冶金专业外文翻译----铬-钼-_v钢的回火脆性(编辑修改稿)

冶金专业外文翻译----铬-钼-_v钢的回火脆性(编辑修改稿)内容摘要：

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。 on five samples 3 mm in diameter. Figure 1 shows the variation of the mechanical properties of heat 1 with the tempering temperature. The mechanical properties of this heat are almost constant after tempering at 100600 176。 . When the tempering temperature is raised from 600760 176。 the strength characteristics decrease sharply, while the ductile characteristics increase. Changing the vanadium concentration affects the stability of the steel during tempering. For the steel without vanadium the strength begins to decrease around 500 176。 . For heat 1, beginning with tempering at temperatures around 300 176。 , Tso increases and reaches a maximum value at 500600 176。 . As pared with the quenched condition the increase of Tso at the peak is 100 176。 . 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。 lower than for heat 1, and amounts to 70 177。 10 176。 . After tempering at 730 176。 the value of Tso is practically the same for heats 27 (110 to 130176。 ). The height of the peak and its position depends on the vanadium content of the steel. When the vanadium concentration is changed from 0 to % the peak rises %60 176。 and at the same time shifts ~100 176。 . Comparing heats 1 and 3, 6, differing in their metallurgical prehistory but similar in vanadium content (~%), one can see that the increase of Tso in the region of the peak is almost the same as for the quenched condition. In amounts of and %, phosphorus has no effect on Tso after the heat treatments tested. The changes in the mechanical properties of the steel during tempering evidently depend on changes in fine structure. Figure 3 shows the microstructure of heat in the quenched condition, after tempering at 600 176。 , corresponding to the edge of the plateau of the strength characteristics and the peak of Tso, and after tempering at 760 176。 , 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 600 176。 for 10 h the overall character of the dislocation arrays and the fragmentation of the crystals are retained. The average size of the laths (width and length)and the average size of the colonies remain unchanged. The only noticeable change is the precipitation of finely dispersed carbide phases. The size of the particles is 150200 A and the average density ~1015cm2. They are precipitated on dislocations and evently distributed through the bulk of the martensite laths. Larger precipitates with the shape of needles (platelets) ~250 A in diameter and ~2103A long are located near highly misoriented boundaries (grains, colonies of martensite laths, the most misoriented laths, etc.) and in the boundaries themselves. Precipitates of this type were identified by microdiffraction techniques as MTCa carbide. The structure of the steel changes sharply after tempering at 760 176。 : the dislocations are polygonized. The dislocations distributed throughout the bulk are rebuilt into energetically more suitable configurations–ce。