Welding Chromolly with a mig

MIG works fine on Chrome-moly, but because the MIG process is so fast, it is recomended that you heat treat the welds with a torch afterwords.

All you have to do is stress relieve them to about 600 deg F. It takes very little time with a rosebud tip in an oxy-acet. torch. Buy a Tempilstik to hit the temperature.

Motor oil flashes off at about 650 degF, so you can just keep warming a joint until a drop of oil flashes off. Crude but it works.

If you are dealing with 4130 in "N" or Normalized condition - and most raw

In his book, "Engineer To Win", Carroll Smith said, " Since I believe that not heat-treating 4130 fabrications is DUMB (if you don't heat-treat, you end up with an expensive part with the same strength as 1020 - and brittle weld areas) Smith's law says to use heat-treatable rod for EVERYTHING. I heat-treat 4130 fabrications to a Rockwell C scale 26 to 30 - no higher. This amounts to an ultimate tensile strength of about 130,000 p.s.i. with sufficient ductility that I do not have to worry about brittle parts."

That would suggest TIG and/or Oxy-Acetylene welding with the correct filler rod.

According to Machinery's Handbook, "N" condition 4130 has a strength of

1020 mild steel has an "as rolled" strength of 65,000 p.s.i. while 1040 mild steel has an "as rolled" strength of 90,000 p.s.i.

If you are spending the dough for 4130, why not get the most out of it with post-fabrication heat-treating?

If you are not going to heat treat, simply use 1040. It will be approximately the same strength as untreated, "Normalized" 4130, weld well with MIG - or any other process, not potentially create brittle areas in the HAZ, and cost a lot less for raw materials.

Bob Paulin - R.A.C.E. Race Car Chassis Setup and Dial-in Services

Justin Dupuy wrote in article ...

No pun intended, right Ernie? ;-)

Jeremy

Bob

Do you know what the strength value is for 1025 steel?

FThera wrote in article ...

In his book "Engineer To Win" published in 1984, Carroll Smith has this to say.....

"SAE 1025...This is the best of the low-carbon steels. To the best of my knowledge, it is now available only as seamless round tubing - and that rarely. Before 4130 was developed, 1025 was the standard aircraft structural tubing. We don't use it simply because it is difficult to find and, if a tube fabrication deserves something better than 1020, it deserves to be made from 4130, and heat-treated."

Again, keep in mind that this book was written 20 years ago, and 1025 - which was rare then - may have fallen off the face of the earth by now.

Bob Paulin - R.A.C.E. Race Car Chassis Setup and Dial-in Services