The profile at any section of the steel can be determined by carrying out the required profile test. A profilometer is used for this purpose. The system consists of a mechanical body with a tip or sensor to analyse the surface, along with a computer to digitally/graphically show the result. The process is highly automated and the sensors can be easily adjusted on the surface of the metal for movements in X, Y and Z directions. The characteristics of the surface are determined and the flaws in the micron range are acquired with this process. Profilometry techniques can vary according to different steels.
Hardness is one of the most important aspects that need to be considered while examining steel for any application. There are different types of equipment used to examine the hardness of the metal in different scales like Brinell hardness (BHN), Rockwell hardness, Vickers hardness, Knoop hardness etc. The hardness test is carried out by implementing a determined load on the surface of the metal by an indenter, and then measuring the depth of the indentation. The sample under testing is not damaged except for slight indentation. The hardness of the metal is attained by either hardness number indicator or a digital system showing the hardness in given scale.
The magnetic properties of the metal become very important for some applications. Processes like welding and cold working disintegrate the magnetic properties of the metal and proper testing is required. To efficiently carry out the test, a modern-day probe with a sensor is used directly on the metal along with a digital indicator to display the result. The instruments used are calibrated as per standards followed by the company. Sometimes the testing might also be used under quality control as well as detecting flaws in the metal. With this, other magnetic parameters can also be determined.
Concentricity test is carried out in the pipes and tubes to study the alignment of the metal. The symmetry of the product is also measured by the test. A gauge type mechanical testing equipment is usually used to check the concentricity and if any deviation, it is displayed by the pointer on the scale. The pointer in the equipment is initially set to zero by measuring it on an ideal sample. And is then used on the products to check the deviation from zero. Least count according to the product is set. The test may not always be accurate but it can suitably point out the deviation in the metal.
The chemical composition is one of the most important specification for the alloy to be used in any application. The microstructure needs to be thoroughly analysed for any adulteration. There are various tests used to indicate the chemical composition of a metal. Metals are normally manufactured in the desired chemical composition. As per the requirements, there are specific tests that indicate the presence of certain elements and nature of the metal in the chemical. For example; nitric acid reaction test can indicate if the steel is stainless or not. For the application, the metal might be tested with a chemical of the required environment. Molybdenum spot test will indicate if molybdenum is present in the component. There are advanced techniques like plasma spectrometry, optical emission spectrometry, etc. used to sort metal according to their chemical composition.
This test is an economic and reliable method for inspecting surface defects. A dye is used for determining principle capillary action. The process is as follows:
The method is also called liquid penetrant inspection and comes quite handy and conventional. For knowing the depth of the defects, methods like Ultrasonic testing could also be used.
Ultrasonic testing is a non-destructive testing method used to determine physical as well as geometric properties of the material. It uses electrically generated sound waves of a very high frequency that could be penetrated through steel and detect flaws. It requires high-end machinery and a skilled management. It is used to accurately detect any 3-dimensional flaw with its exact location including surface flaws and subsurface flaws. Information about flaws, like its type and dimension can be revealed by ultrasonic testing. The ultrasonic testing equipment can be made highly flexible and adaptive in accordance with the given dimension of steel.
Impact tests determine the impact strength of the metal. In other words, it measures the load-bearing capacity of the metal which is to be used in dynamic applications. The strength basically calculates the energy absorbed by the sample during fracture. The type of fracture is then classified into two categories; immediate deformation or significant ruptures. The tests involve shock loading of a weight from a specific height on the material rigidly fixed at a place. The collision between the two can also be used to determine properties like fracture resistance, toughness, impact resistance, etc. The tests normally performed for impact testing are Izod test, Charpy V-notch test, and tensile impact test.
Surface fineness is tested for quality after all machining processes. The surface texture becomes very important since it is directly exposed to the applications and might contain obscure flaws or irregularities. Surface finish can be measured either by contact or non-contact type methods. The contact type method involves the use of a stylus with a diamond tip which is physically moved on the surface in a certain direction. If the stylus moves seamlessly from up and down, the metal is considered to be free of irregularities but in case of any irregularities, the deviations are plotted with respect to the reference surface and a detectable graph. Non-contact methods include interferometry, optical profilometers, etc.
The grain structure of the metal needs to be analysed since most of the properties like corrosion resistance, physical properties, etc. depend upon the grain structure. After every service or process like heat treatment, hot working, cold working, threading, drawing, rolling, forging, etc., the grain structure of the material is subject to change. For example, the austenitic phase of the steel might be converted to the brittle martensitic phase. The phase will require tempering for it to be ductile again. The process of converting the metal back to its original state is known as metallurgical testing. Equipment involved in metallurgic testing are optical microscopy, X-ray diffraction, electron microscopy, etc. Skilled technicians are required to handle the equipment.