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Tools/mig/induction: Difference between revisions
→Main level 2 induction
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** But if your welds are structural or otherwise sensitive to contamination, don't use it
* Welding hardening steels
** Attempting to weld hardened or heat-hardenable steels by conventional approaches will usually result in cracking
** Consider what wire material you want to use, given the strength of joint you need.
*** Aluminium is the very softest wire, but can only be used on aluminium or titanium
*** Bronze is the softest and most compliant wire usable on steel and is very unlikely to result in cracking
*** Stainless steel is harder and stronger but does carry more risk of cracks and needs more care
*** Using a hardenable wire gives the strongest result but has the highest risk of cracking
** Differential heating and fast cooling causes the trouble
*** If the steel is hardenable then it WILL harden along the edges of the weld
*** Hardening steels normally contract and pull away from the weld resulting in high tensile and sheer stresses
*** Hardened steels are brittle and easily cracked by tensile stress
*** Most of the trouble occurs because the heat-affected zone around the weld is small and cools very rapidly while the bulk of the material remains unaffected.
** Heat control and management will be needed to prevent cracking
*** Parts can (and usually should) be pre-heated because having the bulk material hot will mean the weld bead cools more slowly
*** Pre-heat temperature is a difficult balance, you'll need to research the metal you're welding and work out if there are any temperature bands that shouldn't be used. If you can't get detailed guidance then temperatures in the range of 250C-400C are normally good. Higher temperatures make the metal harder to handle and increase oxidization but reduce thermal stresses.
*** Work out your clamping arrangements and how you're going to have to move the work around before you start pre-heating, you cannot use clamping magnets because at these temperatures the magnets will be permanently degraded.
*** For small work the [[Tools/oven|materials oven]] may help, for larger workpieces then the blowtorches can be used.
*** Post-heating is used to try to prevent the weld bead from becoming over-hardened
*** This can take the form of simply wrapping the work in insulation to slow it's cooling, or using the blowtorch or oven.
*** Cooling times will vary with weld size, for large welds several hours may be needed
** Post-annealing can help if it's done fast
*** Heating the metal up to annealing point and cooling very slowly can be very effective in relieving stresses in the metal
*** But be aware it may change the bulk properties of the workpeice
** Weld peening can help in difficult situations
* Welding mild steel in position 3
*
* Changing the gas bottle
* Changing wire, torches and liners, proper setting of wire feed and tension
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