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Metallurgical Aspects of Induction Heating, Microstructures, Residual Stress [.pdf format]

Metallurgical insights for induction heat treaters. Part 6: Stripping phenomenon

Author: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 11/1/2008

This article is one of series of articles devoted to metallurgical aspects of induction hardening and discusses a stripping phenomenon. Heat-treat practitioners sometimes observe unusual effects in induction hardening, such as a striping phenomenon, a barber-pole effect, and a snakeskin effect. The appearance of a striping phenomenon is discussed in this article.

Metallurgical insights for induction heat treaters. Part 5: Super-hardening phenomenon

Authors: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 9/1/2008

This article is one of series of articles devoted to metallurgical aspects of induction hardening and discusses a super-hardening phenomenon. Specifics of induction hardening process and prior microstructure have a pronounced effect on the appearance of the super-hardening phenomenon. Fine grain homogenous normalized structures, as well as quenched and tempered structures have more of a chance to exhibit super-hardening. The phenomenon of super-hardening of induction surface (case) hardened parts is particularly noticeable in steels with a carbon content of 0.35 to 0.65%, case depths less than 0.125 in. (3.2mm) and heat times less than four seconds. The super-hardening phenomenon could allow a user to apply a lower steel grade (lower carbon content) without sacrificing the desired surface hardness and hardness profile of the product. Case study is provided here as well.

Intricacies for the successful induction heating of steels in modern forge shops.

Authors: Valery Rudnev, Doug Brown, Chester J. Van Tyne, Kester D. Clarke
Publication: Proceedings of 19th International Forging Congress, Chicago, IL
Date: 9/7/2008

Over the past three decades, induction heating has become an increasingly popular in forge shops. Among other subjects, this paper discusses:

  • Trends in forging steels. Selection of forging temperatures.
  • Intricacies of process requirements associated with recent knowledge related to theory and practice of induction heating.
  • Novel induction billet heater design concept.
  • Temperature uniformity requirements. Common misassumption.
  • "Stand-by" and "Rapid start" features of modern induction heaters.

Metallurgical insights for induction heat treaters. Part 4: Obtaining fully martensitic structures using water spray quenching

Authors: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 3/1/2008

This article is one of series of articles devoted to metallurgical aspects of induction hardening. In induction hardening of steels, the ability to obtain a certain degree of martensitic structure is often the measure of the success of the process. Martensite is a supersaturated solid solution of carbon in ferrite with a body-centered tetragonal (BCT) structure. Upon rapid cooling, carbon is trapped in the crystal structure. The high hardness developed in the steel is due to the distortion that occurs during the transformation from face-centered cubic (FCC) austenite to BCT martensite. Article discusses an ability of obtaining martensitic structures in induction hardening applications.

Metallurgical insights for induction heat treaters. Part 3: Limitations of TT and CTT diagrams

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 11/1/2007

This article is one of series of articles devoted to metallurgical aspects of induction hardening. Article discusses applicability of TTT and CCT diagrams in induction hardening applications. Both the TTT and CCT diagrams were developed assuming homogeneous austenite, which is not always the case in induction hardening. Rapid induction heating appreciably affects the kinetics of austenite formation and carbon distribution within it. Results of computer modeling of induction scan hardening of shaft using numerical computer modeling are shown here as well.

Metallurgical insights for induction heat treaters. Part 2: Spray quenching subtleties

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 8/1/2007

This article is one of series of articles devoted to metallurgical aspects of induction hardening. Spray quenching is typically used in induction hardening applications. In induction hardening of cylindrically shaped parts (axle shafts, spindles, rods, camshafts, and gears, for example), spray quenching works best if the component is rotated during the quenching operation, which ensures cooling uniformity. Presentation discusses specifics of spray quenching, difference in cooling curves, "cold sink" effect, and other important phenomena related to cooling stages during spray quenching.

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