Hiroyoshi Yashiki

Effect of hot-band grain size on magnetic properties of non-oriented electrical steels

Hot-band grain size of 0.5% Si steels was changed from 42 to 115 μm by various combinations of several hot rolling and annealing conditions. The hot-bands were cold rolled from 2.3 to 0.50 mm and finally annealed for 1 min at several temperatures between 750 °C and 950°C. The values of magnetic induction B50 in the directions of 0° and 90° from the rolling direction increase, whereas that of 45° direction decreases a little with an increase in the hot-band grain size. The core loss W15/50 in 0°, 45° and 90° directions decreases altogether with an increase in the hot-band grain size. The change in B50 with an increase in the hot-band grain size is caused by decreases of (110) component in the annealing texture. The change in W15/50 with an increase in the hot-band grain size is accounted for both of the grain size and texture effects.

Effects of manganese and sulfur contents and slab reheating temperatures on the magnetic properties of non-oriented semi-processed electrical steel sheet

The effects of manganese and sulfur contents and slab reheating temperatures (SRTs) on the magnetic properties of non-oriented semi-processed electrical steel sheets were investigated. The core loss W15/50 of the steels increases with an increase of sulfur content in each steel with different manganese contents, while, the magnetic induction B50 hardly changed with an increase of the sulfur content at any manganese level. The SRTs affect the core loss in steels without hot band annealing, and in steels processed at an SRT of 1273 K showed the lowest core loss. Steels with higher sulfur content processed at an SRT of 1523 K showed deterioration of the core loss caused by the retardation of the grain growth at the recrystallization annealing by the fine MnS (ca.0.1 μm in diameter).

Effect of hot-band annealing on anisotropy of magnetic properties in low-Si semi-processed electrical steels

Abstract Hot-band annealing at higher temperatures is effective for improving the magnetic properties, while it enhances their planar anisotrophy. These effects are explained by the texture development.

Magnetic and Mechanical Properties of Newly Developed High-Strength Nonoriented Electrical Steel

New, nonoriented electrical steel featuring great strength and low core loss has been developed. The strengthening mechanism that was mainly applied was dislocation strengthening. The typical properties of developed steel of 690 and 780 MPa grades in tensile strength with a thickness of 0.35 mm were 46 and 51 W/kg in W 10/400 , respectively. The core loss of the 780 MPa grade developed steel was a third part of that of a 980-MPa grade dual-phase steel in W 10/400. Furthermore, the fatigue strength of the 780-MPa grade developed steel was found to be superior to that of the 980-MPa grade dual-phase steel. These excellent characteristics were ascribed to the specific microstructure of the steel, in which dislocations introduced by cold rolling were rearranged and a few recrystallized grains were formed within the dislocation-reduced deformed matrix. Solute Nb would be responsible for this favorable microstructure evolution through moderate suppression of dislocation annihilation and consequent retardation of recrystallization during annealing. Another outstanding characteristic of the developed steel was its nickel-free chemical composition, by which a rise in alloying costs could be minimized.

Effect of metallurgical factors on the magnetic properties of non-oriented electrical steels under PWM excitation

Abstract Magnetic properties of non-oriented electrical steel sheets under PWM voltage excitation as well as those under sinusoidal excitation have been investigated from a metallurgical point of view. The core loss under PWM excitation is slightly larger than that under sinusoidal excitation. The induction dependence of the core loss difference between the two excitation conditions changes by changing Si content and grain size. The higher the induction, the larger the core loss difference of 0.2% Si steel with small grains. In the case of higher Si steels and 0.2% Si steel with large grain sizes, however, the core loss difference at inductions over 1.3 T decreases with increasing induction. At low induction levels the core loss difference has little relationship to the grain size. On the other hand, at high induction levels this difference decreases with increasing grain size.

Secondary recrystallization behavior in grain-oriented 2.3% Si-1.7% Mn steel

Abstract The secondary recrystallization behavior in 2.3% Si-1.7% Mn steel containing 0.012% sol.Al has been investigated under the conditions of slab soaking at 1150°C and secondary recrystallization annealing at 950°C. Complete secondary recrystallization and good magnetic properties, equivalent to those of regular grade for grain-oriented electrical steel, have been obtained using an N2-containing atmosphere during the heating stage of secondary recrystallization annealing.

Influence of Magnetic Anisotropy on Hysteresis Loss of Non-oriented Electrical Steel Sheet

変圧器やモータの効率向上のため,鉄心材料である電磁 鋼板の鉄損低減が要求されている。鉄損は渦電流損とヒス テリシス損の和であり,それぞれに低減する手段がある。 渦電流損は交流で磁化された鋼板内で発生する渦電流に よって生じるジュール熱であり,その低減には板厚低減, SiやAlなどの合金含有量増加による比抵抗増加および磁 区幅の減少が有効である。一方,ヒステリシス損は交番磁 界の増減に伴う磁束密度の増減の軌跡が異なることによっ て生じるエネルギー損失であり,その低減には結晶粒径の 大径化,析出物や介在物の低減および集合組織制御などが 有効である。 渦電流損は,電磁鋼板内の磁化変化が均質であれば,板 厚の2乗に比例し比抵抗に反比例するいわゆる古典的モデ ル で表すことができ,磁区幅が大きく,磁化変化が不均 一な場合には磁壁近傍の局所的な磁化変化を考慮した渦電 流損モデル でおおよそ記述できる。一方,ヒステリシス 損への影響因子としては,粒径,析出物および集合組織な ど冶金的な要因に加え,飽和磁歪定数,結晶磁気異方性お よび応力などがある。従来個々の影響因子について検討し た例は多数報告されている 。例えば,Steinmetzはヒス テリシス損が磁束密度の1.6乗に比例するというモデル 11) を,Kerstenは保磁力が結晶磁気異方性や非磁性不純物の存 在率に比例し,非磁性不純物の直径に反比例するというモ デル を提唱している。しかしながら,Steinmetzのモデル はヒステリシス損と磁束密度の関係の経験則に基づいた モデルであり,それ以外の影響因子を分離して評価できな い。また,Kerstenのモデルは,析出物のサイズや存在比率 および結晶磁気異方性の影響を取り入れたモデルである が,結晶粒径,集合組織や応力などの影響は考慮していな い。 筆者らは,交番磁化過程において磁壁が移動した部分の 体積とヒステリシス損の間に相関がある ことに着目し, ヒステリシス損の各影響因子が,磁壁が移動した部分の体 積に寄与するものと,その移動の阻害因子に寄与するもの に分類できると考えた。筆者らが提案するモデルでは,磁 壁が移動した部分の体積V[m]は180°磁壁と90°磁壁が 移動した部分の体積の和として式(1)のように表される。 この式(1)を用いて,ヒステリシス損は式(2)のように記 述できる。

Effect of antimony surface treatment on nitrogen absorption during batch annealing of an electrical steel sheet

Nitrogen absorption is usually observed during batch-type hot-band annealing of electrical steel sheets containing aluminium. This nitrogenizing causes the deterioration of magnetic properties, such as core loss and induction. In order to prevent nitrogenizing, we investigate an antimony treatment on the hot strip surface of electrical steel sheets containing aluminium. Potassium antimonyl tartrate and colloidal antimony oxides (Sb2O5) are effective against nitrogenizing. It seems that active sites on the surface of the hot strip after pickling are covered with antimony oxides to block the adsorption of nitrogen. Magnetic properties, after cold-rolling and continuous annealing of the nitrogenizing hot band, deteriorate due to small grains near the surface whose boundaries are pinned by aluminium nitrides.