Controlled cooling and rapid spheroidization process of high carbon chromium bearing steel bar after rolling
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/*728*90 created on 2018/5/16*/ var cpro_id = "u3440131"; Home>Bearing knowledge>High carbon chromium bearing steel bar after rolling control and cooling spheroidizing process Controlled cooling and rapid spheroidization process of high carbon chromium bearing steel bar after rolling
1 Experimental method High-carbon chromium bearing steel bar after rolling control and cooling spheroidization process experiment is carried out under normal production rolling conditions; experimental material is GCr15 bearing steel; chemical composition Note: experimental steel is Φ55mm round steel . /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
Under normal rolling conditions; Φ50mm GCr15 bearing round bar is cut into a fixed length and then traverse; rapid cooling by primary and secondary water cooler. When the steel is water-cooled at the beginning; the lowest temperature is 860 ~ 870 °C; the highest temperature is 920 °C or so. The cross-section temperature curve of the round steel after 2 times of rapid cooling is shown in Figure 1. When the outer surface temperature of the round steel is 920 °C, it enters the 1# water cooler; the external temperature of the water cooler drops to 400-500 °C; After; steel temperature returns to 600 ~ 700 °C; enter 2 # water cooler for secondary cooling. Out of 2 # water cooler steel appearance temperature is usually 400 ~ 460 °C; through the roller to the collection of steel temperature rise back to 550 ~ 650 °C; then the steel temperature drops. The experimental results indicate; each time in the water cooler fast cooling; the steel surface temperature should not be lower than 300 °C; to avoid the martensitic arrangement in the steel surface.
The air-cooled material and the controlled cooling material rolled by the same rolling process are annealed in a continuous annealing furnace or simulated by successive annealing criteria for spheroidizing annealing. Arrangement and function comparison. 2 Experimental results and analysis 2. 1 Cooling water pressure and The effect of steel red return temperature on the arrangement Φ50mm round bar after water cooling, the highest return red temperature and cooling water pressure contact as shown in Figure 2 (885 °C start water cooling). When the steel speed must be maintained; with cooling water The pressure is increased; the temperature of the steel returning red is lowered; the cooling can be increased.
The experimental results indicate that when the steel temperature is 885 °C and the rapid cooling is started; only one quick cooling is used; the steel red return temperature reaches 780 °C; it is checked by metallographic and electron microscopy; it can be seen at the edge of the circular section and 1/4 The flaky and anomalous pearlite and a few reticulated carbides are obtained at the diameter; the middle part is the fine-grained pearlite and the reticulated carbide. The secondary hot-cooled bearing steel rod; the maximum red return temperature is 630-660 °C; its side and diameter 1/4 are abnormal Sorbite and some spherical or hemispherical carbide. The single local has very fine and extremely thin network carbide. The heart is arranged as intermittent fine-leaf pearl Body, sorbite, with a few fine mesh carbides.
2. The effect of cooling water pressure on the reticulated carbide of bearing steel bar is Φ55mm bearing steel round bar as an example; the rapid cooling at 870 °C is added with water pressure; the metallographic sample has a lower grade of carbide carbide; Not large. The mesh carbide grade is less than 2. 5 (YJZ-84); the mesh is usually presented in the heart.
2.3 The effect of the initial cooling temperature on the bar network carbide is marked; the cooling temperature increases with the opening; the mesh carbide level decreases; above 875 °C; the opening cooling temperature does not affect the mesh carbide separation. Significant; this is because the meshed carbides in the bearing steel have a temperature of between 960 and 700 °C under deformation conditions; the amount of separation is lower at high temperatures; the temperature scale is from 700 to 750 °C; the carbides are most severely separated. If the temperature of the steel after the high rolling is cold, it can be separated by the carbide in this temperature range.
Thus; if the water is cooled immediately after rolling; the bar is cooled to above 800 °C; the grain growth can be avoided; the deformed austenite grains are further refined. Because the deformation promotes the carbide separation temperature, Arcm progresses; After that, the temperature of Arcm is lowered; the amount of carbides is reduced. Together with the austenite grain refinement; the carbides are separated and thinned. When the second quick cooling is carried out; the temperature of the steel can be lowered to 650 °C. Below; it can hinder the further separation of the network carbide.
If it is a rapid cooling, the reddening temperature is in the temperature range where the carbide is strongly separated; there is no secondary cooling immediately; the steel rod is slowly cooled in this temperature range; then a coarse mesh carbide arrangement is obtained. .
The effect of the stop temperature of the rapid cooling on the reticulated carbide grade after the rolling is very important process parameter; it determines the self-returning temperature of the different section size steel after cooling The concave and convex. After rolling the Φ34～55mm bearing steel bar, it is quick to cool to the external temperature of 450~500 °C; after the red return, its steel temperature can be controlled at 550~650 °C; then air cooling; can be compared Arrangement of ambition.
It is necessary to use the repeated cooling process for large-section round steel; together, it must be separated between the two water cooling; the intention of returning to the steel surface to return red; and preparing for the next cooling; the reddish temperature of the reddish temperature depends on the demand Controlled cooling process guidelines.
For example, rolling Φ55mm GCr15 bearing steel bar; when the opening cooling temperature is 893 °C; after one cooling, the steel red return temperature is 690 °C; after secondary cooling, the red return temperature is 640 °C. The steel is cooled between 893-700 °C The speed is faster; the temperature difference between the surface and the surface is better than that of the screen. The rolled carbide has a reticulated carbide grade of 2. 5; and the surface is relatively uniform. The cooling temperature of the other rolling stock is 925 °C; After one water cooling, the red return temperature is 760 °C; after the second water cooling, the maximum red return temperature is 680 °C; because it stays at 700-760 °C in one water cooling to the second cooling, it is in the strong separation of carbides. Temperature; thus the reticular carbide grades along the section reach level 4.
2.5. The effect of the controlled cooling process on the spheroidizing annealing process. Immediately after rolling, the intention of rapid cooling is in addition to the reduction of the network carbide grade; another important intention is to avoid the austenite grain growth after deformation; Coarse pearlite pellets; together increase the degree of subcooling to reduce the temperature of Arcm and Ar1; to reduce the interlamellar spacing of pearlite; and can form degraded pearlite and degenerate sorbite; facilitate spheroidization; shorten spheroidization Annealing time.
In the experiment, the spheroidizing annealing process of GCr15 bearing steel controlled cooling material and air-cooled material was studied; and compared.
The chilling material used for spheroidizing annealing is selected from steel materials under different controlled cooling conditions as experimental materials and air-cooled experimental materials; the controlled cooling process is as follows:
(1) The reddening temperature after secondary water cooling is 630 °C, 640 °C and 660 °C, respectively.
(2) After one water cooling, the reddening temperature is 780 °C water-cooled material.
(3) Air-cooled materials.
The above three types of steel have the same rolling process; the spheroidizing annealing test is carried out in a 98m long continuous annealing furnace; spheroidizing annealing is performed at different steel walking speeds. In order to modify the temperature standard of each part of the spheroidizing annealing; Heating furnace; according to the temperature criterion of each section of the continuous heating furnace and the different steel walking speed to simulate the spheroidizing annealing process of the continuous furnace. The steel walking speed in the furnace is 3m/h, 4m/h, 5m/h, 6m/h and 7m/h.
The experimental results show that the spheroidal annealing of the air-cooled material at a steelmaking speed of more than 4m/h cannot obtain a qualified spheroidizing arrangement. The controlled cooling material with a red return temperature of 630 °C is selected; the steel moving speed is from 5m/h to 7m/h. The annealing can obtain the qualified spheroidization arrangement (2~2. 5). On the contrary; if the steel is still annealed after the water cooling at 3m/h; the spheroidizing arrangement is roughened; reach 3. 5-6 Grade. When the water return temperature is higher than 640 °C; the steel speed is more than 5m/h; the spheroidization arrangement after spheroidization is unqualified (less than 2). The experiment indicates; the spheroidizing annealing time of the water-cooled material is faster than the spheroidization of the air-cooled material. The annealing time is significantly shortened.
In the experimental plan; the heating temperature of the spheroidizing annealing was reduced from 820 °C to 800 °C; and the two ends of the furnace tails of 690 °C and 660 °C were shortened; the length of each section was shortened from 1h to 37 minutes to 39 minutes. The cooling rate was accelerated. The steel speed is 5m/h; the total annealing time is 6h 38min, the steel moving speed is 6m/h, the total annealing time is 5h 38min, the steel moving speed is 7m/h; the total annealing time is 4h 46min.
The results indicate that the spheroidizing annealing arrangement of air-cooled materials with a speed of more than 5m/h is below level 2; the chilled material after primary cooling is only spheroidized with a spheroidizing arrangement of 5m/h. After the subcooling, the water-cooled material is spheroidized at a speed of 6m/h, and a qualified spheroidizing arrangement can be obtained. The pre-arrangement before annealing at a red-back temperature of 630 °C is better; even if the steel is spheroidized at a speed of 7 m/h; The spheroidal arrangement is also level 2.
Because the arrangement of the chilled material after rolling is anomalous with a thinner anisotropy and lamellar spacing. The carbon atom dispersion journey is short during spheroidizing annealing; the carbide is simply dissolved; the number of carbonized material points remaining after dissolution is large; During the cooling process, the carbide is separated and supplied to more parts; it can be selected to be faster than the speed of cooling. Together; the interlayer interval. Envy 缑嫦嘤υ龆啵 缑婺 缑婺 黾 黾 ç° ç° ç° é¸¬ 鸬 鸬 鸬 鸬 åƒSuffering from uranium and plutonium. After rolling, the chilled material is manipulated; the cementite in the pearlite is intermittent; it becomes hemispherical; it is beneficial to the spheroidization process;
2.6 The effect of controlled cooling on the function of the bearing steel bar The hardness of the chilled and air-cooled material is increased with the progress of the spheroidizing speed; as shown in Figure 3. Under the same steel speed; The hardness of the chilled material is lower than that of the air-cooled material; because the speed of the steel is improved; the annealing time is shortened; the spheroidizing arrangement of the steel is lowered; therefore, the hardness of the steel is increased; and the chilled material is simply spheroidized than the air-cooled material; the same annealing time; After the material is annealed, the spheroidization arrangement level is higher than that of the air-cooled material. The carbide particles are uniform in size; the dispersion is dispersed; therefore, the hardness of the controlled cooling material is low.
The touch fatigue life of the chilled material is higher than that of the air-cooled material; Table 2 shows the results of the touch fatigue life of the Φ50 mm GCr15 bearing steel raft and air-cooled annealed material.
Because the carbide particles of the annealed material after Φ50mm bearing steel water cooling are finer than the carbide particles of the annealed material after air cooling; the former has a diameter of 0.53 μm, while the latter has a thickness of 0.63 μm and the carbide particles are evenly spaced by 1.28 μm and 1 respectively. 34μm.
3 Determination of GCr15 bearing round steel; diameter in the range of Φ34 ~ 55mm; select the appropriate post-rolling rapid cooling process; can reduce the network carbide grade; make it less than 2. 5 grade. Shorten the spheroidizing annealing time to obtain the fit YJZ -84 standard 2 to 3 spheroidal arrangement; therefore; large-section bearing steel bars use post-rolling rapid cooling process and rapid spheroidizing annealing process; both theoretically and theoretically marked as a leading rolling production Process; should be implemented.
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