On Friday, April 12, 2019
April is National Welding Month which according to the American Welding Society, is a "time to recognize and reflect on the impact welding has on our daily life... The month of April is a chance to spotlight the welding industry's past, present and future through education mentorship and recognition."
As Advanced Heat Treat Corp. works with parts that are oftentimes welded post-heat treatment (and sometimes prior to heat treatment), we felt it necessary to recognize this celebratory month, so we asked Dr. Edward Rolinski to discuss heat treatments for parts that require welding. Continue reading to learn more...
Surface Hardening, Masking & Welded Materials
In manufacturing, it is important to consider the sequence of various operations and their effect on the engineered components - this is especially true for parts that require surface hardening and welding.
Nitriding: The Preferred Method for Welded Materials
Surface hardening by induction or flame method, for example, cannot be carried out on the welded portion of the surface since the content of carbon in the steel is very low and martensite cannot be formed. On the other hand, surface hardening by nitriding or carburizing of the welded components can be done easily if the residues of the welding operation are removed from the surface.
The preferred hardening method for welded components should be nitriding/nitrocarburizing since it is carried out at low temperatures of 932 - 1070ºF (500-570ºC) and therefore no dimensional changes occur after the treatment. An example of plasma nitriding of stainless steel tubes is shown in Fig. 1 below.
Post-Heat Treat Welding - Limitations
On many occasions, finished components are welded together. For example, transmission parts are joined with their partners to make a complete device. Nitrided surfaces cannot be welded easily because of the strong outgassing and porosity formation. In this situation, welding can only be performed on the surface which was properly protected from nitriding or carburizing.
Masking for Gas Nitriding
Masking from hardening in the gas process can be done using a special paint. In the plasma/ion process, mechanical masking such as shim stock, tubes, etc., eliminates contact of plasma with the specific surface. Fig. 2 below shows plasma nitrided tubes, which were masked off at the ends to allow welding them into longer sections.
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Stainless Steel Tubes After Ion/Plasma Nitriding
Note masked off end of the tubes for allowing welding them together into longer sections. Picture courtesy of Advanced Heat Treat Corp. Monroe, Michigan.
Learn more about ion/PLASMA nitriding