【正文】 ions–cell walls–not coinciding with longrange fields. The average size of the cells is ~ 181。. In steels containing more effective carbideforming elements than iron the formation of nuclei of special carbides begins around 350 176。 . It is highly probable that among the highly dispersed carbide phases there are also more thermodynamically stable phases of the Mo2C and VC type not detected by physicochemical analysis [6]. It follows from our experimental results that embrittlement occurs during tempering of Cr–Mo–V steels, manifest as a distinct peak on the curve of Tso vs Ttemper. The peak is not associated with the presence of phosphorus in the steel but varies with the concentration of vanadium and is located in the temperature range of carbide formation, which develops with inheritance of the dislocation arrays. Tso reaches a peak at those temperatures where Fe3C transforms to more stable M7C3. A similar phenomenon has been observed in chromium steels [5]. Embrittlement may be due to both volume and boundary effects. In the case of Cr–Mo–V steels the secondary hardening manifest in the increase of the strength at Ttemper = 300–500 176。 , corresponding to the edge of the plateau of the strength characteristics and the peak of Tso, and after tempering at 760 176。. With further increase of the tempering temperature Tso decreases, which coincides with the beginning of weakening. For heats 27 the overall character of the variation of Tso with Ttemper is the same, although the peaks occur at lower temperatures. For the steels in the quenched condition Tso is ~90 176。 for 10 h. After quenching and lowtemperature tempering, all heats had a typical martensitic structure, but after hightemperature tempering (above 600 176。在高峰期（ Tso）的上限， 在 正值溫度下材料開始削弱。更有效地遏制電石， 在鋼中容納更多的 碳化物 成形元素比鐵中 350℃ 左右開始 的特殊碳化物的原子核鋼 的成形 ，尤其是 M7C3 [8]。這個(gè)假設(shè)是證實(shí)了電子顯微鏡分析結(jié)果：在矩陣（位錯(cuò)密度，碎片大小條件）引起材料的 [8， 9]實(shí)力的增強(qiáng)，保持不變直至 Ttemper = 600 176。它的峰值并沒有關(guān)聯(lián)的磷在鋼存在，但與釩的濃度各不相同，在碳化物的形成，與繼承發(fā)展脫位陣列的溫度范圍內(nèi)位置。該階段碳化物形態(tài)的也有 變化。唯一的變化是明顯的 沉淀 分散的碳化物階段。圖 3顯示了在熱淬火 Tso顯微條件后，在 600℃ 回火，對(duì)應(yīng)于對(duì)強(qiáng)度特性 極值 邊緣與 Tso高峰在 760 176。 ）實(shí)際上是相同。 。 Tso的 確定 是通過 55 毫米的切口 1毫米深（根半徑 ）沖擊試驗(yàn)樣品。 熱 件 1（ ％的 V， ％ P）重四十一噸是偽造的，以一個(gè) 550毫米的大小 , 15毫米厚的板材被切斷他們。另外，在一個(gè) 100公斤 的 感應(yīng)爐加熱熔化 。Tso被認(rèn)為是 在 斷裂 50％ 纖維 下 的 測試溫度 。 熱 件 1開始 時(shí) 回火溫度大約 300℃ ， Tso的增加達(dá)到 500600度 的 最高值。 它的峰高 和 立場取決于釩鋼的內(nèi)容。 的回火 之后 ，強(qiáng)度和 Tso達(dá)到 最低的。粒子的大小是 150 至 200 A， 平均密度 為 ~1015cm2。微細(xì)分散的大小圓形 的 沉淀 ? 250 A的位錯(cuò)在位于網(wǎng)絡(luò)的連接處。 Tso達(dá)到高峰時(shí)的溫度在 Fe3C的變換更穩(wěn) ，與 M7C3類似的現(xiàn)象已在鉻鋼觀察 [5]。 。沉淀 物 均勻分布在整個(gè)體積的位錯(cuò) 位置 ，低角度的板條馬氏體的界限，高角度的板條殖民地邊界，他們加強(qiáng)了矩陣和削弱（脆化）邊界。 2。 ) a sorbite structure. The austenite grain size of the laboratory heats was smaller (grade 89) than in the mercial heat (grade 4), with greater dispersity and homogeneity of the structural ponents. Embrittlement was determined from the variation of Tso with Ttemper , where Ttemper is the tempering temperature of the quenched steel and Tso is the ductile brittle transition temperature, which most pletely characterizes embrittlement. Tso was determined on impact test samples 5 5 mm with a notch 1 mm deep (root radius mm). Tso was taken as the testing temperature at which the fracture was 50% fibrous. The tensile strength was determined at 20 176。 lower than for heat 1, and amounts to 70 177。 , where the strength and Tso are lowest. After quenching, the structure consists of lath martensite with welldeveloped dislocation arrays. The laths are slightly misoriented with respect to each other, with an average width of ~ μ and length ~5μ, and are grouped in colonies ~5 5μ. The laths are filled with evenly distributed dislocations with a density ~1011cm2. No carbide phase was observed in the quenched steel. After tempering at 60