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Tempering quenching of species

Date锛2013-10-29 9:34:18

1,270 ℃ ~ 350 ℃ embrittlement : Also known as quenching and tempering resistance, mostly in carbon and low alloy steels.
2,400 ℃ ~ 550 ℃ embrittlement : usually constructed with steel and then this temperature range is easy to produce embrittlement .
3,475 ℃ embrittlement : refer in particular to the Cr content exceeds 13% of the ferritic stainless steel at 400 ℃ to 550 ℃ tempering treatment applied between , the resulting increase in hardness and embrittlement phenomenon particularly noticeable at about 475 ℃ forward .
4,500 ℃ ~ 570 ℃ embrittlement : common working tool steel , high speed steel and other materials, will precipitate carbides at this temperature , resulting in secondary hardening , but it can also lead to increased brittleness .
( 3 ) of alloying elements on the impact of changes in temper
Hardened alloy steel for tempering , its organizational transformation and carbon steel similar to However, due to alloying elements added to the tempering transition has the following characteristics:
1, to improve the stability of hardened steel hardened tempered steel during tempering , resisting strength, hardness decreased ability is called tempering stability .
2 , resulting in secondary hardening hardening steel in the temperature range of 500 ~ 600 ℃ tempering , the hardness increased the phenomenon known as secondary hardening .
3 , resulting in temper brittleness hardened alloy steel tempered at a temperature range occurs when dropped dramatically impact toughness of the phenomenon , known temper brittleness.
( 4 ) cast iron tempered and quenched
The so-called material is quenched from the austenite region temperature very fast rate will lower the temperature in order to prevent the formation of pearlite or sorbite , district cooling from the austenite temperature because time is too short to Ms carbon diffusion does not occur , basic directly into martensite , this organization is very hard but very brittle , so that it can be softened tempering method , in order to improve the toughness , so after return at different temperatures can be obtained with different hardness , strength and toughness combination. The so-called hot-melt quenching or quenching constant , ie salt and metal bath quenching , resulting in an intermediate phase or bainite organizations , often in cast iron quenching and tempering treatment is spheroidal graphite cast iron, gray cast iron for terms , compared with no special significance , a maximum of gray cast iron to improve the abrasion strength quenched considered only when , in fact, this result can be reached by surface treatment . The spheroidal graphite cast iron , the treatment after quenching and tempering , the cast can be obtained with the same intensity or normalization process , but with a higher yield strength , to give greater flexibility , in particular to get a high toughness, as after quenching and tempering, the bases containing high carbon , while in this case than in the Bayesian tissue comprising a surface hardening treatment is easy .
    If the air-cooled , non-alloy and low alloy cast iron for the curing is not high enough , some of the liquid must be quenched in order to avoid thermal cracking occurs when the quenching , quenching liquid used is preferably oil or a suspension of avoid the use of water from liquid , the quenching temperature gradient inside the casting , and because of the time difference , as caused by the formation of martensite volume change rate is not the same , while the casting increases the internal stress , it is thermal cracking easily formed or formed in casting high internal stresses , in this case , the oil bath temperature should be increased to between 50 ~ 100 ℃ , to avoid the formation of stress , the thickness difference is large the castings , in particular, the thicker part carefully , first toward the quench liquid , and so can reduce the thermal stress suffered by the thinner portion , and the fluid oil must be stirred , or to make it flow , or the casting in the quench fluid stop shaking.
    Cast iron quenching temperature should be 820 ~ 920 ℃ , and the average temperature of the most commonly used plant is between 850 ~ 900 ℃ . When the quenching temperature is too low , it will result in lower carbon content of austenite after quenching is relatively soft, while the formation of martensite strength is relatively low , on the contrary if the quenching temperature is too high , the austenite carbon is too high , quenching occurs when increased risk of thermal cracking , opportunities of forming residual austenite becomes large .
After quenching the cast iron is actually high brittleness , containing both high internal stress , in order to improve its hardness and toughness after tempering treatment, the process similar to steel , the heating rate should be less than 100 ℃ / h , tempering temperature to be between the 450 ~ 600 ℃ , tempering time is about 4 hours , tempering time is too long or the temperature is too high , it will be a lot of strength and hardness decreased , but can improve flexibility , longer at lower temperatures by time for tempering , can result in fairly uniform tempering effect, while the characteristics of the casting are also quite uniformly distributed , in order to prevent the re- occurrence of internal stress , especially for complex castings , tempered to be gradually cooled to below 200 ℃ .


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