Development of Ultra Fine Grain Steel for Carburizing

Kurebayashi, Yutaka; Nakamura, Sadayuki

doi:10.4271/950209

Cited by 3 publications

(1 citation statement)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, several recent studies have considered alloy and process modifications designed to produce suitable precipitate distributions to suppress austenite grain coarsening at carburizing temperatures. [7][8][9][10][11][12][13][14][15][16][17] Previous studies have considered processing to control aluminum nitride precipitates 8) and alloying to control precipitates based on titanium and nitrogen additions, 7) niobium, 9) or titanium plus niobium additions. [10][11][12][13][14][15][16] While the previous studies have illustrated the potential of utilizing precipitates to limit austenite grain coarsening during carburizing, there have been no systematic studies designed to provide the necessary fundamental information to optimize precipitate distributions to minimize grain coarsening during carburizing.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Niobium Microalloying on Austenite Grain Coarsening Behavior of Ti-modified SAE 8620 Steel

2007

View full text Add to dashboard Cite

The potential for suppressing unacceptable austenite grain growth during carburizing by Nb microalloying additions in the range of 0.02 to 0.11 wt% to a Ti-modified SAE 8620 carburizing steel were evaluated. Alloys, were designed based on fundamental equilibrium thermodynamic analyses, as part of an extensive study on the effects of alloy composition, thermomechanical history, and pseudo-carburizing conditions on austenite grain coarsening behavior. Laboratory samples were produced to simulate both conventional hot rolling and controlled rolling practices designed to produce different initial precipitate distributions. Pseudocarburizing heat treatments, i.e. without a carburizing atmosphere, were performed in the temperature range of 950 to 1 100°C for holding times of 30 to 360 min. Precipitate distributions, including size, number density, morphology, distribution, and chemical composition in selected samples from the as-rolled and pseudo-carburized conditions were evaluated with transmission electron microscopy on extraction replicas. Results showed that increasing Nb additions to the Ti-modified SAE 8620 steel restrained austenite grain coarsening, and increased the grain coarsening time, especially at temperatures below 1 050°C. The Nb-free (Ti-modified) steel yielded either severely duplex grain structures or pseudo-normal grain growth (with very large mean grain diameter). However, holding a Ti-Nb-modified steel (e.g. 0.06 Nb wt%) at 950°C for 6 h or at 1 000°C for 4 h. produced fine and uniform austenite grain structures (with a mean grain diameter less than 20 mm). The finer grain sizes observed in the Ti-Nb-modified steels were due to the presence of Nbrich precipitates that hinder austenite grain coarsening, and precipitate distributions and grain growth behaviors are also influenced by the steel rolling history. The results indicate that Nb can successfully be used to suppress grain growth in carburizing steels.KEY WORDS: niobium microalloying; carburizing; precipitation; abnormal grain growth. © 2007 ISIJ Alloy and Process Design 2.1. Thermodynamic Basis for Alloy SelectionExperimental alloys, intended to assess the ability of niobium additions to suppress austenite grain coarsening at elevated temperatures, were developed based on fundamental equilibrium thermodynamic analyses of niobium-carbide precipitate formation. Following the previous work of Davidson et al.,7) which showed that a maximum retardation effect on austenite grain coarsening at carburizing temperatures was observed in a Ti-modified SAE 8620 steel with a Ti : N ratio close to stoichiometric (3.42 by weight), the experimental alloys were developed based on the following assumptions: i) Titanium added stoichiometrically to the SAE 8620 steel will precipitate N as TiN; ii) In the Ti-modified SAE 8620 steel, added niobium will precipitate as NbC; and iii) Maximum temperatures experienced during solid-state processing are below about 1 300°C. With these assumptions, the desired niobium levels were determined based on solubility product ...

show abstract

Section: Introductionmentioning

confidence: 99%

The Influence of Niobium Microalloying on Austenite Grain Coarsening Behavior of Ti-modified SAE 8620 Steel

2007

View full text Add to dashboard Cite

show abstract

Development of steel grades for heat treated power train components: a review

Kimura

2009

International Heat Treatment and Surface Engineering

View full text Add to dashboard Cite

The development of new carburising steel grades by Daido Steel for heat treated transmission parts is reviewed. These developments are driven by the need for cost reduction, weight saving, fuel economy and higher mechanical performance in new car models under development in response to environmental and economic demands. The next generation of gears will be peened, then vacuum carburised to improve fatigue and impact strength in lighter components designed with smaller tooth cross-sections, and new steels giving improved performance have been developed. Case studies of new steels for pulleys (allowing shorter carburising times) and constant velocity joints are also described.

show abstract