Inspection of stainless steel

Stainless steel factories produce all kinds of stainless steel, and all kinds of inspections (tests) must be carried out in accordance with the corresponding standards and technical documents before leaving the factory. Scientific experiment is the foundation of the development of science and technology, it marks the level of the development of science and technology, and is an important means to promote the development of science and technology. Use various effective means to inspect the quality of semi-finished products and finished products, and the inspection process must be regarded as an important process in the production process.

Steel quality inspection is of great practical significance to guide metallurgical factories to continuously improve production technology, improve product quality, produce steel products that meet standards, and guide users to choose steel materials reasonably according to inspection results, and to perform cold, hot processing and heat treatment correctly.

1 Inspection standard

Steel inspection method standards include chemical composition analysis, macroscopic inspection, metallographic inspection, mechanical performance inspection, process performance inspection, physical performance inspection, chemical performance inspection, non-destructive inspection and heat treatment inspection method standards, etc. Each test method standard can be divided into several to a dozen different test methods.

2 Inspection items

Due to different stainless steel products, the required inspection items are also different. The inspection items range from a few items to more than a dozen items. Each stainless steel product must be carefully inspected one by one according to the inspection items specified in the corresponding technical conditions. Each inspection item must be Meticulous implementation of inspection standards.

The following is a brief introduction to the inspection items and indicators related to stainless steel.

(1) Chemical composition: Each stainless steel grade has a certain chemical composition, which is the mass fraction of various chemical elements in the steel. Guaranteeing the chemical composition of steel is the most basic requirement for steel. Only by analyzing the chemical composition can it be determined whether the chemical composition of a certain grade of steel meets the standard.

(2) Macroscopic inspection: Macroscopic inspection is a method of inspecting the metal surface or section with the naked eye or a magnifying glass no greater than 10 times to determine its macroscopic structural defects. Also known as low-magnification tissue inspection, there are many inspection methods, including acid leaching test, sulfur printing test, etc.

Acid leaching test can show general porosity, central porosity, ingot segregation, point segregation, subcutaneous bubbles, residual shrinkage cavity, skin turning, white spots, axial intergranular cracks, internal bubbles, non-metallic inclusions (visible to the naked eye) And slag inclusions, heterogeneous metal inclusions, etc. have been evaluated.

(3) Metallographic structure inspection: This is to use a metallographic microscope to inspect the internal structure and defects in steel. Metallographic inspection includes the determination of austenite grain size, the inspection of non-metallic inclusions in steel, the inspection of the depth of decarburization layer, and the inspection of chemical composition segregation in steel, etc.

(4) Hardness: Hardness is an index to measure the softness and hardness of metal materials, and it is the ability of metal materials to resist local plastic deformation. According to different test methods, hardness can be divided into several types such as Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness and microhardness. The scope of application of these hardness test methods is also different. The most commonly used methods are the Brinell hardness test method and the Rockwell hardness test method.

(5) Tensile test: Both the strength index and the plastic index are measured by the tensile test of the material sample. The data of the tensile test is the main basis for selecting materials in engineering design and mechanical manufacturing parts design.

Normal temperature strength indicators include yield point (or specified non-proportional elongation stress) and tensile strength. High temperature strength indicators include creep strength, enduring strength, high temperature specified non-proportional elongation stress, etc.

(6) Impact test: The impact test can measure the impact absorption energy of the material. The so-called impact absorption energy is the energy absorbed when a test of specified shape and size breaks under an impact. The greater the impact energy absorbed by a material, the higher its ability to resist impact.

(7) Non-destructive testing: Non-destructive testing is also called non-destructive testing. It is an inspection method to detect internal defects and judge their type, size, shape and location without destroying the size and structural integrity of structural parts.

(8) Surface defect inspection: This is to inspect the steel surface and its subcutaneous defects. The content of steel surface inspection is to inspect surface defects such as surface cracks, slag inclusions, oxygen deficiency, oxygen bite, peeling, and scratches.