Bearing steel quality requirements and shortcomings (4)

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Bearing steel quality requirements and shortcomings (4)

Source: China Bearing Network Time: 2013-04-10
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Uneven annealing schedule: The annealing arrangement of bearing steel is required to spread uniform or spherical pearlite. Because the steel strip is severe; the cooling after casting and rolling is not proper; or the annealing process is not correct, the annealing arrangement can be uneven. When the shape is severe; the carbon-poor zone between the two zones undergoes overheating of the coarse layered pearlite during the annealing process. The cooling after casting is too slow to occur not only in the form of a network; but also the uniqueness of the hand-punched layered pearlite; The carbide center is cut; then the partial arrangement of the original arrangement and the dissemination of the extremely coarse coarse-grained carbides are carried out in the annealing arrangement. If the original arrangement of the steel is normal; and the annealing temperature is too high, coarse layered pearlite will occur. Annealing temperature When it is low, it will show fine-grained or fine-grained pearlite. The annealing arrangement is uneven; the cutting performance of the steel is deteriorated; the parts after quenching are unevenly arranged; then the life of the bearing parts is reduced.
Quality inspection of bearing steels Inspection methods for bearing steels 1. Appearance of steel exterior quality View: The quality of steel appearance is usually viewed with the naked eye; Annealed and unannealed thermal steel; if necessary, it can be ground with a pneumatic or electric portable grinding wheel. The cold drawn annealed strip steel and steel tube can be twisted into three or four circumferential smooth surfaces on the whole data by a thin flat boring tool; the naked eye can be viewed with the naked eye. The steel wire disc is usually also viewed with the naked eye; in addition, it can also be viewed by pickling; Take 250mm long at each end of the disk; pick it up by picking it in a low-acid pickling process and seeing its appearance.
2, steel scale view: annealed and non-annealed hot-rolled round steel; with a reading value of 0. 1mm vernier caliper or caliper for scale viewing. Cold drawn steel and steel wire with a scale value of 0. 01mm micrometer for viewing. The outer diameter scale and wall thickness difference of the hot-rolled and cold-drawn steel tubes are respectively read with a reading value of 0.1 mm. The vernier caliper and the graduation value are 0. 01 mm micrometer. The thickness of the cold-rolled steel sheet and the steel strip is viewed with a micrometer. The length of the steel. The width is viewed with a steel ruler. The bending of various steels (except the coil) can be viewed with a double ruler or feeler gauge.
3. Identify steel types. Viewing steel types is usually viewed with a portable spectroscope and spark discrimination. The portable spectroscope is a semi-quantitative spectrometer; it can semi-quantitatively view the primary alloying elements in the steel; Chromium, manganese, nickel, molybdenum, tungsten, vanadium, etc. Spectral view can identify the steel number of the steel to be inspected and the presence or absence of mixed steel. The spark view is based on the spark characteristics to determine the steel number of the steel to be inspected.
4. Hardness view: The Brinell hardness test should be carried out on the cold drawn annealing strip and hot rolled annealed steel. The Brinell hardness test method is carried out according to the GB231-84 specification.
5. Fracture inspection: cold-drawn annealing and hot-rolled annealed steel with a diameter of 30mm or less should be fractured. Cut a notch at one end of the steel with a hammer or cut a fracture specimen with a press. See if there is any shrinkage on the cross section with the naked eye. Holes, white spots, cracks; overheating and other shortcomings.
6. Low-order arrangement view: Annealed steel and non-annealed steel with diameter greater than 30mm are usually viewed at low magnification. That is, the sawing thickness (annealing material) and the grinding wheel cutting machine (not annealed material) are cut at a thickness of 12~15mm at one end of the steel. The sample of the sample is ground with a grinder. After hot pickling, the nakedness is used to see the segregation, the degree of porosity is not shrinkage, the white point crack, the over-burning, etc. The hot pickling is 50% Industrial hydrochloric acid aqueous solution; heated to 70 ± 5 ° C; pickling time is 30 ~ 40min; after the sample is taken out, washed with alkaline water; then washed with 80 ° C hot water.
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