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

AlOgab, Khaled A.; Matlock, David K.; Speer, John G.

doi:10.2355/isijinternational.47.307

Cited by 67 publications

(47 citation statements)

References 25 publications

(25 reference statements)

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“…The laboratory melted alloys were processed to simulate conventional hotrolling (HR; finish rolling temperature of 1 100°C) or controlled-rolling (CR; finish rolling temperature of 850°C) and details of the alloy design and processing history are summarized elsewhere. 1,22) Data are also presented on a Nbfree steel examined previously.…”

Section: Experimental Materials and Proceduresmentioning

confidence: 99%

“…vacuum) carburizing processes with processing temperatures up to 1 100°C, new steel alloys based on microalloy additions of Ti and Nb are being developed to produce specific precipitate dispersions that are effective in minimizing austenite grain growth. [1][2][3] In carburizing gear steels, the importance of minimizing austenite grain coarsening in order to maximize fatigue performance has been clearly demonstrated. 4,5) Austenite grain growth in microalloyed steels is influenced by numerous factors, including austenitizing time and temperature, alloy composition, thermomechanical history, initial grain size distribution, and rate of heating to the austenitizing temperature.…”

Section: Introductionmentioning

confidence: 99%

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The Effects of Heating Rate on Austenite Grain Growth in a Ti-modified SAE 8620 Steel with Controlled Niobium Additions

2007

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The effects of heating rate on austenite grain growth and precipitate distribution in Ti-modified SAE 8620 steels with Nb additions of 0.02, 0.06 and 0.1 wt% were evaluated with pseudo-carburizing, i.e. without a carburizing gas, heat treatments characteristic of high temperature vacuum carburizing. Laboratory plates were produced to simulate conventional hot-rolling and controlled-rolling processes. Specimens were heated at rates between 10 and 145°C min Ϫ1 to 1 050 and 1 100°C, held at the desired austenitizing (carburizing) temperature for 60 min, and immediately quenched in iced-water. Austenite grain structures developed at the austenitizing temperatures were evaluated with light optical metallography, and precipitate dispersions were evaluated using extraction replicas in the transmission electron microscope. Abnormal grain growth was observed in all samples processed at the highest heating rate to 1 050°C, but was suppressed at the lower heating rates with additions of 0.06 and 0.1Nb. Suppression of abnormal grain growth was correlated with the development of a critical distribution of fine NbC precipitates, stable at the austenitizing temperature. The importance to industrial carburizing practice of heating rate effects on precipitates and austenite grain size evolution are discussed.

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Section: Experimental Materials and Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Effects of Heating Rate on Austenite Grain Growth in a Ti-modified SAE 8620 Steel with Controlled Niobium Additions

2007

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“…Many studies have been indicating that prior austenite grain size control in carburizing steel can be effectively achieved by using niobium microalloying in combination with other microalloys such as titanium, aluminum and nitrogen [13][14][15][16][17][18][19][20]. The developed concepts have been used to generally refine and homogenize the grain size under standard case carburizing conditions.…”

Section: Controlling Grain Size In Carburizing Steelsmentioning

confidence: 99%

Optimizing Gear Performance by Alloy Modification of Carburizing Steels

Tobie

Hippenstiel²,

Mohrbacher

2017

Metals

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Both the tooth root and tooth flank load carrying capacity are characteristic parameters that decisively influence gear size, as well as gearbox design. The principal requirements towards all modern gearboxes are to comply with the steadily-increasing power density and to simultaneously offer a high reliability of their components. With increasing gear size, the load stresses at greater material depth increase. Thus, the material and particularly the strength properties also at greater material depth gain more importance. The present paper initially gives an overview of the main failure modes of case carburized gears resulting from material fatigue. Furthermore, the underlying load and stress mechanisms, under particular contemplation of the gear size, will be discussed, as these considerations principally define the required material properties. Subsequently, the principles of newly developed, as well as modified alloy concepts for optimized gear steels with high load carrying capacity are presented. In the experimental work, the load carrying capacity of the tooth root and tooth flank was determined using a pulsator, as well as an FZG back-to-back test rig. The results demonstrate the suitability of these innovative alloy concepts.

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“…3 Influence of single alloying elements on the increase of the hardenable diameter using Grange's technique [8] Fig . 4 Hardness loss of the carburized case after exposure (2 h) to elevated temperature in low-molybdenum and high-molybdenum alloyed steels [9] small particles in the steel matrix [10][11][12][13][14][15][16]. These particles have the potential of pinning the austenite grain boundary.…”

Section: Alloy Concepts For High Hardenability and Tempering Resistancementioning

confidence: 99%

Metallurgical concepts for optimized processing and properties of carburizing steel

Mohrbacher¹

2016

Adv. Manuf.

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Carburized steel grades are widely used in applications where high surface near hardness is required in combination with good core toughness as well as high strength and fatigue resistance. The process of carburizing lower to medium carbon containing steel can generally provide this combination of properties and has been practiced for several decades. Such steel is essential in the vehicle power-train, machines and power generation equipment. However, the increasing performance demands by such applications as well as economical considerations forced steel producers to develop better alloys and fabricators to design more efficient manufacturing processes. The present paper describes recent concepts for alloy design optimization of carburizing steel and demonstrates the forthcoming beneficial consequences with regard to manufacturing processes and final properties.Keywords High temperature carburizing Á Grain size control Á Distortion control Á Integrated manufacturing Á Plasma nitriding Á Micro pitting Á Tooth root fatigue strength Á Molybdenum steel Á Niobium microalloying 1 Motivation for optimizing carburizing steel Case carburizing steels (alternatively known as case hardening steels) are widely used in applications where high surface-near hardness is required in combination with good core toughness as well as high strength and fatigue resistance. These steels have been the material of choice for several decades to manufacture components like gears, shafts or bearings. Depending on the application and the component size the following alloy systems have been established: (i) Chromium steels for smaller components when only low hardenability is required. (ii) Manganese-chromium steels with medium hardenability for passenger vehicle components. (iii) Chromium-molybdenum steels with medium/high hardenability for passenger and commercial vehicle components. (iv) Chromium-nickel-molybdenum steels with high hardenability for severely loaded machinery and commercial vehicle components. (v) Nickel-chromium steels with high hardenability for components with extraordinary toughness requirements.Within these alloy systems, standardized steel grades are available in different major markets offering a guaranteed spectrum of mechanical properties. Case hardening steels have reached a high degree of technical maturity, which is due to the materials specification as well as a high standard in processing [1]. The manufacturing of a component involves a complex sequence of individual forming, machining and heat treatment operations including the actual case hardening treatment (see Fig. 1). During case carburizing the component is heated to a temperature in the austenite range in presence of a carbon containing gas atmosphere. Most of the established industrial processes limit this temperature to 950°C. During extended holding under these conditions carbon diffuses into the surface-near layer. With the holding time increased, the diffusion depth increases. At the end of the diffusion time a concentration

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

Cited by 67 publications

References 25 publications

The Effects of Heating Rate on Austenite Grain Growth in a Ti-modified SAE 8620 Steel with Controlled Niobium Additions

The Effects of Heating Rate on Austenite Grain Growth in a Ti-modified SAE 8620 Steel with Controlled Niobium Additions

Optimizing Gear Performance by Alloy Modification of Carburizing Steels

Metallurgical concepts for optimized processing and properties of carburizing steel

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