Yan-ping Bao

Separation and Recovery of Phosphorus from P-bearing Steelmaking Slag

In order to recycle the phosphorus from P-bearing steelmaking slag, the influences of magnetic field intensities, slag particle sizes and slag compositions were investigated by magnetic separation experiments. SiO2, Al2O3 and TiO2 melting modification of converter slag was made respectively and phosphorus-rich phase was extracted by magnetic separation. The results show that MgO, MnO, Na2O and CaF2 have little effect on the phosphorus recovery, whereas the addition of SiO2, Al2O3, and Ti2 has great effect on phosphorus enrichment in slag and magnetic separation. With adding the reagent of SiO2, Al2O3 and TiO2, recycled non-magnetic substances are increased obviously and P2O5 content in non-magnetic substances and phosphorus recovery rate are also increased. The phosphorus recovery rates of modified slag No. 8 (SiO2 modification), slag No. 10 (Al2O3 modification) and slag No. 11 (TiO2 modification) are 84.75%, 82.16% and 74.46 %, respectively. Then, most of phosphorus was recycled.

Influence of slag composition on bearing steel cleanness

Abstract Al2O3 and high Al2O3 content composite oxides are the main types of inclusions in aluminium killed bearing steel, and these also have the most significant impact on rolling contact fatigue (RCF) life. The calculation results in the phase diagram by using the FactSage showed that the activity of Al2O3 reached the minimum with the slag composition in a low melting point area at a MgO content less than 5%; a basicity of 5 to 8 and a ratio of CaO/Al2O3 of 1·5 to 2·0 in slag. This slag was most effective in improving the absorption ability of slag for inclusions in bearing steel. By using the experimental slag, the total oxygen could be reduced to 7–10 ppm at Hangzhou Iron and Steel Group Company (HIRGC).

The Composition and Morphology Evolution of Oxide Inclusions in Ti-bearing Ultra Low-carbon Steel Melt Refined in the RH Process

Before deoxidation, the main inclusions were Fe–Mn–O inclusions in Ti-bearing ultra low-carbon steel melt. After 3 min Al addition, the inclusions changed to be granular and spherical Al2O3. Al2O3 cluster, composed of granular and spherical particles with diameter 1–2 μm, formed in 7 to 10 min after Al addition into the melt. Al2O3·TiOx inclusions with the Ti/(Al+Ti) between 0.15 and 0.30 formed 3 min after ferro-titanium addition and Al2O3·TiOx cluster formed because rich [Ti] and poor [Al] regions existed around the ferro-titanium particles and Al2O3 cluster. The Ti3O5 was hard to be formed when acid-soluble aluminum exceeded 0.035% with titanium blow 0.08%. The activity of Ti3O5 in the complex liquid phase inclusions increased remarkably with the decrease of acid-soluble aluminum and increase of titanium.

Effects of Non-metallic Inclusions on Machinability of Free-Cutting Steels Investigated by Nano-Indentation Measurements

In the present paper, the nano-indentation technique is used to investigate the effects of inclusions on machinability of free-cutting steel. Firstly, the hardness, elastic moduli, and load–displacement curves of inclusions are analyzed and compared with matrix. Secondly, the effects of inclusions on machinability are investigated using nano-indentation measurements and thermodynamic calculations. Lastly, errors of nano-indentation measurements and macrohardness tests are analyzed. The hardness of BN is lower than that of MnS. Both of them have lower hardness than those of matrices. Since the hardness of Al2O3 and TiN is higher than that of matrices, they exist as hard spots in steels. The elasticities of BN and MnS are much better than those of Al2O3, TiN, and matrices. BN and MnS which have lower hardness values and better elasticities than matrices can improve the machinability of steel effectively. Special attention should be paid to the effects of inclusions in steel on the results of nano-indentation measurement and macrohardness test.

Physical model of fluid flow characteristics in RH-TOP vacuum refining process

To understand the characteristic of circulation flow rate in 250-t RH-TOP vacuum refining process, the l:4 water model test was established through the bubble behavior and gas holdup in the up-leg to investigate the effects of different processes and equipment parameters on the RH circulation flow rate. With the increases of lifting gas flow rate, lifting bubble travel, and the internal diameter of the up-leg, and the decrease of nozzle diameter, the work done by bubble floatage and the circulation flow rate increase. The expression of circulation flow rate was derived from the regression analysis of experiment data. Meanwhile, the influences of vacuum chamber pressure and nozzle blockage situation on the circulation flow rate were discussed in detail by the bubble behavior and gas holdup in the up-leg. It is necessary to maintain a certain vacuum chamber liquid level in the molten steel circulation flow. Compared with a nozzle with symmetrical blockage in the up-leg, when a nozzle with non-symmetrical blockage is applied, the lifting gas distribution is non-uniform, causing a great effect on the molten steel circulation flow and making the circulation flow drop largely.

Control of the precipitation of TiN inclusions in gear steels

In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10−6 and 29 × 10−6, respectively, during ladle furnace (LF) refining and during the casting process from ladle to tundish. The protective casting is the key to decrease the N content. The results of thermodynamic calculations and a growth kinetics investigation show that TiN formation occurs only when the solidification fraction is greater than 0.533 under the controlled conditions used in this study for the manufacture of 20CrMnTi steel; the radius of TiN particles decreases as the Ti and N contents decrease and as the cooling rate increases. Furthermore, the theory of austenite grains controlled by second-phase particles was analyzed. The elemental analysis results showed that the Ti content was controlled at 0.04wt%–0.06wt% and the N content decreased to 0.005wt%, which satisfy the requirements for grain refinement but can also effectively prevent the precipitation of TiN inclusions in 20CrMnTi steel.

Basic Research on Precipitation and Control of BN Inclusions in Steel

The influencing factors on precipitation and the suitable controlling conditions of BN inclusions were not reported until now, although it has been proven that BN could improve the cutting performance of steel. The precipitation and control of BN inclusions have been investigated in detail in this article. First, the precipitation behaviors of main inclusions in steel have been investigated by theoretical calculation, especially those of BN inclusions. Then, the directional solidification and heat treatments were applied to study the precipitation of BN inclusions realistically, and the microstructures of steels under different cooling rates have been analyzed. The variation laws of size, distribution, and area ratio of BN inclusions were discussed under conditions of quantitative control of chemical composition and cooling rate of steel. The variation laws and the main influencing factors of precipitation of BN inclusions in steel have been obtained and the suitable controlling conditions have been proposed. Finally, it is validated with a cutting experiment that the cutting performance and the chip-breaking performance of steel have been greatly improved by BN inclusions precipitated in the suitable control conditions.

Precipitation behavior of BN type inclusions in 42CrMo steel

Automobile crankshaft steel 42CrMo, which requires excellent machinability and mechanical properties, cannot be manufactured by traditional methods. To achieve these qualities, the formation behavior of boron nitride (BN) inclusions in 42CrMo steel was studied in this article. First, the precipitation temperature and the amount of BN type inclusions with different contents of boron and nitrogen in molten steel were calculated thermodynamically by FactSage software. Then the morphology and the size of BN type inclusions as well as the influence of cooling methods on them were investigated by scanning electron microscopy. Furthermore, the effects of cooling rate and the contents of B and N in molten steel on the morphology, size, and distribution of BN type inclusions were studied quantitatively and detailedly by directional solidification experiments. It is found that different BN inclusions in molten steel can form by controlling the cooling rate and the contents of B and N, which is important for obtaining the excellent machinability of 42CrMo steel.

Precipitation and control of BN inclusions in 42CrMo steel and their effect on machinability

The precipitation and control of boron nitrogen (BN) inclusions in 42CrMo steel were investigated and their effect on machinability was analyzed. First, the precipitation regularity of BN in 42CrMo steel was studied by theoretical calculation. Then, the machinability of the steel was investigated through contrast cutting experiments, and the composition and cooling rate of the steel were controlled to analyze the variation laws of the size, distribution, and area ratio of BN inclusions. Finally, the results were combined with the machinability of the steel to analyze the relationship among them. It is found that the machinability of the steel is mainly influenced by the diameter and quantity of BN inclusions. Fine and dispersedly distributed BN inclusions are more beneficial for the improvement in machinability of 42CrMo steel than coarse and sparse BN inclusions.

A method for observing the three-dimensional morphologies of inclusions in steel

A method for observing the three-dimensional morphologies of inclusions by deeply eroding a steel sample with a kind of organic solution composed of bromine water, acetone, and HCl (volume ratio, 45:45:10) was introduced. Four different kinds of inclusions in ultra low carbon steel were compared by metallographic observation and erosion observation. The results show that the three-dimensional morphologies of different kinds of inclusions could be observed clearly and simply after erosion. The method is useful for the observation and analysis of inclusions made by deep erosion. It also provides a new way to control and remove inclusions based on the true morphologies of inclusions.