Welding Tips and Tricks

Had a job come in the shop yesterday which involved welding sleeves around soild 3'' pieces of round A2. Welding supply stores are closed on saturday and we dont keep tool steel filler on hand so I tried using some stainless/chromoly/nickel bastard filler called Royal T220. Long story short, the first piece looked great.......... until it cooled, after that i noticed some very small cracks at the end of the weld, across the center of the face.

Any thoughts?

note: material was preheated to 400 degrees before welding, and i backed off the current slowly at the end of each weld.

M.Fluxxer.

As you wrote, "Until it cooled", is the key. Without preheat and slow cooling after welding, the metal will become excessively hard. By allowing the weld to cool very slowly, the metal solidifies into metallurgical structures that are less hard. The following links attached below explain it better than me.

A2 is an alloy that was air hardened and probably is being used in cold work operations. To maintain as close as possible the characteristics after your repair welding, it is important to choose a compatible filler metal. I tried unsuccessfully to find a data sheet for the filler metal "Royal T220", in order to understand if it is compatible. Please write us the complete name of the manufacturer, and check the brand of filler, in order to find their website and locate a data sheet for it.

If you have the material certificate of that particular A2 steel, then you know its his history (example: the manufacturer, the hardness etc.). Often the manufacturer on their websites will supply the data sheet for that type of steel and its recommendations for using it ... including welding.

Tanks.
Alexa

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"... Welding (...) Use air hardening tool steel filler material. (...)
Annealed Material:Preheat to 400/600F(205/315C). Maintain above 400F(205C) during welding. Reanneal or temper 1400F(760C) 6 hours. (...)
Hardened Material: Preheat to 25F(15C) below original tempering temperature (300F(150C) minimum). Maintain above 300F(150C) during welding. Cool to 150F(65C) after welding. Temper 25F(15C) below original tempering temperature. ..."
Source: http://www.simplytoolsteel.com/A-2-tool ... sheet.html

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Welding of Tool Steel

It is sometimes necessary to weld finished or partly finished tool steel parts. Welding tool steels differs from welding the low carbon machinery steels since tool steels, because of their alloy content and the welding temperatures will actually harden to maximum hardness in and near the area welded. Such localized hardening can cause severe cracking and it is, therefore, necessary that all possible precautions be taken to prevent, or at least reduce, the stresses that cause this cracking.

We offer the following suggestions for optimum results in the welding of tool steel parts with the warning that as the alloy content and the hardness of the steel to be welded increases the danger of post-weld cracking increases. Note also that while the heat of welding will harden the higher alloy tool steels, it may actually soften the lower alloy grades to an unacceptable degree and the part may have to be re-heat treated after welding. Even in the higher alloys there will be a soft or overtempered zone between the weld and the base metal, but in these grades this soft zone is generally acceptable.

PROCEDURE

"... Preheat the part to as high a temperature as is consistent with the final hardness requirements, preferably in the range of 400-1000F (250-538C). The preheat temperature for hardened tools should not exceed the original draw temperature. Furnace preheating is desirable but torch preheat is widely practiced. Welding may then be performed using either shielded arc techniques (Heliarc or Atomic Hydrogen) with uncoated tool steel welding wire or electric arc methods using specially coated electrode. (...)

Often a stainless rod is used for non-critical areas. After welding, equalize in a furnace at the preheat temperature and cool slowly to room temperature. Following this you must slow cool with a tempering treatment at a temperature just below the original tempering temperature. Postheat hardened tools for 1 hour per inch, 2 hours minimum, at 50F below the original tempering temperature. Annealed tools should be re-annealed. This serves both as a stress relieving operation as well as to minimize the hardness gradient across the weld area. Local conditions may vary the welding methods, but the principle of preheating and slow cooling should be respected to minimize risks. ..."
Source: http://www.diehlsteel.com/technical-inf ... steel.html

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pages 11 - 13 of the link:
http://www.bucorp.com/files/UddeholmWel ... lSteel.pdf

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probably many more ...

here is a link to the composition of the filler metal. http://www.crownalloys.com/MSDS/MSDS-RO ... 20-TIG.pdf

I preheated the materials to 400 F.....I post heated by slowly backing off the arc as the shop I work for doesnt have an oven. Perhaps it wasnt enough post heat.

A trick Werspace shared for postheat and slow cool... Bury the part in a bucket of (dry) vermiculite from the garden center of your local home store. It will hold heat for hours.

Steve S