Weldability 1045 & 4140

Date 01-21-2011 01:15

The carbon content of AISI 1045 is nominally 0.45% carbon. That is only slightly higher than the nominal carbon content of the 4140 which has a nominal value of 0.40% carbon. However, what is not being considered is the sum of the effects of the other alloying constituents; chrome and molybdenum in the 4140 alloy.

A carbon equivalency formula (there are several in use) can provide some insight about the total effects of the alloying elements. The alloy with a higher carbon equivalency has poor weldability (higher susceptibility to hardening) compared to an alloy with low carbon equivalency, assuming both alloys are welded with the same procedure.

You can used the following equation to compare the carbon eqivalency of the two alloy systems, i.e., 1045 vs 4140. The alloy with the lower Ce is "easier" to weld, that is, it is less likely to crack when compared to the alloy with the higher Ce.

Pcm = C +(Si/30)+(Mn/20)+(Cu/20)+(Ni/60)+(Cr/20)+(Mo/15)+(V/10)+B

You need to use the same formula for both alloys. You cannot compare two alloys using two different formulas. Its the old apples to apples thing.

Best regard - Al

By zambrota (**)

Date 01-21-2011 05:01

Thanks Al,

I agree with you. You are in line with my way of thinking. But, if I apply your formula on 1045 steel, I get CE=0.50 and for 4140 steel the same CE=0.50 . IMHO, the reason for that is your formula for CE that suits more alloy steel,i.e. 4140 than carbon steel 1045. On the other side if I calculate CE using IIW formula (C+Mn/6+Cr/5+Mo/5+V/5+Ni/15+Cu/15) result would be:
-1045 steel CE=0.58
-4140 steel CE=0.78
Please your comment. Also I would appriciate your explanation if the actual grain size of steel has any impact on weldability. If YES, how would you take it into account in welding procedure?

By 803056

Date 01-21-2011 16:15

Different equations produce different results as expected, but each equation is used with different guidelines for preheat, interpass temperature, etc.

The carbon equivalency equations are simple one tool in the welding engineer's tool box. Like any toolbox, there is one tool the serves a purpose better than another. The equation I used was just one of several and it was handy. It was meant to be an example of a carbon equivalency equation that listed all the alloying elements present in the alloy system you are dealing with. The guidelines used with the equation are going to "kick in" at different Ce than a different equation with different guidelines. I use the one I listed becuase the guidelines take into account the hydrogen level of the welding process and filler metal as well as the degree of restraint.

The equation you listed simply has different guidelines that are applied at different levels of Ce.

As for grain size, that has more influence on toughness than weldability. The welding procedure used can influence the grain size, hardness, and toughness of the completed weld. The grain size is not going to affect tensile strength or guided bend test results significantly when dealing with the two materials you listed. Both have significant levels of carbon that are on par with each other. The influences of chrome and molydenum on the Ce are to a lesser extent. Simply put, you can add carbon or other alloying constituents to the base metal. The one that has the most significant affect on weldability is carbon, so it may be better to reduce carbon and add other alloying constituents in its stead to maintain good welding characteristics. However, chrome and molylbdenum are much more expensive than carbon.

I wasn't able to plug in the numbers because I didn't have the actual chemistry of the 4140 available. I am surprised that the two alloys were exactly the same. I wouldn't expect that. Again, it is a case of picking the right tool, oops, equation for the alloys you are working with. That can be a problem when they are from two different alloy families. What you found is one area that you must consider. If you were to apply the same equation to austenitic stainless steel and carbon steel the results would be totally misleading.

Best regards - Al