J. F. Libsch

On the nature of embrittlement occurring while tempering a Ni-Cr alloy steel

Data are presented to show that embrittlement in a Ni-Cr alloy steel proceeds by one mechanism at 925°F and by a different mechanism at 1250°F. The embrittlement occurring at 925°F may be removed completely by reheating to higher temperatures for very short times and has no influence upon further embrittlement at 1250°F. The embrittlement occurring at 1250°F appears related to a permanent structural change which has a significant retarding influence upon subsequent development of embrittlement at 925°F. It is suggested that retrogression phenomena are not necessary to explain embrittlement; on the other hand, segregation of solute atoms to prior austenite and ferrite grain boundaries may provide a better explanation of the occurrence of the two modes of embrittlement.

High saturation magnetic alloy with a rectangular hysteresis loop

A study has been made of magnetic alloys which have a nearly rectangular hysteresis loop. This characteristic is desirable for materials used in saturable reactors, magnetic amplifiers, pulse transformers, and other nonlinear circuit elements.

Effect of annealing in a magnetic field upon iron-cobalt and iron-cobalt-nickel alloys prepared by powder metallurgy

Iron-cobalt and iron-cobalt-nickel alloys prepared by powder metallurgy have been heat treated in a magnetic field. The 50 pct iron-cobalt alloy exhibits optimum magnetic properties and an essetially rectangular hysteresis loop when subjected to the best magnetic annealing cycle developed. Small amounts of nickel, appear to be detrimental in the alloys studied.

Influence of Additives in the Production of High Coercivity Ultra-Fine Iron Powder

The effects of several additives upon the reduction characteristics of hydrogen-reduced ferrous formate are described. The various additives inhibit sintering of the reduced iron particles by apparently different mechanisms. The magnetic properties of the low density compacts produced from the resulting ultra-fine iron powders were improved markedly.

Ordering and Magnetic Heat Treatment of The 50 Pet Fe-50 Pet Co Alloy

The 50 pet Fe-50 pet Co alloy undergoes a transformation from disorder to an ordered structure of the CsCl type reportedly in the vicinity of 732°C. During this process, the coercive force goes through a maximum, apparently as a result of strains associated with the coherent nucleation and growth reaction. This magnetic alloy also shows a marked increase in the ratio of residual to saturation induction, which is associated with annealing to a high degree of order with the continuous application of a magnetic field. The increase in ratio can be explained on the basis of a decrease in 90° domain boundaries and, perhaps, by an increase in anisotropy resulting from lattice distortion.

Isoembrittlement in Chromium and Molybdenum Alloy Steels During Tempering

Isoembrittlement curves depicting the influence of time and temperature in the range 800° to 1260°F (425° to 680°C) on the development of embrittlement in a commercial chromium alloy steel and a commercial molybdenum alloy steel are presented. Two distinct regions of embrittlement occur in the chromium alloy steel: 1—at 800° to 1000°F (425° to 540°C) and 2—in the region just below the lower critical temperature. Embrittlement is most pronounced at 800° to 1000°F, decreasing very rapidly with increasing temperature above this region, only to increase again as the lower critical temperature is approached. The data suggest two distinct modes of embrittlement with possible superposition of the two modes at extended embrittling times in the temperature range 1100° to 1150°F (590° to 620°C). While the molybdenum alloy steel shows little susceptibility to embrittlement at 800° to 1000°F (425° to 540°C), considerable embrittlement may occur just below the lower critical temperature.

Rapid Tempering of High Speed Steel

1—Rapid induction tempering of W-Mo high speed steel produces mechanical properties, as indicated by hardness and bend test results, which are approximately equal to those resulting from conventional long-time tempering treatments. 2—Short-time tempering data for high speed steel exhibits a lack of conformance to the tempering parameter T (c + log t). It appears that tempering reactions are accelerated by rapid induction tempering to rates considerably greater than those predicted by the parameter. Plastic deformation or thermal strain during the heating part of the short tempering cycle is thought to be the cause of the tempering anomaly. It is believed that such strain accelerates the tempering reactions during rapid heating so as to place the steel in an advanced state of tempering at the instant the tempering temperature is reached. This advanced state will not proceed significantly until after a period of time depending on the extent of advancement. Induction-tempered, high speed steel which is held at the tempering temperature by short power impulses is found to undergo additional acceleration of the tempering reactions during the holding period. This is thought to be due to small thermal strain produced by the temperature oscillations. By this method of tempering maximum secondary hardness may be reached in at least a few minutes at a temperature which would normally require 1 hr by conventional methods. 3—At maximum secondary hardness, high speed steel which is induction tempered by rapid heating exhibits a slightly greater proportion of retained austenite than does the steel which is conventionally tempered for long times. 4—Maximum bend strength for high speed steel whether tempered rapidly by induction or slowly by salt bath approximately coincides with the completion of the retained austenite transformation.

Role of Gases in the Production of High Density Powder Compacts

1—Data are presented to show the influence of various pressing and sintering conditions upon the process have an important influence upon the final density of compacts sintered to achieve theoretical density. I. this, connection, high compacting pressures, rapid heating rates, and high sintering temperatures exaggerate the effect of evolved gases and promote the formation of large initial pores which are eliminated during continued sintering only with difficulty.