回火温度对1500MPa级Nb-Ti低合金直接淬火钢组织与性能的影响

通过低成本成分设计,在控制轧制的基础上,应用直接淬火+回火工艺制得抗拉强度1 500 MPa级经济型低合金高强高韧钢,测定了该合金成分体系的连续冷却转变曲线,研究了不同回火温度对直接淬火钢组织与力学性能的影响.结果表明:随着回火温度的升高,试验钢抗拉强度逐渐下降,屈服强度先升高后降低,-40℃冲击功则呈现出先升高、后降低、再升高的趋势.回火温度为200℃时,试验钢获得了最优的综合力学性能,抗拉强度达到1 730 MPa,屈服强度为1 400 MPa,-40℃冲击功为43 J.     

Effect of process temperature on the microstructure and properties of gas oxynitrocarburized 35CrMo alloy steel

In the present investigation, 35CrMo alloy steel was gas oxynitrocarburized at 550 °С, 570 °С and 610 °С for 2 h by applying a low-temperature gas multi-elements penetrating system. Microstructure, surface composition, case depth, microhardness, wear and corrosion resistance were analyzed. The compound layer consisting of γ′-Fe₄N and ε-Fe₃N and oxide layer of Fe₃O₄ and Fe₂O₃ were formed on the ground reference surface after treated. Compared with the conventional gas nitrocarburizing, a larger effective case depth was obtained successfully in a short time after treatment. The microhardness and the properties of wear and corrosion resistance were improved obviously and the properties of samples treated at 570 °C are optimum when compared with the samples treated at 550 °С and 610 °С for the same duration.     

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel was studied. The hot-rolled ferrite-pearlite showed low monotonic and cyclic strengths with high ductility in terms of true fracture strain and a high shreshold stress intensity. The quenched and tempered low carbon martensite showed high monotonic and cyclic strengths and high ductility. However, the threshold stress intensity was significantly lower than that of the ferrite-pearlite. Both the strength and threshold stress intensity of an austempered bainite and a duplex ferrite-martensite are greater than those of the hot-rolled ferrite-pearlite. At a same strength level, the ductility and the threshold stress intensity of the low carbon martensite are higher than those of a medium carbon martensite.     

Effect of microstructure on mechanical properties in weld-repaired high strength low alloy steel

To understand the effect of microstructure on mechanical properties of weld-repaired high strength low alloy (HSLA), as-received and weld-repaired HSLA with and without buffer layers (BLs) were prepared. Microstructure analysis was carried out using optical microscope and SEM, and mechanical properties were measured by Vickers hardness test and fatigue test.The fatigue resistance of weld-repaired HSLA without BL was deteriorated with comparing to parent metal (PM). Meanwhile, Vickers hardness (VH) showed an obviously reduction in the melted parent metal (MPM), which was due to formation of predominately block ferrite. For the weld-repaired HSLA with BL, the VH and fatigue resistance increased with the incorporation of 4 mm BL, which was mainly due to formation of lath ferrite and fine-grained pearlite and bainite. When BL thickness increased to 10 mm, the VH and fatigue resistance decreased, which was because the thick BL diluted the MPM. VH number from low temperature (below melting point) heat affected zone (HAZ) fluctuated, but had a little scatter. However, the fatigue crack growth rate from HAZ was not obviously affected by the welding as comparison with the PM.     

Effect of tempering temperature on the microstructure and properties of ultrahigh-strength stainless steel

The microstructure, precipitation and mechanical properties of Ferrium S53 steel, a secondary hardening ultrahigh-strength stainless steel with 10% Cr developed by QuesTek Innovations LLC, upon tempering were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile and impact tests. Based on these results, the influence of the tempering temperature on the microstructure and properties was discussed. The results show that decomposition occurred when the retained austenite was tempered above 440 °C and that the hardening peak at 482 °C was caused by the joint strengthening of the precipitates and martensite transformation. Due to the high Cr content, the trigonal M₇C₃ carbide precipitated when the steel was tempered at 400 °C, and M₇C₃ and M₂C (5–10 nm in size) coexisted when it was tempered at 482 °C. When the steel was tempered at 630 °C, M₂C and M₂₃C₆ carbides precipitated, and the sizes were greater than 50 nm and 500 nm, respectively, but no M₇C₃ carbide formed. When the tempering temperature was above 540 °C, austenitization and large-size precipitates were the main factors affecting the strength and toughness.     

Influence of austempering temperature on the mechanical properties of a low carbon low alloy steel

In this investigation, a new low alloy and low carbon steel with exceptionally high strength and high fracture toughness has been developed. The effect of austempering temperature on the microstructure and mechanical properties of this new steel was examined. The influence of the microstructure on the mechanical properties and the fracture toughness of this steel was also studied.Test results show that the austempering produces a unique microstructure consisting of bainitic ferrite and austenite in this steel. There were significant improvement in mechanical properties and fracture toughness as a result of austempering heat treatments. The mechanical properties as well as the fracture toughness were found to decrease as the austempering temperature increases. On the other hand, the strain hardening rate of steel increases at higher austempering temperature. A linear relationship was observed between strain hardening exponent and the austenitic carbon content.     

The effect of single and double quenching and tempering heat treatments on the microstructure and mechanical properties of AISI 4140 steel

This investigation is concerned to evaluate the effect of double quenching and tempering (DQT) with conventional quenching and tempering (CQT) heat treatment processes on microstructure and mechanical behavior of a commercially developed hot rolled AISI 4140 type steel. Comparison of microstructure and mechanical properties of DQT and CQT heat treated specimens have been established in details. Optical and scanning electron microscopies have been used to follow impurity concentration and microstructural changes, and their relation to the associated mechanical properties. The results indicate that the improvement of mechanical properties particularly impact toughness of DQT heat treated specimens is much higher than that of the CQT condition, and this observation is rationalized in terms of finer austenite grain size developed in the DQT condition providing much finer martensitic packets within the grains and a lower level of impurity concentration of sulfur (S) and phosphorus (P) near the prior austenite grain boundaries as well.     

Effect of tempering temperature on monotonic and cyclic properties of a high–strength low–alloy chain steel

Abstract

The influence of tempering temperature in the range 200–600°C on the monotonic and cyclic response of a high-strength, low–alloy steel used for haulage chains has been investigated. Static properties are little affected by tempering up to 400°C, with a small loss of strength arising from carbide coarsening. At higher tempering temperatures, dislocation annihilation is substantial and the strength falls markedly. On undergoing high–strain fatigue, the alloy exhibits cyclic softening at all tempering temperatures, but with a maximum of about 25% after a 400°C temper. The microstructural changes producing this are difficult to detect directly, but it is thought that dislocation unpinning has an important role. For tempering temperatures in excess of 400°C, the reduced softening can clearly be equated with a dislocation redistribution and the formation of cell substructure within the ferrite grains. Estimations of the magnitude of the various components of strength are made.

MST/199     

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200 °C for 60 min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600 °C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400 °C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.     

回火温度对MC3钢碳化物析出及力学性能的影响

由于工作环境的恶劣性,冷轧辊在工作过程中常会发生断辊.为使冷轧辊用MC3钢获得良好的强韧性匹配,避免断辊的发生,本文采用扫描电子显微镜、X射线衍射仪、能谱分析仪等研究了不同回火温度对冷轧辊用MC3钢显微组织和力学性能的影响.研究表明:经550-750℃回火处理的MC3钢组织均为回火索氏体组织,随着回火温度的升高,析出的...     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.     

The dependence of mechanical properties on structure in low alloy steel forgings

The mechanical properties of two heat-treated steel forgings, manufactured from medium carbon Ni-Cr-Mo-V steels have been measured and compared. Microstructural characteristics such as martensite packet and lath size, dislocation density and precipitate size and distribution were measured and used in a detailed quantitative analysis of the relation between microstructural characteristics and proof stress. It was found that the microstructural differences identified could well account for the differences in tensile strength between the materials. Electron microcopy indicated that temper embrittlement leading to intergranular fracture may be responsible for the differences in transition temperature.     

烧结温度对多孔TiNi合金微观结构和力学性能的影响

采用Ti、Ni纯元素混合粉末真空烧结技术制备了孔隙分布均匀且力学性能优良的多孔TiNi形状记忆合金(SMA),并利用X射线衍射仪、金相显微镜、扫描电子显微镜及电子万能试验机研究对比了900、950、1000、1050、1100和1150℃6个不同烧结温度对合金微观结构和力学性能等的影响。结果表明,烧结温度是影响多孔TiNi合金性能的决定性因素,通过调节烧结温度可有效调节合金的相组成、孔隙特征和力学性能。随着烧结温度的升高,合金的次生相逐渐减少,相组成成分更加均一;致密度不断提高,由59%上升到62%,孔隙分布愈加均匀且孔隙形貌由多尖角形趋于球形化;抗拉强度由72.43MPa增加到160.12MPa,弹性模量从1.08GPa增加到1.32GPa。     

Precipitation,microstructure and mechanical properties of low nickel maraging steel

Abstract

A maraging steel with a composition of Fe–12·94Ni–1·61Al–1·01Mo–0·23Nb (wt-%) was investigated. Optical, scanning electron and transmission electron microscopy and X-ray diffraction analysis were employed to study the microstructure of the steel after different aging periods at temperatures of 450–600°C. Hardness and Charpy impact toughness of the steel were measured. The study of microstructure and mechanical properties showed that nanosized precipitates were formed homogeneously during the aging process, which resulted in high hardness. As the aging time is prolonged, precipitates grow and hardness increases. Fractography of the as forged steel has shown mixed ductile and brittle fracture and has indicated that the steel has good toughness. Relationships among heat treatment, microstructure and mechanical properties are discussed. Further experiments using tensile testing and impact testing for aged steel were carried out.     

Effect of rolling temperature on microstructure and mechanical properties of 6063 Al alloy

Aluminium alloy (6063) was severely rolled upto 92% thickness reduction at liquid nitrogen temperature and room temperature to study the effect of rolling temperature on its mechanical properties and microstructural characteristics by using tensile tests and SEM/electron back scattered diffraction (EBSD), transmission electron microscope (TEM), DSC, X-ray diffraction (XRD) as compared to room temperature rolled (RTR) material with the same deformation strain. An improved strength (257 MPa) of cryorolled 6063 Al alloy was observed as compared to the room temperature rolled alloy (232 MPa). The improved strength of cryorolled alloy is due to the accumulation of higher dislocation density than the room temperature rolled material. The tensile properties of cryorolled alloy and the alloy subjected to different annealing treatments were measured. The cryorolled alloy subjected to annealing treatment at 300 °C for 5 min exhibits an ultrafine-grained (UFG) microstructure with improved tensile strength and ductility.     

Effect of chromium content on the microstructure and mechanical properties of multipass MMA,low alloy steel weld metal

Effect of chromium content in the range of 0.05–0.91 wt% on the microstructure and mechanical properties of Cr–Ni–Cu low alloy steel weld metal was investigated. All welds were prepared by manual metal arc welding technique in flat position. Microstructure of the welds was examined by optical and scanning electron microscope in both columnar and reheated regions of the weld metal. The results showed increase in acicular ferrite and microphases formed at the expense of primary ferrite and ferrite with second phase with steady refinement of microstructure. According to these microstructural changes, yield and ultimate tensile stresses, Hardness and Charpy V-Notch impact toughness increased, whereas elongation decreased. Increase in Charpy impact value is thought to be due to fine dispersed spheroidized dark microphases at high chromium contents.     

卷取温度对钛微合金化钢组织与性能的影响

与铌钒微合金化钢相比,钛微合金化钢有更低的成本,因此设计了一种低碳钛微合金化热轧高强钢,并利用扫描电镜(SEM)和透射电镜(TEM)等仪器研究了不同卷取温度对实验钢组织和性能的影响.结果表明:卷取温度对实验钢的组织与力学性能有较大的影响,300℃卷取时得到板条贝氏体和粒状贝氏体的混合组织,400和470℃卷取时得到粒状贝氏体组织;实验钢的屈服强度和抗拉强度均随卷取温度的升高呈现出先下降再上升的规律,延伸率呈现出先升高再下降的规律,分析认为力学性能的变化主要由相变强化、析出强化以及M-A岛的尺寸和形态共同决定;470℃卷取时实验钢有较好的综合力学性能,屈服强度和抗拉强度分别达到了700和865 MPa,延伸率达到了18.9%.     

Laser-shock processing effects on surface microstructure and mechanical properties of low carbon steel

The effects of laser-shock processing (LSP) on the microstructure, microhardness, and residual stress of low carbon steel were studied. Laser-shock processing was performed using a Nd:glass phosphate laser with≈600 ps pulse width and up to 120 J pulse energy at power densities above 10¹² W cm⁻². The effects of shot peening were also studied for comparison. Laser-shock induced plastic deformation caused the surface to be recessed by≈1.5 μm and resulted in extensive formation of dislocations. Surface hardness increased by up to 80% after the LSP. The microstructure and mechanical properties were altered up to≈100 μm in depth. The LSP strengthening effect on low carbon steel was attributed to the presence of a high dislocation density. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than did LSP.     

Effect of heat input on microstructure and mechanical properties of dissimilar joints between super duplex stainless steel and high strength low alloy steel

In the present study, microstructure and mechanical properties of UNS S32750 super duplex stainless steel (SDSS)/API X-65 high strength low alloy steel (HSLA) dissimilar joint were investigated. For this purpose, gas tungsten arc welding (GTAW) was used in two different heat inputs: 0.506 and 0.86 kJ/mm. The microstructures investigation with optical microscope, scanning electron microscope and X-ray diffraction showed that an increase in heat input led to a decrease in ferrite percentage, and that detrimental phases were not present. It also indicated that in heat affected zone of HSLA base metal in low heat input, bainite and ferrite phases were created; but in high heat input, perlite and ferrite phases were created. The results of impact tests revealed that the specimen with low heat input exhibited brittle fracture and that with high heat input had a higher strength than the base metals.     

石墨化温度对炭纤维微观结构及其力学性能的影响

以通用型PAN基炭纤维为原材料，通过1800℃～3000℃连续高温石墨化处理，制备了不同性能的炭(石墨)纤维；采用SEM、XRD、RAMAN、元素分析仪、万能材料测试机等分析手段研究了石墨化温度对炭(石墨)纤维微观结构、元素含量、表面形态及其力学性能的影响。实验表明：随着热处理温度的提高，炭纤维中非碳元素(氮、氢)的含量逐渐减少而碳元素质量分数却从92．62％增加到99．99％；纤维的微观结构也从二维乱层石墨结构向有序的三维层状结构发展，表现为石墨晶体层间距d。随处理温度的提升逐渐减小、d100和d110与La和Lc不断增大，纤维抗拉强度呈下降趋势、弹性模量呈上升趋势。