Showing papers on "Microalloyed steel published in 1984"

Mechanical properties and machinability of a high-strength, medium-carbon, microalloyed steel

Abstract: The development of a high-strength (tensile strength beyond 900 N/mm2), medium-carbon, vanadium microalloyed steel for hot-forged automotive components has been reviewed in the paper. The influence of different alloying elements was investigated. The most effective elements to increase the strength were chromium and manganese. In TEM investigation, it was found that, in comparison with the lower-strength melt, chromium plus manganese alloyed steel showed a high density of small V(C, N) precipitates. Mechanical properties were studied in tensile, impact, fatigue, and fracture mechanics tests. Most mechanical properties of the microalloyed and quenched and tempered steel were essentially equal. Exceptions were the lower impact strength and higher fatigue strength of the microalloyed steel. Possibilities to improve the impact strength of the microalloyed steel are being considered. Machinability was tested in different operations. Generally, the machinability of the high-strength microalloyed steel was comparable with quenched and tempered steels. However, a different behavior was found in deephole drilling. The use of calcium treatment to improve the machinability is discussed. The high-strength microalloyed grade developed can substitute for alloyed quenched and tempered steels in most components. When weight saving is desired, the possibility of substituting the high-strength grade for lower-strength microalloyed steels is considered.

The effects of microstructure and texture on toughness of control-rolled steel bars.

Abstract: Texture, microstructure and mechanical properties of low carbon microalloyed steel bars control-rolled in an oval/round process have been studied. Strength can be increased by decreasing rolling temperature without significant ductility loss. This can be explained in terms of microstructural refinement as well as ferrite work hardening by rolling in γ/α duplex phase region. Ductile/brittle transition temperature (VTS) in Charpy impact test is also remarkably decreased by lowering rolling temperature, e.g., VTS and a {111} -{211} , respectively. Fractographic examinations revealed that cleavage cracks either perpendicular to rolling direction or parallel to the rolling planes initiate within relatively coarse grains of the cube orientation elongated in the rolling direction and that the propagation of such cracks is arrested by the surrounding extremely fine grained area of different orientations such as {111}-{211} . The initiation of separations cannot be explained by the Chao's plastic anisotropy model.

Machining characteristics of microalloyed forging steels

Abstract: In this paper the machinability of forging steel grades, microalloyed with vanadium for precipitation hardening and used in the air-cooled condition, are compared with those of hardened and tempered steel grades. Standard laboratory tests, employing both high-speed-steel and cemented carbide tooling, have been used. In most instances, microalloyed steel proved to be at least as machinable as hardened and tempered steel grades of similar strength level. However, because of a higher dependence of machinability on workpiece hardness, microalloyed steels may have inferior machinability to hardened and tempered alloy steels, at tensile-strength levels above 1000 MN m−2. This higher dependence on workpiece hardness has been investigated using a range of experimental techniques and a tentative mechanism has been proposed. Finally, compositional adjustments have been proposed, which might improve the machinability of microalloyed steels and thus eliminate this one potential problem area.

Process for producing weldable large pipe sheets of fine grain structure

Abstract: In a process for producing weldable large pipe sheets of fine grain structure from a microalloyed steel by thermomechanical rolling, a steel having 005 to 007% of carbon, 15 to 20% of manganese, 001 to 04% of titanium, 0001 to 0003% of sulphur, 0005 to 0008% of nitrogen, 025 to 040% of silicon, 003 to 005% of aluminium and up to 008% of niobium, the remainder being iron and usual impurities, is produced The titanium content is adjusted to the nitrogen content Continuously cast slabs are heated to 1120-1160 DEG C In this way, niobium precipitations are dissolved and, on subsequent cooling during deformation, predominantly precipitated as strength-increasing niobium carbide A coarsening of titanium nitride precipitations, taking place during this heating, proves to be harmless The deformation is at least 55% This is followed by thermomechanical rolling at a temperature of at most 850 DEG C and by finish-rolling at a temperature above 650 DEG C This may be followed by intensified cooling to temperatures between 550 and 500 DEG C

Microalloyed Dual-Phase Steel for Mechanical/Machined Components

Abstract: Dual-phase steels have been used primarily for reducing weight of complex shaped automotive parts which could not be made with less formable, conventional high strength steels. Recently, a microalloyed dual-phase steel was found also to possess superior machining characteristics. This paper describes laboratory data which compare machinability of dual-phase steel with that of conventional steels. The effects of material strength, tensile prestrain, and cutting depth on machined surface quality are elucidated. The improved machinability of dual-phase steel was explained on the basis of its unique microstructure. In addition, two applications of dual-phase steel are discussed. In one application, broaching is the critical machining step, and dual-phase steel is currently used in production. In the other, turning is the critical step, and further studies are under way.

Micromechanics of fracture in microalloyed steel

Abstract: A quantitative investigation of the micromechanics of fracture has been carried out in hot-rolled microalloyed steel. The inclusion size and inter-inclusion spacing distribution have been determined using statistical analysis. Tensile properties and toughness data have been obtained and used for determination of stress and strain distribution in the vicinity of crack tip. The fracture strain and dimple sizes for fracture are found to be highly sensitive to triaxiality factor. The process zone size has been determined from the critical strain level in the fracture toughness (FT) specimen and related to the dimple size. The effective inclusion size governing the ductile fracture process has been identified.

The Effects of Microstructure and Texture on Toughness of Control-rolled Steel Bars

Abstract: Texture, microstructure and mechanical properties of low carbon microalloyed steel bars control-rolled in an oval/round process have been studied. Strength can be increased by decreasing rolling temperature without significant ductility loss. This can be explained in terms of microstructural refinement as well as ferrite work hardening by rolling in γ/α duplex phase region. Ductile/brittle transition temperature (VTS) in Charpy impact test is also remarkably decreased by lowering rolling temperature, e.g., VTS and a {111} -{211} , respectively. Fractographic examinations revealed that cleavage cracks either perpendicular to rolling direction or parallel to the rolling planes initiate within relatively coarse grains of the cube orientation elongated in the rolling direction and that the propagation of such cracks is arrested by the surrounding extremely fine grained area of different orientations such as {111}-{211} . The initiation of separations cannot be explained by the Chao's plastic anisotropy model.

Continuously annealed hot rolled dual phase steel (processing-properties-applications)

Abstract: A microalloyed steel is heated by continuous annealing and then quenched to produce a microstructure consisting of 75-85% by volume of ferrite with the remainder being predominantly martensite. The resulting steel is called "dual phase" because of its twin constituents--ferrite and martensite. The continuous annealing process is contrasted with the "as-rolled" process to demonstrate that the former is the preferred production means. The resulting basic properties are then discussed with the intention of maximizing their influence in applications where the important attributes are strength, fatigue life, and machinability. Eight years after its introduction in the United States, applications for dual phase steel are being matched to its unique properties. The components examined are bumpers, wheels, and several mechanical components.