Purity analysis of GCr15 Bearing Steel in the tria

2022-09-22
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Purity analysis of GCr15 Bearing Steel in trial production of converter

Abstract: GCr15 bearing steel is produced by converter, refining (lf+rh) and rectangular billet continuous casting. Take samples at each steelmaking process stage to detect the changes of non-metallic inclusions in quantity, morphology and composition, and analyze the purity of GCr15 bearing steel

now Sumitomo of Japan, tyssen of Germany and Kawasaki iron company of Japan have successively developed the production process of smelting GCr15 bearing steel with molten iron through converter, and cooperated with LF ladle refining and RH vacuum treatment process to improve the purity of molten steel to produce GCr15 bearing steel. Benxi Iron and Steel Co., Ltd. has excellent mineral resources, and all kinds of harmful impurities are very low, which provides a guarantee for the production of high-quality steel. Benxi Iron and Steel Co., Ltd. built a four strand rectangular billet caster in the steel plant in 2005, and has successfully pilot produced GCr15 bearing steel. In order to understand the purity of GCr15 Bearing Steel in each smelting stage, samples were taken from converter, LF refining, RH vacuum treatment, tundish and continuous casting slab respectively to analyze the state of non-metallic inclusions

1. Smelting process of GCr15 bearing steel

process route: hot metal pretreatment → it is planned to launch the government funded R & D project Maxim converter smelting → LF ladle refining → RH vacuum circulation degassing → rectangular billet continuous casting

2. GCr15 bearing steel smelting process steel purity analysis

2.1 non metallic inclusion state after converter smelting

after converter smelting, take samples in molten steel to analyze the state of non-metallic inclusions: the distribution is relatively concentrated, there are more large-size cluster non-metallic inclusions, and a few large-size massive non-metallic inclusions. The cluster composition is Al2O3-SiO2, and the massive inclusion composition is CaO-Al2O3. All iron charging and single slag smelting methods are adopted for converter smelting. Lime and refining slag are added during tapping to improve the ladle top slag. Through the detection of inclusions, the size of non-metallic inclusions is relatively large, and the treatment is not very perfect

2.2lf ladle refining non-metallic inclusion status

after LF ladle refining, take samples in molten steel to analyze the status of non-metallic inclusions: dispersed distribution, a small number of clustered non-metallic inclusions, individual large-size spherical non-metallic inclusions. The cluster composition is CaO-Al2O3, the spherical inclusion composition is cao-al2o3-mgo, and the Zr element is brought from the sampler. According to the constant oxygen value, the "white slag" process is applied to adjust. After refining, the inclusions change, and the size of clustered non-metallic inclusions is significantly reduced. However, due to the combination of deoxidation products and slag, the size of non-metallic inclusions is larger according to the above definition. The inclusion control of refining process needs to be improved

2.3state of non-metallic inclusions after RH vacuum cycle degassing

after RH vacuum cycle degassing, take samples in molten steel to analyze the state of non-metallic inclusions: dispersed distribution, mainly small-size non-metallic inclusions, and a few large-size massive non-metallic inclusions. The composition of the larger size inclusion is Cao, and the output of white paperboard is about 14.51 million tons; The output of cultural paper excluding coated paper, household paper, paper and special paper is 28.31 million tons -al2o3, and the majority of small-size spherical inclusions are al2o3-mgo-sio2-cas. Cluster like inclusions were not found at this stage, but due to the presence of 15.8 μ The inclusion of about M indicates that the treatment of molten steel needs to be improved in the refining stage

2.4 the state of non-metallic inclusions in the water of Zhongbao steel

the state of non-metallic inclusions in the water of Zhongbao steel is analyzed by sampling: scattered distribution, a small number of small-size clustered non-metallic inclusions, most of which are small-size spherical inclusions. The composition of small-size non-metallic inclusions is al2o3-mgo-cao-k2o. The small-size cluster inclusions detected here are caused by the sampling process, which is formed in the gap between grains

3. Quantitative metallographic analysis of non-metallic inclusions in rectangular billets

analyze the state of non-metallic inclusions at different thicknesses of rectangular billets. Samples were taken at 10mm, 1/4 thickness, center and 3/4 thickness from the rectangular billet to the upper surface, and then the number and size of non-metallic inclusions were counted with 100 sampling fields under 500 times. It can be seen from the slab that the non-metallic inclusions are dispersed and small in size. The non-metallic inclusions are not the composite inclusions composed of Al2O3 MgO SiO2 CAS and TiO, which are the components of the oil return valve of the manual oil delivery valve

4. Conclusion

1. In the process of steel smelting, the purity of molten steel is constantly improving

2. Through the analysis of non-metallic inclusions in each process, the composition of the main inclusions is mainly Al2O3 MgO Cao. The total number of non-metallic inclusions is relatively small, and the overall size is 10 μ Small size inclusions below m are dominant; There are some large-size inclusions, mainly composed of Al2O3. It shows that the size control level of inclusions needs to be improved, and the treatment after deoxidation needs to be further adjusted

3. because there is a very small amount of K2O, which is caused by a small amount of protective slag left in the molten steel, attention should be paid to the control of protective slag in the smelting process of molten steel

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