Determination of the ductile-brittle transition temperature from the microplastic-strain rate

The possibility of the determination of the tendency of cast and deformed steels to brittle fracture using the temperature dependence of the small-plastic-strain rate is studied. The temperature corresponding to the maximum in this curve is found to indicate an abrupt decrease in the steel plasticity, which makes it possible to interpret it as the ductile-brittle transition temperature depending only on the structure of a material.     

应变速率对Q460连铸坯高温力学性能的影响

摘要：采用Gleeble-3500热模拟试验机和金相法测试了不同应变速率下建筑用钢Q460连铸坯的高温力学性能,获得了600~1200℃范围内Q460连铸坯的高温强度、热塑性和最终室温组织随拉伸温度和应变速率的变化规律。结果表明,当Q460连铸坯在较高的应变速率（10s-1）下进行高温拉伸时,试样的断面收缩率随着拉伸温度的升高而升高,没有出现高温脆性区;在较低的应变速率（10-3s-1）下进行高温拉伸时,试样的断面收缩率出现了2个脆性区,第1个在1100℃至熔点温度,第2个脆性区间在700℃附近。总体来说,实验钢种的高温断面收缩率均大于65%,表明建筑用钢Q460连铸坯具有较好的高温热塑性。此外,同一应变速率下,Q460连铸坯的抗拉强度随着拉伸温度的升高而降低,而伸长率随着拉伸温度的升高而升高。     

Effect of strain rate on high temperature mechanical properties of Q460 continuous cast slab

Gleeble 3500 thermal simulation testing machine and metallographic method were used to test the high temperature mechanical properties of construction steel Q460 continuous cast slab at different strain rates, and the high temperature strength, hot ductility and final room temperature microstructure of Q460 continuous cast slab at different strain rates in the range of 600℃ to 1200℃ were obtained. The results show that when Q460 continuous cast slab is performed at a higher strain rate (10s-1), the reduction of area increases with the increase of the tensile temperature without obvious high temperature brittle zone. But when the strain rate is (10-3s-1), the curves of the reduction of area has two brittle regions. The first one is located at 1100℃ to the melting point temperature, and the second is near 700℃. In general, the reduction of area of this steel grade is greater than 65%, indicating that construction steel Q460 continuous cast slab has good high temperature hot ductility. In addition, under the same strain rate, the tensile strength of Q460 continuous cast slab decreases with the increase of tensile temperature, while the elongation increases with the increase of tensile temperature.     

Effect of the strain rate and test temperature on the mechanical properties of a Ti-Ni-Fe shape memory alloy

The test temperature (from ?196 to +50°C) and the strain rate (from 10^?4 to 10³ s^?1) are found to affect the character of deformation of a shape memory alloy TN1K based on titanium nickelide and alloyed with iron. The shapes of the tensile and compressive curves are shown to depend on the position of the test temperature with respect to the characteristic phase-transition temperatures. The mechanical properties are extremal in the temperature ranges corresponding to the R phase region. As the strain rate increases in the quasi-static range, the strength characteristics of the material increase and the plastic characteristics decrease. As the strain rate increases in the quasi-static range, the yield strength changes analogously; in this case, a yield drop appears in the compressive and tensile stress-strain diagrams. The data obtained are used to optimize the technology of the thermomechanical joints of pipelines and construction elements.     

The effects of hydrostatic pressure on fracture and the ductile-brittle transition in polycrystalline molybdenum

The tensile properties of polycrystalline molybdenum were investigated in the ductile-brittle transition temperature region at atmospheric and superposed hydrostatic pressures, H, extending to 275 MNm⁻². Down to 180 K, at all pressures, the yield stress, σ_Y, and (below the ductility transition temperature, T_T the brittle fracture stress, σ_F, increased with decreasing temperature. T_T was lowered from ∼209 K by ∼0.17 K per MNm⁻² of superposed pressure, which had no effect on the values of the stresses for yielding or brittle fracture, whichever occurred. There was a continuity, as a function of temperature (down to 180K), between the values of the tensile yield and brittle fracture stresses and the compressive yield stress. In the temperature region immediately above T_T, at any pressure, failure took place by cleavage at approximately the same stress as at T_T. The application of H raised the value of the required applied stress for failure by the magnitude of H, i.e. ductile cleavage occurred at a constant value of the maximum principal stress, postulated to be the crack propagation stress. Below T_T the critical stage in brittle fracture, however, apperars to be crack nucleation, as the process took place at a constant shear stress. The data are consistent with T_T, at all pressures, being determined by the condition that the stresses for yielding (approximately the same as for crack nucleation) and crack propagation are equal.     

锻造温度对含钼粉末热锻合金显微组织及力学性能的影响

采用粉末热锻工艺制备Fe-1C-2Cu-xMo (x=0.50, 0.85, 1.46, 质量分数)合金, 分析锻造温度和Mo质量分数对烧结态及锻造态合金密度、显微组织、静态力学性能和动态摩擦性能的影响。结果表明: 锻造工艺能够有效提高材料密度, 锻后合金相对密度可达到98.5%, 锻态合金组织主要由贝氏体、马氏体和残余奥氏体组成。合金硬度随Mo质量分数的增加而提高, 随锻造温度的升高先降低后提高, 1050 ℃锻造Fe-1C-2Cu-1.46Mo合金硬度可达HRB116.38。Mo质量分数和锻造温度共同影响合金横向断裂强度, 1000 ℃锻造Fe-1C-2Cu-0.50Mo合金强度最高可达2608MPa, 合金断裂方式为韧脆混合型断裂。材料动态摩擦性能随Mo质量分数的增加显著提升, 当锻造温度为950 ℃且Mo质量分数为1.46%时, 材料的摩擦系数仅为0.088, 明显低于其他材料且波动较小。     

Effect of molybdenum additives on the mechanical properties of iron-copper pseudoalloys

The effect of molybdenum additives (10%) on mechanical properties and the microstructure of iron-copper (Fe-30% Cu) pseudoalloys is investigated. The tensile strength, hardness, and electrical resistivity are determined, and the microstructure of specimens is analyzed quantitatively. It is established that during both solid-and liquid-phase sintering, no solid-phase solutions are formed, and a stable heterophase microstructure develops as the components undergo mutual diffusion. The heterophase nature of structure hinders grain growth of the refractory phase. The grain size of the sintered specimens does not exceed 1–5 µm. The plasticity of Fe-30% Cu-10% Mo pseudoalloys obtained during solid-phase sintering is increased significantly as compared with Fe-Cu alloys, and the elongation is 13.8% at a porosity of about 1%. Specimens produced by liquid-phase sintering experience greater elongation, but during prolonged liquid-phase sintering (more than 10 min), grain growth is restored, and the plasticity of the Fe-Cu-Mo specimens is reduced.     

Effect of the strain rate on the properties of electrical copper

The effect of the strain rate on the texture and strength characteristics of electrical copper is analyzed using an industrial experiment on low- and high-speed wire drawing. The mechanical properties of the product are determined. The strength of the wire drawn at a high speed is found to be about 20 MPa higher than that of the wire drawn at a low speed. Metallographic analysis shows no differences in the wire structures, and texture analysis reveals differences in the behavior of dominant texture components. The directions of the dominant texture components are found to rotate near the periphery of the workpiece (i.e., at the workpiece surface). The solution of the drawing problem by the finite element method demonstrates an analogous rotation of the principal elongation directions.     

Effect of the strain rate on the mechanical properties of a sheet TRIP steel with a high martensite content

The laws of changing the mechanical properties of sheet austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel are studied when the static strain rate changes in the range 0.1–20 mm/min (8.3 × 10^–5–17 × 10^–3 s^–1). The 0.35-mm strip under study is characterized by a high martensite content (≈100%) in the surface layer at an average content of 80–85%. The transformation induced plasticity effect is maximal at a strain rate of 0.1 mm/min (8.3 × 10^–5 s^–1).     

水温对冷轧马氏体钢板淬火冷却速度和性能的影响

冷轧马氏体钢板以其高强度特点,在汽车零部件制造中具有较大的减重潜力,逐步获得越来越多的应用.冷轧马氏体钢板一般采用具有水淬冷却功能的连续退火机组生产,水淬过程工艺参数对马氏体钢板的组织和性能影响很大.以C-Mn系冷轧马氏体钢板为研究对象,研究水温对淬火冷却速度、钢板的力学性能和组织的影响.结果表明,在室温较低的情况下,马氏体薄钢板的冷速可达近1 000 K/s.随着水温的变化,不仅平均冷却速度发生改变,而且瞬时冷却速度曲线的形状也发生较大的变化.水温提高导致冷却速度下降,从而导致马氏体钢板强度和组织的较大变化.这种变化规律,对于马氏体钢板性能稳定控制有一定的参考意义.     

Special features of the ductile-brittle transition in iron-based powder materials. II. Physicomechanical model of the ductile-brittle transition in cracking resistance tests

Conclusions The presence of pores in the material leads to the redistribution of stresses in the material and to localization of strains in small volumes between the pores. The susceptibility to ductile failure increases with increasing porosity.At –196°C, the failure mechanism of the porous materials based on iron changes from ductile to brittle (cleavage) with decreasing porosity. The dependence of cracking resistance on the porosity of these materials is nonmonotonic and the maximum cracking resistance is recorded at porosity values at which the failure mechanism changes. The nonmonotonic nature of cracking resistance reflects the high sensitivity of this characteristic to the change of the stress state in the material. The change of the stress state in the ductile-brittle transition temperature range can be described by the condition _f = _T. In the porous materials examined this condition is valid because of the specific form of the _f- and _T- dependences. The model of the ductile-brittle transition proposed in this work can be used to determine the analogy between the cold brittleness temperature T_br and the critical value of porosity _c corresponding to the point of intersection of the _f- and _T- curves for the porous materials.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 39–42, March, 1988.     

Effect of the chemical composition of Fe-Mn-C-P alloys on the brittle-ductile transition temperature in the solidification range

The brittle-ductile transition temperature in the solidification range depends on the composition of the phase which solidifies as the last one. The paper presents a thermochemical study of Fe-Mn-C-P system, determining the conditions of crystallisation of carbides, phosphides and the pseudo-ternary eutectic M^L-M₃C-M₃P. Manganese raises the phosphorus concentration in eutectic. The eutectic temperature attains its maximum at about 6% of Mn. Then the brittle-ductile transition temperature is about 30 K higher than in ternary Fe-C-P alloy. A further raise is possible when the alloy is modified by an element forming stable, solide carbide, for ex. titanium. The results of theoretical analysis were verified by experimental work. The influence of titanium on the inclusions appearing in the vicinity of hot cracks of Hadfield cast steel has been studied.     

Test temperature and strain rate effects on the properties of a tungsten heavy alloy

Liquid phase sintered tungsten heavy alloy specimens with a 90W-7Ni-3Fe composition were tested for temperature and strain rate effects on mechanical behavior. Both fracture stress and strain were measured for samples tested at 20, 300, or 600 °C, with crosshead speeds ranging from 0.004 to 400 mmJs in an argon atmosphere. Fracture surface examinations showed a dramatic increase in tungsten cleavage as the ductility increased. The effect of an increasing strain rate is a slight strength increase with a concomitant ductility decrease. Alternatively, higher test temperatures degrade strength with a nonsystematic effect on ductility; maximum ductility occurs at 300 °C and a slow strain rate. Surface oxidation at 600 °C greatly degrades ductility. The results are mathematically modeled using classic strain rate dependent equations.     

Effect of molybdenum and chromium additions on the mechanical properties of Fe3Al-based alloys

A combined addition of molybdenum and chromium to Fe₃Al-based alloys results in a significant improvements of yield strength and creep life at the temperature of 600C. The chromium addition to Fe₃Al-based alloys decreases the solubility of molybdenum. Precipitates with complex composition form in the Fe-28Al-(2–5)Cr alloys which containing more than 1% molybdenum. With the increase of the molybdenum addition to the Fe-28Al-(2–5)Cr alloys, the fracture mode changes from a mixed one of transgranular cleavage and intergranular failure to entire transgranular cleavage.     

Effect of copper and molybdenum additions on the microstructure and mechanical properties of steel shot

The effect of copper and molybdenum additions on the microstructure of particles produced by the atomization of an iron-carbon melt by an air-water jet using a new atomizer unit has been studied. The application of air-water atomization instead of water atomization is shown to intensify the solidification of particles with a fine microstructure. The introduction of molybdenum (up to 0.6 wt %) into a melt refines the structural constituents of the granules and decreases the fraction of the retained austenite, and the introduction of copper (up to 0.8 wt %) leads to the opposite results. The addition of copper (up to 0.6 wt %) and molybdenum (up to 0.6 wt %) to a melt results in a homogeneous microstructure consisting of fine acicular martensite and fine molybdenum carbides. Low-temperature vacuum tempering at 350°C for 1 h leads to insignificant decarburization of the martensite and the precipitation hardening of the base metal due to copper alloying. The microstructure of a steel alloyed by molybdenum and copper provides an increase in the wear resistance of the steel shot by a factor of 1.5–2 and high quality of the shot (close to the best foreign analogs).     

Si和La元素对Mo丝显微组织与力学性能的影响

系统研究了La、Si单元掺杂和复合掺杂对钼丝的显微组织和力学性能的影响及其作用机制,优化出具有优异力学性能的Mo-Si-La合金丝的成分为Mo-0.15Si-(0.5～0.8)La.MoSi2与Mo原位反应生成Mo5Si3和Mo3 Si硬质相,起到良好的晶粒细化作用和弥散强化作用.La2O3颗粒通过延迟微裂纹的形成和扩...     

Effect of intercritical annealing temperature and cooling rate on the microstructure and mechanical properties of low-carbon aluminum killed steel

In this study,the intercritical annealing process for a typical low-carbon aluminum killed steel is investigated.A cold-rolled sheet was annealed at intercritical temperatures ranging from 730 ℃ to 770 ℃ and then cooled in air or water.The annealed steel was then baked at 210 ℃,and its mechanical properties and microstructures were analyzed in detail.It is shown that after the air-cooling process,the strength of steel decreased and ductility increased with an increase in the annealing temperature.However,after water-cooling,the strength and ductility both increased with the increase of annealing temperature.These results are attributed to the propertyoptimization of the steel.