Hardness Testing of Metallic Materials.
Determining the hardness of metallic materials by using the Rockwell scale
One of the mechanical properties of materials that might be essential to consider is hardness. It is portrayed as the resistance to indentation, and it is obtained by measuring the permanent depth of the indentation. There are some hardness testing methods used to obtain the hardness value of the materials.
These are some examples of the methods used in this testing procedure.
• Rockwell Hardness Testing
• Brinell Hardness Testing
• Vickers Hardness Testing
• Knoop Hardness Testing
• Case Depth Hardness Testing
The Rockwell hardness testing method is the most frequently used hardness testing method. It is commonly very easier to perform and more factual than other hardness testing methods. The machine called Rockwell hardness tester is used to test the hardness of the metallic material.
It gives a force/load on the selected specimen surface using a diamond spheroconical intender or a tungsten carbide ball intender with some determined conditions. It measures the difference in depth of the indentation by expanding the applied preload from a beginning point up to a specific indicated end point and once it achieved that end point again it starts to decrease to the beginning point. Furthermore, it is known as the resistance of the indentation. So here a difference in the depth by the indentation is created which is known as the hardness number (HR). The hardness number is measured directly from the scales. Additionally, the last estimation of the HR number ought to be given in an entire number without decimals.
The two general classifications,
? Rockwell hardness (what we use here for our practical)
? Rockwell superficial
Hardness measurements speak to a standout amongst the most helpful methods for quality confirmation in the field of mechanical characterization of materials. Because of its effortlessness and its quickness of execution, Rockwell hardness test is the most generally utilized. In the case of the Rockwell hardness test, two levels of forces are connected to the indenter at determined rates and with particular stay times. Unlike other hardness testing method the Rockwell hardness of the material depends on the difference in the depth of the indenter at two particular circumstances amid the testing cycle. The estimation of hardness is computed using a formula that was determined to yield a number falling within an arbitrarily defined range of numbers known as a Rockwell hardness scale.
The indenter is carried into contact with the material to be tested, and a preliminary force (formally alluded to as the minor load) is applied to the indenter. The preliminary force is typically held steady for a set timeframe, after which the depth of the indentation is estimated. After the estimation is made, an extra amount of force is connected at a set rate to build the applied power to the total force level (formally alluded to as the major load). The total force is held steady for a set time period, after which the additional force is evacuated, returning to the preliminary force level. After holding the preliminary force constant for a set time period, the depth of indentation is estimated a second time, followed by the expulsion of the indenter from the test material. The determined difference between the first and second indentation depth measurements, “h”, is then used to compute the Rockwell hardness number.
Rockwell Hardness Value = (N-h/s)
N – Number specific to the Rockwell hardness scale
h – Permanent depth of indentation (measured in mm)
• For spheroconical diamond indenter:
HR = 100 – h/0.002
• For ball indenter:
HR = 130 – h/0.002
Scale symbol Pre-load
Kg (N) Abbreviation Indenter Load Use
A 10(98) HRA Diamond (cone120 degree 0.2 tip radius) 60kgf (589N) Thin steel
B 10(98) HRB 1/16 inch-diameter (1.588) steel sphere 100kgf (981N) Non-ferrous, soft steel
C 10(98) HRC Diamond (cone120 degree 0.2 tip radius) 150kgf (147N) Harder steels
Following tables will show the information about the Rockwell hardness scale:
Table 1: Rockwell Hardness Scales
Scale Symbol Dial Figure Large Pointer Position (initial) Small pointer position
A Block 0 or C Red spot (3)
B Red 30 or B 2 division (2)
C Block 0 or C Red spot (3)
Table 2: Rockwell Tester Scales
MATERIALS AND APPARATUS
• Rockwell hardness tester machine
• Spheroconical diamond indenter
• Flat specimen support
• Specimen-mild steel
• Appropriate example was chosen for the testing procedure.
• Temperature was checked and reasonable point was kept without intruding the practical.
• Surfaces of the example were cleaned and adjusted.
• Thickness of the material was estimated.
• A flat surface was picked as the need of the rigid support for the example.
• Dial gauge pointer was balanced.
• Selected example was set over the rigid support.
• Larger point was acclimated to the initial point.
• Huge load was applied and afterward expelled then the dial gauge reading was taken straightforwardly.
• Reading was determined by the scale.
• Finally, the blacksmith’s iron was evacuated and the diamond intender was cleaned.
Dial gauge readings:
Sample (Hard steel) Value
01 72.5 HRC
02 85.5 HRC
03 86.0 HRC
04 88.5 HRC
05 82.5 HRC
06 80.0 HRC
07 84.5 HRC
08 85.0 HRC
Average = Total values/8
Indentation hardness tests are utilized as a part of mechanical engineering to decide the hardness of a material to twisting. A few such tests exist, wherein the inspected material is indented until the point that an impression is shaped; these tests can be performed on a macroscopic or microscopic scale. Like the Brinell, Vickers, Knoop, Scleroscope and Leebtests – all of which fall in the general class of indentation hardness tests – the Rockwell test is a measure of the resistance of material, particularly metals, to permanent indentation. The method of this hardness testing using Rockwell testing method and the theory of this method are clearly explained before.
The indenter is pushed into the work piece that will be had a go at using a preliminary power (minor load with an estimation of 10kg at first). At this stage the indenter is inverse to the surface of the material. By then nearby the fundamental load, another load is incorporated. This is done by moving the lever from exchange position to loaded position. Then again it is moved back to its underlying position. In the midst of this methodology a permanent indentation is made on the material that is being used to test. The favored stance behind after this method is that be material same used once can be annihilated for a couple of line.
? Discussion about the obtained results of the practical
The practical was repeated several times and a few measurements of hardness were obtained because to reduce the error value. The obtained measurements are marked clearly in the observation sheet and the average value also determined by adding the measurements taken and dividing the sum value by the number of measurements taken.
? Discussion about the importance of hardness testing
The hardness of a material is the property that empowers it to oppose disfigurement, twisting, scratching, scraped area, or cutting. On the off chance that you work in materials fabricating, you most likely definitely realize that a hardness test is a urgent advance in the generation procedure for your items and the items you get from outsider providers. You have to set pattern estimations and guarantee that your items meet particular models for quality. Yet, in the event that you’re not a materials engineer, you might be shocked to realize that the hardness of any material isn’t an inherent property directed by exact definitions and basic units of mass, length, or time. Rather, the estimation of a material’s hardness is the aftereffect of a particular estimation method.
Hardness testing is commonly very easy and inexpensive. A hardness estimation affirms that material synthesis, heat treatment, surface conditions, and process specification. Customarily no exceptional example required to be prepared, and the testing mechanical apparatus is relatively inexpensive. The test is non-damaging also.
? Discussion about the shortcomings of this testing method and how to improve the accuracy of the hardness test
The selected specimen surface was not smooth. A flat surface is needed to the testing procedure. Identifying a smooth surface and making the intender to touch that surface became very difficult. So it caused to do the practical for several times. The suitable temperature to do this testing was not checked. Processing plant creation hardness tester may have free structure result to flimsy esteem in light of the fact that the encompassing condition endured the effect of vibration. Rockwell hardness ought to be installed in the place without vibration or detached from the area of the source. Automated hardness testing with 3D technology will improve the accuracy of the hardness test. Instead of manual tester automated testers will give the accurate hardness values and users will feel easy to handle it during the testing procedure.
Hardness is an important mechanical property of materials. Indentation thought is utilized for the Rockwell hardness analyzer since it’s not hard to utilize and has different purposes of intrigue. One of the purposes of intrigue is, prepared to post the estimation sporty and the precision level of the hardness respect is higher than substitute examinations. Along these lines Rockwell test is utilized as the fundamental Indentation test for investigate office tests. This methodology for testing hardness of material is for the most part used since it is essential, capable and exact. A segment of the mix-ups which we looked in the midst of the test was condition and human bumbles. The advantage of Rockwell test is we can read the estimations straightforwardly and the primary hardness estimation of the material is some to some as what we measured from the test there for the exactness level of the Rockwell test is enormously enhanced than exchange preliminaries. So through this practical we got to know about the hardness and Rockwell hardness testing method also.