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Defective heating and control technology

Defective heating and control technology

Date:2013/10/28 9:52:03

A, overheating
We know that the heat treatment process most likely to result in overheating of the heating coarse austenite grains , the mechanical performance of the part .
A general overheating : heating temperature is too high or too long holding time at high temperatures , causing the austenite grain coarsening called overheating. Coarse austenite grains can cause decreased strength and toughness , brittle transition temperature, increases the deformation hardening tendency to crack . And the reason is cause overheating furnace instrumentation control or mixing ( often understand processes occurring ) . Organizations can overheat after annealing , normalizing or tempering after repeated under normal circumstances re- austenitizing the grain refinement .
2 Genetic fracture : the organization of overheating steel reheating after quenching , although make austenite grain refinement , but sometimes still appear coarse granular fracture. Generated more controversy fracture genetic theory is generally believed that the heating temperature is too high but had sort of debris leaving the MnS dissolved in austenite grain and enriched in the interface, and cooling of these inclusions will precipitate along the grain interfaces , by the shock easily fracture along the coarse austenite grain boundaries .
3 thick tissue Genetic : There are coarse martensite , bainite, Wilcoxon tissue piece of steel re- austenitizing when heated to a slow conventional quenching temperature , and even much lower , its austenite grain coarse grains is still a phenomenon known as hereditary organization . To eliminate hereditary thick tissue , can be repeated intermediate annealing or tempering treatment .
B, over-burning phenomenon
Heating temperature is too high , not only causing austenite grain coarsening , and the emergence of local grain boundary oxidation or melting , causing grain boundary weakening , called over-burning . Steel had seriously deteriorated after burning properties , quenching to form cracks. Burnt tissue can not be restored , only to be scrapped. So at work to avoid the occurrence of over-burning .
C, decarburization and oxidation
Heating steel , the surface of the carbon with the medium ( or the atmosphere ) of the oxygen, hydrogen, carbon dioxide and water vapor react reducing the surface carbon concentration is called decarburization off after quenching steel surface hardness, fatigue strength and resistance to grinding is reduced, and the surface is easy to form to a residual tensile stress crack surface mesh .
When heated , the surface of iron and alloy steel, the element with the medium ( or the atmosphere ) of the oxygen, carbon dioxide , water vapor produced by the reaction of the oxide film is called oxidation. High temperature ( generally above 570 **  ) oxidation of the workpiece dimensions accuracy and surface brightness deterioration , having an oxide film of poor hardenability steel hardened soft spot prone .
In order to prevent oxidation and decarbonization reduction measures are: the surface coating, with a stainless steel foil heat sealed packaging , the use of salt bath furnace heating , heating using a protective atmosphere ( inert gas , such as purified , carbon potential control of the furnace ) , the flame burner ( the furnace gas was reducing )
D, hydrogen embrittlement
High- strength steel is heated in a hydrogen-rich atmosphere, ductility and toughness when the phenomenon known as hydrogen embrittlement . Hydrogen embrittlement occurs through the addition of hydrogen workpiece handling ( such as tempering, aging , etc. ) can also eliminate hydrogen embrittlement , vacuum , low hydrogen atmosphere or an inert atmosphere heating to avoid hydrogen embrittlement .

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