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Welding Medium-Carbon to High-Strength Steel

Q: We need to weld a 1-in.-thick AISI 1050 carbon steel plate to a 2-in.-dia. A514 steel shaft. The AISI 1050 has a yield and tensile strength of 95 KSI and 115 KSI, respectively. We know we should preheat, but we're unsure of what temperatures to use or what filler metal to select. Could you please advise?

A: Here are some other important things to consider for this job.

Welding process, maximum interpass temperature, cooling rate after welding, and post-weld heat-treat (PWHT) are all variables that need to be specified and controlled for this application.

Preheat and maximum interpass temperatures on the AISI 1050 steel are thickness- and carbon equivalency-dependent. If you have a material certification from the steel supplier, you can calculate the carbon equivalency (online calculators are readily available) to determine specifically what the temperatures should be. If you don't have this information, we recommend a preheat temperature of no more than at least 300 degrees F and a maximum interpass temperature of no more than 700 degrees F for a 1-in.-thick plate.

Since the A514 gets its properties from quenching and tempering, be sure you don't overheat this material or you will degrade its mechanical properties. For the A514 shaft, it too is thickness- and/or grade-dependent. The minimum preheat temperature should be at least 175 degrees F, and maximum interpass temperature no more than 400 degrees F.

For preheating and maximum interpass temperatures, the A514 is the controlling material. When preheating, apply and achieve the preheat temperatures as recommended for the steel type (each base material side of the weld joint). The maximum interpass temperature during welding should not exceed 400 degrees F for the welded joint.

The AISI 1050 steel, depending upon carbon equivalency, may benefit from a PWHT application; however, it is not recommended that the A514 steel be used in the PWHT condition. Therefore, it's best that no PWHT process be used for this application, but it is still important for you to control the postweld cooling rate. After you complete the application, try submersing the hot welded parts in a dry medium, such as a clay floor or dry sand, or cover the parts with a ceramic or fiberglass insulating blanket.

When choosing a filler metal, don't try to overmatch the filler metal strength to the base material strength. In fact, if the application is limited to a single-pass weld, there will be some alloy recovery from the base material during welding, which may slightly increase the strength of the weld joint.

The A514 should have a yield strength of at least 100 KSI and a tensile strength of 110 to 130 KSI for this material thickness.

For this application, we recommend a filler metal from the E110 classification. The welding process used is not critical for weld soundness or strength, but it should be a low-hydrogen process (H4 designation). Welders should use a stringer-bead technique and make sure the joint is free of rust, mill scale, paint and any other impurities. 


This article originally appeared in The WELDER magazine.
It is reprinted here with permission of the Fabricators & Manufacturers Association, Intl.

Posted in Filler Metals , Tagged with Steel