Showing papers on "Microalloyed steel published in 1982"

The formability of dual-phase steels

Abstract: The formability of both heat-treated and as-hot-rolled dual-phase steels was evaluated in neck- and fracture-limited forming modes and compared with the formability of conventional high-strength low-alloy (HSLA) or microalloyed steels. For both production routes the formability of dual-phase steels was found to be sensitive to tensile strength, improving as the tensile strength decreased. Forming-limit diagrams developed for the dual-phase steels were consistent with those reported in earlier studies and are superior to those of microalloyed steels of equivalent tensile strength. Conversely, the hole enlargement and transverse bend data showed that the dual-phase steels are somewhat poorer than comparable HSLA steels in fracture-limited formability. In the stretch-bend test, which combines bending and tensile stresses, the dual-phase steels were once again found to be superior to equivalent HSLA grades. Also, while the method of dual-phase steel production had no significant effect on the forming limit diagrams, the heat-treated dual-phase steels in this study exhibited poorer sheared-edge stretchability, bendability, and stretch bendability than as-hot-rolled dual-phase steels.

Influence of dynamic recovery and dynamic recrystallization on coarsening of Nb(CN) in Nb microalloyed steel

Abstract: The influence of deformation on the rate of coarsening of Nb(CN) was studied in 0·018%Nb steel by carbon extraction replication. Size distributions were determined in samples containing static precipitates which were also undergoing dynamic precipitation at 925°C. The mean particle radius r decreased while dynamic precipitation was taking place and then increased due to dynamic coarsening. It was found that the dynamic coarsening rate parameter K′ increased with increasing mean particle radius ro (ro is the mean radius after dynamic precipitation is complete and at which particle coarsening begins). In terms of the static model for particle growth, the apparent dependence of K′ on rosuggests that the particle/matrix interfacial energy increases with ro The particle size distributions were also measured after increasing amounts of strain preceded by the completion of static precipitation at 900, 925, and 975°C. At 900°C, for example, the mean radius of static precipitates was 23·5 nm, which w...

The isothermal austenite-ferrite transformation in some deformed vanadium steels

Abstract: The effect of vanadium on the isothermal austenite-ferrite transformation, between 725 °C and 775 °C, of a hot-deformed microalloyed steel has been studied by examination of the microstructure and measurement of the volume fraction of ferrite in specimens quenched from the reaction temperature. The accompanying precipitation was studied by transmission electron microscopy of thin foils and carbon extraction replicas and by electron energy-loss spectroscopy. Very early in the transformation a continuous band of fine-grained ferrite forms at austenite grain boundaries. After some time some of these grains coarsen to form large equiaxed ferrite grains. It is found that vanadium has no effect on the time to the start of coarsening but thereafter accelerates the rate of formation of ferrite. Interphase precipitation of VN occurs throughout the transformation in the vanadium steels and this is thought to influence the rate at which the ferrite coarsens at the lower temperatures (750 ° and 725 °C) in the range studied.

Controlled quenching of hot rolled steel rods - to give fine pearlitic-ferritic, lower bainitic or martensitic structure

Abstract: Steel rods are subjected to accelerated cooling from the rolling temp. to a temp. dependent on the compsn. of the steel, the dia. of the rods and the speed at which the rods have the rolling mill. Large dia. microalloyed steel rods are pref. cooled to a temp. at which the major part of the rod section transforms to a fine pearlitic-ferritic structure; medium dia. rods of good bainitic quenchability (pref. contg. boron) are pref. cooled to a temp. at which the cores of the rods transform to a lower bainitic structure, opt. followed by tempering for a few mins. at 500-600 deg.C; and small dia. rods of sufficient quenchability are cooled to a temp. at which practically the whole rod section transforms to a martensitic structure. The accelerated cooling may be preceded by natural cooling to 750-800 deg.C. Steel rods, of up to 80 mm. dia. and having good mechanical properties, are produced in an economical manner using in-line cooling installations of reasonable length (30-50m.).

The effect of thermal and mechanical treatments on the structure and properties of A588 Grades A and B steels.

Abstract: An experimental study was carried out on ASTM A588 microalloyed steel, Grades A and B, to determine their strength and toughness behavior during and after strain aging process. The effect of stress relief heat treatment on the mechanical properties of these steels was also Investigated. The results showed that A588, either in as rolled or normalized condition, is sensitive to strain aging phenomena. The straining process increased the yield strength anywhere from 124 to 221 MPa (18-32 ksi) above the value of as received material, the extent of increase depending on the percentage of strain employed. An additional increase of strength, 14-35 MPa (2-5 kai), was produced by a subsequent strain aging mechanism. Stress relief heat treatment at 620°C (1150°F) for 2 hours decreases yield strength anywhere from 103 to 152 MPa (15-22 ksi) below the corresponding strain aged condition for all the strain (2, 5 or 10Z) levels studied. Further stress relief for 8 additional hours, decreases yield strength a little more, but still leaves it above the as received value for both materials. The ultimate tensile strength behave in the same pattern but its variation increments are much smaller than the yield strength ones. For both steels and in both tested conditions, the variation in toughness follows the same pattern regardless the amount of prestrain. The maximum loss of this property, measured by the impact transition temperature, occurs as a result of the straining process. Later aging increases the transition temperature, but only by 10°C (18°F) at most. Subsequent stress relief heat treatment partially restores the toughness of these steels, but their final value of impact transition temperature is much higher, about 40°C (72°F), than the as received material. It must be mentioned that the initial impact transition temperature for normalized is much lower, about 80°C (1AA°F) , than the value of the as rolled condition for both steels.

The fracture behavior of A737 Grade B microalloyed steel weldment.

Abstract: A research program was conducted on a microalloyed steel weldment to provide information on the mechanical behavior of the weld metal and heat affected zone (HAZ). The effect of stress relief on the mechanical properties was also investigated. The weldment consisted of two 100mm (4 in.) thick plates of A737 Grade B Nb treated steel welded together with Armco W-19 wire and Linde 709-5