What are the main common defects of oil quenched spring steel wire steel?
There are three main categories of common defects in oil quenched spring steel wire
- Surface quality defects B. Internal quality defects C. Dimensional defects
First, the surface quality defects
1, surface cracks: refers to the phenomenon of linear cracks on the surface of the steel, generally should be consistent with the direction of forging or rolling.
Formation reasons: mainly because of processing (forging, rolling, heat treatment and tempering) process due to surface overburning, decarburization, loosening, deformation and excessive internal stress and surface sulfur, phosphorus impurity content and more hairline, thermal cracking and cold cracking.
Surface cracks can be inspected by visual observation, pickling, magnetic particle inspection, coloring inspection and metallurgical methods. In confirming the cracks, attention must be paid to distinguish the surface of the steel oxide itself is brittle and loose after a slight bending and presents cracks, while the steel itself does not have cracks.
2, heavy skin and folding: steel surface adhesion of the “tongue” or “scale-like” metal sheet, the formation of local surface overlap, with obvious folding lines.
Reasons for formation: In the hot processing process due to the billet on the fly, burrs, depressions, inclusions, subcutaneous porosity and surface laxity, etc., in the thermal deformation of metal rheology, opening on the surface to form a heavy skin and folding.
3, ears: refers to the steel surface along the rolling direction of the extension of the concave.
The formation of the reason: the mill hole gap is too large, so that the surface of the steel along the hole to form a bump.
4, scratch: also called scratch, refers to the steel surface under the action of external forces in a straight or arc-shaped groove marks (can be seen at the bottom of the groove).
Second, internal defects
1, segregation: is actually a general term for the phenomenon of uneven distribution of chemical composition in steel. In the acid dip specimen, when the segregation is susceptible to corrosion or gas inclusions gathered is dark in color, irregular in shape, slightly depressed, flat at the bottom, and many dense microporous spots, if the corrosion-resistant elements gathered, it is light in color, irregular in shape, relatively smooth micro-concave spots. According to the location and shape of the deviations, they are usually grouped into the following categories.
①Center deviations: appearing in the center part, presenting irregularly shaped dark spots.
② Ingot type deviations: dark spots concentrated in a closed zone with different widths and shapes of the original ingot cross-section (usually square), so ingot type deviations are also called box deviations.
③Pitting deviation: the spots are generally larger, with darker color and slightly depressed figure, oval or melon shape. The general distribution is called general punctate deviation: the distribution in the edge part of the steel is called edge punctate deviation.
Causes of formation: segregation is the aggregation of certain elements caused by selective crystallization and diffusion during the solidification process of ingot pouring. Bias is generally unavoidable in the production situation.
2, looseness: pores inside the steel, such pores in low times on the sample generally show irregular polygons, the bottom of the sharp narrow craters, usually more appear within the bias spots. In severe cases, there is a tendency to form a sponge. According to the distribution of sparseness they are divided into two categories of central sparseness and general sparseness.
① Center sparseness: in the central part of the low times specimen is concentrated voids and dark dots. The longitudinal fracture is slightly laminated, and the increase of pearlite at the central laxity can be seen under the microscope, which means that the carbon content at the central laxity is increased.
②General laxity: the organization is dense on the low specimen, showing scattered small pores and small dark dots. The pores are mostly irregular polygons or figures, distributed in the entire section except for the edge part.
Central sparsity is generally found in the head and middle of the ingot, and the difference between general sparsity is that it is distributed in the steel section and the central part rather than the whole section. Usually the higher the carbon content of the steel, the more serious the central sparring.
Formation causes: ingot in the solidification process, due to intergranular part of the low melting point material after solidification shrinkage and release of gas to produce voids, and in the hot processing process is not matched with welded pipe. In the steel, a slight segregation, a higher level of looseness is allowed to exist.
3, inclusions: inclusions are divided into metal inclusions and non-metal inclusions.
① metal inclusions: mainly in the casting process, metal bars, pieces, blocks mistakenly fall into the ingot mold or at the end of the smelting added to the iron alloy block and other defects formed by the melting, in the low times on the sample, showing more clear edges, color and the surrounding geometry is significantly different.
② non-metallic inclusions: in the pouring process, did not have time to float the slag or flake to the steel lining and refractory materials on the inner wall of the pouring system, etc. Larger non-metallic inclusions are well identified, while smaller inclusions corrode and flake off, leaving small round holes.
4, shrinkage: in the low times on the sample, shrinkage is located in the central part, its surrounding is often deviated, inclusions or sparse dense, sometimes in the corrosion can be seen before the cave or gap. After corrosion, the pores are partially darkened and are irregularly folded holes.
Formation reasons: ingot pouring, after solidification of the part (heart) steel solidification shrinkage is not filled and left behind macroscopic pores, shrinkage is mainly formed in the ingot head (cap end).
5, bubbles: on the low times sample, is roughly perpendicular to the surface of the crack, near a slight oxidation and decarburization phenomenon, the presence of the location below the surface is called subcutaneous bubbles, deeper subcutaneous bubbles called pinholes.
Formation reasons: defects caused by the gas generated and released during the casting of ingots.
6, crack: in the low times the sample, the axial location along the intergranular cracking, into a spider web, in serious cases, radial cracking.
Formation reasons: mainly two, one is the ingot in solidification and cooling, for some reason and the internal tearing, failure to weld in the forging and rolling process; the other is due to improper forging and internal cracking.
7, white spots: in the low times on the sample is a thin short crack, generally concentrated in the interior of the steel, in the thickness of 20-30mm surface layer is almost no, because the crack is not easy to distinguish, should be supplemented by fracture test to verify. White spots on the fracture shows a coarse grain-like silver bright white spots.
Formation reasons: It is generally believed that the role of hydrogen and tissue stress, that is, hydrogen decomposition set into the lax microporous huge pressure and the local internal stress generated when the steel phase change joint caused by the small crack.
Third, the shape and size defects
1, size difference: including the length, diameter, thickness, positive and negative tolerances, grinding depth, width and other dimensions of steel does not meet the requirements of the ordering standard.
2, ellipticity: refers to the difference between the larger and smaller diameter of the steel cross-section of the circular section.
3, curvature: steel in the length and width direction is not straight, different materials have different names for curvature, profiles to curvature; plates, strips are sickle bend, wave bend, floating curvature.
4, twist: strip steel twisted into a spiral along the axial direction.
