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Difficulties in Stainless Pipe Fitting Processing and Common Problems in Welding

1. Difficulties in processing stainless steel pipe fittings

What are the difficulties in processing stainless steel pipe fittings?

As the scope of use of stainless steel profiles becomes more and more common, the demand for stainless steel profiles is also increasing, which has promoted the development of stainless steel precision machining to a certain extent. The following explains the difficulties that may arise in the processing of stainless steel pipe fittings:

(1) Severe work hardening of stainless steel pipe fittings: the work hardening tends to be high during cutting, and the tool cutting in the work hardened area will shorten the life of the grinding tool.

(2) High cutting force and high cutting temperature: Stainless steel pipe fittings have high strength, large tangential stress and large plastic deformation during cutting, so the cutting force is large. In addition, due to the poor thermal conductivity of stainless steel, and the high temperature tends to be concentrated in the narrow area near the cutting edge of the tool, it is easy to accelerate the wear of the related tool.

(3) Stainless steel pipe fittings are easy to stick to the knife: any stainless steel has the characteristics of tough chips and high cutting temperature during processing. When tough chips flow through the rake surface, the tool wear will accelerate.

2. Common problems when welding stainless steel pipe fittings

(1) In order to prevent the weathering corrosion due to processing heating, the welding current of weldable stainless steel pipe fittings should not be too sticky, and it is more suitable to be 20% less than carbon steel electrode. The arc should not be too long, and the inter-layer cooling should be narrow.

(2) The hardenability of weldable stainless steel pipe fittings is sticky after welding, and cracks are prone to occur. If typical weldable stainless steel pipe fittings are used for welding, preheating above 300°C and slow cooling at 700°C after welding are required. If the weldment cannot be subjected to post-weld heat treatment, stainless steel pipe fitting electrodes should be used.

(3) For weldable stainless steel pipe fittings, appropriate amount of invariant elements Ti, Nb, Mo, etc. are added to improve corrosion resistance and weldability, the weldability of which is better than weldable stainless steel pipe fittings. When using the same type of chromium stainless steel electrode, it should be preheated above 200℃ and tempered at 800℃ after welding. If the weldment cannot be heat treated, chromium-nickel stainless steel electrode should be used.

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