One Minute Mentor: Effect of Ledeburite Carbides
November 13, 2015
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For ledeburitic tool steels (typical 8-12%-Cr cold-work tool steels and high-speed steels) the interaction of carbides with the matrix must be taken into account, especially when these carbides are strongly oriented after plastic deformation (rolling, forging) of the pre-material.
The longitudinal direction of the carbides is usually parallel to this forming direction. Different authors suggest that the orientation of forming is the preferred direction of change in length caused by hardening. For the tool maker it is important to take this behavior into account.
Results from investigations of a ledeburitic cold work tool steel are shown in the graph. The micromechanical interactions between carbides and the matrix cause an inhomogeneous change in length during austenitizing as well as during quenching. Finally, an elongation in the longitudinal direction and a shrinking in the transverse direction remain.
Volume 4D, Heat Treating of Irons and Steels -> Tool Steels -> Distortion in Tool Steels -> Nature and Causes of Distortion
For ledeburitic tool steels (typical 8-12%-Cr cold-work tool steels and high-speed steels) the interaction of carbides with the matrix must be taken into account, especially when these carbides are strongly oriented after plastic deformation (rolling, forging) of the pre-material.
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One Minute Mentor: Austenitizing Tool Steel
October 16, 2015
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Austenitizing Tool Steel
Austenitizing is the heat treatment in which the final alloy element partitioning between the austenitic matrix (which will transform to martensite) and the retained carbides occurs. This partitioning fixes the chemistry, volume fraction, and dispersion of the retained carbides. The retained alloy carbides not only contribute to wear resistance but also control austenitic grain size. The finer the carbides and the larger the volume fraction of carbides, the more effectively austenitic grain growth is controlled. Thus, if the tool steel is austenitized at too high a temperature, undesirable grain growth may occur as the alloy carbides increasingly coarsen or dissolve into the austenite.
The graph shows that tempering by a combination of retained austenite transformation and secondary hardening, will eventually raise the hardness of as-quenched structures with large amounts of retained austenite. Not shown is the deleterious increase in austenite grain size that develops as more and more carbides dissolve at the higher austenitizing temperatures.
Volume 4D, Heat Treating of Irons and Steels -> Heat Treating of Carbon and Low-Alloy Steels -> Introduction to Heat Treating of Tool Steels -> Heat Treatment Applied to Tool Steels
Austenitizing is the heat treatment in which the final alloy element partitioning between the austenitic matrix (which will transform to martensite) and the retained carbides occurs.
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One Minute Mentor: Steps for Hardening of Tools as a Function of Time, Temperature, and Phase Transformation
October 9, 2015
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Steps for Hardening of Tools as a Function of Time, Temperature, and Phase Transformation
After hot forming, tool steel usually is submitted to heat treatment processes that may be split into two major steps. The first step (shown last week) is done to produce a low-hardness condition. The second step involves this homogeneous microstructure being converted to a higher-hardness condition, usually by martensite formation during the hardening and tempering heat treatments.
In a graphical form, the graph shows the typical processing and heat treatment sequences for hardening of tool steels, as a function of time, temperature, and phase transformation.
The graph shows plots of temperature versus time showing sequence of operations required to produce tool steels. Hardening heat treatment. L, liquid; A, austenite; C, cementite; F, ferrite; Ms, temperature at which martensite starts to form on cooling; RT, room temperature.
Volume 4D, Heat Treating of Irons and Steels -> Heat Treating of Carbon and Low-Alloy Steels -> Introduction to Heat Treating of Tool Steels -> Heat Treatment Applied to Tool Steels
After hot forming, tool steel usually is submitted to heat treatment processes that may be split into two major steps.
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One Minute Mentor: Heat Treatment Applied to Tool Steels
September 30, 2015
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After hot forming, tool steel usually is exposed to a heat treatment process done to produce a low-hardness condition. Low hardness is important for machining, but the treatment also should promote a homogeneous microstructure, usually referred to as the annealed condition. The graph shows the process condition as a function of time, temperature, and phase transformation.
Volume 4D, Heat Treating of Irons and Steels -> Heat Treating of Carbon and Low-Alloy Steels -> Introduction to Heat Treating of Tool Steels -> Heat Treatment Applied to Tool Steels
After hot forming, tool steel usually is exposed to a heat treatment process done to produce a low-hardness condition.
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One Minute Mentor: Sinter Hardening
September 24, 2015
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Sinter Hardening
Sinter hardening refers to a process in which the cooling rate in the cooling zone of the sintering furnace is fast enough to transform a significant portion of the powder metal steel matrix into martensite.
The sinter hardening route has become increasingly widespread due to its cost effectiveness. Advantages include:
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treating of Carbon and Low-Alloy Steels ⇒ Heat Treatment of Powder Metallurgy Steels ⇒ Sinter Hardening
Sinter hardening refers to a process in which the cooling rate in the cooling zone of the sintering furnace is fast enough to transform a significant portion of the powder metal steel matrix into martensite.
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One Minute Mentor: Tempering Powder Metallurgy Steels
September 18, 2015
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Tempering Powder Metallurgy Steels
Usually, powder metallurgy steel parts having a density greater than 6.7 g/cm3 (0.242 lb/in.3) should be tempered after hardening. Recommended tempering temperatures for PM parts range from 150 to 200°C (300 to 390°F) with 175°C (350°F) being common. The effect of tempering temperature on impact properties is shown in the graph for FL-4205 at various densities.
Tempering above 200°C results in improved toughness and fatigue properties of the hardened part, while making a compromise in tensile strength and impact resistance. However, when tempering at temperatures higher than 200°C, care should be exercised as entrapped oil can ignite.
Volume 4D, Heat Treating of Irons and Steels -> Heat Treating of Carbon and Low-Alloy Steels -> Heat Treatment of Powder Metallurgy Steels -> Quenching and tempering
Usually, powder metallurgy steel parts having a density greater than 6.7 g/cm3 (0.242 lb/in.3) should be tempered after hardening. Recommended tempering temperatures for PM parts range from 150 to 200°C (300 to 390°F) with 175°C (350°F) being common.
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Dual chamber furnace enables simultaneous hardening and tempering
June 23, 2015
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Lucifer Furnaces, Warrington, Pa., announces that a Red Devil dual chamber furnace has been added to the line of analytical equipment at Laboratory Testing Inc., Philadelphia. Dual chamber furnaces allow hardening in the upper chamber while tempering in the lower oven, without waiting for a single-chamber unit to cool. The furnace is capable of meeting AMS 2750 requirements for aerospace, and its large work zone can accommodate larger parts.
LTI uses the furnace for heat treating to various specifications for ASTM, AMS, GE, ASME, and other customer requirements, including solution treatment cycles, aging cycles, post-weld heat treat, normalizing, hardening, and tempering. With both chambers 12x14x24 inches, the upper chamber is programmed to heat to 2200°F, while the lower oven reaches 1200°F. Both chambers are lined with 4.5 inches of multilayer lightweight firebrick insulation and mineral wool backup precision dry fit, to allow for thermal expansion while minimizing heat loss. Easy-to-replace heating elements simplify maintenance.
For this furnace, Lucifer customized a standard Red Devil Model RD8-KHE24 with Eurotherm 3204 programmable controllers and Honeywell UDC1200 over-temperature controllers. The upper chamber was modified with a gas spring vertical lift door.
Laboratory Testing Inc. specializes in metals testing through destructive testing methods, including mechanical, metallurgical, chemical, and corrosion testing, as well as nondestructive testing methods.
www.luciferfurnaces.com
Lucifer Furnaces, Warrington, Pa., announces that a Red Devil dual chamber furnace has been added to the line of analytical equipment at Laboratory Testing Inc., Philadelphia.
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