20.4 Welding Chrome-Moly Steels
David Colameco, M.Ed.
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 in fabrications such as pipes that will be under pressure and elevated temperatures for long periods of time in service. Creep is the stretching and deformation of a fabrication’s shape over time at elevated temperatures. 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 these products maintain their shape over time.
Chrome-moly alloys also 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. Proper fit up and cleanliness is important to a good weld of chrome-moly.
This section on chrome-moly is short, but many students find it interesting. If you are interested, take charge of your career and look into career opportunities. Your particular welding program will likely not have chrome-moly material on hand to weld but that doesn’t mean that you can not prepare for welding chrome-moly by getting very good at the welding processes on another material.
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. It may be possible to get chrome-moly donated to your program but you likely need to show your instructor and program that you are excelling in your welding. Saying that you are interested is different than proving that you are interested. This would make the extra effort of getting chrome-moly material into your program worthwhile. It never hurts to ask your program because the worst thing they can say is no.
Uses of chrome-moly steels in industry today
In general, chrome-moly is used in structural applications such as roll cages for race cars, and in high temperature and 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 likely see it in the first two general applications of roll cages and high temperature and pressure piping.
Welding processes used with chrome-moly steels in industry today
GTAW, GMAW, FCAW and SMAW are used for welding chrome-moly alloys in industry, however each specific industry that uses chrome-moly will dictate which process is acceptable.
In the racing industry, GTAW is required by the National Hot Rod Association (NHRA) when welding alloy 4130, while NASCAR on the other hand, uses GMAW-S when welding chrome-moly for its cars (Uttrachi, 2018). For pipe welding, welding consumable manufacturers such as Hobart recommend SMAW and FCAW as the recommended processes (Hobart Brothers, 2023).
An element that is added during the creation of metal at a foundary that provides the chemical composition needed to create the desired metal alloy.
An alloy consisting of the elements chromium and molybdenum.