| With the development of economy and construct inland, good-sizedstrip mine whole set equipment, petroleum chemical equipment, oceanengineering and traffic machine etc. are developing toward macro-scaleoperations technology, lightweighting, which require to improvecontinuously useful intension level of material, but the brittlefailure question of material with high intension at low temperaturestands out all the more.At present low alloy steel against low impact performance has beenresearched and produced in many fields all over the world. For examplethe steel which is used to make pressure vessel (ethylene,chemicalfertilizer,city,coal gas,carbon dioxide etc. using vessel at lowtemperature), forged piece, steel tube, flange, pipe piece, along withsuperconduct electricity machine and good-sized superconductmagnetizer of nucleus fusion equipment. And temperature has also brokenthrough, low steels from -40℃,-70℃to -101℃both are opening upand applying.Since the last century, the brittle failure of steel atlow temperature is a hot spot all the while for researchers. But thereisn`t any great breakthrough at all times, research work does not stop.To this century, This field obtained some important achievements onpaper and practice, especially the development of rupture mechanicsprovide a favorable means for brittle failure question at lowtemperature. But hitherto this question still have not been solvedquite, low temperature brittle failure accident still happen now andthen. The research on low brittle failure question of low alloy steelis provided with important theory value and practicality significance. The task based on part and components of high speed train whichwork in Jack Frost field appear low rupture now and then, which effectbadly working of train. And, at present low temperature steels willgenerally not be applied until they be made into board by rolling, thenconnect them by jointing method. For some complicated parts, due towelding joint can not content request, so people put application ofcast whack molding on the agenda. About low temperature performanceof cast steel, in former literatures this is provided almost. Thecurrent trail emphasize on adding different alloy elements into caststeel, research the low temperature performance, and put forward therequired attentive questions in cast steel production. Finally,according to conclusion of current trial give out the best match andperformance datum. In low temperature cast steel production, there are some fieldswhich require to be thought over from melting course up to machineprocess course, especially lard on low temperature rupture behavior,is all the times attentive emphases. Controlling production process,namely try our best to decrease lard production of steel underreasonable match precondition. Researching performance stand or fall of low temperature steelbegin with following several aspects: 1.Ballistic work values. Scale steel quality uppermost isperformance trial datum of its correlative aspects. The paper go alonganalysis to low temperature ballistic work datum on orthogonality trial,obtain the primary and secondary degree of every element which is addedto low temperature toughness of steel. Educe the best match. 2.rigidity values. Rigidity decide directly machine process characteristic of steel, this is a characteristic index of steel also. 3. macroscopical fracture. Throughout looking into macroscopical fracture of charpy sample, can deduce stand or falloff against ballistic performance. 4. metallic phase photos. Performance and organization of steel are corresponding basically. In fact production steel, it is inevitable to exist lard and component aliquation. The refining of grains increase greatly the area of grain boundary, make lard and aliquation on grain boundary smaller and more dispersive. This may reduce the harm degree to steel performance due to them. 5. Electron scan snap picture. On SEM pictures, distinctness performances of brittleness rupture are cleavage pattern and norm cleavage pattern. Toughness rupture manifest on many pits namely cavities with different dimensions. Dimension, depth and distributing equality degree of cavity decide the discretion of toghness. Action of additive alloy elements in steel: 1. Action of manganese in steel: a part of manganese solid inferrite (or austenite), another part of it come into being alloycementite with manganese, it is a element which can enlarge austenitephase field, and with increasing of content, critical temperature willgo up, it can reduce carbon content of eutectoid, except that it canreduce eutectoid temperature. So, at the same carbon content andcooling speed, with manganese content in steel, pearlites inmicrostructure will not only refine but also increase quantity,accordingly intensity and rigidity of steel go up. In addition, thedecline of A3 (GS) temperature curve makes at first eutectoid ferriteseparate out at more low temperature to refine. The decline of A1 canrestrain carbide separation out of overcooling austenite grainboundary, make steel keeping higher plastic, reduce thetoughness-brittleness transition temperature of steel, so manganeseis one of the mostly alloy elements in low temperature steel. 2. Action of nickel in steel: nickel in steel only come into beingsolid, not carbide, is a element which can enlarge austenite phase field,it solid into steel, which make the temperature of phase transformationfall, make austenite going along decomposition at more low temperature.At the same time nickel make the expanding speed of elements in steelfall, so increase the stability of overcooling austenite, make C curveshift towards right side. Nickel may not only improve toughness andplastic of steel at room temperature, but also meliorate the toughnessat low temperature, make toughness-brittleness transition temperaturefall, nickel is also the mostly alloy element in low steel. 3. Action of lanthanon elements: In steel going into an amountof elements have a to oxidize and to decarbolize action, but ifexcessive, this will come into being new lard, and reduce the... |
PDF Full Text Request