(1), shrinkage cavity, liquid steel in the process of condensation after pouring, due to the volume shrinkage hole in the center of the ingot formation, called the shrinkage cavity.
In order to reduce the harm of pipe steel, thus in the liquid steel casting, to adopt reasonable in the process of crystallization process, the volume shrinkage of the hole to move to the head of the ingot, the ingot after the breakdown, the shrinkage cavity local cut off, but, because of the improper casting, cooling technology, such as unreasonable set, lack of ingot head insulation, sufficiently ingot head after excision quantity is little, etc, make the residual shrinkage cavity in steel, macroscopic examination, will emerge.
(2), white spots: after pickling of steel sample horizontal section center or the neighbourhood area present short, discontinuous, ordinary went into a state of radiation scattered hair filamentous opened seam, or present appearance in steel on the longitudinal fracture of lubrication, approximate circular or oval shape of the white spots, known as the white dots.
White point of reason, it is the presence of hydrogen in steel, the second is steel forging in 600 ~ 300 ℃ after slow cooling, hydrogen energy diffusion, tissue stress and cracking.
Have white steel or parts, the longitudinal and transverse mechanical properties are significant to land, in white is a steel or parts without using value.
(3), burnt: ingot or billet in forging heating, high temperature weather, outside surface oxygen invasion and the oxide along the grain boundary.
At the grain boundary and some branches between the major axis of low melting point compound condensation, causing cracks or holes after condensation.
This phenomenon is called burnt.
Steel after burn, will start again when forging cracking, even without cracking, fill in the day bath in the strength and impact toughness are greatly reduced, so can't use.
(4), bubble: steel to gases dissolved in the liquid state than solid is big, the liquid steel in the cooling process, the escape of gas from the liquid steel, such as too late, the porosity.
In addition, the ingot mould bake bad, will contain water or gas in steel mould appearance, and bad appearance within the ingot mould coating, constitute a large amount of gas, the liquid or gas to discharge the liquid steel, are the subcutaneous bubbles.
The existence of the bubble is greatly reduced the strength of the steel.
(5), segregation: in the steel surface in the process of coagulation, due to various kinds of chemical composition of carbon in steel, chromium, tungsten, phosphorus and other elements of crystallization, diffusion velocity of different chemical composition is not the average is called segregation.
The existence of the segregation can give after deformation processing hard formation, analysis of sulfur are prone to heat brittle, the segregation of phosphorus are prone to cold short.
The existence of segregation easily provoked metal fatigue fracture.
6, osteoporosis: liquid steel in the cooling process, due to the volume contraction and a tiny pore of called osteoporosis.
Scattered scattered tiny pore called ordinary osteoporosis.
Scattered tiny pore in the center of the steel parts referred to as the center of osteoporosis.
Osteoporosis reduces the density of steel, landed the mechanical properties significantly, reduce the use of the bearing life.
