The physical metallurgy of steels

A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.

Quenching and partitioning martensite-a novel steel heat treatment

Introduction to Magnetic Measurements Fundamentals of Magnetic Measurements Historical Background Main Terms The Magnetization Process of Ferromagnetic Materials Anisotropy and Texture Electromagnetic Loss Influence of the Magnetic Field on Physical Properties of a Material Magnetic Resonance Superconductivity Used in Magnetic Measurements Main Rules of Magnetics The Physical Principles of Magnetism The Magnetic Hysteresis Sources of a Magnetic Field The Samples and Circuits of the Material under Test Magnetic Shielding Magnetic Materials Soft Magnetic Materials: General Information Silicon Iron Electrical Steel Nickel- and Cobalt-Based Alloys Amorphous and Nanocrystalline Alloys Soft Ferrites Hard Magnetic Materials Special Magnetic Materials Magnetic Sensors General Remarks Induction Sensors Fluxgate Sensors Magnetoresistive and Magnetoimpedance Sensors Hall-Effect Sensors Resonance Sensors SQUID Sensors Resonance Sensors and Magnetometers Other Magnetic Sensors Testing of Magnetic Materials AC Testing of Soft Magnetic Materials DC Testing of Soft Magnetic Materials Testing of Hard Magnetic Materials Special Methods of Testing of Magnetic Materials Magnetic Field Measurements and Their Applications Environment Magnetic Fields Applications of Magnetic Field Measurements Magnetic Diagnostics Index References appear at the end of each chapter.

Handbook of Magnetic Measurements

The effect of phosphorus and silicon on the formation of retained austenite has been investigated in a low-carbon steel cold rolled, intercritically annealed, and isothermally held in a temperature range of bainitic transformation followed by air cooling. The steel sheet containing phosphorus after final heat-treatment consisted of ferrite, retained austenite, and bainite or martensite. Phosphorus, especially in the presence of silicon, in steel was useful to assist the formation of retained austenite. Mechanical properties, such as tensile strength, uniform elongation, and the combination of tensile strength/ductility, were improved when phosphorus was increased up to 0.07 pct in 0.5 pct Si steel. This could be attributed to the strain-induced transformation of retained austenite during tensile deformation. Furthermore, two types of retained austenite were observed in P-containing steel. One is larger than about 1 μm in size and usually exists adjacent to bainite; the other one is of submicron size and usually exists in a ferrite matrix. High phosphorus content promotes the formation of stable (small size) austenites which are considered to be stabilized mainly by their small size effect and have a different formation mechanism from the coarser retained austenite in the lower P steels. The retained austenites of submicron size showed mechanical stability even after 10 pct deformation, suggesting that these small austenites have little effect on ductility. The 0.07 pct P-0.5 pct Si-1.5 pct Mn-0.12 pct C steel showed a high strength of 730 MPa and a total elongation of 36 pct.

Effect of phosphorus on the formation of retained austenite and mechanical properties in Si-containing low-carbon steel sheet

Characterization of the microstructure obtained by the quenching and partitioning process in a low-carbon steel

High-purity Fe-C alloys containing up to 5.8 pct Al were quenched from 730°C, then aged at temperatures up to 400°C. Precipitation of a carbide transition phase (presumably e) and of cementite were followed by transmission electron microscopy, coercive force measurements, and changes in yield strength. The presence of aluminum increases the temperature at which cementite begins to precipitate during aging. This effect is similar to that produced by silicon in ferrite, and opposite to that produced by manganese. It is suggested that the effects of Si, Mn, and Al on cementite precipitation from ferrite arise from the effects of these elements on the stability of cementite, as reflected in the equilibrium partition of carbon between cementite and ferrite.

Precipitation of carbides in low-carbon Fe-AI-C alloys

A machine manipulates a laser beam substantially transversely across a moving sheet of flat or curved material. This machine includes a rotating optical system which focuses and moves an elongate beam spot across the moving sheet of flat or curved material, at a high rate of speed. In methods of applying these instruments to produce reductions in watt loss in coated ferromagnetic sheet without damage to the coating, the speed of laser scanning, S 2 (inches/minutes), and the incident power, P (watts), of the beam are selected such that the function, PS 2 -1/2 is between about 0.1 to about 7.

Laser scribing apparatus and process for using

Localized laser heating was used to alter the magnetic characteristics and domain size of high‐permeability grain‐oriented silicon steel. A continuous‐wave CO2 laser was used to scribe narrow transverse stripes on fully processed, Forsterite‐coated strip. The laser power was maintained at 32 W, and the power density applied to the strip was controlled by varying the scan speed. The spacing of the scribe lines was varied between 3 and 13 mm. A decrease in core loss was observed at a scan speed of 169 mm/s and a scribe spacing of 6 mm. Losses decreased 9% at 1.7 T and 18% at 1.0 T. A maze domain structure, indicative of a compressive stress, was observed in the laser‐affected regions. The average 180° domain size was reduced by scribing; as the scan speed was reduced and the scribe spacing decreased, the domain size decreased. Although the Forsterite coating was not visibly damaged by the laser heating, polishing and etching of the steel substrate revealed localized slip lines in the laser‐affected zones. The hysteresis loss component was increased by laser scribing, and thus we attribute the observed loss reduction to a decrease in the eddy current loss component caused by the decrease in domain wall spacing.

Effect of laser scribing on the magnetic properties and domain structure of high‐permeability 3% Si‐Fe

In this paper we present three techniques which provide improved permanent ferromagnetic‐particle images of domain structures. A normal field, supplied by flexible permanent magnet strip, is used for all three. The first method employs a pigmented strippable coating which is peeled from the specimen after drying. The result is a high‐resolution mirror image of the domain structure; the method can be used to study parts of large specimens nondestructively. In the second method, the coating is examined while still in place; its contrast can be increased by adding more white pigment and by painting the specimen white before application. The third method uses noncolloidal Fe3O4 powder in artist’s matte medium to provide domain images, on a white‐painted specimen, with higher contrast but lower resolution.

Enhanced domain imaging techniques

/pdf/development-of-110-001-texture-in-low-alloy-iron-by-primary-mc692oj10b.pdf

Gary C. Rauch

Papers

Precipitation of carbides in low-carbon Fe-AI-C alloys

Laser scribing apparatus and process for using

Effect of laser scribing on the magnetic properties and domain structure of high‐permeability 3% Si‐Fe

Enhanced domain imaging techniques

Development of (110) [001] texture in low-alloy iron by primary recrystallization and normal grain growth