Vacuum heat treatment quality inspection

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The vacuum heat treatment quality inspection of parts is an important link and process in the vacuum heat treatment process. For batch-operated parts, the first piece inspection or the first batch quality inspection should be carried out according to the provisions of the process documents. Only when the metallographic structure, hardness, surface condition of the parts Batch vacuum heat treatment can be carried out only after other properties meet the requirements. The inspection items and methods as well as the judgment standards are implemented according to drawings, process cards, technical standards, etc. Generally speaking, the quality inspection of parts vacuum heat treatment includes the following five aspects: appearance, deformation, hardness, and metallographic structure. and brittleness, etc.

Vacuum heat treatment quality inspection requirements

The quality inspection of parts after vacuum heat treatment is carried out according to its technical requirements and inspection procedures. Commonly used quality inspections of vacuum heat treatment include appearance inspection, deformation detection, hardness inspection, metallographic inspection (structure, infiltration layer, brittleness, etc.), Non-destructive testing, etc.

① Vacuum heat treatment inspection of general parts requires more information

The inspection content after vacuum heat treatment of general parts can be carried out according to relevant standards or technical requirements.

②Quality inspection requirements for tools and molds

The vacuum heat treatment quality inspection of tools and molds is an important link and process in the vacuum heat treatment process. For batch-operated tools and molds, the first piece inspection or the first batch quality inspection should be carried out according to the provisions of the process documents. Only when the metallographic structure and hardness of the tools and molds are inspected , surface condition and other properties meet the requirements before batch vacuum heat treatment can be carried out. The inspection items and methods as well as the judgment standards are implemented according to drawings, process cards, technical standards, etc. Generally speaking, the quality inspection of tool and mold vacuum heat treatment has the following five aspects: appearance, deformation, hardness, metallography organization and brittleness, etc.

a.Vacuum heat treatment quality inspection of hot work die steel

Appearance inspection: After vacuum heat treatment, no cracks or deep scratches (marks) visible to the naked eye are allowed anywhere in the mold cavity and working parts. There must be no obvious bumps on the surface. There should be no surface peeling or sanding after chemical vacuum heat treatment. Corrosion is strictly prohibited on the polished working surface.

Inspection of deformation: Use a knife-edge ruler or a flat ruler to check the flatness or parallelism of the mold surface. If necessary, use a feeler gauge to measure. It is usually stipulated that the deformation should be less than 1/3 to 1/2 of the grinding allowance.

Inspection of hardness: Grind the parts to be tested (polished or polished), and select a hardness tester according to the process regulations. Generally, a Rockwell hardness tester is used to test 3 to 4 points. Microscope, Vickers, and Brinell, Shaw, Richter and other tests. According to the test results, adjust the temperature of vacuum tempering or aging of the mold. For molds with low hardness, it is recommended to continue polishing there to determine the real cause of low hardness. If necessary, perform spark identification or component testing. The purpose is to find the reason why the hardness does not meet the requirements.

The surface hardness of molds undergoing chemical vacuum heat treatment is often tested using a surface Rockwell or Vickers hardness tester. At this time, the smoothness and grinding degree of the mold surface will affect the test results, so attention should be paid.

b.Vacuum heat treatment quality inspection of cold work die steel

Appearance inspection: The surface of the mold is not allowed to have bumps, scratches, ablation, severe oxidative decarburization, corrosion pitting and rust. There must be no cracks visible to the naked eye. The surface of the mold is clean, there is no salt residue at the holes, and the wires are tied. Other attachments should be cleaned up.

Inspection of deformation: The deformation of the mold after vacuum heat treatment should not exceed 1/3~1/2 of the grinding allowance.

Hardness inspection: All molds should be inspected for hardness after vacuum heat treatment. For large and batch molds, if instruments cannot be used for inspection, files and other inspections should also be used.

The hardness requirements of the mold blank after annealing are: 180~~207HBW for carbon steel, 207~241HBW for low alloy tool steel, and 217~255HBW for high (medium) alloy steel.

The hardness inspection parts of punching dies and punching dies should be carried out within 5mm from the cutting edge. The hardness must meet the requirements and there must be no soft spots or soft bands. The main stress-bearing parts of cold forging, cold extrusion, bending and drawing dies should be Meet technical requirements. The hardness of the fixed part at the tail of the carbon tool steel small punch should be controlled at 30~40HRC, and the hardness of the remaining parts should meet the requirements of the drawing.

For large molds with flame surface quenching, the hardness of the working surface is greater than the upper limit of the specified hardness value. Tempering zones and low hardness areas are generally not allowed. For complex structures and shapes, hardness areas of no more than 20 mm are allowed, but the hardness value cannot be lower than the following. Limit value 10HRC.

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