Weiqing Chen

Improving Inner Quality in Continuous Casting Rectangular Billets: Comparison Between Mechanical Soft Reduction and Final Electromagnetic Stirring

The comparison between the mechanical soft reduction (MSR) and final electromagnetic stirring (FEMS) on center carbon macrosegregation and v-segregation has been investigated in order to improve the inner quality of high carbon 82A steel with a section of size 180xa0mmxa0×xa0240xa0mm. A heat transfer calculation model by using C++ programming language is developed and applied to calculate the appropriate casting speed of continuous casting during the FEMS and MSR processes. The calculated action zone of FEMS and MSR is at the location with a solid fraction of 0.28–0.41 and 0.30–0.90, respectively. The industrial results show that the effects of MSR in improving the center carbon segregation, reducing the shrinkage cavity and suppressing the V-segregation are more effective than FEMS. The mean center carbon segregation degree reduces from 1.19 to 1.15 with FEMS and decreases from 1.19 to 1.07 with MSR. Besides, compared with FEMS, MSR can eliminate shrinkage cavity and V-segregation but may generate center negative segregation and transverse cracks subjected to reduction pressure.

Influence of calcium treatment on cleanness and fatigue life of 60Si2MnA spring steel

Contrasting experiments of Al killed 60Si2MnA spring steel were carried out between using and excluding calcium treatment under LF refining slags with low and high basicity ratios (R: CaO/SiO2u2009=u20093.4, 5.0), respectively. Results showed the high basicity refining slag had a certain effect on controlling inclusions and improving the cleanness of spring steel similarly to calcium treatment. The T.[O] (total oxygen) content of steel without calcium treatment got to below 15u2005ppm and the fatigue life was long, up to 7.8u2009×u2009106u2005cycles. But in order to reduce the T.[O] below 10u2005ppm, as well as inclusion number and size in spring steel further, meanwhile, the appropriate calcium treatment should still be used. Besides, as the [Ca] content in the steel with calcium treatment increased, inclusions transformed from Al2O3–SiO2–CaO–MgO to Al2O3–SiO2–CaO–MgO–CaS completely, which reduced the formations of voids between inclusions and steel matrix, and voids decreased with the increase of CaO/Al2O3 value and CaS content of inclusions. Finally, the fatigue life of spring steel with high basicity slag and calcium treatment increased to 9.1u2009×u2009106 cycles.

Effect of Tin, Copper and Boron on the Hot Ductility of 20CrMnTi Steel between 650 °C and 1100 °C

Abstract The hot ductility of 20CrMnTi steel with x% tin, y% copper and z ppm boron (xu2009=u20090, 0.02; yu2009=u20090, 0.2; zu2009=u20090, 60) was investigated. The results show that tin and copper in 20CrMnTi steel are detrimental to its hot ductility while adding boron can eliminate the adverse effect and enhance hot ductility greatly. Tin is found to segregate to the boundaries tested by EPMA in 20CrMnTi steel containing tin and copper and tin-segregation is suppressed by adding boron, moreover, copper was found not to segregate to boundaries, however, fine copper sulfide was found from carbon extraction replicas using TEM. The adverse effect of tin and copper on the hot ductility was due mainly to tin segregation and fine copper sulfide in the steel. The proeutectoid ferrite film precipitating along the austenite grain boundary causes the ductility trough of the three examined steels. Tin and copper in 20CrMnTi steel can retard the occurrence of dynamic recrystallization (DRX) while boron-addition can compensate for that change. The beneficial effect of boron on 20CrMnTi steel containing tin and copper might be ascribed to the fact that boron segregates to grain boundaries, accelerates onset of DRX, retards austenite/ferrite transformation and promotes intragranular nucleation of ferrite.

Effect of Tin on Hot Ductility and High-temperature Oxidation Behavior of 20CrMnTi Steel

Abstract The hot ductility and high-temperature oxidation behavior of 20CrMnTi steel with 0.02% Cu and x% Sn (0.004u2009⩽u2009xu2009⩽u20090.049) were investigated. The results show that tin has no significant effect on tensile strength of sample with less than 0.049% Sn. The critical temperature where the hot ductility reduces dramatically rises with the increase of tin content while the hot ductility decreases with its increase. The average tin content at austenite grain boundaries (GB) and substrate is 0.108% and 0.045% respectively in the specimen containing 0.049% tin quenched after heated to 1223 K and held for 600 s. Sn-segregation at the GB deteriorates the hot ductility. There is no direct relationship between the cause of the ductility trough and tin. However, Sn-segregation at the GB causes it to deepen a lot. The tin content should be controlled below 0.021%, which would not deteriorate the hot ductility significantly. There is no tin-enrichment at the scale/substrate interface when tin content is less than 0.049%. Moreover, although Sn is enriched under the steel surface, any liquid Sn-enrichment wasnt observed at the oxide/steel interface even in as high as 0.45% Sn-bearing steel with 0.02% Cu.

Effect of Al antioxidant in MgO–C refractory on the formation of Al2O3-rich inclusions in high-carbon steel for saw wire under vacuum conditions

Al2O3-rich (>70u2005wt-%) inclusions generally hard and non-deformable are extremely detrimental for saw wire. In order to explore the source of this type of inclusion and provide solutions, experiments on the interaction between Al-containing MgO–C refractory and high-carbon steel for saw wire was conducted on a laboratorial scale using a cold crucible levitation melting furnace under vacuum conditions. [Al]S (acid-soluble Al), [C] and [Mg] concentrations in steel, Al2O3 concentration in inclusions and microstructure of refractory/steel interface, etc. were analysed to clarify the influence of vacuum pressure, refractory addition amount and interaction time. Based on the experimental results and thermodynamic calculations, a presumable impact mechanism of Al antioxidant in MgO–C refractory on the formation of Al2O3-rich inclusions in high-carbon steel for saw wire under vacuum conditions was deduced, which in turn provided a reference for the control of Al2O3-rich inclusions in high-carbon steel for saw wire.

Effect of permanent magnet stirring on internal quality of steel

ABSTRACT Permanent magnet stirring (PMS) featuring low power dissipation and high-intensity magnetic field was investigated as a means of decreasing internal solidification defects. In this study, the magnetic Taylor number (Ta) was used to quantify the melt flow. Initial research of PMS involved a laboratory study of the solidification of Sn–20 wt-% Pb alloy. An industrial plant trial with continuously cast tire cord steel confirmed that PMS, in accord with the laboratory findings, produced an improvement in central cavities in the cast product. Moreover, it was established that PMS is an alternative method for reducing carbon macrosegregation in tire cord steel billets with different section sizes. It was also found that PMS (Tau2009=u20098.97u2009×u2009107) was more effective for improving central carbon macrosegregation of tire cord steel than electromagnetic stirring (Tau2009=u20096.33u2009×u2009107) due to the larger Ta related to the driven-flow intensity of the residual melt.

Influence of Copper on the Hot Ductility of 20CrMnTi Steel

Abstract The hot ductility of 20CrMnTi steel with x% copper (xu2009=u20090, 0.34) was investigated. Results show that copper can reduce its hot ductility, but there is no significant copper-segregation at the boundary tested by EPMA. The average copper content at grain boundaries and substrate is 0.352% and 0.318% respectively in steel containing 0.34% copper tensile-tested at 950 °C. The fracture morphology was examined with SEM and many small and shallow dimples were found on the fracture of steel with copper, and fine copper sulfide was found from carbon extraction replicas using TEM. Additionally, adding 0.34% copper caused an increase in the dynamic recrystallization temperature from 950 °C to 1000 °C, which indicates that copper can retard the dynamic recrystallization (DRX) of austenite. The detrimental influence of copper on hot ductility of 20CrMnTi steel is due mainly to the fine copper sulfide in the steel and its retarding the DRX.

Influence of Different Levels of Cu Equivalent on the Hot Ductility of 20CrMnTi Steel

Abstract The hot ductility of 20CrMnTi steel with different levels of Cu equivalent was investigated. The results show that Sn and Cu in 20CrMnTi steel are detrimental to its hot ductility. Sn was found to segregate to the boundaries tested by EPMA, moreover, Cu was not found to segregate to boundaries, however, the fracture morphology was examined with SEM and showed many small and shallow dimples on the fracture of steels with large Cu equivalent (>0.15) and fine copper sulfide was found from carbon extraction replicas using TEM. The adverse effect of large Cu equivalent (>0.15) on the hot ductility was due to Sn segregation and fine copper sulfide in the steel as well as their retarding the occurrence of dynamic recrystallization (DRX). The proeutectoid ferrite film precipitating along the austenite grain boundary causes the ductility trough of the five examined steels. Moreover, in this case, the level of Cu equivalent should be controlled below 0.15, which would not deteriorate the hot ductility significantly.