Microstructure and Strengthening Mechanisms in an HSLA Steel Subjected to Tempforming

An effect of tempforming on the microstructure, the carbide precipitation, and the strengthening mechanisms of high-strength low-alloyed steel has been analyzed. The quenched steel was subjected to 1 h tempering at a temperature of 873 K, 923 K, or 973 K followed by plate rolling at the same temperature. Tempforming resulted in the formation of an ultrafine grained lamellar-type microstructure with finely dispersed carbides of (Nb,V)C, Fe3C and Cr23C6. A decrease in tempforming temperature resulted in a reduction of the transverse grain size from 950 nm to 350 nm. Correspondingly, the size of Fe3C/Cr23C6 particles decreased from 90 nm to 40 nm while the size of (Nb,V)C particles decreased from 17 nm to 4 nm. Refining the tempformed microstructure with a decrease in thetempforming temperature provided an increase in the yield strength from 690 MPa to 1230 MPa.

A Brief Review on Validation for Heat Treatment Simulation

Heat treatment simulation has progressed to the stage where several commercial software are available. Validations of simulation functions using experimental results contributed to this realization. Organizing information on the validations may be effective for maintaining the functions and educating users about the nature of the phenomena. For this reason, the author here briefly reviews mainly his validation cases. Since experiments using specimens having relatively simple shapes can reveal the essence of complex phenomena, the results have been used in the validations. When the basic functions such as heat transfer, phase transformation, latent heat, and hardness prediction were comprehensively validated in the early stages of software development, the author used experimental results of the inverse hardening in quenched steel cylinders. After that, his validations of the software at the stage where adding stress and strain analysis functions, used effectively measurement data of length and diameter changes, and residual stress distributions in normally quenched steel cylinders. While, it was also worth to validate curving in long specimens cooled unevenly, which included a case of specimens with a similar cross-section to the Japanese sword. In addition, the author validated distortions and residual stresses in carburized and quenched, induction hardened, and also nitrided specimens.

On self-organization of the surface layer of structural steel in dry sliding against quenched steel under electric current

Using optical and confocal laser microscopes it was shown that dry sliding of structural steel against hardened steel under electric current of density higher 250 A/cm2 was accompanied by the formation of composite tribolayers. By X-ray phase analysis of the surface layers of the sample and counterbody was shown that they contain α-Fe, γ-Fe, and FeO. It is noted that the self-organization of the tribosystem under conditions of dry sliding under electric current can be represented as a hierarchy of structural states of the surface layers of contacting materials. It was found that the nominal sample area had two sectors. The character of the contact interaction in the sectors differs from each other.

Effect of Sub-Zero Treatments and Tempering on Corrosion Behaviour of Vanadis 6 Tool Steel

Sub-zero treatment of Vanadis 6 steel resulted in a considerable reduction of retained austenite amount, refinement of martensite, enhancement of population density of carbides, and modification of precipitation behaviour. Tempering of sub-zero-treated steel led to a decrease in population density of carbides, to a further reduction of retained austenite, and to precipitation of M3C carbides, while M7C3 carbides precipitated only in the case of conventionally quenched steel. Complementary effects of these microstructural variations resulted in more noble behaviour of sub-zero-treated steel compared to the conventionally room-quenched one, and to clear inhibition of the corrosion rate at the same time.

Effects of Heat Treatment on the Corrosion Behavior of ASTM A-36 Steel

The effects of different tempering temperatures and heat treatment times on the corrosion resistance of rolled ASTM A-36 steel in various concentrations of hydrochloric acid (HCl) and sodium chloride (NaCl) were studied in this work, using the conventional weight loss measurement. Rolled and heat-treated specimens were placed in the acidic media for five days and for seven days in NaCl, respectively, and the corrosion rates were evaluated. The microstructure of steel before and after heat treatment was studied. Corrosion resistance revealed remarkable changes from the effect of tempering after water or oil quenching of steel. Generally, the corrosion rate increases from the effect of steel hardening. Tempering of water-quenched steel at 450Co for one hour highly improves the corrosion resistance of 0.27% carbon steel.

Preparation and performance analysis of gas-quenched steel slag beads

The low utilization rate of steel slag in China has exposed serious environmental and social problems. In the present work, the basic oxygen furnace (BOF) slag was modified by blast furnace (BF) slag and then beaded by the means of gas quenching. The gas-quenching rate, bead formation rate, physical properties, microscopic characteristics and free lime (f-CaO) of gas-quenched slag beads were analyzed to broaden the utilization of BOF slag. The results show that the more BF slag is added, the higher the gas-quenching rate is, and the lower the bead formation rate becomes. When no BF slag is added, the beads are mainly composed of magnetite, limonite and melilite. After BF slag is added, a large amount of glass phase and a little amount of Ca2SiO4 and MgO are found in beads. The content of f-CaO beads decreases after the modified slag is gas quenched at high temperature. Moreover, the more BF slag is added, the higher the elimination rate of f-CaO becomes. Considering the industry standard of steel slag sand in China as well as the gas-quenching rate, physical and chemical properties, the gas-quenched steel slag beads with 5 and 15% BF slag better meet the medium sand standard, which can be used as fine aggregate.

Age Hardening in COR-Ten Steel

Weathering steels developed under the name COR-TEN steels, established themselves as a promising material to meet the demand for atmospheric corrosion resistance and eliminate the need for painting. COR-TEN steel is resistant to corrosive effect of weather such as rain, snow, ice, fog, etc. A coating of dark brown oxidation is developed over the metal surface, when it comes in contact with the environment thereby inhibiting the deeper penetration and negating the need for painting and reducing the rust-prevention cost over the years. Thus the steel is allowed to rust which forms a protective layer and slows down the rate of corrosion. The present study emphasizes the age hardening behavior of COR-TEN steel. The steel was subjected to solution treatment at 1000°C following accelerated cooling with water, oil and air. The oil quenched steel was then subjected to aging treatment at 400°C and 500°C for various times ranging from 5 min to 1500 min followed by water quenching. In order to ascertain the response to aging hardness measurement were conducted by employing a load of 20 Kgf. Metallographic examinations were also conducted to study the resulting structural transformations in various stages of investigations.