of the metallurgy of the base material and the weld metal that develops from an admixture of the 4130 and the filler metal.

The graph on the left was taken from a US Steel "Atlas of Isothermal Transformation Diagrams."  These graphs define the metallurgical structure that occurs in various steels when they are cooled.  This one defines that we can expect to have high hardness, brittle Martensite form when 4130 is cooled at a particular rate. 

The graph at the bottom of the page shows the structure that formed when a bar of 4130 was heated to 1550 deg F then one end spayed with water.  Note that from about 3/16 inch from the quenched end the microstructure is almost all Martensite.  The hardness in this area is 50 RC.  The equivalent tensile strength for that hardness is about 250,000 psi.  Very strong but also brittle meaning a small crack will easily propagate.  If one made a chisel from that material it would break on the first blow!  If we wanted a chisel we would heat it after quenching to "Temper" the Martensite to a lower strength and make it far less brittle.

The reason for understanding the 4130 IT diagram, particularly the End Quench Hardenability Test  (Called a Jominy Bar, after the inventor, Walter E. Jominy) will become apparent as we present additional information below.

Many years ago, for a Masters Thesis, I made a Jominy bar from a weld deposited in a steel that had about 105,000 psi yield and about 120,000 psi ultimate strength.  I also plotted the cooling curves at numerous points along the Jominy Bar.  (Walter Jominy only sited cooling rates at 1100 deg F, not sufficient for my Professor!  Had to use a fast response Light Beam Visicorder, thermal coupes at 1/8 inch intervals along the bar etc!) Calculations were also made defining the cooling rate in welds made in 1 inch thick plate with the submerged arc welding process.  The accompanying graph was developed from that data.  The cooling rates for TIG welds made in thin material are also noted on the graph.

The cooling rates for TIG welds are slower than one would intuitively think for this thin material.  This is for several reasons; 1) the thin material does not conduct heat away rapidly, 2) welding volts and amps are relatively low and 3) the energy efficiency of TIG is  low , ~50%.

From the IT diagram we can estimate a continuous cooling diagram using a technique suggested by Grange and Kiefer.  It is shown in green superimposed on the IT diagram.  Also shown is the cooling rate of the 1/4 inch Jominy point which has a cooling rate of 50 deg F/sec at about 1100 deg F.  This is approximately the cooling rate  for TIG welds in 0.040 inch material.  For 1/16 inch thick material the TIG cooling rate  would be about  62 deg F/sec.  This information is directly related to the weld heat affected zone (HAZ).  These cooling rates will produce a significant amount of Martensite in the HAZ.  The structure in the weld metal will depend on the weld rod or wire selected as well as the amount of admixture of 4130.  For example, very small fillet welds may have mostly melted 4130 in the deposit which can create potential cracking problems.

The table on the left shows the estimated weld metal structure of: 1) a weld made in 4130 without filler metal (called an autogenous deposit), 2) with 30% ER80S-2 diluted into the 4130 and 3) ER70S-2 rod diluted the same 30% into the 4130.  The resulting chemistry is a simple ratio of the materials assuming TIG welding with Argon shielding gas and minimum carbon or other element loss.

The data showing "Critical Diameter" was developed from a book on Steel Hardenability by Crafts and Lamont.  It defines the diameter of a bar, that when heated to 1500 deg F and quenched in water will have 50% Martensite in the center.  Notice the deposit with 30% ER80S-D2 filler rod is much more hardenable than even the 4130.   An austenitized and  quenched bar 3.9 inches in diameter of this material would have 50% Martensite in the center versus only a 2.8 inch bar for 4130 .  The deposit has significantly higher Manganese and Moly than the 4130 or the deposit made with ER70S-2.

A deposit made with ER70S-2 will most likely have a slightly lower tensile strength than Normalized 4130.  If diluted as noted, probably 85,000 to 90,000 psi versus the 100,000 psi in 4130 depending on how the material was processed.  This reduced strength may be acceptable if gussets are used or for intersecting tube joints by making the fillet size slightly larger. 

CHECK WELD QUALITY

It is very important to check weld quality and understand the types of defects that could be encountered when welding 4130.  Check your weld procedures and keep them consistent.  You should make some sample welds and bend them to destruction to assure failure occurs only after considerable bending has taken place.  Look for porosity or cracks that may have been present in the weld.  It would be a wise investment to hire the services of an American Welding Society (AWS) Certified Welding Inspector (CWI).  There are some 20,000 registered.  In fact many of them are members of the  50,000 member AWS.  They can advise on procedures and what to check for such as small undercuts at the weld toe of fillet welds that can lead to premature failure.

Consistently following the proper weld procedures and knowing how to check for possible weld problems is of major importance. Be sure to employ the skills of a qualified welder who has experience welding this material.  Also inspection of the final welds by an Certified Welding Inspector (Certified by The American Welding Society) is highly recommended.

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This is a photo from an interesting article in the March 2007 issue of "Hot Rod Magazine."  The whole ridged elaborate cage was made from 4130 tubing.

Note they used ER70S-2 welding rod and made all joints with TIG welding.  Have to believe this was a mocked up photo since the description says the tube ends were ground to almost a "press fit."  This is far from that and unacceptable for making any type of weld!

If a Search Engine Found This Page 1st- - - We'd Suggest a Visit to The Basic Welding 4130 Page; Then Return.  Click Here

This page presents the technical information that supports the reasons for the suggestions found on the "Basic, Welding 4130" page.

Like Math?  Want to see the calculations for weld cooling rates and references?  CLICK HERE.

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This Page Presents Technical Details of Welding 4130 for Other Information:

Click for BASIC 4130 WELDING DETAILS

Click for  EQUATIONS defining weld cooling rate in tubing

Click for WELDING HEAT TREATED 4130 CHROME MOLY

Click for METALLURGICAL DEFINITIONS

Click for WELDING A BETTER STEEL;  HY 130

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