low-Si Steel Research Articles

Transformation Behavior of Low Carbon Steels Containing Two Different Si Contents

Continuous cooling transformation behaviors of low carbon steels with two Si contents (0.50% and 1. 35%) were investigated under undeformed and deformed conditions. Effects of Si contents, deformation, and cooling rates on y transformation start temperature (A, r3 ), phase microstructures, and hardness were studied. The results show that, in the case of the deformation with the true strain of 0. 4, the length of bainitic ferrite laths is significantly decreased in low Si steel, whereas, the M/A constituent becomes more uniform in high Si steel. An increase in cooling rates lowers the A, r3 greatly. The steel with higher level of Si exhibits higher A, r3 , and higher hardness both under undeformed and deformed conditions compared with the steel with a lower Si content. Especially, the influence of Si on A r3 is dependent on deformation. Such effects are more significant under the undeformed condition. The hardness of both steels increases with the increase of cooling rates, whereas, the deformation involved in both steels reduces the hardness.

Influence of Continuous Annealing Parameters on the Mechanical Properties of Cold Rolled Ultra High Strength Steels

Two C-Si-Mn cold rolled ultra high strength steels are investigated to study the effect of cooling parameters on the mechanical properties. The fast cooling start temperature and fast cooling end temperature as well as overageing temperature have significant influence on the yield and tensile strength of the experimental steels. It is found that tensile strength as high as 980Mpa can be achieved when the cooling speed exceeds 50°C/s. The yield strength and tensile strength can also be increased by increasing the fast cooling start temperature and meanwhile maintain relatively high fast cooling speed. The strength is significantly reduced if the steel is overaged at temperature of 350°C or above. Microstructure study reveals obvious decomposition of martensite and precipitation of cementite at high overageing temperatures. Other than these, it is found that the high Si steel has better elongation and lower YP/TS ratio than low Si steel at identical tensile strengths.

Comparison of Cold Formability of Cold Drawn Non-heat-treated Steels Having Similar Strength

The cold formability of the drawn non-heat-treated steels, i.e. dual phase (DP) steel, low Si steel and ultra low carbon bainitic (ULCB) steel, was examined in terms of the deformation resistance and the forming limit. The present investigation was aimed at elucidating the effect of drawing on the cold formability of non-heat-treated steels which is directly affected by drawing since no heat treatment are involved during forming processes for them. A special care was taken for the present steels to exhibit the similar strength after drawing, so eliminating the strength effect. The present steels after drawing revealed the elastic-near perfect plastic behavior in compression. After drawing, the low Si steel exhibited the lowest deformation resistance estimated by the absorbed energy during deformation. In case of the forming limit in terms of the critical strain under which no cracking occurs during the upsetting test of the drawn steels, the low Si steel and the ULCB steel were better than the conventional heat-treated steel. Accordingly, among several non-heat-treated steels which can replace the conventional heat-treated steel as forging steels, the low Si steel seems to exhibit the best performance if they have the similar strength. The compressive deformation behavior of the present drawn non-heat-treated steels was discussed in association with the strain hardened state and the Bauschinger effect developed by drawing. In addition, their cold formability was explained by the plastic incompatibility between the constituent phases of each steel.

Evolution of magnetic properties and microstructure of high-silicon steel during hot dipping and diffusion annealing

Hot dipping and diffusion annealing is an alternative production process to obtain steel with high silicon contents while avoiding rolling problems. Surface alloying with Si and Al is achieved on a low-Si steel substrate (/spl ap/ 3%Si) by hot dipping in a hypereutectic Al-27%Si molten bath. To obtain a sufficient amount of Al and Si in solid solution over the thickness, a diffusion annealing treatment is performed after hot dipping. A diffusion annealing at 1250/spl deg/C allows the homogenization of the composition obtaining a concentration of 6.3% Si and 4.5% Al over the thickness. The evolution of microstructure, crystallographic texture, and magnetic properties in each step of the process is reported. After dipping and annealing, the losses decreased proportionally with the total Si-Al concentration achieved during the process. Values as low as 0.6 W/kg at 50 Hz (1T) and 10 W/kg at 400 Hz (1T) have been obtained in the experimental materials with high Si + Al content and 0.35-mm thickness.

Influence of composition and hot rolling parameters on the magnetic and mechanical properties of fully processed non-oriented low-Si electrical steels

The influence of composition (Si, Al, Mn. P and B) and hot rolling parameters on the properties of fully processed ultra-low carbon. low Si, non oriented electrical steels was investigated. Nine steels were examined, using twelve combinations of slab reheating temperature, finishing temperature and coiling temperature. It was found that maximisation of the polarisation through composition generally causes an increase in core losses. Hot band and final grain size influence the magnetic and mechanical properties more than composition. The grain boundary segregation of P results in finer grains and lower polarisations. Increasing the Mn and/or Al content coarsens the final grains as a result of coarser MnS.and/or AIN precipitates.

Basic Investigation of CVD Method for Manufacturing 6.5% Si Steel Sheet.

It has been known for a long time that 6.5% Si steel sheet has excellent soft magnetic properties that make it well suited for use as a magnetic material. However, steel of that composition is brittle and has little ductility; for this reason, the material could not be manufactured on an industrial scale with conventional cold rolling methods. Here, the authors studied and devised a method for continuously producing 6.5% Si steel sheet utilizing the CVD (Chemical Vapor Deposition) method. In this method, 6.5% Si steel sheet is continuously produced with the following procedure: first, low-Si steel, an easy-to-roll material, is rolled beforehand to produce thin strip; then, the CVD treatment using a gas containing SiCl4 is applied to the strip so that silicon is permeated through the surface of the steel strip; and finally, the strip is given a diffusion annealing to uniformly distribute the silicon throughout. While the siliconizing of steel has previously been studied as a way to improve the corrosion resistance of steel, this work marks the first study of this method as a way to produce 6.5% Si steel sheet on an industrial scale. The authors examined the basic conditions required for the process–the process for manufacturing 6.5% Si steel sheet utilizing this type of CVD-based siliconizing treatment technology–by carrying out a theoretical study of related chemical reactions and performing basic research with a simple test apparatus. Based on the results, the authors next conducted an investigation to develop a method for continuously manufacturing the steel in coil form and finally proposed an overall process configuration to realize such a production system.

Prevention of Red Scale Formation during Hot Rolling of Steels.

Red scale defects usually observed in high Si hot rolled strip were reproduced in a laboratory 3 stand tendem mill. The effects of hot rolling and descaling conditions on the strip surface color and scale structure were examined.Irrespective of Si content in steel, the hot rolled strip surface became red when the scale thickness before rolling was above 20 μm and the rolling temperature was below 900°C. It was found that surface part of the scale (mainly FeO) was broken to powder by hot rolling at the temperature below 900°C. The red scale of Fe2O3 was formed by the oxidation of powdered scale during cooling. Thick scale formed during slab soaking was completely removed by hydraulic descaling before rolling in low Si steel, whereas that was not removed in high Si steel. This remained scale caused the red scale defects after rolling and cooling. The application of obtained results to the hot strip mill production of red scaleless strip was discussed.

Synergistic influence of alloy grain size and Si content on the oxidation behavior of 9Cr−1Mo steel

The synergistic influence of prior-austenite grain size and silicon content of 9Cr−1Mo steel on the resistance to scale spallation has been studied in air at 773 K (for 500 hr) and 973 K (12 hr). Two steels, irrespective of their grain size and Si content, did not show spallation during oxidation at 773 K. Spallation occurred at 973 K, and fine-grain steels exhibited less spallation resistance than coarse-grain ones (in low-as well as high-Si steels). Among the four possible combinations of grain size ans Si content, the steel with low Si and fine grains showed least resistance to spallation, while the steel with high Si and coarse grains showed the best resistance. Spallation was found to initiate in the areas adjoining the oxide ridges formed at the alloy grain boundaries. Oxide scales at the ridges and within the grains were analyzed by scanning electron microscopy (SEM/EDX) and secondary-ion mass spectrometry (SIMS). These analyses suggest depletion of silicon from the areas adjoining grain boundaries, resulting in thicker scaling that triggers spallation in such areas. For similar grain-size materials, the necessary thickness for spallation was attained earlier with low-Si steel rather than in high-Si steel.

はだ焼鋼の回転曲げ疲れ特性に及ぼす合金元素の影響

A study was made on the effects of alloying elements such as Si, Mn, Cr, Ni and Mo on the rotating bending fatigue properties of carburized steels.At first, the effect of Si was studied using commonly used grades, SCM 420 and SNCM 420. It was shown that decreasing the Si content remarkably reduced internal oxidation and resulted in higher fatigue limit. Next, in order to clarify the effects of other alloying elements fatigue testings were carried out on low Si steels, where the Si content was less than 0.15%. Internal oxdation was reduced and fatigue strength rose with increasing of Ni, Mo contents and with decreasing of Cr, Mn contents, when maintaining the constant core hardness. 0.2% C-3% Ni-0.45% Mo steel, for example, showed the highest fatigue limit of 100kgf/mm2. High Ni-high Mo-low Mn-low Cr steels are considered to exhibit superior fatigue resistance by suppressing the internal oxidation and by the greater fracture toughness of carburized case.

Effects of Alloying Elements on the Rotating Bending Fatigue Properties of Carburized Steels

A study was made on the effects of alloying elements such as Si, Mn, Cr, Ni and Mo on the rotating bending fatigue properties of carburized steels. At first, the effect of Si was studied using commonly used grades, JIS SCM420 and SNCM420. It was shown that the decrease in Si content remarkably reduced internal oxidation and resulted in higher fatigue strength. In order to clarify the effects of other alloying elements, fatigue tests were carried out on low Si steels where the Si contents were less than 0.15%. Internal oxidation was reduced and fatigue resistance was improved with increasing Ni and Mo contents and with decreasing Cr and Mn contents when keeping the core hardness constant. The 0.2%C-3%Ni-0.45%Mo steel showed the highest fatigue limit of 100kgf/mm2. High Ni-high Mo-low Mn-low Cr steels are considered to exhibit superior fatigue resistance by supressing internal oxidation and by the greater fracture toughness of carburized case.

Can Fitting in Green Beans: Effect of Growing Season, Base Steel Composition, Tinplate Thickness, Can Vacuum and Storage Conditions

ABSTRACTSpring and fall grown green beans were packed under high and low vacuum conditions in high and low residual Al, Ni, Cu, Si, S, and Mn base steel .25 and .50 electrotin plated J‐enamel cans and evaluated during storage at 38°C and room temperature for pitting on and under the s deseams. Cans containing spring grown beans were more severely pitted than those of the fall pack. High residual (0.061%) Cu steel cans were more severely pitted than other treatments. The .25 electrotin plated cans were more severely pitted in high Cu residual cans, as were the low vacuum spring pack cans at 38°C storage.

The Mechanism of Reducing “A” Segregates in Steel Ingots

The mobility of interdendritic liquid metal under the semi-solid state was measured by sucking the liquid to a vacuum chamber. Si and Mo contents in steel investigated were varied by lowering the Si content or by adding Mo in order to study the reducing mechanism of “A” segregates in steel ingots. The experimental results obtained are summarized as follows:(1) The amount of metal sucked decreases as the fraction of solid increases. An abrupt increase in the fluidity resistance takes place at a lower fraction of solid in the case of low Si steel as compared with that of high Si steel. The effect of Si is notably clear in the case of low-alloy steel containing Ni, Cr, Mo and V.(2) These phenomena can not be explained only by the difference in the density or in the viscosity between the interdendritic fluid liquid and the remaining bulk liquid. Consequently they are explained in terms of the morphology of dendrite when the solidification front is being formed in the semi-solid region.(3) The effects of Si and Mo contents on the reducing mechanism of “A” segregates can be explained as follows; The solidification front is formed at a lower fraction of solid when the Si content is lowered or Mo is added. Accordingly the driving force to float up the solute-enriched liquid does not become large enough to form “A” segregates since the solute is not sufficiently enriched in the interdendritic liquid at the solidification front.To conclude, the reducing mechanism of “A” segregates can be explained in terms of a shift of the solidification front to the side of lower fraction of solid resulting from the change in the morphology of dendrite.