Hardness testing of knowledge

Hardness testing of knowledge
Hardness is one of the important properties of materials, especially metal materials. In aviation, weapons, special equipment, mining equipment and metal cutting, the hardness of materials is particularly important.
Hardness, a professional term in physics, refers to the ability of a material to locally resist hard objects pressing into its surface. The local resistance of a solid to the invasion of external objects is an indicator for comparing the hardness and softness of various materials. Since different test methods are specified, there are different hardness standards. Various hardness standards have different mechanical meanings and cannot be directly converted to each other, but can be compared through tests.
There are many kinds of hardness testing methods,
Hardness is divided into:
① Scratch hardness (e.g. Mohs hardness).
② Indentation hardness (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.).
③ Rebound hardness (e.g. shore hardness and Richter hardness).
1. Mohs hardness: it is a standard to indicate the hardness of minerals. It was first proposed by the German mineralogist Frederich Mohs in 1812. It is a standard used in mineralogy or gemology.
The hardness is expressed in ten grades by the measured depth of the scratch (scoring method):
Talc 1 (minimum hardness), gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10.
The Mohs hardness value is not an absolute hardness value, but a value expressed in the order of hardness.
Mohs hardness ranking of common metals
Mohs hardness pen
Mohs hardness pen
Use steps of Mohs hardness pen:
1. First, the hardness of the sample shall be indirectly and visually assessed;
2. Find an inconspicuous place and mark the sample with a hardness pen of 1 to 2 lower than the visual hardness. If it is not moved, it indicates that the hardness of the sample is higher than the hardness of the hardness pen. Then mark with a hardness pen of a higher level and repeat the operation. If there is only a slight trace, it indicates that the hardness of the sample is equal to the hardness of the hardness pen. Then mark with a hardness pen of a higher level and repeat the operation. If there is a trace, it indicates that the hardness of the sample is lower than the hardness of the hardness pen, At this time, the hardness or its range of the measured sample can be judged;
3. Pay attention to the moderate degree of engraving, neither too light nor too heavy
4. Because the hardness is measured by direct scoring method, it is harmful to gemstones. In general, it is not allowed to use this method for finished gemstones
Because Mohs hardness is not accurate enough, it is rarely used in quality control, but only in scientific or informal occasions.
2. Rockwell hardness (HRC) is generally used for materials with high hardness, such as the hardness after heat treatment.
Rockwell hardness is usually HRA, HRB and HRC,
HRA: it is the hardness obtained by using 60kg load and diamond cone indenter. It is used for materials with extremely high hardness (such as hard alloy).
HRB: the hardness obtained by using 100kg load and 1.58mm diameter hardened steel balls is used for materials with low hardness (such as annealed steel and cast iron).
HRC: it is the hardness obtained by using 150kg load and diamond cone indenter. It is used for materials with high hardness (such as quenched steel).
In order to expand the measuring range of Rockwell hardness, different indenters and different total loads can be used to make different scales of Rockwell hardness. There are 15 scales for Rockwell hardness, which are HRA, HRB, HRC, HRD, HRE, HRF, HRG, HRH, Hrk, HRL, HRM, HRP, HRR, hrs, HRV;
Surface Rockwell hardness scale: hr45n, hr30n, hr15n and hr45t, hr30t, hr15t.
Rockwell hardness tester
3. Brinell hardness (HB):
It is generally used when the material is soft, such as non-ferrous metals, steel before heat treatment or after annealing. The measuring principle of Brinell hardness is to press a quenched steel ball or hard alloy ball with a diameter of D (mm) into the surface of the tested metal (Fig. 1) with a certain test force F (n) (the unit of force is usually kg force KGF, note: 1kgf = 9.8N, KGF is the force of one kilogram), remove the test force after holding it for a specified time, measure the average indentation diameter D (mm) with a reading microscope, and then calculate the Brinell hardness HB value according to the formula, Or find out the HB value from the prepared Brinell hardness table according to d.
The symbol of Brinell hardness is represented by HBS or HBW.
HBS indicates that the indenter is a hardened steel ball, which is used to measure materials with a Brinell hardness value below 450, such as mild steel, gray cast iron and non-ferrous metals.
HBW indicates that the indenter is hard alloy and is used to measure materials with a Brinell hardness value of 650 or less.
Brinell hardness tester
4. Vickers hardness
5. Richter hardness:
The Richter hardness is expressed in HL. The Richter hardness test technology was invented by Dr. Lieber of dilma, Switzerland. It uses an impact body with a certain quality and a tungsten carbide ball head to impact the surface of the test piece under the action of a certain force, and then rebound. Due to the different hardness of materials, the rebound speed after impact is also different. A permanent magnet material is installed on the impact device. When the impact body moves up and down, its peripheral coil will induce an electromagnetic signal proportional to the speed, and then convert it into a Richter hardness value through an electronic circuit.
The portable Leeb hardness tester can be converted into Brinell (HB), Rockwell (HRC), Vickers (HV) and shore (HS) hardness after measuring with the Leeb (HL). Or directly measure the hardness value with Brinell (HB), Rockwell (HRC), Vickers (HV), Richter (HL) and shore (HS) according to the Richter principle.
There are seven kinds of Richter hardness: D, DC, D + 15, C, G, e and DL:
D: External dimension: F20 × 70mm, weight: 75g. Universal type, used for most hardness measurements.
DC: external dimension: F20 × 86mm, weight: 50g. The impact device is very short and is mainly used in very confined places, such as holes or cylinders.
D + 15: external dimension: F20 × 162mm, weight: 80g. The head is small and used for measuring the surface hardness of grooves or recesses.
C: External dimension: F20 × 141mm, weight: 75g. Minimum impact energy, used for measuring small light and thin parts and surface hardened layer.
G: External dimension: F30 × 254MM, weight: 250g. High impact energy and low requirements for measuring surface. Used for large, heavy and rough surface forging castings.
E: External dimension: F20 × 162mm, weight: 80g. The indenter is made of synthetic diamond, which is used for measuring materials with extremely high hardness.
DL: overall dimension: F20 × 202mm, weight: 80g. The head is smaller and used for measuring the hardness of narrow groove and gear surface.
Portable Richter hardness tester
6. Shore hardness
Shore hardness, also known as shore hardness, is a method to indicate the hardness level of materials. Shore hardness is divided into shore indentation hardness and shore rebound hardness,
Place the sample to be tested for shore indentation hardness at a proper position on the table of the hardness tester, and immediately read the indentation hardness readings indicated by the numbers 0-100 after being pressed for a specified time. The indentation hardness tester used has three scale models: type A, type C and type D; The hardness readings are represented by ha, Hb, and HC, respectively. Shore A is suitable for soft plastics and rubber, while shore C and D are suitable for hard or hard plastics and vulcanized rubber. When measuring shore hardness, our country is consistent with ISO regulations, and only type A and type D are used.
The shore rebound hardness is measured with a shore rebound hardness tester. A punch with a total weight of about 3 G and a diamond on the top is used to drop vertically from a glass tube with a height of about 300 mm onto the test piece. The vertical rebound height is read from the scale of the glass tube.
Shore a hardness tester
Shore hardness tester
The above is the introduction of six commonly used hardness measurement methods
Next, we will introduce the testing method of paint film hardness,
The Pendulum damping test method has not been used, and it seems that it is not commonly used. It is not introduced here. The pencil method is commonly used to determine the hardness of the paint film,