AN INTERNAL FRICTION STUDY OF VERY LOW CARBON MARTENSITE (thesis)

Technical Report · Thu Jun 01 00:00:00 EDT 1961

OSTI ID:4817803

Jackson, J K

The structure of martensite in iron-nickel-carbon alloys containing less than 0.015 wt% carbon was investigated by measuring the 40 deg C carbon diffusion internal friction peak. Measurements of the internal friction in alloys containing 0.0, 2.5, 5.1, 6.5, 10.5, and 16.5 wt% nickel were made at low frequencies with a torsion pendulum. By evaluation of the effects of varying nickel content and heat treatment on the nature of this peak, the existence of a structure in which the carbon atoms are ordered was revealed in specimens which had been quenched from temperatures at which austenite is stable. It is proposed that this structure is tetragonal martensite and that the tetragonality of the structure persists at these very low carbon contents because of the ordering influence of the residual accommodation stresses exerted on the martensite by the austenite matrix. Resolution of these stresses on the basis of the most successful of the proposed crystallographic mechanisms of martensite transformation showed that stress conditions favoring ordering can exist whether the martensite forms as plates or needles. It was found that the tetragonality of the structure disappeared on high temperature tempering and that a tetragonal structure could not be produced in binary iron-carbon alloys at this low carbon level. The amount of tetragonal phase which could be produced by quenching iron- nickel - carbon alloys increased with increasing nickel content and with increasing quenching rate. In iron-nickel-carbon alloys with a ferritic structure, the addition of nickel decreased the height and area of the 40 deg C peak, shifted its Position to a lower temperature, but caused the peak to be only slightly broadened, if at all. The decrease in peak height with increasing nickel content was approximately linear and the amount of decrease was about 8% of the peak height in the binary iron- carbon alloy per wt% nickel. The observed peak positions at a measuring frequency of one cycle per second are 38.5 deg C for 0% nickel, 37.5 deg C for 2.5 wt% nickel, and 35.8 deg C for 5.1 wt% nickel. The shift in the peak position with increasing nickel content indicated that there is a long range effect of nickel on the movement of the carbon atoms within the lattice, and the change in the diffusion coefficient for carbon alloy ferrite with increasing nickel content was estimated from the magnitude of the shift. The reduction in peak area with increasing nickel content implied that short range interactions with the nickel atoms prevent some of the carbon atoms from participating in the relaxation processes which give rise to the peak under investigation. The peak broadening was analyzed by considering that the measured internal friction peak is a convolution of the theoretical peak for a single relaxation time density function. This density function, and its in tegral, the relaxation time distribution function, were determined by graphical trial and error solution for a quenched and tempered 5.1 wt% nickel alloy specimen. The density function was unimodal within experimental error. (auth)

• Research Organization: Purdue Univ., Lafayette, Ind.
• NSA Number: NSA-16-019368
• OSTI ID: 4817803
• Report Number(s): TID-15643
• Resource Relation: Other Information: Orig. Receipt Date: 31-DEC-62
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

METALS, CERAMICS, AND OTHER MATERIALS
ALLOYS
ATOMS
AUSTENITE
CARBON
CONFIGURATION
CRYSTALS
DENSITY
DIAGRAMS
DIFFUSION
DIFFUSION LENGTH
DISTRIBUTION
ERRORS
FREQUENCY
FRICTION
HEAT TREATMENTS
HIGH TEMPERATURE
INTERACTIONS
IRON ALLOYS
IRON OXIDES
LATTICES
LOW TEMPERATURE
MARTENSITE
MEASURED VALUES
MECHANICAL STRUCTURES
NICKEL
NICKEL ALLOYS
PENDULUM
PHASE DIAGRAMS
PLATES
ROTATION
STABILITY
STANDARDS
STRESSES
TEMPERATURE
TEMPERING
TRANSIENTS
VARIATIONS