One Minute Mentor: Alpha-Prime Inhibits Toughness in Ferritic Stainless Steels
June 3, 2016
Source:
The graph shows how alpha-prime formation reduces toughness in ferritic stainless steels. The worst toughness-inhibiting effects come from interstitial elements in grain boundaries: oxygen, carbon, and nitrogen. Stabilizing removes the interstitial carbon and nitrogen, along with oxygen and sulfur, from solution. This does not produce a major softening, however, because the precipitate itself has a hardening effect.
Because stabilized alloys are ferritic at all temperatures, there is no automatic grain-refining transformation as exists in carbon steel. If grains grow large from annealing at high temperatures or welding, then the transition temperature increases. Section size also has an effect. Stabilized ferritic stainless steels are seldom used in thicknesses of over several millimeters because of decreasing toughness.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Ferritic Stainless Steels ⇒ Properties
The graph shows how alpha-prime formation reduces toughness in ferritic stainless steels.
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One Minute Mentor: Influence of Chromium on Ferritic Stainless Steels
May 26, 2016
Source:
Ferritic stainless steels are quite similar in their mechanical behavior to carbon steel. The main influence of chromium is to produce some solid solution hardening. As noted, intermetallic phases may increase hardness (sometimes usefully) and decrease ductility, notch toughness, and corrosion resistance. For example, the graph shows the hardening effect of alpha prime.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Ferritic Stainless Steels ⇒ Properties
Ferritic stainless steels are quite similar in their mechanical behavior to carbon steel.
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One Minute Mentor: Tempering Corrosion-Resistant Tool Steels
May 6, 2016
Source:
The graph shows the tempering behavior of two corrosion-resistant tool steels: AISI 420 and the nitrogen-alloyed M333 (AISI 420 Mod). During tempering, the combination of properties such as hardness, toughness, and corrosion resistance, as well as residual stresses, can be adjusted within a wide range. Very low tempering temperatures (<300°F) are uncommon, as they result in very low impact toughness and high internal stresses.
With increased tempering temperatures, toughness properties can be improved significantly with only limited loss in hardness, as shown in the graph.
The precise behavior strongly depends on the uniformity of the microstructure and on chemical composition, with advantages shown by nitrogen-alloyed lower-carbon grades. Typical tempering temperatures for small and simple-shaped tools vary between 390 and 750°F. In the case of large and complex dies, such tempering temperatures can still lead to very high internal stresses, resulting in early tool failure despite good impact toughness.
Volume 4D, Heat Treating of Irons and Steels ⇒ Tool Steels ⇒ Heat Treating of Mold Steels and Corrosion-Resistant Tool Steels ⇒ Recommended Heat Treating Practices
During tempering, the combination of properties such as hardness, toughness, and corrosion resistance, as well as residual stresses, can be adjusted within a wide range
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One Minute Mentor: Carburizing Tool Steels
April 22, 2016
Source:
P20 mold steel is seldom carburized for molds used in compression molding, particularly for molding the more abrasive plastics. Carburizing temperatures no higher than 1650°F are recommended for this steel because higher temperatures may impair polishability; otherwise, conventional carburizing practice is used, and molds may be quenched in oil directly from the carburizing temperature. A common working range is 54 to 58 HRC.
The graph shows tempering characteristics of carburized mold steels.
(a) Upper curve represents steel carburized in hardwood charcoal 1675 to 1700°F for 8 hours, air cooled in pack, reheated at 1725 to 1750°F, cooled in air, and tempered. Middle curve represents steel carburized in cast iron chips at 1725 to 1750°F, removed from pack, cooled in air, and tempered.
(b) Surface hardness after heating at temperature for 2 hours in carburizing compound, followed by oil quenching and tempering.
Volume 4D, Heat Treating of Irons and Steels ⇒ Tool Steels ⇒ Heat Treating of Mold Steels and Corrosion-Resistant Tool Steels ⇒ Recommended Heat Treating Practices
P20 mold steel is seldom carburized for molds used in compression molding, particularly for molding the more abrasive plastics.
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One Minute Mentor: Tempering Temperature and Corrosion Properties
March 31, 2016
Source:
One Minute Mentor: Tempering Temperature and Corrosion Properties
The graph shows the corrosion resistance of martensitic stainless steels with high hardness. It compares nitrogen alloyed grade (M340 = AISI 440Mod) with the standard grade AISI 440C.
For the application of higher tempering temperatures, corrosion properties also have to be taken into consideration. Usually the minimum in corrosion resistance can be found slightly above the secondary hardening maximum. In 17%-Cr high-carbon grades such as AISI 440C, corrosion resistance already starts to deteriorate at tempering temperatures higher than 390°F, as shown in the graph; lower-carbon grades like AISI 420, and even more the nitrogen-alloyed grades, show a significant drop in corrosion resistance only at tempering temperatures higher than approximately 840°F.
Volume 4D, Heat Treating of Irons and Steels -> Tool Steels -> Heat Treating of Mold Steels and Corrosion-Resistant Tool Steels -> Recommended Heat Treating Practices
The graph shows the corrosion resistance of martensitic stainless steels with high hardness. It compares nitrogen alloyed grade (M340 = AISI 440Mod) with the standard grade AISI 440C.
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One Minute Mentor: Tempering Behavior of Corrosion-Resistant Tool Steels
March 24, 2016
Source:
During tempering, the combination of material properties such as hardness, toughness, and corrosion resistance, as well as residual stresses, can be adjusted within a wide range. Very low (<300°F) tempering temperatures are uncommon, as they result in very low impact toughness and high internal stresses.
With increased tempering temperatures, toughness properties can be improved significantly with only limited loss in hardness, as shown in the graph. The precise behavior strongly depends on the uniformity of the microstructure and on chemical composition, with advantages shown by nitrogen-alloyed lower-carbon grades. Typical tempering temperatures for small and simple-shaped tools vary between 390°and 750°F. In the case of large and complex dies, such tempering temperatures can still lead to very high internal stresses, resulting in early tool failure despite good impact toughness.
Volume 4D, Heat Treating of Irons and Steels -> Tool Steels -> Heat Treating of Mold Steels and Corrosion-Resistant Tool Steels -> Recommended Heat Treating Practices
During tempering, the combination of material properties such as hardness, toughness, and corrosion resistance, as well as residual stresses, can be adjusted within a wide range
Continue reading
One Minute Mentor: Hardness Gradients in Nitrided High-Speed Tool Steel
March 4, 2016
Source:
The graph shows the effect of bath conditions and immersion time on hardness gradients in Type T1 high-speed tool steel.
It compares the hardness gradients obtained on specimens of T1 high-speed steel nitrided at 565°C (1050°C) for 90 minutes in a new bath and for various lengths of time in an aged bath. Nitriding of decarburized high-speed steel tools should be avoided because it results in a brittle surface condition. For those surfaces that have been softened from grinding, nitriding is frequently employed as an offsetting corrective measure.
Volume 4D, Heat Treating of Irons and Steels ⇒ Tool Steels ⇒ Heat Treating of High-Speed Tool Steels ⇒ Recommended Heat-Treating Procedures
The graph shows the effect of bath conditions and immersion time on hardness gradients in Type T1 high-speed tool steel.
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One Minute Mentor: Tempering Tool Steels
February 26, 2016
Source:
As shown in the graph for an M2 steel austenitized at 2225°F, the hardness of high-speed steel is directly affected by tempering temperature and time. From the slopes of the curves, it can be seen that M2 undergoes secondary hardening at temperatures above approximately 700°F, and that secondary hardening proceeds at higher temperatures up to about 1100°F, depending on time at temperature.
These temperatures approximate the practical limits for most tempering operations; lower temperatures do not evoke the secondary hardening response, and higher temperatures produce hardness considerably lower than usually desired.
Volume 4D, Heat Treating of Irons and Steels -> Tool Steels -> Heat Treating of High-Speed Tool Steels -> Recommended Heat-Treating Procedures
As shown in the graph for an M2 steel austenitized at 2225°F, the hardness of high-speed steel is directly affected by tempering temperature and time.
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One Minute Mentor: How Austenitizing Temperature Affects High-Temperature Hardness
February 18, 2016
Source:
The austenitizing temperature affects not only the final hardness but also the grain size. Owing to the high amount of alloying elements dissolved in the matrix, prior austenite boundaries are preferentially etched instead of martensite structure, enabling the quantification of austenite grain size. A continuous increase in austenite grain size with the hardening temperature is observed.
The graph shows the reduction in high-temperature hardness of M2 tool steel that results from austenitizing at relatively low temperatures.
Volume 4D, Heat Treating of Irons and Steels ⇒ Tool Steels ⇒ Heat Treating of High-Speed Tool Steels ⇒ Recommended Heat-Treating Procedures
The austenitizing temperature affects not only the final hardness but also the grain size.
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One Minute Mentor: Effect of Austenitizing Temperature on Hardness
February 11, 2016
Source: ASM International
The graph illustrates the improved toughness of M2, as measured by the Izod unnotched impact test, that results from the use of lower-than-normal austenitizing temperatures.
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