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| 5CrMnMoShaft heat treatment technology was studied |
| Time：2015-12-04 Source：《Heat Treatment》Magazine Views：3484 |
1 5 crmnmo
5 crmnmo steel, with 5 crnimo similar performance, suitable for making requires high strength and high wear resistance of forging die and other parts. 5 crmnmo steel good hardenability and the relatively stable austenite.
(1) the chemical composition of the chemical composition of 5 crmnmo as shown in table 1.
The chemical composition of table 1 5 crmnmo mass fraction (%)
C 0.50 ~ 0.60 Si 0.50 ~ 0.60 Mn 1.20 ~ 1.60 Cr 0.60 ~ 0.90 Mo 0.15 ~ 0.30 P 0.030 or less S 0.030 or less
(2) heat treatment point 5 crmnmo heat treatment of critical point as shown in table 2
Table 2 ⒌ CrMnMo heat treatment of critical point (℃)
Ac1 710 Ac3 760 Ar1 650 Ms 220
2 5 crmnmo spindle heat treatment difficulty
(1) the basic situation of 5 crmnmo spindle Mandrel dimension as shown in figure 1, 42 ~ 47 HRC hardness requirements.
(2) 5 crmnmo spindle heat treatment difficulty analysis Parts size is longer, the largest size of Φ 180 x 960 mm, and the shaft up stairs, deformation is not easy to control, and because the parts is too long, can't use charcoal box way of protection, easy oxidation and decarburization phenomenon in the heat treatment process. If more oxide skin, the surface oxidation can cause surface rough, affect the cooling uniformity, caused by uneven hardness after quenching parts scrap; Decarburization can cause insufficient hardness after quenching, or a soft point, affect the parts performance. If on the other hand, for 5 crmnmo steel quenching cooling time is too long, prone to crack, cooling time is too short, only get austenite, can not meet the performance requirements.
(3) to sum up, the parts quenching has three difficulties: (1) prevent mandrel oxidation decarburization; (2) to ensure that the spindle quenching deformation in allowed range; (3) strict control over the precooling of spindle and oil cooling time.
Three heat treatment process
(1) class and operation personnel issue to study the parts heat treatment process, analysis of possible problems (such as the position of deformation, deformation uniformity, hardness, etc.). Heat treatment in order to ensure the construction smoothly and can achieve the ideal effect, we proposed the following solution heat treatment.
(2) the plate made of Q235 steel after 5 mm protection plate, plate size: 1200 mm * 200 mm * 250 mm (length x width x height). Plate for spare parts, and placed on parts of charcoal protection.
(3) the heat treatment process Profit in order to eliminate the parts in the mechanical processing processing, and to avoid the thermal stress caused by rapid heating, artifacts in 650 plus or minus 10 ℃ heat preservation after 1.5 ~ 2 h preheated continues to heat up to 860 plus or minus 10 ℃ insulation 3.5 h, the social security the RJX - 75-9 box-type resistance furnace.
(4) cooling because of 5 crmnmo steel hardenability and the austenite more stability, to reduce the number of parts produced in the process of cooling thermal stress, reduce the deformation and cracking tendency, parts will be released in the air precooling (precooling time is 4 ~ 6 min, parts about 730 ℃ or so), and then into the N32 by mechanical blending oil cooling, open pump circulation, lead to the compressed air at the same time. Parts in oil cooling after 25 ~ 35 min took out (to prevent parts in Ms speed too fast cause cracking under cold, cold parts in oil until 220 ℃, and probably out within 150 ~ 200 ℃).
(5) check the deformation after tempering oil deformation (< 0.5 mm), hot correction, immediately into the tempering furnace. Putting the parts into HVS100 tempering furnace, sphere (280 + 10) 2 ~ 2.5 h, 450 ℃ heat plus or minus 10 ℃ insulation 3.5 ~ 4 h from air cooling. Heat treatment process curve is shown in figure 2.
(6) test Cloth's durometer hardness examination, the result is 2.9 HBd 47 (HRC), conform to the requirements of the drawings.
4 conclusion
(1) quenching process to prevent the spindle oxidation decarburization and guarantee of quenching deformation of spindle in allowed range is the difficulty and key of spindle heat treatment.
(2) in the process of heat treatment, we will strictly control the precooling and oil cooling, quenching and tempering as soon as possible after that.
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