1. How to control the amperage in MIG process?The electrode wire is fed from a spool which is attached to the wire driving system and passes through a set of rolls which is driven by a variable speed electric motor. By varying the speed of the motor we can adjust the level of the welding current. High wire feed speed gives high welding current.High voltage give longer arc lengths.(Arc length can also be varied by altering the voltage.) 2. How we found SS is overheated? What is the after effect.

THIS INFORMATION MUST BE USED WITH CARE WHEN INTREPETING THE HINT TINT COLOURS OBSERVED ON STAINLESS STEEL SURFACES AS THE HEATING CONDITIONS ARE NOT SPECIFIED.Colour FormedApprox Temperature C

pale yellow290

straw yellow340

dark yellow370

brown390

purple brown420

dark purple450

blue540

dark blue600

1. 300 series stainless steels contain roughly 18 percent chromium. That is the main ingredient that makes it stainless.2. Chromium and carbon seem to look for and find each other kind of like a drug user and a drug dealer.3. When things get heated up, the carbon tries to find the chromium and latches on to it to form chromium carbides.4. When that happens there are areas that are depleted of chromium that lose the stainless properties and rust , corrode, and even crack .There you have it a down and dirty explanation of carbide precipitation and why you dont want to overheat stainless steel welds.Speed cooling doesnt hurt it and can actually help as long as you dont use tap water with chlorine.So here is the thing, if you are a contractor and you are interested in getting the job done, blowing on your stainless socket welds with an air nozzle from a nearby air hose could actually be helpful and it wont harden the weld.the worst thing for 300 series stainless is to keep it hot for a long time during welding.Keeping it above the 900f range for extended periods can actually cause loss of corrosion resistance.In short, the stainless might rust, or even crack from the chromium combining with carbon to cause what is called carbide precipitation...3. What does mean the L in 316 L?The H and L designators indicate a specific composition of the electrode. More specifically, they refer to the carbon percentage in the electrode, with H electrodes in the high end and L electrodes in the low end of the electrodes carbon range. An E308 type stainless steel electrode must have a maximum of 0.08% by weight of carbon (C). An E308H electrode however, must have at least 0.04%C, up to a maximum of 0.08% C. Carbon content in the range of 0.04 0.08% provides higher tensile and creep strengths at elevated temperatures. They are primarily used in industrial equipment at high service temperatures (sometimes over 2,000F (1,093C). Therefore, an E308H electrode would be the appropriate choice for your furnace rack project. Conversely, an E308L electrode can have no more than 0.04% C. The L type electrodes are sometimes referred to as ELC (extra low carbon) types. The lower carbon content helps minimize the damaging effects to the corrosion resistance of the heat affected zone (i.e. sensitization) caused by intergranular carbide precipitation. They are most often used for weldments that operate in severe corrosive conditions at temperatures under 800F (427C)4.General purpose pipe manufactured to ASTM Specification 519Similar to 4140 (which has a lower carbon level), 9CR has improved hardenability and is more commonly used in the higher strength >= 110ksi condition.