True or False? Putting Galvanized Steel Hardness to the Test
Heat treatment and cold working change the hardness of steel.
TRUE! Steel undergoes processes during production that have the potential to alter its hardness, which is why testing is important. Galvinfo says that these tests are designed to be fast, and placed at key intervals in the stages of production.
Keep in mind that if you test older steel, it may show a higher value than it did during processing. That’s because some steels “age harden.” Galvinfo says that while aged steel may test higher, it could still be okay to use as intended.
A hardness test can be used in place of a tensile strength test.
FALSE! A hardness test can estimate the approximate tensile strength of steel, but it shouldn’t be used as a replacement. Hardness alone doesn’t provide enough information of what the steel may do during forming, stretching or drawing.
However, Galvinfo says, “a hardness test can easily distinguish amongst full hard, ½ hard, ¼ hard, and fully annealed sheet steel.”
Indentation hardness testing is the only method used on steel products.
TRUE! While there are three main methods of hardness testing, the only one used on steel products is indentation hardness. The most common and widely accepted of these is the Rockwell test, which Galvinfo says is capable of covering the range of hardness in steel products.
A Rockwell test takes less than 10 seconds to complete.
TRUE! In most cases, this test takes only 5 to 10 seconds. In hard steels, the Rockwell test numbers will be high, and in soft steels, they will be low. Of the two types of Rockwell tests – Regular and Superficial – Galvinfo says only three or four scales are suitable.
It’s important that the tester be well versed in which scale to use, and that the indenter and anvil be cleaned and well positioned. The steel should also be clean, dry, smooth and thoroughly checked for debris,.
Hardness testing done with the coating on is just as reliable.
FALSE! Galvinfo says, “it is the usual practice in coated sheet producing mills to strip the metallic coating off before hardness testing.” That’s because the hardness is based on the steel substrate, and performing the test with the coating on is known to affect the results.
Given that fact, it makes sense that the heavier the coating, the less reliable the reading.
Want to know more about hardness testing? Read the Galvinfo note: Hardness Measurement of Coated Steel Products.