Question: My job is to do machine shop welds and repair machines and structures in the field. I almost never have the benefit of knowing what kind of metal I’m welding. Can you please provide some advice on how I might determine the type and grade of metal I am working with?
A: The best advice I can give is if you don’t know what it is, don’t try to solder it. This particularly applies to critical parts where failure can cause injury or death.
Welding certain metals using improper welding procedures can cause defects in the base metal, the weld, or both.
When asked to weld unidentified material, how can you tell what it is? First of all, you should be able to narrow down the possibilities with the help of a baseline assessment. Look at the surface of the material and see how heavy it is. This should allow you to put the material into broad categories, such as carbon or low alloy ferrous material, stainless steel or nickel alloy, or aluminum alloy. Assessing the area where you will need to weld can also give you important clues. Is there any evidence that the part was welded in the original manufacture? If so, it is a good indicator that the material is weldable. Is there any evidence that a previous weld repair has been attempted? If previous solder repairs have failed, this is a red flag telling you to be very sure what you are working with before attempting a new repair.
If you are performing a repair on a piece of equipment, you can call the original manufacturer to ask what material was used. Some items are usually made from a certain material. For example, aluminum handrails are typically made from grade 6061. Doing a little research on the materials commonly used to make the article to be welded can help you narrow down your options.
Since you are working with a machine shop, you should be able to get very good information about the material from the machinists. If it was a new material that they machined, the machinist can know exactly what it is. They can give you good information about the material based on its machining characteristics. You should be able to estimate the hardness of a steel based on the feed rate and speed used in the machining process. The way in which machining chips are formed also provides useful information. You should avoid welding steels that produce small chips, as this is likely a loose machining grade that is prone to hot cracking when welding.
Spark tests on steel and cast iron can give you a general idea of how much carbon is in the material. Spot chemical tests can also determine if specific alloying elements are present.
Chemical analysis will provide some of the best information to help identify the quality of the material. In many cases, you can submit machining chips from the material for analysis. If machining chips are not available, if possible remove a small piece of material to be analyzed, approximately 1 inch. square. Chemical metal analysis is available at most testing labs and in many cases costs less than $ 200.
The bottom line is that spending time and maybe some money to get a really good idea of the material you are going to weld is important if you want to make a safe and durable repair.