In order to ensure the quality of the induction heating furnace forgings, quality inspection must be performed. Determine if the drawing technical requirements or technical standards are met. The content of quality inspection includes: the appearance inspection ( geometry and size and surface quality ) of the forging, the internal quality inspection, the chemical composition inspection, etc.
(1) Chemical composition inspection
The chemical composition inspection is not carried out for general billet forgings, and its chemical composition is based on the sampling analysis before the induction heating furnace during smelting . But for important or questionable forgings. Some chips can be cut from the forging and the chemical composition can be checked by chemical analysis or spectral analysis.
(2) Appearance shape and size inspection
Use visual inspection, template or scribing method. Inspect the surface defects, shape errors and sizes of the forgings. To determine if the forging meets the pattern size.
(3) Macro organization inspection
Macrostructure inspection, also known as low magnification inspection, is to inspect the macrostructure of the surface or section of the forging with the naked eye or a magnifying glass no greater than 10 times. The main methods are sulfur printing, hot acid dipping, cold acid dipping and fracture.
(4) Microstructure inspection
Microstructure inspection, ie metallographic examination, is to observe, identify and analyze the microstructure state and distribution of forgings under an optical microscope, thereby helping to understand the relationship between microstructure and forging performance. In addition to examining the microstructure, metallographic examination can also show segregation and the distribution of some compounds, and can be used to evaluate the grain size and non-metallic inclusions.
(5) Ultrasonic flaw detection
Ultrasonic flaw detection is a non-destructive inspection. It is to inspect the internal or surface defects of apricot forgings without damaging the forging. In addition to ultrasonic flaw detection, there are also magnetic flaw detection and ray flaw detection. Due to its advantages of high penetration, high sensitivity, simple operation, fast speed, and harmless to human body, ultrasonic flaw detection has become the main method for inspecting internal defects of large forgings.
The main symptoms and common causes of common defects are shown in Table 1 . Table 2 lists the inspection items and requirements of various gear tooth blank forgings.
Table 1 Main symptoms of forging defects and causes of quality inspection methods
Appearance defect | Appearance defect | ||||
Defect name | Main sign | cause | Defect name | Main sign | cause |
eccentric | For multi-step gear shaft forgings, the center of each diameter section is not the same, and for gear forgings, the center of the inner and outer holes is offset. | Uneven heating temperature | Surface transverse crack | Shallow transverse crack | 1. Submerged bubbles in the steel ingot cannot be welded when exposed to the surface |
2. Improper forging process or operation | 2. The relative feeding amount is too large when pulling out | ||||
3. The punch was not aligned before punching | |||||
bending | Bending deformation of centerline of gear shaft forging | 1. Improper forging and straightening | Surface longitudinal crack | Cracks appearing in the longitudinal direction of the ingot when drawing and upsetting | 1. The inner wall of the steel ingot mold is defective, and the new steel ingot mold is not properly heat treated before use. |
2. Improper heat treatment operation | 2. Improper molten steel casting operation | ||||
Uneven | Deformation of ring and cake forgings | 1. Improper forging process or operation | 3. Improper cooling of steel ingot after demolding | ||
2. Improper heat treatment operation | |||||
fold | It is similar to a crack in appearance, but it is actually a metal streamline that bends | 1. Anvil fillet is not suitable | 4. Excessive reduction during chamfering | ||
2. The feed amount is less than the reduction amount | |||||
Surface transverse crack | Deeper transverse crack | 1. The ingot mold is defective or the new ingot mold is not well tempered before use. | Cracked surface | Tortoise-like shallow cracks on the surface of the forging | 1. The content of copper, tin, arsenic and carbon in steel is too high |
2. Improper cooling after demolding | 2. Initial forging temperature is too high | ||||
Internal crack | Cracks appear in the central area of the forging | 1. Heating is not burned through, the internal temperature is too low | loose | The loose structure along the center of the steel ingot is not forged, and it often coexists with non-metallic inclusions, etc. | 1. Improper selection of ingot type |
2. Improper forging ratio and improper deformation scheme | |||||
2. On stretching circular anvil member 3.V swage angle is too large | 3. Relative feed is too small | ||||
4. Incorrect tool shape | |||||
Shrinkage residue | Irregular wrinkles on dark test pieces, dark brown or off-white | 1. Improper ingot mold design and improper control of casting process | White dot | Round or oval silver-white spots on the longitudinal section of the forging | 1. The hydrogen content in the steel is too high |
2. Cut the head forging inadequate | 2. Improper cooling or annealing process after forging | ||||
overheat | Due to the excessively high heating temperature, the grains are coarse, and some alloy steels also have MnS precipitation. | 1. Improper forging process or operation 2. Improper heat treatment operation | Non-metallic inclusions | Metal inclusions that are elongated or broken in the forging | 1. The products during the steelmaking process or the refractory sand fall into the molten steel |
Table 2 Inspection items and requirements for various gear tooth blanks | |||
Test items | General inspection | Routine inspection | strict requirements |
chemical composition | May not check | Spot check | Inspection of important forgings with the same furnace number |
Visual inspection | Meet processing requirements | Meet processing requirements | Meet processing requirements |
Low purity tissue | Do not check | According to contract requirements | According to contract requirements |
Grain size | Do not check | Sampling check grain size above 5 | Gradually check the grain size above 7 |