Basics of Welding Chrome-Moly Steels

Molybdenum is used as an alloying element to increase hardenability and improve wear resistance in metal alloys. Molybdenum is also used for creep resistance—creep is the stretching and deformation of a fabrication’s shape over time when at elevated temperatures—in fabrications such as pipes that will are under pressure and elevated temperatures for long periods of time in service.. For refineries and other chemical processing plants that use high temperatures to process their products, it is very important that the tanks and pipes that are transporting the products maintain their shape over time.

Chrome-moly (chromium molybdenum alloy) alloys come in many shapes that you are familiar with, such as plates and pipes. Like stainless steel, chrome-moly alloys require more cleanliness than mild steel does prior to welding. Therefore, proper fit up and cleanliness is important to a good weld of chrome-moly.

Your particular welding program will likely not have chrome-moly material on hand to weld but that doesn’t mean that you cannot prepare for welding chrome-moly by getting very good at the welding processes on another material. It may be possible to get chrome-moly donated to your program, but you likely need to show your instructor that you are excelling in your welding. Speak with your instructor or career office about local industries that may use chrome-moly and see if there are internships available so you can try it out. Saying that you are interested is different than proving that you are interested.

Uses of Chrome-Moly Steel in Industry Today

In general, chrome-moly is used in structural applications, such as roll cages for race cars, and in high-temperature and high-pressure applications, such as piping for refineries. Chrome-moly is also used in applications such as chain links due to the increased wear resistance that chrome-moly provides; however, as a welder you would not likely see it in this application.

Welding Processes Used With Chrome-Moly Steel in Industry Today

GTAW, GMAW, FCAW, and SMAW are used for welding chrome-moly alloys in industry. However, each specific industry or provider that uses chrome-moly will dictate which process is acceptable.

For instance, in the racing industry, GTAW is required by the National Hot Rod Association (NHRA) when welding alloy 4130. On the other hand, the National Association for Stock Car Auto Racing (NASCAR) requests the use of GMAW-S when welding chrome-moly for its cars (Uttrachi, 2018). For pipe welding, welding consumable manufacturers such as Hobart Filler Metals recommend the SMAW and FCAW processes (Hobart Brothers, n.d.).