As-rolled Condition Research Articles

Acicular Ferrite Microstructures and Mechanical Properties in a Low Carbon Wrought Steel

In this work, the formation of acicular ferrite in a low carbon wrought steel has been investigated. After austenitizating at 1250°C for 45 minutes, the steel has been subjected to isothermal heat treatments in the range of 550-350°C for different times. The microstructure obtained is mainly composed of acicular ferrite. Widmanstatten and allotriomorphic ferrite have also been found nucleating at the prior austenite grain boundaries. The volume fraction of these phases decreases remarkably when the isothermal treatment temperature is diminished. It has been observed that acicular ferrite is nucleated at non-conventional metallic inclusions such as multiphased inclusions composed of Al, Si and Mn oxides and MnS inclusions, which are covered, in both cases, by a shell of a hexagonal CuS phase. The mechanical properties of the steel in the as-rolled condition and after the generation of acicular microstructures have been measured showing the improvement obtained with acicular ferrite.

Grain boundary segregation and intergranular fracture in Ferrite containing Mo, Si or Al

Roles of molybdenum, silicon or aluminum in ferrite on grain boundary segregation and hence on intergranular fracture have been investigated by using Auger electron spectroscopy (AES) and tensile test. Competitive segregation between sulfur and carbon or nitrogen, which caused the decrease below 700°C of sulfur content at the grain boundaries, was observed in the pure iron. The intergranular brittleness of the pure iron was caused by sulfur at the grain boundaries. When molybdenum was added to the pure iron, the sulfur contents at the grain boundaries were lowered in comparison to those in the pure iron. The molybdenum-bearing alloy showed higher fracture strength than that of the pure iron, and fractured mostly in the transgranular mode. This arises from the intrinsic effect of molybdenum on the grain boundaries as well as the decrease in sulfur content. Tn the 3.37 wt.%Si alloy, silicon and carbon or nitrogen competitively segregated to the grain boundaries, and such a competitive segregation was also observed between sulfur and carbon or nitrogen. The sulfur content at the grain boundaries decreased with increasing silicon content. The fracture modes in the 3.37- and 4.26 wt.%Si alloys were transgranular in the rolling direction, but were mostly intergranular in the transverse direction and in the as-rolled condition. The intergranular characteristic in the fracture behavior may be attributed to the detrimental effect of silicon as well as sulfur on the intergranular cohesion. Carbon and aluminum only were found at the grain boundaries of the aluminum-bearing alloy. This suggests that aluminum is a strong repulser of sulfur or nitrogen at the grain boundaries. Additionally, it was found that aluminum has a detrimental effect on grain boundary strength of ferrite.

Effect of alkali metal impurities and cerium modification on the fatigue behaviour of 8090 alloy sheets

In the present study, experiments were carried out to investigate the fatigue behaviour of 8090 alloy sheets with different concentrations of alkali metal impurities and Ce alloying addition. Test results show that, with increasing total content of Na and K in 8090 alloy sheets, the fatigue life increases and the fatigue crack propagation rates decrease, in particular in the regions of the shorter fatigue life and higher fatigue crack propagation rates. In the process of the solution heat treatment of the alloy sheets in the as-rolled condition, the alkali metal impurities tend to accelerate the recrystallization of the matrix phase and to form a non-uniform microstructure, which results in the intergranular propagation of fatigue cracks in 8090 alloy sheets. If the total content of the alkali metal impurities is below a certain limit, the microalloying addition of 0.05% Ce in 8090 alloy sheets can reduce the detrimental effects of Na and K on the fatigue life and the fatigue crack propagation rates. The reason behind this may be that the alloying addition of a minor amount of Ce element could delay the recrystallization and decrease the grain size in recrystallized zones of the alloy sheets.

Formation of metastable phases in a spray deposited 2024 aluminium alloy

The microstructures of a spray deposited 2024 aluminium alloy in the hot rolled condition were investigated by transmission electron microscopy. It was found that there exist amorphous and quasicrystalline phases in the spray deposited preform, and neither metastable phase is able to undergo structural change in the 400 °C as-rolled condition, showing high termal stability. A reasonable mechanism for the formation of both metastable phases is described using a spray model.

The effect of alloying elements on the structure and mechanical properties of ultra low carbon bainitic steels

Microalloying with Nb and B leads to a granular bainite microstructure which is composed of a bainitic ferrite matrix and a uniformly distributed martensite/austenite-constituent in the as-rolled condition. Due to this transformation strengthening mechanism, high strength and toughness could be achieved even though the C content was extremely low. It was found that both dissolved Nb in austenite and free B are prerequisites for granular bainite formation. Furthermore, there is a critical B content to achieve the complete bainitic transformation strengthening effect. The critical B content increases with C content. C thus diminishes the effect of B in promoting bainite transformation, due to the formation of boron carbides or the depletion of dissolved Nb in austenite. The effect of Mn, Mo and Ni on the decomposition of austenite is similar. A parameter“Mneq” which relates the effect of these alloying elements on the Bs temperature was derived. It was confirmed that the strength of bainitic steels is inversely proportional to theBs temperature.

The effect of titanium and nitrogen contents on the microstructure and mechanical properties of plain carbon steels

Three series of titanium-containing steels with different nitrogen contents were used to evaluate the effect of a small titanium addition on properties. With the addition of titanium, an obvious ferrite grain refinement was observed in the as-rolled condition. This refinement is attributed to the TiN grain-boundary-pinning effect. The TiN grain-boundary-pinning effect is most effective when the titanium content is around that in the titanium-to-nitrogen stoichiometric ratio, i.e. 3.42. Also the grain refinement effect from TiC might be obtained when the titanium content is higher than that in the titanium-to-nitrogen stoichiometric ratio. In contrast with the observed grain refinement, the yield strength of steels with a titanium content around that in the titanium-to-nitrogen stoichiometric ratio suffered a considerable loss when compared with plain carbon steels. This loss is due to the depletion of free nitrogen for solid solution hardening. However, the toughness was improved through grain refinement and depletion of free nitrogen. When the titanium content was over the stoichiometric ratio, a precipitation-hardening effect resulting from TiC was observed which resulted in the increase in strength and deterioration of toughness.

The Effects of Hot Rolling on AA2124 15 v/o SiC Whisker Composites

Mechanical and microstructural studies were performed on a rolled sheet of AA2124 15 volume percent SiC whisker composite. Tests were done in both the as-rolled condition and after a T6 heat treatment. It was confirmed that hot rolling significantly reduces the tensile strength of a heat treated composite and that a T6 heat treatment re stores this strength. It has been suggested by previous investigators that this reduction and recovery in tensile strength was due to the creation and healing of interfacial voids. How ever, the present study shows that the loss in strength is mainly due to simple overaging of the rolled composite which occurs during cooling. A T6 heat treatment restored the strength of the rolled composite by dissolving the large precipitates. The ductility of the composite was also increased significantly as a result of the heat treatment.

Processing titanium aluminide foils

In an effort to extend the available manufacturing technologies for Ti3Albase aluminides, the potential success of a new hot-rolling process for the production of high-quality foils has been investigated. Processing of Super-α2 aluminide foils approximately 0.15 mm thick takes full advantage of the combined benefits of controlled rolling and a unique pack rolling process. Based on the results of a study of phase transformation kinetics, microstructure and hardness of continuously-cooled and isothermally transformed specimens, the processing parameters are optimized to provide enhanced surface quality and superior ductilities in the as-rolled condition.

The effect of sulphide and oxide inclusions on the wear rates of a standard C-Mn and a Cr-Mo alloy rail steel

Hot-rolled plates of standard C-Mn and Cr-Mo alloy rail steel compositions were prepared with different sulphide and oxide contents. One Cr-Mo plate contained rare earth additions. Inclusions in all hot-rolled plates were characterized by an image analysing computer. Standard C-Mn disks were tested in a wear machine in either (a) the soft (22 HRC) as-rolled pearlitic condition or (b) after oil quenching and tempering to either pearlite (38 HRC) or bainite (42 HRC). The microstructure of the Cr-Mo specimens was pearlitic, of hardness 38 HRC. The disks generally simulated the high (outer) rail in heavy duty curved unlubricated track conditions but one disk was continuously lubricated with grease during its test. This disk had a significantly lower wear rate and shear deformation at the surface than all other specimens. Marked linear increases in wear rate were observed with increases in the sulphide parameter length/unit area of field for the microstructures tested dry and containing MnS inclusions. However, the softer C-Mn as-rolled specimens were found to have steeper wear rate-sulphide length slopes than the OQ & T pearlite and therefore larger differences in wear rate occur for the different hardnesses at high sulphur levels. It is postulated that these dry wear effects arise from the deformation of MnS inclusions which were almost invariably found in subsurface cracks in the work-hardened, worn, surface shear layers. Hard oxides (Al 2O 3, silicates) play a minor role in the type of flaking wear observed in the present tests.

Microstructures of Linepipe Steels

Linepipe steels may exhibit many different microstructures both in the as-rolled condition and in the weld heat-affected zone (HAZ). Because the properties of the steel are strongly dependent upon the microstructural features, an attempt is made to characterize the polygonal ferrite, acicular ferrite, bainite and martensite-retained austenite (M/A) constituents, and to describe the conditions under which they form. The kinetics of the austenite to ferrite transformation are examined to show the role of the processing parameters (temperature, composition and deformation) in determining the as-rolled microstructure.HAZ microstructures are formed under very different conditions from as-rolled microstructures. Development of the four distinct regions which make up the HAZ is related to the peak temperatures attained during welding. Résumé Les aciers de pipelines peuvent posséder des microstructures trés differentes, aussi bien après laminage que dans la zone affectée par la chaleur (ZAC) lors du soudage. Parce que les propriétés des aciers dépendent fortement de leur microstructure, on essaye d'en caractériser les différents constituants (ferrite polygonale, ferrite aciculaire, bainite et martensite–austénite retenue), et de décrire les conditions de leur formation. La cinétique de la transformation austénite–ferrite est étudiée afin de montrer l'importance des paramètres de laminage (température, composition et déformation) sur la formation de la microstructure.Les conditions de formation des microstructures de la ZAC sont très différentes de celles obtenues après laminage. Les quatre régions distinctes de la ZAC sont formées suivant les températures maximales atteintes pendant le soudage.

BETHSTAR 80

Abstract BETHSTAR 80 steel plate is a high-strength product with an 80,000 psi minimum yield strength. It attains this strength in the as-rolled condition through the combination of a low-carbon microalloyed chemistry and controlled (proprietary) processing. It offers substantial cost savings when compared with quenched-and-tempered steel plate. BethStar 80 plate can be machined, formed and welded readily. It is used in several constructional applications and has the potential for many more applications. This datasheet provides information on composition, physical properties, microstructure, elasticity, and tensile properties as well as fracture toughness. It also includes information on forming, heat treating, machining, and joining. Filing Code: SA-385. Producer or source: Bethlehem Steel Corporation.

Work hardening of dual-phase steels

A detailed qualitative and quantitative microstructural examination of four dual-phase steels has been carried out. Dual-phase structures were produced in three of these steels by intercritical annealing; the other was in the as-rolled condition. Similar combinations of tensile properties were obtained with all four steels. In intercritically annealed material, greater austenite hardenability was encountered with the two steels containing strong carbide-forming elements (vanadium or titanium) than with a similar plain carbon steel. It has therefore been proposed that the carbonitride precipitates (which are present during the anneal) inhibit the movement of the austenite/ferrite interface during the post-anneal quench; strong metallographic evidence has been provided to support this view. It has been found that during tensile deformation, martensite islands do not deform until strains well in excess of the maximum uniform strain have been reached; this observation has enabled the successful application of Ashby's work-hardening theory to dual-phase steels. This theory predicts that the work-hardening rate is dependent on √f/d, where f is the volume fraction of second phase and d is the mean secondphase island diameter. Thus, it is demonstrated that optimization of dual-phase properties may be achieved by refining the distribution of second phase, since this leads to increased work-hardening rates and hence increased maximum uniform ductilities, for a given tensile strength; the tensile strength is determined primarily by the volume fraction of second phase.

A New HSLA Plate Product with 80 ksi Yield Strength in the As-Rolled Condition

A New HSLA Plate Product with 80 ksi Yield Strength in the As-Rolled Condition

Using CCT Diagrams to Optimize the Composition of an As-Rolled Dual-Phase Steel

A continuous-cooling transformation (CCT) diagram study was conducted for the purpose of optimizing the composition of a Mn-Si-Cr-Mo as-rolled dual-phase (ARDP) steel. The individual effects of chromium, molybdenum, and silicon on the allowable cooling rates were determined. On the basis of the CCT diagram study and other available information, an optimum composition was selected. Data from recent mill trials at three steel companies, involving steels with compositions in or near the newly recommended range, are presented and compared with earlier mill trial data. The comparison shows that the optimized composition is highly effective in making the steel’s properties more uniform and reproducible in the as-rolled condition.

USS AR

Abstract USS AR is a medium-carbon, low-alloy steel used in the as-rolled condition for resistance to abrasion. It is a relatively low-cost steel and is employed in applications involving smooth-sliding abrasion, where abrasive materials such as grains, coal, ore, cement, gravel, light aggregate and earth are being handled. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SA-324. Producer or source: United States Steel Corporation.

REPUBLIC 100-AR

Abstract REPUBLIC 100-AR was developed to provide a minimum yield strength of 100,000 psi in the as-rolled condition. It also has exceptional wear resistance, good toughness and design flexibility. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fracture toughness and fatigue. It also includes information on corrosion and wear resistance as well as forming, heat treating, machining, and joining. Filing Code: SA-307. Producer or source: Republic Steel Corporation.

Ductile-brittle transition of thoriated chromium

Unalloyed chromium and chromium containing approximately 3 wt pct ThO2 (2.2 vol pct) were prepared from powder produced by a chemical vapor deposition process. When rolled to sheet and tested in tension it was found that the thoriated material had a lower ductile-to-brittle transition temperature (DBTT) than unalloyed chromium. This ductilizing was evident both in the as-rolled condition and after the materials had been annealed for 1 hour at 1200°. The DBTT values were: Open image in new window The improved ductility in thoriated chromium may be associated with several possible mechanisms: 1) particles may disperse slip, such that critical stress or strain concentrations for crack nucleation are more difficult to achieve; 2) particles may act as dislocation sources, thus providing mobile dislocations in this normally source-poor material, in a manner similar to prestraining; and 3) particles in grain boundaries may help to transmit slip across the boundaries, thus relieving stress concentrations and inhibiting crack nucleation.

MAX-EL 2-B

Abstract Max-EL 2-B is a general purpose free-machining steel offering a good combination of strength, toughness and abrasion resistance, as well as excellent machinability. It is generally used in the as-rolled condition at a Brinell hardness of 200-235. This datasheet provides information on composition, hardness, and tensile properties. It also includes information on forming, heat treating, machining, and joining. Filing Code: CS-15. Producer or source: Crucible Steel Company of America.

REPUBLIC 70

Abstract REPUBLIC-70 is a precipitation hardenable low alloy steel which will meet 70,000 psi minimum yield point in the as-rolled condition followed by a precipitation hardening heat treatment. This datasheet provides information on composition, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SA-104. Producer or source: Republic Steel Corporation.

REPUBLIC 65

Abstract REPUBLIC-65 is a precipitation hardenable low alloy steel which will meet 65000 psi minimum yield point in the as-rolled condition followed by a precipitation hardening heat treatment. This datasheet provides information on composition, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SA-98. Producer or source: Republic Steel Corporation.