Materials and Processes #1

An electric current that flows steadily in one direction is called direct current. This means that the flow of electrons is constant and does not change direction. Direct current is commonly used in batteries and electronic devices that require a continuous flow of electricity. It is different from alternating current, where the flow of electrons periodically changes direction. Full wave current and half wave current are not accurate descriptions of a current that flows steadily in one direction.

To effectively evaluate a defect, an inspector must possess knowledge of the test being conducted, as this will determine the criteria for identifying and assessing defects. Additionally, a knowledge of the material being tested is essential, as different materials may have unique defect characteristics and requirements. Finally, a knowledge of the applicable codes is necessary to ensure that the evaluation is in compliance with industry standards and regulations. Therefore, the correct answer is "all of the above" as all three factors are crucial for an inspector to accurately evaluate a defect.

The correct answer is "all of the above." This means that all of the mentioned reasons (inherent defects, service defects, and processing defects) can justify the rejection of some parts during the inspection. Inherent defects refer to defects that are present in the part from the beginning, service defects are defects that occur during the part's use, and processing defects are defects that occur during the manufacturing or processing of the part. Therefore, any of these defects can be valid reasons for rejecting parts during inspection.

All of the factors listed - grain size, grain orientation, and grain boundary composition - can have a negative influence on some nondestructive tests. These factors can affect the ability of the tests to accurately detect and analyze flaws or defects in materials. For example, variations in grain size or orientation can impact the propagation of ultrasonic waves, making it difficult to detect flaws. Similarly, differences in grain boundary composition can affect the magnetic properties of a material, making it challenging to perform magnetic particle testing. Therefore, all of these factors can negatively impact the effectiveness of nondestructive tests.

Discontinuities are most likely to occur at junctions between light and heavy sections on a casting. This is because these junctions create areas of stress concentration, where the material transitions from a thicker section to a thinner section. These stress concentrations can lead to defects such as cracks or voids, making it the most logical place to look for discontinuities.

A procedure (instruction) provides the NDT inspector with a brief outline of the steps to perform a test on a specific item. It serves as a guide for the inspector, detailing the necessary actions and sequence of steps to follow in order to carry out the test accurately and efficiently. Procedures ensure consistency and standardization in the testing process, allowing for reliable and repeatable results. Codes, standards, and specifications may provide additional guidelines and requirements, but a procedure is specifically designed to outline the steps for conducting a test.

Stress risers are areas of a material that are more prone to experiencing stress concentration, which can lead to cracks or fractures. Punch marks, corrosion grooves, and corrosion pits can all create stress risers. Punch marks are indentations made by a punch tool, which can create localized stress concentrations. Corrosion grooves are linear depressions caused by corrosion, which can weaken the material in those areas. Corrosion pits are small holes caused by corrosion, which can also create stress concentrations. Therefore, all of the given answers can cause stress risers.

Porosity in a weldment can occur due to improper cleaning or insufficient preheating of the weldment. When the base metal or filler metal is not properly cleaned, contaminants such as dirt, oil, or rust can be trapped in the weld, leading to porosity. Similarly, if the weldment is not preheated adequately, moisture can be present on the base metal or filler metal, which can vaporize during the welding process and cause porosity. Therefore, porosity is a common defect that can be attributed to these factors.

Permanent deformation refers to a type of material failure where the material undergoes a non-reversible change in shape or size due to the application of stress. Unlike fracture, which involves the breaking of a material into separate pieces, permanent deformation occurs when the material is unable to return to its original form after the stress is removed. This can happen due to the material's inherent properties or the magnitude and duration of the applied stress.

In the context of 3D printing technology, plastic is one of the most commonly used materials. 3D printers can create objects by layering and melting plastic filament, allowing for the production of various plastic-based items. While other materials like metal, ceramics, and composites can also be used in 3D printing, plastic is widely accessible and used for a wide range of applications due to its versatility and ease of use in the 3D printing process.

When two different materials with specific properties are combined to form a composite, the resulting material can possess a combination of properties that are better than either of the individual components alone. In this case, the composite can have improved resistance to heat, increased strength in tension per unit weight, and increased stiffness per unit weight. Therefore, the correct answer is "any of the above" as the composite can have all of these properties depending on the specific combination of materials used.

A stress corrosion crack is a defect that occurs in a metal due to the combined action of corrosion and applied stress in a service environment. This means that the crack is not a result of casting, welding, or metal forming processes, but rather it develops over time during the service life of the metal. The corrosive environment, along with the presence of stress, leads to the formation and propagation of the crack. Therefore, the correct answer is service.

Powder metallurgy as a manufacturing method offers several advantages. Firstly, it allows for the production of parts with closer tolerances, meaning that the final products can be made with higher precision and accuracy. Secondly, it enables the mass production of hard-to-shape parts, which would otherwise be difficult or costly to manufacture using traditional methods. Lastly, powder metallurgy can produce parts with a high strength to weight ratio, making them lightweight yet strong. Therefore, all of the mentioned advantages can be considered as benefits of powder metallurgy as a manufacturing method.

The inverse quantity of electrical resistivity is conductivity. Conductivity is a measure of how easily an electric current can flow through a material. It is the reciprocal of resistivity, which measures the opposition to the flow of electric current. Therefore, conductivity and resistivity are inversely related. Higher conductivity indicates a material that is a good conductor of electricity, while lower conductivity indicates a material that is a poor conductor.

The correct answer is "any of the above" because all three options (bloom, billet, and bar) can be used as the work metal for working with a forging hammer. Each option represents a different form or shape of metal that can be used in the forging process. A bloom is a large mass of metal that is typically obtained directly from a smelting furnace. A billet is a smaller, rectangular piece of metal that is often used as a starting material for forging. A bar is a long, cylindrical piece of metal that can also be used for forging. Therefore, any of these options can be used as the work metal when using a forging hammer.

Most manufacturing defects in a tube are axial in direction. This means that the defects occur along the length of the tube, rather than around its circumference or on the outside. These defects can include cracks, splits, or other imperfections that run parallel to the axis of the tube. Axial defects are typically caused by issues during the manufacturing process, such as improper handling or inadequate material quality control.

In a rolling mill, the process of flattening and elongating metal is primarily achieved by applying compressive forces. These forces exert pressure on the metal, causing it to deform and change its shape. Compression helps to reduce the thickness of the metal and increase its length, resulting in a flattened and elongated product. Tensile stresses, bending forces, and high frequency cyclic loads may also play a role in the overall process, but the main mechanism responsible for the desired outcome is the application of compressive forces.

In spot welding, the process involves applying pressure and heat to two or more metal surfaces to join them together. Filler metal is not added in this process because the heat generated by an electric current passing through the metal surfaces causes them to melt and fuse together. Therefore, spot welding does not require the use of filler metal.

A cold shut is a generally smooth indentation on a cast surface that occurs when two streams of metal coming from different directions fail to fuse together. This happens when there is insufficient fluidity or poor gating design, causing the metal to solidify before proper fusion occurs. Cold shuts can weaken the cast and lead to structural defects.

In a blast furnace, coke is added as a source of carbon, which acts as a reducing agent to remove oxygen from the iron ore. The ore itself is added as a source of iron. Limestone is added to remove impurities such as silica and alumina, forming a slag that can be easily separated from the molten iron. Finally, air is added to provide oxygen for the combustion of coke, generating heat and maintaining the high temperatures required for the chemical reactions to occur. Therefore, the combination of coke, ore, limestone, and air is necessary to remove iron from the ore in a blast furnace.

The correct answer is "find all discontinuities that the proper use of the test method is capable of indicating". This means that the function of any NDT inspection is to identify and locate all the defects or discontinuities that can be detected using the appropriate testing method. It does not necessarily mean finding all defects in the part or ensuring the safety of all tested parts, but rather focusing on detecting the specific discontinuities that the chosen test method is capable of indicating.

Incomplete joint penetration refers to a welding defect where the weld does not fully penetrate the joint, leaving a gap or void. This defect occurs in the root pass and runs parallel with the weld. In contrast, incomplete fusion between beads refers to a defect where the individual weld beads do not fuse together properly. An icicle is a term used to describe a defect where excess filler metal protrudes from the weld. A crater crack refers to a crack that forms at the end of a weld. Therefore, the correct answer is incomplete joint penetration.

When a metal or alloy cools from a liquid to a solid state, the lack of molten metal to feed the shrinkage will result in the formation of pipes, voids, and cavities. These are caused by the contraction of the metal as it solidifies, creating empty spaces within the structure. Additionally, the rapid cooling can lead to a sponge-like appearance and the formation of hot tears, which are cracks or fractures that occur due to the internal stresses caused by the solidification process. Therefore, both options a) and b) are correct explanations for the consequences of the lack of molten metal to feed the shrinkage during cooling.

Steels that contain more than 0.30 percent carbon are prone to heat-affected zone cracking when welded. This means that when these steels are subjected to high temperatures during the welding process, the heat-affected zone (the area surrounding the weld) can develop cracks. This is due to the high carbon content, which makes the steel more susceptible to cracking when exposed to heat.

The cause of cracks in the heat-affected zone is a thermal cycle that increases hardness and brittleness. When the material undergoes a thermal cycle, it experiences rapid heating and cooling, which can lead to the formation of residual stresses. These residual stresses can cause cracking in the heat-affected zone, especially if the material becomes harder and more brittle due to the thermal cycle.

Discontinuities can propagate and become defects, whereas defects refer to internal flaws that may or may not have originated from errors in processing. This means that a discontinuity is a potential precursor to a defect, as it has the ability to develop and transform into a more significant issue. On the other hand, defects can arise from various sources, not just external natural boundaries, and can have different levels of severity. Therefore, this statement best explains the difference between a defect and a discontinuity.

In resistance spot welding, the heat generated is concentrated at the interface of the two plates to be welded. This is because the welding process involves passing a high electrical current through the workpieces, creating resistance at the interface. The resistance causes the metal to heat up, melting and forming a weld. The heat is concentrated at the interface because this is where the resistance is highest, resulting in localized melting and joining of the two plates.

The correct answer is "indirect." This means that the indications found by NDT methods are not directly observable or obvious. Instead, they require interpretation or inference based on the data obtained through these methods.

A lamination is an extremely thin discontinuity that occurs when pipes or blisters are flattened and made directional through the process of working. It is a common term used in various industries to describe this type of flaw or defect.

Slag inclusions in welds can be caused by both wide weaving and incomplete deslagging of a previous pass. Wide weaving refers to excessive movement of the welding torch during the welding process, which can lead to the entrapment of slag. Incomplete deslagging of a previous pass refers to the failure to remove all the slag from the previous weld, resulting in its inclusion in subsequent welds. Both these factors contribute to the formation of slag inclusions in welds.

Heat treatment cracks can occur in areas of sudden change in thickness because these areas experience uneven heating and cooling during the heat treatment process. The rapid temperature changes can cause thermal stresses, leading to the formation of cracks. This is a common phenomenon in materials with varying thicknesses, such as welds and cast plates. Therefore, the correct answer is "in areas of sudden change in thickness."

Stringers are elongated configurations of foreign substances that are aligned in the direction of working wrought metals. They can be seen as long, narrow streaks or lines within the metal. These stringers can be caused by impurities or foreign particles that are present during the metalworking process. They can weaken the metal and affect its overall strength and integrity. Therefore, stringers are an important consideration in metallurgy and metalworking processes.

Cracks open to the surface are considered the most detrimental to the service life of an item because they provide a direct pathway for external factors such as moisture, chemicals, and contaminants to enter the material, leading to accelerated degradation and potential failure of the item. Subsurface inclusions and subsurface porosity and voids may also weaken the material, but they do not pose an immediate threat like cracks open to the surface.

Shielded metal-arc welding is a process of joining metals that is carried out manually. This means that the welder directly controls the welding process, including the movement of the welding electrode and the application of the shielding gas. Unlike fully automated or semi-automated welding processes, shielded metal-arc welding requires the welder to have hands-on control and skill to ensure the proper fusion of the metals being joined.

Completely recrystallized hot rolled steel products have superior mechanical properties in the direction of rolling. This is because during the hot rolling process, the steel undergoes plastic deformation, which aligns the grains in the direction of rolling. When the steel is subsequently recrystallized, new grains with a more uniform and refined microstructure are formed, resulting in improved mechanical properties in the direction of rolling, such as higher strength and better ductility. In contrast, the mechanical properties in the transverse direction may not be as superior since the grains are not as aligned in this direction.

When pouring steel into a mold, it is important to avoid splashing the steel onto the walls of the mold. This is because splashing can lead to the formation of surface defects known as cold shots. Cold shots occur when small droplets of steel solidify before they fully fuse with the molten steel in the mold. These solidified droplets can create imperfections on the surface of the final product, affecting its quality and integrity. Therefore, care must be taken to prevent the occurrence of cold shots during the pouring process.

A grinding crack is a defect that occurs during the grinding process of a metal. It is caused by excessive heat and pressure, leading to cracks in the metal surface. Unlike other defects mentioned, such as intergranular corrosion, quenching crack, and lamellar tearing, a grinding crack is not influenced by the direction of metal grains. The direction of metal grains is significant in other defects as it can affect the strength and integrity of the metal. However, in the case of a grinding crack, the defect is independent of the direction of metal grains.

Bursts occur when the metal being forged is either too hot or too cold. This can lead to uneven deformation and internal stresses within the metal, causing it to rupture or burst during the forging process. If the metal is too hot, it becomes more ductile and prone to tearing. On the other hand, if the metal is too cold, it becomes brittle and susceptible to cracking. Therefore, it is crucial to maintain the proper temperature range during forging to avoid bursts.

Specialists in non-destructive testing need to be knowledgeable about the materials they inspect and the defects that can form in them. This is important because they need to understand the characteristics and behavior of different materials in order to accurately assess their condition and identify any potential defects. By having this knowledge, they can effectively interpret test results and make informed decisions about the integrity and safety of the materials being inspected. Having an exhaustive knowledge of metallurgy and being aware of the capabilities of materials to sustain deformation without forming defects are also important, but they are not the sole requirements for specialists in non-destructive testing.

In some areas of the weld heat-affected zone, grain size can be smaller than in the unaffected base metal. This statement is correct because during the welding process, the heat affects the microstructure of the base metal, causing changes in the grain size. In certain regions of the heat-affected zone, the rapid heating and cooling can result in a finer grain structure compared to the unaffected base metal. This can have implications on the mechanical properties and performance of the welded joint.

Heat treatment is commonly used to refine the grain size of ferrous metals. During heat treatment, the metal is heated to a specific temperature and then cooled at a controlled rate. This process helps to rearrange the atoms within the metal, resulting in a finer grain structure. By controlling the heating and cooling process, the grain size can be effectively reduced, leading to improved mechanical properties such as increased strength and toughness. Elastic deformation and high frequency mechanical vibrations can also affect the grain size, but heat treatment is the most commonly used method for grain refinement in ferrous metals.

Nondestructive testing helps in identifying any defects or flaws in the stock before it goes through the processing stage. By eliminating poor stock prior to processing, the need for rework or scrap is reduced, resulting in cost savings. This ensures that only high-quality materials are used in the manufacturing process, leading to improved integrity and safety of the final products. Additionally, nondestructive testing does not damage or destroy the tested materials, allowing for increased production rates and reducing the need for additional personnel. Therefore, the correct answer is "eliminating poor stock prior to processing."

Excessive restraint during welding is not a cause of undercutting. Undercutting occurs when the base metal is melted away from the weld, creating a groove or depression. It is typically caused by factors such as excessive amperage, excessive travel speed, or excessive electrode diameter. However, excessive restraint refers to the restriction of movement or expansion of the welded joint, which can lead to distortion or cracking, but it does not directly cause undercutting.

Alkaline solutions are usually used to clean aluminum alloys because they are effective in removing oils, greases, and other organic contaminants from the surface of the alloy. These solutions have a high pH level, which helps to break down and dissolve the contaminants. Acid solutions, on the other hand, can corrode and damage aluminum alloys, so they are not typically used for cleaning purposes.

In a situation where several methods of testing are necessary for complete inspection of a part, the preferred sequence would be to use penetrant inspection before ultrasonic inspection. This is because penetrant inspection is a surface-level test that can detect surface cracks, porosity, and other defects, while ultrasonic inspection is a volumetric test that can detect internal flaws. By performing penetrant inspection first, any surface-level defects can be identified and addressed before moving on to the more comprehensive ultrasonic inspection. This ensures a more thorough inspection and increases the chances of detecting all possible defects in the part.

Laps are a type of discontinuity that can be found in a forging. Laps occur when folds or wrinkles are formed on the surface of the forging due to improper material flow during the forging process. This can happen when there is insufficient material or when the material does not properly fill the die cavity. Laps can weaken the forging and lead to potential failure under stress. Therefore, it is important to identify and address laps to ensure the quality and integrity of the forging.

Grain boundaries in a metal microstructure refer to the interfaces between individual grains or crystalline regions. These boundaries are susceptible to the concentration of impurities, particularly those with lower melting points. Impurities tend to accumulate at grain boundaries, impacting the material's properties. This phenomenon is significant in metallurgy, influencing the material's behavior and characteristics.

Cold working refers to the process of deforming metal at room temperature. This process can cause the metal to become harder and stronger, but it also leads to a decrease in ductility. Ductility is the ability of a material to deform under tensile stress without fracturing. When steel or aluminum is cold worked, the internal structure of the metal changes, causing it to become more brittle and less able to stretch or bend without breaking. Therefore, the correct answer is ductility.

Spot examination refers to the inspection of a number of parts from a lot to determine the quality of the entire lot. It involves randomly selecting samples from the lot and examining them for defects or other quality issues. This method is often used in manufacturing and quality control processes to ensure that the entire lot meets the required standards.

A forging lap is a flaw that can resemble a cold shut. A forging lap occurs when a portion of the metal folds over itself during the forging process, creating a defect that resembles a seam or crack. This flaw can weaken the integrity of the forged part and may lead to failure under stress. It is important to detect and address forging laps to ensure the quality and reliability of the final product.