How to identify the true and false stainless steel?
Source：Wuxi Longchao Hits： Date：2015.08.10
In the society and life, stainless steel products spread to a wide range, large construction, small to each family's table, but there are a lot of people do not know how to distinguish between true and false stainless steel, in most cases to buy back the product Are not the quality of their own want, then how to distinguish the true and false stainless steel? Here are four aspects.
Steps / methods:
Nitric acid point test
One of the salient features of stainless steel pipes is the inherent corrosion resistance of concentrated nitric acid and dilute nitric acid. This performance makes it easy to distinguish from most other metals or alloys. But the high carbon type 420 and 440 steel in the nitric acid point test is slightly corroded, non-ferrous metals encountered concentrated nitric acid will be corroded immediately. The dilute nitric acid on the carbon steel has a strong corrosive.
Second, copper sulfate point test
The copper sulfate point test is the easiest way to quickly distinguish between ordinary carbon steel and all types of stainless steel. The concentration of the copper sulfate solution used is 5 to 10%. Before conducting the point test, the test area should thoroughly remove grease or various impurities, and polish a small area with a soft grind, and then use a drop bottle to clean the area after the infusion of copper sulfate solution. Ordinary carbon steel or iron in a few seconds will form a layer of surface copper, while the surface of stainless steel does not produce copper precipitation or show the color of copper.
Three sulfuric acid test
Sulfuric acid immersed stainless steel tube test can distinguish 302 and 304 from 316 and 317. The trimming of the sample shall be finely ground and then washed and passivated for half an hour in nitric acid (specific gravity 1.42) at a volume concentration of 20 to 30% and at a temperature of 60 to 66 ° C. Sulfuric acid test solution volume concentration of 10%, heated to 71 ° C when .302 and 304 steel immersed in this hot solution, the rapid corrosion and produce a large number of bubbles, the sample in a few minutes black; and 316 and 317 steel Of the sample is not subject to corrosion or reaction is very slow (no bubbles), the sample does not change color within 10 to 15 minutes. The test can be made more accurate by comparing the samples with the known composition at the same time.
The magnetic test is the simplest way to distinguish annealed austenitic stainless steels and ferritic stainless steels. Austenitic stainless steel is non-magnetic steel, but by the cold down after cold processing will have a mild magnetic; and pure chrome steel and low alloy steel are strong magnetic steel.