The influence of stirring method on hydrogen removal during ladle treatment

A mathematical model based on fundamental transport equations for vacuum degassing in an Asea‐SKF ladle furnace was developed earlier and predicted hydrogen values from the model were found to agree well with experimental measurements from plant trials. In the present study, the mathematical model was used to predict the hydrogen removal for four different stirring methods: 1–2) combined gas and induction stirring with the inductive stirrer working upwards or downwards and 3–4) gas stirring with two different locations for two porous plugs. Plant data was used as input to the calculations. The hydrogen calculation was validated by simulation of an actual heat and comparison with measured data. After 44 minutes of stirring the predicted and measured hydrogen contents were 1.6 and 1.8 ppm, respectively. This agreement was considered satisfactory and the model was then used to study the effect of different stirring methods on hydrogen refining. A change in the stirring method was found to affect the hydrogen refining. Combined gas and induction stirring using downward stirring was found to result in the lowest final hydrogen content in the steel as it rendered the most favourable kinetic conditions for hydrogen refining.     

30NiCrMoV12金属轴承锻件热处理过程数值模拟研究

通过Deform-HT软件,以30NiCrMoV12金属轴承锻件为研究对象,对调质热处理工艺进行了数值模拟,获得了热处理过程中温度场和组织场的变化规律。模拟结果表明,由于金属轴承采用空心化设计,锻件在油淬过程中,芯部与外表面温度差小,芯部可以快速的升温或降温,淬透性好。在淬火过程中,锻件组织完成转变,在回火升温过程中,新相组织混合物逐步形成,体积含量为96%,为实际生产工艺提供理论指导。     

Variation of mechanical properties in large steel forgings

In a continuing effort to reduce mechanical property variation in large, low alloy, steel forgings, the effects of forging reduction on mechanical and metallurgical properties were examined. This included tensile strength, ductility, impact energy and fracture toughness. Also examined were nonmetallic inclusion content and microstructure. In addition, the consequences of ingot solidification could not be ignored, therefore, the aspect of chemical homogeneity was considered. For these ingots and the range of forging reductions investigated (1.5:1 to 10:1), a reduction of approximately 3:1 produced optimum values in pct reduction of area, Charpy impact energy, and plane strain fracture toughness. The significant variations statistically determined in these parameters were accompanied by real variation in carbon concentration. Therefore, segregation of carbon on a macro scale was shown to be a major contributor to mechanical property variation in large steel forgings produced from statically cast ingots. Indeed, mechanical working alters segregation patterns but will not eliminate them.     

Present quality level of large heat resistant rotor forgings made of 1% CrMoV steel – Part II

While in part I mainly mechanical and toughness properties together with structural aspects have been dealt with now design properties are described. The basic properties for heat resistant rotor materials are traditionally the creep properties. So they are here investigated more in detail and it is shown that modern 1% CrMoV rotor steels have a quite similar creep behaviour both oil and air quenched. Long term high temperature exposure and its influence on the properties are as well mentioned as heat stability behaviour.     

Present quality level of large heat resistant rotor forgings made of 1 % CrMoV steels – Part 1

The mechanical and toughness properties of steam turbine rotors of different production methods and different heat treatments are described and compared. Air and oil quenched rotors have similar properties in respect to creep behaviour while the toughness level of the oil quenched rotors is better. Rotors manufactured since about 1975 have a better level of all properties than older ones which is due to higher degree of purity, lower level of trace elements and a today better controlled temperature process during the whole manufacturing.     

On the problem of zinc extraction from the slags of lead heat

The possibilities of zinc extraction from the slags of lead heat are studied as applied to the ZAO Karat-TsM lead plant to be built for processing ore lead concentrates. The process of zinc extraction into commercial fumes using the technology of slag fuming by natural gas developed in Gintsvetmet is recommended for this purpose. Technological rules are developed for designing a commercial fuming plant, as applied to the conditions of the ZAO Karat-TsM plant.     

Precipitation reactions during the heat treatment of ferritic steels

The precipitation reactions in two ferritic steels, 9Cr-lMo-V-Nb and 12Cr-lMo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-lMo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-lMo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-lMo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-lMo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-lMo-V-Nb alloy, a combination of chromium-rich M₂₃C₆ and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-lMo-V-W alloy were identified as chromium-rich M₂₃C₆ and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations. This paper is based on a presentation made at the “pcter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

Effect of deoxidation practice and heat treatment on the hydrogen attack of carbon steels

The hydrogen attack (HA) kinetics of an electroslag refined (ESR) and a rare earth metal (REM)-treated steel in the Q. and T. condition were investigated by a highly sensitive dilatometer. Measured activation energies for bubble growth of 108 to 203 kJ/mol and pressure exponents of 0.9 to 1.6 are rationalized in terms of surface or grain boundary self-diffusion of iron as the rate controlling mechanisms depending on the external hydrogen pressure and temperature. Comparisons of the HA susceptibility of these steels with published work show that although the HA resistance of the ESR steel is not influenced by the heat treatment, the REM steel shows a significant decrease in the rate of sample expansion. SEM observations indicate that the improvement in the HA resistance of the REM steel is related to the presence of a very low density of methane bubbles.     

Lithium depletion during heat treatment of aluminum-lithium alloys

The loss of lithium from the near surface region during heat treatment of two commercial aluminum-lithium alloys was studied using a nuclear reaction analysis technique. A finely collimated 2.5 MeV beam of³He ions was used to stimulate the⁷Li(³He,p)⁹Be reaction in samples of BAACo 8090 and 8091 alloys heat treated for 1, 4, and 16 hours at 500 °C. The emitted protons were detected as a cross section of the sample was traversed through the beam, thereby determining the lithium content as a function of distance from the external surface. Suitable calibration and control samples were used to validate the technique. The lithium concentration data were fit with assumed concentration profiles calculated from diffusion equations and modified for the particular experimental configuration employed. Extensive lithium depletion was found in both alloys, and the concentration profiles were found to be accurately predicted by the diffusion calculations. For heat treatment in either wet or dry air, the depth of lithium loss was the same, and can be approximately given as x = 1.5 √Dt. When heat treated in an argon atmosphere, the depth of lithium loss was reduced. The lithium loss appeared to be limited by the diffusive flux of lithium to the surface of the sample in wet and dry air, but was limited by other factors in argon. Porosity was observed in the lithium depleted region; this was ascribed to the accumulation of vacancies generated by the unequal fluxes of aluminum and lithium atoms.     

15-5PH不锈钢大型锻件冶炼脱氧工艺研究

摘要：以实际工艺流程50t EBT-VOD-LF-VC冶炼15-5PH不锈钢为背景,通过FactSage 8.0和经典Wagner模型研究冶炼硅铝复合脱氧过程中钢液中的铝含量、炉渣组成以及冶炼温度等因素对钢液中氧含量的影响进行了热力学研究。结果表明：Al-Si复合脱氧为15-5PH不锈钢冶炼过程中的最佳脱氧工艺,为了保证脱氧的冶炼效果,应控制钢液中的酸溶铝的质量分数在0.015%左右;降低冶炼温度有利于降低钢液平衡氧含量;考虑炉渣的物理性能和钢渣界面平衡反应得出脱氧工艺的最优炉渣成分,碱度为2.5~3.0,w（(Cr2O3)）=0.5%,w（(Al2O3)）=20%,w（(MgO)）=5%,w（(CaF2)）=5%;经过工艺优化后生产的15.5PH不锈钢中氧含量明显降低,均满足产品要求,炉渣碱度对平衡氧含量和实际生产全氧含量的影响规律基本相同。     

大直径锻造耐磨钢球热处理工艺的优化

通过对淬火温度、自回火温度和贝氏体等温转变时间对大直径锻造钢球的硬度、冲击韧性以及组织的影响的研究,对比分析了不同热处理工艺的微观组织和性能的关系.研究结果表明:锻后空冷利用余热淬火时,较优淬火温度为750℃;淬火后自回火温度较高时,钢球芯部马氏体/下贝氏体复相组织中贝氏体组织含量较高且硬度较低,为了保证淬火后钢球具有高硬度及自回火的过程,则较优自回火温度为160℃;随着贝氏体等温转变时间的延长,贝氏体含量及冲击韧性显著提高,当贝氏体等温转变时间超过110 s时,硬度明显降低,即贝氏体较优等温转变时间为110 s.与常规淬回火相比,可得到钢球组织和性能的较优匹配,综合性能优于淬回火处理.     

Increase in the efficiency of induction heating during heat treatment of wires

The energy indices of the equipment for induction heat treatment of several bundled wires are studied by a model simulation. The minimum current frequency that ensures an efficiency of 70% upon heating of wires of various diameters is determined.     

Simulation of alloying-element diffusion during electrodiffusion heat treatment of steels

The effect of an electric current on the diffusion of alloy-forming components and vacancies in alloy steels subjected to electrodiffusion heat treatment has been studied. The diffusion coefficients of chromium, silicon, and aluminum are shown to increase by one to three orders of magnitude as compared to the reported data.