Steel microstructureanalysis

Steel is one of the most important metallic alloys in the world today. Consequently, steel alloy production is an essential part of the global industrial infrastructure. With over 2,500 varieties of alloy and a broad range of properties, new steel grades are being developed for new, more demanding products and applications. Steel production runs through several steps: the extraction of iron ore from rock, the smelting of the ore to obtain base iron, and the use of the oxygen convertor process to convert carbon-rich pig iron into steel [1,2]. It has been known since many years that the steel microstructure (inclusions, grains, precipitates, and other phases) has a large influence on the alloy properties and quality [1,3-6]. For steel manufacturers to remain competitive in a global market, they must use materials analysis to assess accurately steel quality. Knowing the quality of steel is important for many types of products and applications, e.g., new alloys, vehicles, buildings, ships, pipelines, and recycling. Typically, steel inclusions are classified by imaging with optical microscopy having sophisticated analytical software which then classify them according to standard characteristics (refer to figure 1) in terms of dimensions, color/shade, shape, and arrangement [3,5-6]​​​​​​​. However, the composition, i.e. oxides, sulfides, silicates, nitrides, etc., also matters. Furthermore, global networking of industrial materials has forced manufacturers to make readily available the property and specification data of their steel alloys, so they can be easily compared to established regional and international standards.

Reverse the direction you are turning the tee-handle tap wrench if and when you feel the resistance from the tap increase. This will break the shavings and chips coming from the metal. This makes the process of threading the metal easier.

Select the “drill bit” from the set that matches the size recommended on the chart we have provided. Secure the tooling in the drill motor and put on your safety glasses and other safety equipment.

Drill the hole into or through the metal, depending on the type of metal and the application. Liberally apply cutting and tapping fluid to the “drill bit” while you drill to lubricate and cool the drill bit. Remember that slower RPM rates are better than faster ones.  Too fast and you will damage the “drill bit” or maybe even your part.

0.4 carbonsteel microstructure

In most cases, accurate, reliable data for rating steel quality based upon its inclusions (Fig. 1) are critical for making confident decisions, despite limited time and budget. A 2-in-1 solution delivers precise, reliable visual and chemical analysis in one instrument [7,9]. The fact that less sample preparation is needed compared to SEM/EDS, there is no sample transfer from one system to another, and the sample is analyzed in air leads to time and cost savings when doing NMI analysis in steel. An example of such a solution is described in this report, the DM6 M LIBS materials analysis system with the Steel Expert software from Leica Microsystems. It combines optical microscopy (visual analysis), laser induced breakdown spectroscopy or LIBS [1-2,8] (chemical analysis), and software specialized for rating steel NMIs [3], including comparison with established standards [3,5-6], such as ASTM E45, ISO 4967, DIN 50602, etc. Advantages of a 2-in-1 solution for steel are described below.

Obtaining composition information requires an additional analytical technique which implies more sample preparation, transfer of the sample between instruments, and then relocating the region of interest. Thus, the result is a more complex, longer workflow.

Low carbonsteel microstructure

Simultaneous visual and chemical analysis of steel inclusions was done with the 2-in-1 solution from Leica Microsystems. Images of steel inclusions with their composition, rapidly analyzed using LIBS, are shown in figure 3.

The smaller the t-handle tap holder, the better.  Using a larger one causes broken taps often.  As long as you can comfortably turn the tap, you are good.  Look for flexing or twisting in the tap while you go.  If this happens, add more fluid, reverse the rotation for a turn or two to remove chips and continue down.

AutoDrill products are warranted to be free from defects in material and workmanship for a period of one (1) year from the date of shipment from AutoDrill. Minor configuration changes and “tweaks” are often covered as well.

Coat the tap with cutting and tapping fluid. Place a bit of fluid on / in the hole to be tapped. Align the tap with the drilled hole in the metal. Start threading the hole in the metal by turning the tee-handle tap wrench clockwise for a right-hand threaded hole or counter-clockwise for a left-hand threaded hole. Make sure that the tap is straight with the hole to ensure that your fastener will seat correctly.

Figure 3 illustrates how NMIs are analyzed in a straightforward way using the combined approach of visual and chemical analysis (microscopy and LIBS). Figure 3A shows an inclusion whose size exceeds that of the laser beam. Its composition is directly revealed by basic analysis using the spectra database. In the presented case, Ca and Al were identified as the main NMI components. With information from the visual inspection, the inclusion can be identified as a Ca-Al oxide. Small and fine NMIs, as seen in figure 3B and 3C, are analyzed by comparing their LIBS spectra to that of the steel matrix. Differences in characteristic elemental signals reveal the chemical composition of the NMIs. The string-like inclusion seen in figure 3B has mainly Mn.  The small orange inclusion in figure 3C contains Ti.

Pearlitemicrostructure

Select the tap from the tap set that matches the size of the fastener you will be installing into the metal and secure the tap in the tee-handle tap wrench.

Remove the tap from the metal, wipe the cutting and tapping fluid from the surface of the metal and turn the threaded fastener into the newly threaded hole in the metal to ensure that the threads are cut correctly.

Image

Different types of inclusions in steel alloys can be rated with specialized software. Inclusions are most often classified by gray value/color, size, shape and geometrical arrangement. Their composition can also be determined. The properties of most inclusions are shown in table 1 below. Depending on the number and size of the different inclusions, a quality rating is generated for the steel sample. An example of an inclusion rating with the Steel Expert software is shown in figure 2.

MicrostructureofsteelPDF

Locate the size of the fastener you need to install in the metal. Identify the thread size and pitch on the drill and tap chart. (The fastener size is generally displayed on the left-hand side of the chart.)

Mildsteel microstructure

Steel inclusion analysis is important for determining the quality of steel. It is frequently used for quality control during production and failure analysis. Often the time and expense allocated for such analysis is limited, but obtaining reliable results and achieving the desired steel quality always remains a goal.

Microstructureof cast iron

A 2-in-1 solution for steel inclusion analysis delivers visual and chemical analysis in one instrument. An example is the DM6 M LIBS system running the Steel Expert software from Leica Microsystems. It offers accurate, rapid visual and chemical analysis in one instrument, reduces sample preparation, eliminates sample transfer, and does not require the sample to be in vacuum. These advantages enable users to perform fast, precise, and more economical steel inclusion analysis.

In this report, the advantages of a 2-methods-in-1 solution, which combines optical microscopy and laser induced breakdown spectroscopy (LIBS), for an efficient workflow when analyzing steel microstructure (inclusions and intermetallic particles) were presented.

Tapping a hole in a metal part can often remove the need for a nut. Rather than passing the bolt through the metal part and putting a nut on the back side, you can sometimes tap the threads right into the metal part and simply tighten down the fastener. Tapping metal creates threads in the metal. You can then put a threaded fastener into these threads.

To create proper threads in metal, you need to drill the correct size hole in the metal. To determine the correct size hole to drill into the metal, you will need to reference a drill and tap chart such as the one at this link:

Nevertheless, very often the analytical workflow is not finished after visual classification. Different types of inclusions can look very similar in color or shade of gray and differ significantly in composition. Oxide inclusions are black or dark gray and can be composed of iron (Fe), manganese (Mn), aluminum (Al) [aluminates], calcium (Ca), chromium (Cr), silicon (Si) [silicates], among other elements [3,5-6]. Sulfide inclusions are light gray and can be composed of Fe, Mn, Ca, magnesium (Mg), and other elements [3,5-6]. Nitride inclusions can have various colors and be composed of titanium (Ti), Al, carbon (C), oxygen (O), among other elements [3,5-6]. For instance, titanium nitride (TiN) inclusions are yellowish pink with a low amount of O, but become yellowish orange as O increases [3,10,11]. With large amounts of O and C, the TiN inclusions become dark blue or black [11]. The composition data is useful for understanding the result of the steel production process as well as determining the final steel quality.

IMPORTANT: Make sure to keep any and all pressure on the tap to a minimum. you only want to press down when starting the tap.  From that point forward, you want to make sure you are only turning the tap and not leaning it from side to side or pressing down.  Some taps are hard and brittle to cut difficult metals. This means that they will snap very easily – especially smaller diameter taps.

Ferritemicrostructure

Analysis of steel NMIs to determine quality is often done during alloy production and failure analysis. In the past, the NMI rating was done manually by comparing images to standard charts. This approach is time consuming and the results are significantly influenced by the judgement of the user. Today visual examination of polished steel is performed with a microscope system having image analysis software that automatically scans the sample, detects the defined inclusions, displays the raw data, and classifies the inclusions according to national and international standards [3,5-6]. For a more reliable determination of steel quality, having both image and composition data of the microstructure would be advantageous. However, elemental/chemical analysis methods, such as energy dispersive x-ray spectroscopy (EDS) performed with scanning electron microscopy (SEM), can be costly and time consuming [7,8].

Simultaneous visual and chemical analysis of steel non-metallic inclusions (NMIs) with a 2-methods-in-1 solution, combining optical microscopy and laser induced breakdown spectroscopy (LIBS), is described here. Steel is used for a large variety of applications in multiple industries. Typical applications are for the transportation (automotive, aerospace, and railway), building and ship construction, and energy (oil and gas pipelines) sectors. Innovative steel alloys for certain demanding applications and steel recycling are also becoming more common. Steel quality depends greatly on its microstructure (inclusions, grains, precipitates, and other phases) and composition. Therefore, metallographic analysis is important for its assessment in accordance with ever stricter international, regional, and organizational standards. To make rapid, confident decisions during inspection, quality control, or failure analysis, data on steel microstructure, morphology, and composition are instrumental. The cost and time for accurate, reliable steel microstructural analysis, i.e., quality rating, can be reduced significantly with a 2-in-1 solution.

Place the piece of metal on a stable work surface. Keep in mind that a properly secured work piece is a safe work piece.  When drilling and tapping, pieces can spin, move or even rise up on the tooling causing damage or worse – personal injury!

If the threaded fastener will not thread into the hole, look for debris or metal shavings in the hole and clean them out. It is almost never necessary to re-cut the threads unless your tap is the wrong size or extremely damaged.

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