What are the quality inspections and requirements for induction hardened forgings?

2019-03-18 11:55:22 2

(1) Visual inspection of the quenched surface


Check the forging surface for cracks, rust, electric shock, local melting, check whether the distribution of the quenching area is appropriate, and whether there are defects such as scratches that affect the use. Cracks mainly refer to quenching cracks and material cracks. Since such cracks are relatively small, the magnetic particle inspection method is usually used for inspection.


(2) Surface etching test

After the quenching forgings are removed by sandpaper to remove the oxide film or scale on the surface, 10%? 25% nitric acid solvent is used as the corrosive agent, and directly coated on the surface of the forging. After 10-20s, the surface of the forging can be displayed with a rough indication. Cracks, soft spots and hardened areas.


(3) Macroscopic inspection of hardened layer

1) Fracture inspection Induction hardened shaft forgings with a diameter less than 25~300mm, grinding a notch on the grinder, then breaking with a hammer or breaking with a press, directly observing the fracture. The hardened layer in the fracture presents a fine grayish white cornice (surface layer) while the middle quenched portion presents a rough cornice.

2) Profile corrosion In the induction hardening zone of the forging, select one or several sections for sectioning, take out the section sample, prepare a sample, subject to corrosion treatment, and then perform macroscopic observation, the hardened layer distribution and more accurate hardening can be obtained. Layer depth.

Corrosive agent: vaporized copper-ammoxidation reagent; nitric acid alcohol solution. A nitric acid alcohol solution with a concentration of about 10%. After etching the sample, the hardened layer is bright white, bright gray or bright black, while the original tissue portion is light gray.


(4) Surface hardness test

1) Hardness test of surface hardness

When the hardened layer of induction hardened forgings is >0.8 mm, the C scale (HRC) of the Rockwell hardness tester is often used for inspection. Hardened layer <0.8mm forgings, surface Rockwell hardness tester and Vickers hardness tester can be used. Surface roughness must be smoothed with a trowel and sandpaper. If the pre-heat treatment of the forged part is normalized or tempered, the scale and decarburization layer must be removed, but the depth of the grinding should not exceed the machining allowance. The number of inspection points per piece should generally not be less than 3 points. Refer to ZBJ 36005 for the range of surface hardness fluctuations of induction hardened parts. The surface hardness test is carried out in accordance with the relevant provisions of JB/T 9201 "Induction quenching and tempering treatment of steel parts".


2) Sickle inspection of surface hardness

Can refer to GB/T 13321 "Steel hardness test method".

(5) Depth measurement of hardened layer and metallographic examination of hardened layer

1) Hardness test of depth of forging hardened layer

The method implements GB/T 5617 "Determination of the effective hardened layer depth after induction hardening or flame quenching of steel", and the effective hardened layer depth is expressed.

2) Metallographic examination of forging hardened layer

Steel inductive quenching metallographic inspection standard ZBJ 36009 is implemented. The most ideal tissue for induction hardening is the 4-6 level organization. When the lower limit of the surface hardness specified by the product pattern is at or equal to 55HRC, the grade 3 is qualified; when the lower limit is lower than 55HRC, the grade 9 is also considered to be barely qualified. The metallographic sample was ground and etched with a 2%-5% nitric acid solution containing a volume fraction. At the same time as the metallographic structure observation and evaluation of the hardened layer, the original structure of the unhardened zone should be inspected to see if there are problems such as coarse grain, large ferrite or band structure, especially the hardness of the quenched forging is insufficient. When the depth of the hardened layer is insufficient or uneven.