1. Effect of particle size of carburizing agent on absorption rate
The carburizing process using carburizing agent includes dissolution and diffusion process and oxidation loss process. The particle size of the carburizer is different, the dissolution and diffusion rate and oxidation loss rate are different, and the absorption rate of the carburizer depends on the comprehensive effect of the dissolution and diffusion rate and oxidation loss rate of the carburizer. In general, the carburizer particles are small, the dissolution rate is fast, and the loss rate is high; the carburizer particles are large, the dissolution rate is slow, and the loss rate is small. For example, in a 110 kg high frequency induction furnace, the carburizer with particle size of 015-018 mm dissolves rapidly. Most of the carburizer has been dissolved in the molten iron before the oxidation loss. Only a small part of the carburizer is lost, so the absorption rate is high. In the 60 kg induction furnace, the diameter and capacity of the furnace are larger, the particle size of the carburant is 015-018 mm, and the relative diameter and capacity of the furnace are too small, the loss rate is fast and the absorption rate is low; while the particle size of 116-312 mm is relative to the diameter and capacity of the furnace, the dissolution rate of the carburant is faster, the loss rate is slower, the dissolution plays a leading role, and the absorption rate is higher. . Therefore, the size of the carburizer is related to the furnace diameter and capacity. Generally speaking, the diameter and capacity of the furnace is large, the size of the carburizer is larger; conversely, the size of the carburizer is smaller.
2. The influence of adding amount of carburizing agent on absorption rate.
Under certain conditions of temperature and chemical composition, the saturation concentration of carbon in molten iron is certain. The dissolution limit of carbon in cast iron is [C%]=113+010257 T-0131 [Si%]-0133 [P%]-0145 [S%]+018 [Mn%] (T is molten iron temperature). At a certain saturation, the more the carburizer is added, the longer the dissolution and diffusion time is required, the greater the corresponding loss, and the lower the absorption rate.
3. The effect of temperature on the absorbance of carburant.
From the point of view of kinetics and thermodynamics, the oxidation of molten iron is related to the equilibrium temperature of C-Si-O system, i.e. the reaction of O in molten iron with C and Si is as follows: [Si]+2 [O] = SiO2 (s), [C]+ [O] = CO (g), SiO2 (s) + 2 [C]+ Si] + CO (g). G 0T = 549359 - 309145 T (3) LG [Si] [C] 2 = 276T + 15147 (4) The equilibrium temperature T varies with the target C and Si content, as shown in equation (4). The equilibrium temperature can be calculated by equation (4). When the composition of iron liquid is 219 ~ 311C and 110 ~ 112Si, the equilibrium temperature is about 1380 degrees. When molten iron is above equilibrium temperature, carbon oxidation is preferentially produced, and C and O generate CO and CO2. In this way, the oxidation loss of carbon in molten iron increases. Therefore, when the equilibrium temperature is above, the absorption rate of carburant decreases. When the carbonization temperature is below the equilibrium temperature, the saturated solubility of carbon decreases, and the dissolution and diffusion rate of carbon decreases, so the yield is also lower. Therefore, when the carbon temperature is at equilibrium temperature, the absorption rate of carburant is the highest. However, in the laboratory and production process, the temperature of molten iron will always be affected by many factors, so the actual temperature of carburization in the calculated equilibrium temperature fluctuates about 10 degrees centigrade.
4. The influence of iron stirring on the absorption rate of carburant.
The stirring time is long and the absorption rate is high before the carburizing agent is completely dissolved. Mixing is conducive to the dissolution and diffusion of carbon, reducing the carburizing agent floating on the surface. Mixing can also reduce the time of carburizing and heat preservation, shorten the production cycle and avoid the loss of alloy elements in molten iron. However, too long stirring time not only has a great impact on the service life of the furnace, but also increases the carbon loss in molten iron after the carburizer dissolves. Therefore, suitable iron stirring time should be guaranteed to completely dissolve the carburizing agent. Five. The influence of chemical composition of iron melt on the absorption rate of carburant.
When the initial carbon content increases by 0.1%, the absorbency of carburant decreases by 1%-2%; when the silicon content increases by 0.11%, the absorbency of carburant decreases by 3%-4%; when the sulfur content increases by 0.1%, the absorbency of carburant decreases by 1%-2%; when the manganese content increases by 0.1%, the absorbency of carburant increases by 2%-3%. Therefore, when the initial carbon content in molten iron is high, the absorption rate of carburant is slow, the absorption amount is small, the burning loss is relatively large, and the absorption rate of carburant is low under a certain dissolution limit. When the initial carbon content of molten iron is low, the opposite is true. In addition, silicon and sulfur in iron melt impede carbon absorption and reduce the absorbance of carburizing agents. Manganese can help carbon absorption and increase the absorbance of carburizing agent. As far as the extent of impact is concerned, silicon is the largest, followed by manganese, and carbon and sulfur are less affected. Therefore, in the actual production process, we should increase manganese first, then increase carbon and finally increase silicon.