Showing papers on "Microalloyed steel published in 1986"

Strengthening of austenite by niobium during hot rolling of Microalloyed steel

Abstract: Austenite in niobium–microalloyed steels at finish rolling temperatures is significantly stronger than austenite in mild steel. The present study, utilizing laboratory scale rolling, plane strain c...

Austenite Grain Refinement and Superplasticity in Niobium Microalloyed Steel

Abstract: Auslenite grain refinement of low carbon steels prepared with or without the addition of a very small amount of niobium was achieved by thermomechanical processing in order to obtain materials with an (α+γ) microduplex structure in the intercritical temperature range. Such materials showed superplastic behavior during high temperature tensile deformation. Large values of elongation to failure, the largest being 738% and high values of strain rate sensitivity exponent, m, of >0.6 were obtained by tensile deformation at 790°C and a strain rate of 5×10-3min-1 in the Nb-microalloyed steel. Moreover, an elongation to failure of about 300% was obtained by tensile deformation at around 800°C and a strain rate of 5×10-1min-1, a set of work condition which may be adaptable to commercial forming processes. The largest elongation to failure value and the highest m-value were, as a whole, obtained at around the temperature where the specimens were composed of nearly equal volume fractions of α and γ phases.Microalloying cf niobium promoted superplasticily of low carbon steel presumably through the suppressive effects of finely dispersed precipitates of niobium carbide (or carbonitride) on grain growth during high temperature deformation.

Sol-gel fluxes for flux cored welding consumables

Abstract: The feasibility of producing high purity homogeneous welding fluxes by the solgel process and the effects that these fluxes have on the welding process were determined. Reagent grade solgel welding fluxes were produced by making systematic variations of the SiO2-CaO-TiO2-l pct Na2O flux system. The resulting fluxes were made into flux cored wires and used to make bead on plate welds on a niobium microalloyed HSLA steel. Solgel fluxes were shown to have excellent homogeneity, low residual hydrogen content, and no apparent water adsorption. The welding behavior of the solgel fluxes was shown to have superior arc stability compared to a commercial flux cored wire and very low weld metal hydrogen content. The chemical behavior of this flux system was characterized with respect to elemental transfer. The weldments exhibited a primarily acicular ferrite microstructure. Analysis of nonmetallic inclusion size distributions was compared to previous investigations and found to be consistent with the formation of high toughness weld metal microstructure.

Microalloyed Steel Bars and Forgings

Abstract: This paper examines microalloyed steels—steels which develop their properties in the as-received condition without requiring further heat treatment, such as quenching and tempering. Microalloyed steel bars and forgings offer a clear cut potential for cost reduction and energy savings. The metallurgy for producing high strength microalloyed bars and forgings is in place. However, significant improvement in the notch toughness of these materials is necessary, and the metallurgy required to achieve this toughness improvement exists. With application of the necessary metallurgical techniques in rolling mills and forge shops, the utilization of high strength microalloyed steel bars and forgings will increase greatly.

The effects of pwht on the toughness of shielded metal arc weld metals for use in canadian offshore structure fabrication

Abstract: The effects of post weld heat treatment (PWHT) on the toughness of shielded metal arc weld (SMAW) metal is investigated. Two C-Mn and two C-Mn-Ni electrodes, chosen from a previous consumable evaluation program, were each used to make four butt welds in a 40 mm thick C-Mn microalloyed steel. One half of each joint was given a PWHT of 2 h at 600°C. Sub-surface and root region Charpy specimens, full thickness, BX2B, CTOD specimens and all weld metal tensile specimens were removed from each test condition (as-welded and PWHT) for all four welds and tested. All four welds showed a decrease in Charpy energy, in the as-welded condition, in the root region when compared with the sub-surface location, as a result of dynamic strain aging. There was no change in Charpy toughness after PWHT for the C-Mn weld metals while the C-Mn-Ni weld metals showed a loss of toughness. Examination of the welds indicates that a softening of ferrite microstructures and removal of strain aging effects with PWHT, which would lead to an improvement in toughness, was counteracted by embrittlement by carbide precipitation. The presence of Ni in the C-Mn-Ni welds is thought to increase the amount of martensite-austenite (M-A) phase present in the as-welded structure compared with C-Mn weld metal, and hence results in more carbide precipitates in the PWHT condition. Three of the four welds showed an improvement in toughness, measured by CTOD, after PWHT. The lack of improvement of one of the C-Mn-Ni welds may be due to a change of cleavage initiation from inclusions to coarsened carbides.

Process for the production of fine-grain weldable sheet stock for large diameter pipe

Abstract: A process for the production of fine-grain, weldable sheet steel stock for large diameter pipes from microalloyed steel by thermomeohanical welding. A steel consisting of 0.05 to 0.07% carbon, 1.5 to 2.0% manganese, 0.01 to 0.04% titanium, 0.001 to 0.003% sulfur, 0.005 to 0.008% nitrogen, 0.25 to 0.40% silicon, 0.03 to 0.05% aluminum, and up to 0.08% niobium, with the remainder of iron and the usual impurities is produced The titanium content is adjusted to the nitrogen content. continuously cast slabs are heated to 1120 to 1160 deg.C. The niobium precipitations are dissolved thereby and during subsequent cooling during deformation precipitated mainly as strength-enhancing niobium oarbide. A coarsening of the titanium nitride precipitations that takes place during this heating has not proved to be detrimental. Deformation amounts to at least 55%. This is followed by thermomechanical rolling at a temperature of at most 850 deg.C, and finish rolling at a temperature above 650 deg.C. lntensified cooling at temperatures of between 550 and 500 deg.C can follow. :

A combined electron microscope and optical metallographic study of microstructures in high-strength, low-alloy (HSLA) steels after welding

Abstract: SUMMARY A combined TEM and optical metallographic technique has been applied to microstructures in the heat affected zone in two high-strength, low-alloy steels with carbon equivalent 0·37 and microalloyed with Nb (0·024%), Ti (0·015%) and Nb (0·025%), V (0·05%) respectively. Volume fraction, size distribution and composition of the carbonitrides of microalloying elements were determined as function of distance from the fusion line and compared with other microstructural features, such as primary austenite grain size. Differences in microstructure are attributed to the higher stability of the Ti, Nb particles during the weld thermal cycle.

Grain Refinement by Recrystallization Hot-Rolling to Achieve High Strength and Notch Toughness in Microalloyed Steel Plate

Abstract: The effects of total strain, strain per pass and final pass temperature on austenite grain refinement in recrystallization hot-rolling of Ti-N-V microalloyed steels are determined with a view to achieving improved strength and notch-toughness in Grade 350 thick plate. Results of (i) cam plastometer hot-compression simulation of recrystallization rolling, and (ii) pilot-scale thick-plate rolling tests, are presented.