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Common problems and solving skills annealing

Author:   Date:2013/10/24
Annealed steel will soften hardened steel will harden , comparison, such as to impose "normalization" process , the obtained organized lamellar pearlite , can effectively improve the machinability of the steel and abrasion resistance, while both will not produce cracks , less deformation and easy operation . However, treatment is more difficult to normalize a heat treatment technology, because the way it uses air cooling is affected by many factors that affect air cooling effects, such as summer and winter, the cooling effect is different workpiece size of the air-cooling rates are different, and even the wind also affect the cooling rate. Therefore normalization process to use a variety of methods to maintain uniformity , can use shade, curtain , potholes , fans, etc. .
 Normalization of the difference between dealing with annealing
Vega normalization process heat to A3 or Acm points or more points 40 ~ 60 ℃ maintained for some time, the steel tissue becomes uniform austenite structure after the still air cooled to room temperature, the heat treatment process. For sub-eutectoid steel , the availability of grain refinement purposes have good strength and toughness ; right eutectoid steel , the iron can prevent snow Voss Tiantie Jing Ming carbon grain boundary precipitates form a mesh to reduce the toughness .
Fully annealed steel main purpose is to soften and improve the machinability of steel and its heat treatment process is heated to a point A3 above 20 ~ 30 ℃ ( sub-eutectoid steel ) or A1 point above 30 ~ 50 ℃ temperature retention time, so that the formation of fully austenitic Organisation ( or austenite plus snow Ming carbon tissue ) , the A1 point below 50 ℃ so full pearlite metamorphosis occurs , is to soften the steel . Another stress relief annealing is in the abnormal points below 450 ~ 650 ℃ heated for a period of time slowly cooled to room temperature , remove the steel inside the cutting , stamping, casting , welding residual stress produced by the process .
How to eliminate the residual stress in the workpiece ?
Stress relief annealing is in the abnormal points below 450 ~ 650 ℃ heated for a period of time slowly cooled to room temperature , remove the steel inside the cutting , stamping, casting , welding residual stress produced by the process . Of carbon steel , the heating temperature of the reference 625 ± 25 ℃; the steel , the heating temperature of the reference 700 ± 25 ℃. Retention time will vary, for steel , the hold time for each 25mm thickness holding for one hour ; against steel , the hold time for each 25mm thickness holding for two hours , after cooling rate of 25mm per order 275 ℃ / h of cooling rates less .
How to prevent heat distortion ?
Prevent the occurrence of thermal deformation , preferably slowly heated and implementing the warm up process . Common steel preheat temperature is selected , according to the following criteria selected preheat temperature: ( 1 ) in the following as the preheating temperature transformation point , for example, ordinary steel is about 650 ~ 700 ℃, high-speed steel in the 800 ~ 850 ℃ or so. ( 2 ) to about 500 ℃ as the preheating temperature . ( 3 ) two-stage preheating , the first paragraph in about 500 ℃ for preheating, after a period of time sufficient warm-up , when the preheating temperature is increased to the A1 transformation point or less. ( 4 ) three-stage preheating, for containing high levels of large steel alloys , such as high-speed steel , sometimes at 1000 ~ 1050 ℃ for third preheating .

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