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Sampling methods for ferrous and non-ferrous metals 1. Sampling method for ferrous metals: Method 1: Weigh 0.2 grams of the sample and place it in a 100 ml two-purpose flask. Add 30 ml of dilute aqua regia (1+2), heat at low temperature until complete dissolution occurs. Rinse the walls of the flask with a small amount of water, bring to a boil, cool to room temperature, dilute to the mark, shake well, and then perform dry filtration before testing. (Apart from medium and high C, W, Nb materials) Method 2: Weigh 0.2 grams of the sample and place it in a sealable polytetrafluoroethylene or polyethylene bottle; add 10 ml of aqua regia and 10 drops of HF acid, then seal the container tightly. Heat it in a water bath at 60–70°C until complete dissolution occurs. After that, cool it to room temperature by running it under flowing water, transfer it to a 100 ml polyethylene volumetric flask, dilute to the mark, mix well, and filter dry before testing. (Method 3 requires a hydrofluoric acid-resistant sampling system.) Weigh 0.2 grams of the sample and place it in a 200 ml conical flask; add 10 ml of aqua regia and heat until the sample dissolves. Then add 14 ml of phosphorus-sulfur mixed acid (1+1+2), and continue heating until white smoke appears. Add nitric acid drop by drop until the carbides are completely oxidized. Allow the mixture to cool slightly, then add 30–40 ml of water along the walls of the flask, stir well, heat to dissolve the salts, cool to room temperature, transfer the solution to a 100 ml volumetric flask, dilute to the mark, stir again, and filter dry before testing. (This method cannot be used for the determination of Si, and the presence of phosphoric acid affects the determination of P.) Method 4: Weigh 0.2 grams of the sample and place it in a 150 ml conical flask; add 85 ml of sulfuric-nitric mixed acid (50+8+942) and heat to dissolve it. Then add 1 g of persulfuric acid and continue heating at low temperature until the sample is completely dissolved. After that, bring the mixture to a boil for 2–3 minutes. If manganese dioxide precipitates form, add a few drops of 1% nitrous acid solution, bring back to a boil for 1 minute, cool to room temperature, transfer the mixture to a 100 ml volumetric flask, dilute to the mark, mix well, and filter dry before proceeding with the analysis. 1. Industrial pure iron: Method 1 can be used; if the impurity content is low, the sample weight can be increased appropriately. 2. Carbon steel: Method 1 can be used. 3. Medium and low-alloy steel: ① Low C: Method 1 can be used (low Si)