Módulo: Mecanizado (MEC)
|AF_FM01_ Fabricació Mecànica. Ferrous Materials. |
|Unit 3 Physical properties of ferrous materials: Strength and Hardness |
Contents
3.1 Mechanical properties
3.2 Questions
3.1 Mechanical properties
One of the characteristic properties of metallic materials is their good behavior when they are subjected to stresses. They generally have high values in mechanical properties like mechanical strength or hardness. For this reason they have been widely used as structural materials.
When talking about a structural material it is important to know its mechanical strength in order to determine if it can withstand the expected loads.
There are 2 methods to determine the mechanical strength:
• The tensile test (direct method, destructive) and
• The hardness test (indirect method, non-destructive).
|HARDNESS |
|A mechanical physical property that measures the difficulty that a material offers in order to be penetrated by another material. Hard materials |
|also have a high resistance to wear. |
The hardness test consists of measuring the superficial hardness of a part and then determining the expected value of a material's mechanical strength using tables. There is a relation between the Carbon content, the hardness and the mechanical strength.
The more carbon content, the more hardness. The more hardness, the more mechanical strength.
Here you will find 3 videos that show us how the different hardness tests are carried out:
|[pic] |BRINELL ROCKWELL (Scale C) VICKERS |
|TO KNOW MORE |
|If you want to know more about hardness tests, you could look into the following norms. |
|[pic] |
|ISO 3738 Hardmetals -- Rockwell hardness test (scale A) |
|ISO 3878 Hardmetals -- Vickers hardness test |
|ISO 22394 Hardmetals -- Knoop hardness test |
|ISO 6508 Metallic materials -- Rockwell hardness test |
|ISO 14577 Metallic materials -- Instrumented indentation test for hardness ... |
|ISO 18265 Metallic materials -- Conversion of hardness values |
| |
|[pic] |Hardness conversion chart for carbon and alloy steels |
Read the paragraph “The Hardness Test” on page 42 at the beginning of chapter 5 in book Steel Metallurgy for the non-metallurgist and answer these questions:
3.2 Questions
1. Name three different tests for measuring hardness.
2. What is the difference between the Rockwell A and Rockwell C tests?
3. In which test is a 10 mm-diameter steel ball used?
4. What is the difference in the indent between Rockwell C and Vickers tests.
5. Is it possible to know the mechanical strength of a steel by measuring its hardness?
6. What is the problem of the tensile strength test?
7. What is an indenter? Tell the different shapes of indenters described in the text.
8. Do Rockwell B and Brinell tests use the same indenter in shape and dimensions?
9. Which hardness tests measure the depth of penetration of the indenter on the sample?
10. What is the test that uses the major weight to determine hardness?
11. Which type of hardness test is more suitable for cast irons?
12. Why do you think Brinell test is not suitable to measure hardened steels?
13. What supposes an advantage of the Brinell test related to the Rockwell test?
14. What is the relation between the hardness measured and the mechanical strength?
15. Which test measures the diagonal length of the indent?.
16. Which hardness test is a one-step test?
17. What values are equivalent to 550 HV in Rockwell C and Brinell scales?
550 HV = HRC = BHN
18. Pearlite has a hardness of about 40 HRC. What is the equivalent to Vickers scale?
40 HRC = HV
19. Martensite has a hardness about 65 HRC. What is the equivalent to Vickers scale?
65 HRC = HV
20. What values are equivalent to 209 BHN in Rockwell B and Vickers scales?
209 BHN = HRB = HV [pic]
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