Microstructure and mechanical properties of a new type of austempered boron alloyed high silicon cast steel

In the present paper, a new type of austempered boron alloyed high silicon cast steel has been developed, and its microstructures and mechanical properties at different temperatures were investigated. The experimental results indicate that the boron alloyed high silicon cast steel comprises a dendritic matrix and interdendritic eutectic borides in as-cast condition. The dendritic matrix is made up of pearlite, ferrite, and the interdendritic eutectic boride is with a chemical formula of M2B （M represents Fe, Cr, Mn or Mo） which is much like that of carbide in high chromium white cast iron. Pure ausferrite structure that consists of bainitic ferrite and retained austenite can be obtained in the matrix by austempering treatment to the cast steel. No carbides precipitate in the ausferrite structure and the morphology of borides remains almost unchanged after austempering treatments. Secondary boride particles precipitate during the course of austenitizing. The hardness and tensile strength of the austempered cast steel decrease with the increase of the austempering temperature, from 250℃ to 400 ℃. The impact toughness is 4-11 J.cm^-2 at room temperature and the impact fracture fractogragh indicates that the fracture is caused by the brittle fracture of the borides.

Improving Corrosion Resistance of Stainless Steel by Yttrium Addition: An AES Analysis

The influence of Y addition on the distribution of element concentrations in the passive film of high silicon stainless steel formed in 93% H2SO4 was comparatively studied by using auger electron spectroscopy (AES). The results show that 0.2%Y addition increases the SiO2 proportion in the passive film of stainless steel so that the formation of SiO2 enriched passive film from silicon in the alloy is brought into full play.

Multiphase microstructure formation and its effect on fracture behavior of medium carbon high silicon high strength steel

This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.

6.5 wt%Si high silicon steel sheets prepared by composite electrodeposition in magnetic field

A new preparation method of near-net-shape 6.5 wt% Si high silicon steel sheets was proposed by combining composite electrodeposition(CED) and diffusion annealing under magnetic field. The obtained sheets were characterized by scanning electron microscopy, energy dispersive spectrometry, analytical balance and a silicon steel material measurement system. The results show that the surface morphology,the elemental distribution, the cathode current efficiency and the silicon content of coatings were obviously influenced by the micro and macro magnetohydrodynamics(MHD) flows under magnetic field.With the effect of magnetic field, the silicon particles content of coatings showed an increasing trend and the diffusion process showed that an approximately uniform 6.5 wt% silicon steel sheet has been successfully obtained. The magnetism measurement showed that the high silicon steel sheet has the lower iron loss, and the iron loss further decreased under magnetic field. The new method proposed in this article,which is more environmentally friendly and low energy consumption, is feasible to prepare high silicon steel sheets.

Characterization of Microstructure and Texture in Grain-Oriented High Silicon Steel by Strip Casting

Grain-oriented 4.5 wt% Si and 6.5 wt% Si steels were produced by strip casting, warm rolling, cold rolling, primary annealing, and secondary annealing. Goss grains were sufficiently developed and covered the entire surface of the secondary recrystallized sheets. The microstructure and texture was characterized by OM, EBSD, TEM, and XRD. It was observed that after rolling at 700 ℃, the 6.5 wt% Si steel exhibited a considerable degree of shear bands, whereas the 4.5 wt% Si steel indicated their rare presence. After primary annealing, completely equiaxed grains showing strong y-fiber texture were presented in both alloys. By comparison, the 6.5 wt% Si steel showed smaller grain size and few favorable Goss grains. Additionally, a higher density of fine precipitates were exhibited in the 6.5 wt% Si steel, leading to a ~ 30-s delay in primary recrystallization. During secondary annealing, abnormal grain growth of the 6.5 wt% Si steel occurred at higher temperature compared to the 4.5 wt% Si steel, and the final grain size of the 6.5 wt% Si steel was greater. The magnetic induction B8 of the 4.5 wt% Si and the 6.5 wt% Si steels was 1.75 and 1.76 T, respectively, and the high- frequency core losses were significantly improved in comparison with the non-oriented high silicon steel.

Preparing High Silicon Steel by Sintering Fe-6.5%Si Powder Compacts in Static Magnetic Field

In this research,sintering Fe-6.5wt%Si Compact specimen in static magnetic field is proposed for preparing high silicon steel.It is found that the densifications of the compacts are affected remarkably by superimposing magnetic field.The density of the compacts can be increased when the MFD is higher than 0.2 T.The highest relative density of the samples is 97.2%.The magnetic property of silicon steel could be improved when superimpose static magnetic field in sintering process,the permeability of the compact are two times of that without magnetic field,and the magnetic property parallel to the direction of the magnetic field was evidently higher than that in perpendicular direction.

Punchability and Punching Fracture Behavior of High Silicon Steel Sheets

The 0.2-0.3mm thick cold-rolled sheets and annealed sheets of high silicon steel were produced by rolling process,then punching tests were carried out at room temperature to 150℃.The punchability and punching fracture behavior were investigated by means of scanning electron microscope（SEM）and electron back-scattered diffraction（EBSD）.It is found that cold-rolled sheets of high silicon steel show good punchability under the condition of 0.01 mm punch-die clearance and at the temperature of 100℃;the punchability of annealed sheets with fine grain size is better than that of annealed sheets with coarse grain size;the punching temperature of 150℃is suitable for annealed high silicon steel sheets especially with coarse grain size on account of punching edge quality.The major cleavage planes of annealed high silicon steel sheets are{100}crystallographic planes on which brittle fracture occurs at low temperatures.The cleavage systems include{100}〈110〉and{100}〈100〉,and cleavage fracture is completed by one or both of them.The punchability of high silicon steel sheets is related with punching temperature,grain size and ordering degree.Reducing ordering degree,increasing punching temperature,as well as refining grain size can improve the ductility and punchability of high silicon steel sheets.