Ren Bo Song

Research on the Microstructure and Microhardness of 9Cr18 Semi-Solid Billet

Formed in the semi-solid state, materials can obtain unconventional microstructures and properties compared with traditional method. In this paper, semi-solid billet of 9Cr18 steel was obtained through a wavelike sloping plate. Microstructure analysis of the semi-solid billet was conducted through scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) test and microhardness test were also used to analyze the properties. The results showed that the structure of 9Cr18 semi-solid billet contained globular primary austenite and secondary austenite-Cr7C3 eutectic. Globular primary austenite grains were first formed during partial solidification in the sloping plate, and then the rest liquid metal formed secondary austenite and Cr7C3 eutectic structure surrounding the primary grains. Cr atoms had a concentration in the rest liquid side, which along with C atoms contributed to the formation of the Cr7C3 carbide. Hardness in the primary solid grain area and the eutectic area was about 330 HV and 650 HV, respectively. These specific properties were important for subsequent thixoforming of the functional graded materials.

Research on Fluctuations in Work Hardening Rate of a Fe-Mn-Al-C Steel

The fluctuations in the work hardening rate of a Fe-12Mn-10Al-0.7C (wt. %) steel have been investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The work hardening rate of the heat treated sample had a tendency of decrease with fluctuations. The first raise in the work hardening rate curve at about 2% true strain is attributed to the shearing of the small ferrite grains by austenite, and the deformation induced twinning can contribute to the raise and drop in the work hardening rate curve. The second fluctuation range at the true strain between 10% and 14% is mainly related to the activation of planar slip on the principle slip plane which is suppressed by twins in austenite.

Continuous Annealing Process and Microstructure Property of 1200mpa High Strength Steel by Ultrafast Cooling

The different dilatometric curves of continuous cooling transformation have been determined by DIL805 thermal mechanical simulate, through metallographic and hardness method to study the effect of different cooling rate on the microstructure of transition. The critical point Ac1 and Ac3 of the tested steel are 709°C and 865°C. With the increase of cooling rate, the hardness of the steel and the content of martensite increase. In the laboratory conditions, the steel in this experiment was heated to 780°C, 800°C, 820°C, 840°C and 860°C, for 80s, then slowly cooled to 680°C, and water quenched to room temperature finally. The aging temperature was 240°C for 300s, and the last the sample was air cooled to room temperature. The results show that the microstructure of the annealed experimental steel belongs to martensite and ferrite. With the increase of annealing temperature, the content of martensite, the tensile strength and yield strength of the experimental steel increase, and the elongation decreases continuously. The sample was annealed at 800°C for 80s, then slowly cooled to 680°C and finally water quenched to room temperature. After overaging at 240°C, the samples were obtained with high mechanical properties. The tensile strength, yield strength and elongation are 1223MPa, 605MPa and 9.2%, respectively.

Working Hardening Mechanism and Aging Treatment Behaviors of D631 Precipitation Hardening Stainless Steel Wire

Precipitation hardening stainless steel has the advantages of both austenitic stainless steel and martensitic stainless steel, including good corrosion resistance, excellent processability and high strength. With the evolution of microstructure and properties of semi-austenitic precipitation hardening stainless steel (D631) during drawing process and aging treatment, the working hardening behaviors, law of phase transition, dissolution and precipitation state of alloying element are investigated to gain the toughness mechanism of D631. The results show that the tensile strength increases with the increase of the reduction of area, on the contrary, the plasticity decreases gradually. The tensile strength is 1529 MPa while the reduction of area is 54%. By means of X-ray diffraction (XRD) and metallograpic observation, the content of martensite increases with the increase of deformation, and makes the higher strength and lower plasticity. The alloying element dissolved in the matrix precipitates in fine particles by aging treatment, resulting in a higher strength of 1948MPa.

Effect of Solid Solution Treatment on the Microstructure and Properties of Fe-Mn-Al Light-Weight Steel

A study was made of the effects of solid solution treatment on the properties of hot rolled Fe-Mn-Al steel and on the microstructure transformation. In the steel, the austenite matrix and ferrite duplex phases were confirmed by micrographs and X-ray diffraction. It was indicated that the hot rolled Fe-Mn-Al steel (6.55g/cm3 in density) is with mechanical properties of tensile strength 1315.6MPa, elongation 14.60%. The tensile strength decreases with increasing temperature. The tensile test displays an outstanding combination of high strength and ductility at room temperature due to continuous strain hardening behavior. The product of tensile strength and ductility can reach 46.5GPa·%. Solution treatment contributes to the dissolution of precipitate, austenite grain growth and banded ferrite crushing.

Fabrication of Semi-Solid Slurry for Steels and Their Rheo-Rolling Process

Semi-solid metal forming (SSM) has been recognized as a new forming technology, which is different from the present metal forming methods. Basic research on SSM has been put into operation and a number of SSM techniques have been widely applied in industry. In the application of SSM technique, at present, it is mainly used to produce the low melting point alloys such as Al-base, Zn-base and Mg-base alloys, but the high melting point alloys, for example steels as the most widely useful metal are not extensively studied and applied. In the present work, the electromagnetic stirring method was used to prepare semi-solid slurry of spring steel–60Si2Mn and stainless steel–1Cr18Ni9Ti. At the same time, spring steel–60Si2Mn and stainless steel–1Cr18Ni9Ti were directly rolled into thick strips in the semi-solid state (Rheo-rolling). It is aimed at studying the microstructure and properties of the strips to establish the feasibility of rheo-rolling for the production of the steel strips. According to the present research work, it has been shown that rheo-rolling process combines the casting and hot rolling into a single step for near net-shape production, compared with the conventional hot-rolled metallurgical process. Besides being such a cost-effective process, rheo-rolling process possesses irregular crystal grains such as rosette-type primary crystals in the microstructures because of sufficient agitation during solidification. The overall homogenization of the macrostructures in the whole part of steel ingot can be achieved.

Solid-state synthesis of Mg2X (X=Si, Ge, Sn and Pb) via bulk mechanical alloying

Magnesium base alloys and compounds are attractive for various applications as a functional material. In particular, a series of binary system by Mg2X (X = Si, Ge, Sn and Pb) has fascinated many researchers and engineers by its thermoelectric properties and semi-conductive performance. Many barriers in its processing rejects precise investigation of these types of semiconductive compounds: high vaporizing pressure and mechanical adhesion of magnesium, reaction of germanium and tin with crucibles, and, difference of melting point among elements, X. Solidstate processing via the bulk mechanical alloying enables us to directly fabricate these Mg2X semiconductive materials in high density performs. The precise control of chemical composition leads to an investigation on the dilution and enrichment of X in Mg2X. Two types of solid-state reactivity are introduced: e.g. synthesis of Mg2Si from an elemental mixture Mg – Si, which is a nucleationcontrolled process, while synthesis of Mg2Sn from Mg – Sn is a diffusion-controlled process. The thermoelectricity of these Mg2X is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.

Effect of Ultra-Fast Cooling Rate on the Microstructure and Mechanical Properties of High Strength Cold-Rolled Sheet under Continuous Annealing

The effect of different fast cooling rates on the microstructure and mechanical properties of the V and Ti microalloyed high strength cold-rolled sheet was studied under laboratory conditions. Five different fast cooling rates were set up as 20°C/s, 50°C/s, 200°C/s, 500°C/s and 1000°C/s, respectively. Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure, and the mechanical properties were also tested. The results showed that with the increase of fast cooling rate from 20°C/s to 1000°C/s, the grains of martensite and ferrite were finer, and the average grain size of both martensite and ferrite decreased from 7.7μm to 3.9μm. The proportion of ferrite in the two phases decreased while that of the martensite increased from 25.7% to 62.1%. The morphology of martensite tended to be lath, and the density of dislocation in the ferrite grains nearby the martensite gradually increased. With cooling rate rising from 20°C/s to 1000°C/s, the yield strength of the experimental steel increased from 381MPa to 1074MPa, and the tensile strength increased from 887MPa to 1199MPa. And the elongation decreased from 14.2% to 7.2%, and the product of strength and elongation decreased from 12.6GPa·% to 8.6GPa·%.

Principle and Model of Phase Transformation in Ultra-High Strength Steel for Cone Crusher

The principle of phase transformation in ultra-high strength steel for cone crusher was studied by DIL805 thermal mechanical simulate, and the critical temperature was determined. The Austenite continuous cooling transformation (CCT) diagram of the steel was confirmed by thermal expansion curve, dilatometry and metallography. The phase transformation model was established and offered a theory for deciding parameters of heat treatment process. The results proved that: when the cooling rate was under 0.5 °C/s, the structure was mainly Pearlite and Bainite. With the increase of cooling rate, the content of lower Bainite increased. When it came to 1°C/s , Martensite start to transform from Austenite. When the cooling rate is 5°C/s, Pearlite disappears, Bainite and Martensite were in the majority. Meanwhile, the mathematical equations of phase transformation have high degree to fit the experimental results, and the phase transformation model is feasible.

Effect of Different Cooling Rates on Microstructure and Property of Continuous Annealing IF Steel

The influence of different annealing cooling rates on microstructure,precipitation of the second phase and mechanical properties of IF steel was studied. The recrystallizing behavior of IF steels was analyzed by batch annealing process. After confirming the recrystallizing temperature of IF steel, the simulations of different continuous annealing cooling rates (5°C/s, 20°C/s, 50°C/s, 200°C/s 500°C/s and 1000°C/s ) were performed. At the same time, combined with TEM and XRD, the precipitating behavior and microstructure texture were analyzed. The results showed that the recrystallization temperature was speculated between 540°C and 560°C. As the cooling rate increased, the grain sizes became smaller and the yield strength increased significantly. And the tensile strength and elongation were more or less static. The tensile strength remained 240MPa and the elongation kept around 50%. With 1000°C/s cooling rate, the sample performed best with the r-value of 3.03. TiN precipitation was observed. The annealed texture is mostly composed of {111} texture.