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Motorsport Fabrication Fundamentals: Stainless Steel

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Stainless Steel


00:00 - One of the more common materials we're likely to choose for the fabrication of exhaust components and exhaust systems is stainless steel.
00:07 Stainless, like chromoly, is a ferrous steel alloy and shares the same major elements of chromium and molybdenum.
00:13 What sets stainless steel apart from chomoly is the higher percentage of chromium with a minimum amount of around 10.5%, compared the chromoly's 1%.
00:23 This results in a bright shine and a high resistance to corrosion.
00:26 This corrosion resistance makes stainless steel a widely used material in a huge range of different industries, from medical as well as food and beverage production through to the marine industry and because of that, this material is available in many different grades.
00:42 Stainless steels can be broken up into 4 main families, based on their different cystalline structures.
00:47 The first structure is known as austenitic stainless steel which is the largest group making up over 60% of total stainless steel production and this includes the 200 and 300 grades of stainless.
00:59 It's the 300 series of stainless that's most commonly used in motorsport and we'll usually choose between 304 or 316.
01:07 304 is made up of 18% chromium and 8-10% nickel, while the 316 grade is made up of 18% chromium, 10-12% nickel and 2-3% molybdenum for greater corrosion resistance.
01:21 In motorsport, the 304 grade is usually sufficient but for all medical or food grade plumbing, 316 is the industry standard.
01:29 These austenitic stainless steels have relatively low yield strengths, meaning that they're not suitable for load bearing applications.
01:36 They are extremely good at elongation and deep drawing though, just look at your kitchen sink as a good example of that.
01:43 The next group is ferritic stainless.
01:46 This contains between 10% and 27% chromium with very little nickel.
01:51 This reduces the cost of ferritic stainless when compared to austenitic and can be found in grades 409 and 430.
01:59 These grades are commonly used in large scale manufacturer of dishwashers and refrigerators as well as in the OEM automotive industry for exhaust systems.
02:07 Unlike austenitic, ferritic stainless is actually magnetic and is the reason that magnets stick to your fridge door.
02:14 It isn't however a material we'd choose for our own fabrication tasks.
02:18 Duplex stainless is next which is a mix of austenitic and ferrittic stainless and is used for structural applications due to its higher yield strength which can be almost double that of austenitic stainless steel.
02:31 For our purposes, there are better materials available for high strength applications and you're not likely to come across this material in the motorsport fabrication industry.
02:41 The last type of stainless you'll find is martensitic which was developed for hardening and tempering through the heat treating process.
02:48 Martensitic stainless steels are used for various industrial components that require wear and hardness protection that aren't relevant to our use.
02:56 Welding stainless steel is done with the TIG welder and requires preparation and care to achieve a strong and attactive weld.
03:04 The use of shielding gas is extremely important with stainless steel and if the work piece is shielded internally through purging, you'll be able to complete weld the inside seam as well as the outside which is important for maximum strength.
03:17 We'll talk more about purging later on in this course.
03:20 Although stainless has some great corrosion resistant properties, we need to be careful of cross contamination when handling and working with this material.
03:28 Most commonly it's carbon steels coming into contact with our stainless that causes problems and it's not uncommon to find workshops in the greater fabrication industry that'll only work with stainless steel in order to avoid any potential issues.
03:42 As motorsport fabricators, that isn't really going to be an option for us as most likely we'll be switching between different materials all of the time.
03:50 There are a few best practices that we can stick to in order to minimise cross contamination though.
03:56 First, when we order lengths of stainless steel, it'll usually arrive wrapped in plastic and it's a good idea to retain this protection as long as you can because it keeps the material free from iron dust and prevents steel rubbing up against it.
04:10 When cutting, filing, grinding or polishing, it's also a good idea to have a dedicated set of tools that you only use with stainless.
04:18 That doesn't mean you need two grinders or two linishers, you just need to have a disc or a belt that's dedicated to stainless steel so that you can easy fit that when required.
04:27 Because we'll be working with stainless a lot for exhaust fabrication, we need to understand that it has a relatively high coefficient of thermal expansion, coupled with low thermal conductivity.
04:40 What this means is that stainless steel expands rapidly with the input of heat and the heat remains close to the heating source.
04:47 This presents a few problems that we need to deal with.
04:50 The first is designing the part and knowing that it's going to distort and grow with heat and the second is welding the part without it serious distorting.
04:58 There are of course solutions to both of these problems and these are covered in our practical welding courses in more detail.

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