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OCT 20 2012

Steel castings


Steel castings
Parts is made with cast steel castings. Similar to cast iron performance, but better than cast iron strength.

For pouring steel castings. Casting Alloy kind. The cast is divided into cast carbon steel, low alloy steel casting and casting of special steel.
(1) Cast Carbon Steel.
Carbon as the main alloying element and containing a small amount of other elements of the cast steel. Carbon less than 0.2% for the casting of low carbon steel, carbon 0.2% to 0.5% for the casting of carbon steel, carbon-containing greater than 0.5% for casting high-carbon steel. With the increase of the carbon content, the strength of the casting of carbon steel is increased, hardness is increased. Cast carbon steel has high strength, ductility and toughness, low cost, heavy machinery used in the manufacture of withstanding a big load of parts, such as rack of the rolling mill, hydraulic press base; force used in the manufacture of railway vehicles parts and withstand shocks such as Bolster, side frames, wheels and coupler.
(2) low alloy steel casting.
Containing the alloying elements such as manganese, chromium, copper and cast. Usually less than 5% of the total amount of alloying elements, has a larger impact toughness, and through a heat treatment to obtain a better mechanical performance. Than carbon steel, low alloy steel casting has the better the performance, part quality can be reduced to improve the service life.
③ casting special steel.
In order to meet the special needs refining alloy steel, variety, usually containing one or more of the high amount of the alloy elements, in order to obtain particular properties. For example, the impact of high-manganese steel capability of 11% to 14% manganese wear, used for mining machinery, engineering machinery wear parts; as the main alloying elements chromium or chromium nickel stainless steel for corrosion or 650 working parts ℃ temperature above conditions, such as the chemical industry with the valve, pump, container or large-capacity power station turbine casing. 1 castings, steel castings, surface and near-surface defect detection
1.1 Liquid penetrant testing liquid penetrant testing used to check various casting surface breaking defects, such as surface cracks, pinholes and other surface naked eye is difficult to find defects. Commonly used infiltration detection is colored detection, it is to have a high penetration ability of the colored (usually red) soaked or sprayed on the surface of the casting liquid (penetrant), penetrants penetrate into the opening of defects inside quickly wipe the surface of the permeate layer, and then the display and easy to dry agents (also called imaging agent) is sprayed onto the surface of the casting, to be remaining in the opening defects penetrants sucked out after the display agent is dyed, which can reflect the shape of the defect, size and distribution. Should be noted that the accuracy of the penetration testing with the surface of the test material increased roughness is reduced, i.e., the surface the more light detector the better the effect, grinder polishing the surface of the detection accuracy of the maximum, can be detected even intergranular cracks. In addition to coloring detection, fluorescent penetrant testing is commonly used in liquid penetrant testing method, it needs to configure the UV lamp irradiation observed high detection sensitivity than coloring detection.
1.2 eddy current testing eddy current testing applicable to the inspection surface following generally not more than 6 ~ 7MM deep defects. Eddy current testing points placed coil and through the coil method. : When the test piece is placed to pass near the coil of the alternating current, the alternating magnetic field can enter the specimen in the specimen induced in the perpendicular direction with the excitation field, was vortex-like flow of current (eddy current), the vortex direction opposite to the magnetic field will produce an excitation field, so that the original magnetic field in the coil of the partially reduced, thereby causing a change in the impedance of the coil. If the casting surface there is a defect, the electric characteristics of the eddy current will be distorted, thereby detecting the presence of a defect, the main drawback is the eddy current testing can not visualize the size and shape of the detected defects, generally only determine where the defect is located at the surface location and depth In addition, it is a small opening in the workpiece surface defects detection sensitivity is not as good as penetrant testing.
1.3 Magnetic Particle Testing Magnetic particle detection is suitable for detecting surface defects and a depth of a few millimeters below the surface defects, it requires DC (or AC) of magnetization equipment and magnetic particle (or maglev liquid) in order to detect the operation. Magnetized equipment used to generate a magnetic field, the magnetic powder or magnetic levitation solution was used to display defect in the inner and outer surfaces of castings. When the magnetic field is generated within a certain range in the casting, the defects within the magnetized region is generated the leakage magnetic field, when sprinkled with the magnetic powder or suspension, the powder is sucked so that it can display defect. So shows that the defect is substantially transverse to the magnetic field lines of the defects are the defects of the long bar parallel to the magnetic lines of force does not show, to this end, the operation need to constantly change the magnetization direction, in order to ensure able to check out the various defects of the unknown direction .
Casting internal defect detection, commonly used in non-destructive testing methods for internal defects ray inspection and ultrasonic testing. Wherein the effect of ray detector is best, it can be obtained reflecting the internal defects of type, shape, size and distribution of the visual image, but for large castings of a large thickness, ultrasonic testing is very effective, can be more accurately measured by the internal position of the defect , equivalent size and distribution.
2.1 ray detection (Micro Focus XRAY) ray detection, general X-ray or gamma-ray as ray source, and therefore need to generate ray equipment and other ancillary facilities, when the workpiece placed ray field irradiation ray radiation intensity will be casting internal defects. Through the radiation intensity emitted by the castings with the defect size, the different nature of the local changes in the formation of a defect-ray image through ray film to be the imaging recording, or real-time detection through the faceplate be observed, or detected by radiation counting instrument. Wherein the recording method by ray film imaging is the most common method, which is commonly referred to radiographic testing, radiographic reflected by the defect image is intuitive, the defect shape, size, quantity, flat position and distribution range It can be presented, but the depth of defect generally does not reflect the need to take special measures and calculations to determine. Now application-ray computed tomographic method, the equipment is more expensive, the use of high cost, there can not be universal, but this new technology represents the future development direction of high-definition-ray detection technology. In addition, the micro-focus X-ray system using the approximate point source actually eliminate blurry edges greater focus equipment, the outline of the image is clear. Improve image signal-to-noise ratio using a digital image system, and to further improve the image sharpness.