Quality control is a set of actions aimed at checking that material characteristics comply with current standards and established technical requirements. It makes it possible to detect defects and deviations from specified parameters, prevent use of poor-quality products in production, minimize scrap, and guarantee high service characteristics of end products. There are several methods of material quality control. Below we will examine each of them in detail.
Visual inspection
The method is based on visual examination of materials or products to detect surface defects, including color mismatch, shape issues, and other visible signs.
Advantages of visual inspection:
- Simplicity and accessibility — no complex instruments or tools are required — ordinary lighting and, possibly, magnifying devices (loupes) are sufficient.
- Speed — inspection is performed quite quickly, making it possible to detect defects promptly.
- Cost-effectiveness — this inspection method does not require significant equipment costs.
Disadvantages of visual inspection:
- Limited accuracy — does not make it possible to detect hidden defects.
- Dependence on operator experience and qualification, which can affect inspection results.
Main defects that can be detected by visual examination:
- Cracks — a defect caused by improper cooling, overloads, or casting errors.
- Porosity — indicates disruption of the casting or cooling process.
- Blowholes — arise due to improper production technology or contamination during the process.
- Corrosion traces — appear on the material surface as spots, rust, or other signs of destruction, indicating unfavorable storage or transportation conditions.
- Scratches — arise from improper handling of materials or tools. Lead to reduced product strength and poorer appearance.
- Burrs — form during cutting and processing of materials. Can lead to geometry violations or damage to other parts of the product.
Visual examination can be carried out both during the production process and at final stages, during final product quality checks.
Dimensional inspection
Involves use of specialized measuring instruments to determine exact physical characteristics of materials: size, shape, weight, and other parameters. More accurate than visual inspection and makes it possible to obtain data with a high degree of reliability. Requires certain skills and specialized equipment.
The most frequently used instrument for dimensional inspection is a micrometer. This is a high-precision tool designed to measure linear dimensions of objects with an error of 2–50 µm, depending on device type and measurement conditions.
In metal strip production, micrometers are used to control product thickness at various production stages, which makes it possible to:
- ensure that finished products meet specified technical characteristics;
- promptly detect deviations from the norm and adjust production parameters;
- prevent release of products that do not meet thickness norms;
- reduce scrap and cut costs of reprocessing or disposal of material.
Micrometers may be mechanical and electronic:
- mechanical ones have a simple design and are most often used for rough measurements;
- electronic ones are equipped with digital displays, have minimal error, and may have additional functions: automatic calibration or saving results to memory.
Measuring instruments reduce the influence of the human factor and provide objective data. Early detection of deviations from the norm helps promptly eliminate problems and minimize the likelihood of releasing defective products.
Chemical analysis
A process used to determine the chemical composition of materials and their compliance with established quality standards. It can be carried out using various methods, such as:
- Spectroscopy — based on interaction of a substance with electromagnetic radiation. Depending on the type of radiation used (ultraviolet, visible, infrared, X-ray, etc.), it makes it possible to determine substance composition, concentration, and other characteristics.
- X-ray fluorescence (XRF) analysis — a method in which the elemental composition of a material is determined by measuring radiation arising under X-ray exposure. Makes it possible to accurately determine chemical composition even in complex multicomponent materials.
- Atomic emission analysis (AEA) — based on measuring the emission spectrum emitted by atoms or ions in an excited state. Used to determine the elemental composition of materials, since each element has a unique emission spectrum.
For express analysis at PZPS a handheld spectrometer is used — an instrument that makes it possible to quickly assess chemical composition, which is especially important in quality control on production lines.
For precise determination of chemical composition, X-ray fluorescence and atomic emission instruments are used. They have increased accuracy and data reliability, which is especially important in production of precision alloys, where even minor deviations from the specified composition can significantly affect finished product characteristics.
Mechanical testing
The method is aimed at determining service properties of steels and alloys, as well as their ability to withstand external loads. The main goal is to obtain information about mechanical properties, such as hardness, strength, ductility, impact toughness, and others.
Main types of mechanical tests:
- Strength tests (tension, compression, bending, impact) — checking the material’s ability to withstand static or dynamic loads.
- Hardness tests — measuring the material’s resistance to deformation under indentation or scratching.
- Ductility check — assessing the material’s ability to change shape without fracture.
Mechanical tests are needed to evaluate specialized materials used in critical structures and extreme conditions. For example, for steel and alloy grades:
- 40KKhNM, 36NKhTYu, 17KhNGT — used in elastic elements: springs, membranes. Must have high strength and elasticity.
- 12Kh18N9, 12Kh18N10T, 10Kh17N13M3T — have high corrosion resistance and are used in aggressive environments.
- 60S2A, 65S2VA, 65G, 70, 70S2KhA — used in production of leaf springs, coil springs, and other products experiencing cyclic loads.
- 20Kh13, KhN78T — used under elevated temperatures and high loads, for example in gas turbine engines and heat exchangers.
Use of various methods and instruments in mechanical testing makes it possible to apply this method in scientific research, design, and quality control.
Physical testing
Aimed at determining physical characteristics of materials needed to assess their properties and compliance with specified requirements. Helps determine:
- Coercive force — the material’s ability to resist magnetization or demagnetization.
- Electrical resistivity — a characteristic determining the material’s ability to resist electric current flow.
- Temperature coefficient of linear expansion (TCLE) — reflects the degree of dimensional change of a product under temperature.
Materials for which physical tests are especially important:
- Strips and sheets of electrical steel grades 20895, 20880, 20860, 20832, 21895, 21880, 21860, 21832 — used to manufacture elements of electrical circuits.
- Soft magnetic alloys 50N, 50NP, 79NM, 80NM, 81NMA, 49K2FA-VI, 27KKh — used in transformer cores, relays, and other magnetic devices.
- Alloys with high electrical resistance Kh15Yu5, Kh23Yu5, Kh23Yu5T, Kh20N80N, Kh15N60N — used in heating elements, resistors, and other devices where maintaining stability of electrical parameters is important.
- Alloys with a specified TCLE 29NK, 36N, 42N — used in precision instruments, glass–metal joints, and other structures where minimizing thermal deformation is important.
Physical tests help ensure steels and alloys meet technical requirements, determine suitability for a specific application, and increase product reliability and durability.
Microscopic analysis
The main goal of the method is to study object microstructure to detect microdefects, structural features, and assess material quality.
Principles of microscopic analysis:
- Research tools:
- reflected-light optical microscopes — make it possible to study surface structures and detect large microdefects;
- scanning electron microscopes (SEM) — used for more detailed microstructure study, helping detect the finest surface and internal structure details.
- Analysis objects:
- metals, alloys, ceramics, polymers, and other materials;
- features such as grain structure, phase composition, porosity, cracks, and other defects are revealed.
- Research process:
- sample preparation: grinding, polishing, and sometimes etching are carried out to make the microstructure more visible;
- analysis under the microscope: the researcher studies the structure in detail and records detected product defects.
Microscopic analysis makes it possible to better understand the nature and behavior of various materials at the micro level, which is especially important in thin strip production.
Non-destructive testing (NDT)
NDT is a set of methods making it possible to assess the quality of materials, products, or structures without destroying or damaging them.
Main NDT methods:
- Ultrasonic testing (UT) — used to detect internal defects: cracks, voids, and delamination. Based on passage of ultrasonic waves through the material.
- Penetrant testing — makes it possible to detect surface cracks using a special dye.
- Magnetic testing — used to detect surface and subsurface defects in ferromagnetic materials.
- Radiographic testing (RT) — makes it possible to detect defects inside the material using X-rays, creating an image of the object structure.
- Electromagnetic and eddy-current testing — used to analyze electrically conductive materials.
- Thermal imaging testing — helps detect defects by changes in surface temperature characteristics of the object.
Non-destructive testing is used to ensure product safety and reliability in the following areas:
- Mechanical engineering and aviation industry
- Weld inspection.
- Detection of cracks, corrosion, and other defects in metal structures.
- Construction
- Assessment of concrete structure strength.
- Detection of cracks and voids in walls, floors, and other building elements.
- Energy
- Diagnostics of pipelines, heat exchangers, turbines and other equipment.
- Detection of corrosion, leaks, and deformations.
- Transport
- Assessment of railway tracks, bridges, and roads.
- Inspection of vehicle parts.
- Chemical industry
- Checking tightness of tanks, vessels, and pipes.
- Detection of leaks and defects in substance storage and transport systems.
Choice of a specific NDT method depends on material type, product or structure features, and the required inspection depth (surface or internal).
PZPS products: quality control at every production stage
With us you can buy high-quality cold-rolled strip conforming to GOST 503-81 requirements, as well as products from special materials, including nichrome, analogues of foreign alloy families, precision alloys 27KKh, Kh20N80 and others.
PZPS guarantees reliability, durability, and compliance of each product with GOST requirements and international standards. We invite you to learn about our services and products and place an order for high-quality strip!
