The metallurgical process of the induction furnace is essentially different from that of the cupola melting. The induction furnace is used to melt the gray cast iron. The molten iron is more hot than the cupola, and the melting and holding time is long. The same chemical composition, casting the same casting castings, the hardness of the castle than the high hardness, cold white mouth tend to large, shorter graphite length, and easy to produce D, E-type graphite, molten iron fluidity is poor, shrinkage increase Large, easy to cause a variety of casting defects (stomata, cold separation, shrinkage, shrink loose, etc.). I plant since 2013, the use of induction furnace production castings since the production is still used in the early stage with the cupola similar to the smelting process, pre-production castings due to castings shrinkage, shrinkage and the process of hard material and other reasons caused by the casting scrap rate More than 10% in 2014, I plant ash cast iron with pretreatment agent SiC pretreatment, add silicon carbide, the graphite shape becomes shorter and shorter, spacing larger, increase the number of eutectic groups to improve the strength and hardness of cast iron, After the frying of molten iron, improve the processing performance of castings.
First, the production conditions
The use of 3t medium frequency induction furnace smelting, charging ratio stabilization: 20% of pig iron, scrap 40%, back to the charge 40%, adding the right amount of carbon agent, ferrosilicon, ferromanganese, SiC, FeS adjust the chemical composition of molten iron, SiC Time for the molten iron melting more than half of the time to join, tensile strength and hardness are Ф30mm single cast tensile test rod, the test bar for the furan resin sand shape.
Second, the test results and analysis.
1. On the shape of graphite
As shown in Fig. 1 and Fig. 2, the samples are sampled as the core of the tensile test.
Figure 1 Chemical composition: wC = 3.18%, wSi = 1.85%, wMn = 0.83%, wP = 0.043%, wS = 0.078%, without SiC pretreatment of molten iron. Graphite form: flake graphite distribution is A-type, folder a small amount of C-type graphite, graphite length of 4 to 5.
Fig.2 The chemical composition of wc = 3.20%, wSi = 1.83%, wMn = 0.86%, wP = 0.043%, wS = 0.076%, and adding 0.8% SiC to pretreatment of molten iron. Graphite form: flake graphite distribution is A-type, folder a small amount of C-type graphite, graphite length of 5 to 6.
2. On the hardness of cast iron tensile strength
To the furnace smelting HT250 production test, the same batch of ingredients to the same as possible to ensure that the chemical composition of the same, iron liquid temperature 1515 ~ 1525 ℃, pouring temperature of 1380 ~ 1430 ℃, the bottom of 0.3% Silicon Barium inoculant Treatment, detection of chemical composition and the corresponding strength and hardness in Table 1. The experimental results show that the mechanical properties and hardness of the iron solution pretreated by SiC are different from those of the untreated iron liquid under the same melting conditions and similar chemical composition.
3. On the processing performance of cast iron
As shown in Figure 3, the piece is 0L59011 left cover is the company's product T165 parts. Material HT200, weight 45kg. The main wall thickness of the piece is 8 ~ 10mm, in the early production process, we mainly through the high silicon ratio of the method to improve its processing performance. As the induction furnace induction furnace smelting cast iron, undercooling large, white mouth is strong, under the same carbon equivalent conditions, with induction furnace smelting cast iron and cupola smelting compared to eutectic transition when the degree of subcooling Much of the castings in the early production of the casting process in the majority of castings for the edge of the castings of white mouth, processing more difficult, only the casting annealing to meet the machining requirements, we improve the carbon equivalent and The use of high silicon ratio of the method did not receive good results. Then we tested the SiC pretreatment process and the high silicon to carbon ratio. The chemical composition of the piece was consistent with the original wC = 3.20% ~ 3.30%, wSi = 2.20% ~ 2.30%, wMn = 0.80%, wP≤0.50%, wS = 0.050% ~ 0.10%, the addition amount of SiC pretreatment agent is still maintained at 0.8%. We have the following two batches of 40 batches for processing and tracking, Of the phenomenon, and processing performance is good, completely relieved the hardening of the machine processing materials.
Third, the conclusion
(1) Pretreatment of molten iron with SiC in the process of melting gray cast iron in induction furnace can improve the morphology and size of graphite.
(2) Pretreatment of molten iron with SiC in the process of melting gray cast iron in induction furnace can improve the tensile strength and hardness. Under the same conditions, the tensile strength can be increased by 20 ~ 30MPa and the hardness can be increased by 10 ~ 25HWW.
(3) Pretreatment of molten iron with SiC in the process of smelting gray cast iron in induction furnace can significantly improve the cutting performance and reduce the tendency of casting white mouth.