High-impact research to be revealed at Heat Treat 2017
October 4, 2017
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More than 125 presentations of original, unpublished work will be delivered when the ASM Heat Treating Society convenes for its 29th conference and exhibition in Columbus, Ohio, October 24-26. The information exchanged in these sessions – as researchers and practitioners share their latest discoveries, theories, and advancements – will have a significant impact on design and manufacturing innovation as well as the fortunes of industry.
One example of the cutting-edge work that will be unveiled is an investigation on the effect of heat treating on additively manufactured medical implants. Additive techniques offer unprecedented design flexibility for dental and orthopedic implants, but the intense heating and cooling spikes associated with direct metal laser sintering can leave the microstructure of titanium – a good bio-material but a poor thermal conductor – in a less than optimum state. To quantify the potential for improvement, researchers evaluated several heat treat processes and measured changes in hardness, residual stress, and corrosion. The promising findings will be shared in a Thursday morning session.
Caption: Optical metallography reveals microstructural differences between the build and deposition planes as well as pores near the surface of an as-printed titanium test sample. Structural mismatch is a source of residual stress, while pores can lead to fatigue fracture and corrosion.
Caption: X-ray diffraction results indicate that heat treating as-printed titanium parts (blue trace) reduces the ratio of α to β phase precipitates as seen in the narrowing of α peaks and the development of β peaks (green, orange, and red traces). This seems to correlate with measured improvements in corrosion resistance because micro-galvanic reactions stemming from phase differences cause pitting in α precipitates, a likely pathway for corrosion.
Another significant accomplishment that will be reported is a new method to predict the quenched and tempered hardness of complex steels based on chemistry data. Two researchers, building on prior attempts to calculate hardness as a function of chemistry, have developed a hybrid model that works for mixed microstructure alloys containing less than 0.5wt%Cr. As Cr levels increase, however, other alloying elements such as Mo and V become more influential, compounding the complexity of the problem. The researchers will describe the new method and its limitations on Tuesday morning.
Caption: A corrective variation on an earlier method for calculating tempered hardness in complex steels based on chemistry shows considerable improvement when measured and calculated data plots are compared side by side.
Caption: Hardness profiles for a 95 mm bar of SAE 4142 steel quenched in water and tempered at 1100°F as calculated from chemistry data using a recently developed method.
The results of several cross-sector efforts will also be presented, including a paper submitted by a group examining the role of vanadium in induction hardened shafts. Vanadium microalloying is common in carbon steel shafts because it increases load capacity. Induction hardening offers additional benefits, but the presence of vanadium adds uncertainty to the process. Seeking clarity, researchers have obtained evidence that, under certain conditions, vanadium carbonitride precipitates formed during induction reduce austenite in the case/core region but not the case. Retained austenite, characterized by compositional gradients and undissolved carbides, is believed to limit case depth and hardenability.
Caption: Cross-sectional images of 1045 steel shafts in various induction hardened conditions reveal distinct differences in case, core, and case/core regions that correspond with the presence of vanadium and its effect on microstructure formation.
Caption: A high volume fraction of martensite (M) revealed by SEM imaging is believed to be the result of a large amount of austenite formed with the help of vanadium during induction hardening of 1045 steel.
More than 125 presentations of original, unpublished work will be delivered when the ASM Heat Treating Society convenes for its 29th conference and exhibition in Columbus, Ohio, October 24-26. The information exchanged in these sessions – as researchers and practitioners share their latest discoveries, theories, and advancements – will have a significant impact on design and manufacturing innovation as well as the fortunes of industry.
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One Minute Mentor: CA-6NM Stainless Steel Casting Alloy
October 24, 2016
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A significant practical advantage of the CA-6NM stainless steel casting alloy is its relative freedom from the rapid drop in hardness when tempered above about 950°F. The graph shows clearly that a given increase in tempering temperature produces a much more gradual decrease in hardness than with CA-15. This makes heat treating much easier and cheaper, and decreases the frequency of rejections and/or the necessity for reheat treatment.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Martensitic Stainless Steels ⇒ Casting Alloys
A significant practical advantage of the CA-6NM stainless steel casting alloy is its relative freedom from the rapid drop in hardness when tempered above about 950°F.
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One Minute Mentor: Tempering Martensitic Stainless Steels
October 17, 2016
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This graph shows AISI Type 410: Effect of tempering temperature on tensile properties. Heated to and held at 1800°F for 30 minutes; oil quenched; tempered 1 to 4 hours. Impact energy test used Izod specimens. Elongation was measured in 2 in.; yield at 0.2% offset.
The nickel-bearing alloys have a restricted upper tempering temperature because of the danger of re-forming austenite, which would then transform to untempered martensite during cooling, requiring a second tempering operation. Intermediate temperatures can lead to temper embrittlement, which is caused by the precipitation of phosphorus and other species, including but not limited to carbides, at prior austenitic grain boundaries. Temper embrittlement is distinct from the precipitation of α', which causes the well-known 890°F embrittlement, which occurs more severely in alloys with higher chromium levels.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Martensitic Stainless Steels ⇒ Tempering
This graph shows AISI Type 410: Effect of tempering temperature on tensile properties. Heated to and held at 1800°F for 30 minutes; oil quenched; tempered 1 to 4 hours. Impact energy test used Izod specimens. Elongation was measured in 2 in.; yield at 0.2% offset.
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One Minute Mentor: Heat Treating of Martensitic Stainless Steels
October 10, 2016
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The effect of tempering temperature on hardness and tensile properties of high-alloy steels appears to have the same general form as those of low-alloy steel. A serious decrease in notch toughness occurs when tempering between about 750 and 950°F, as illustrated in the graph for Type 410.
The graph shows the effect of tempering temperature on impact properties of AISI Type 410. Impact energy tests used Izod, Charpy V-notch, or Charpy keyhole as indicated. Heat treatment of test specimens: heated to and held at 1750°C for one hour; oil quenched, temperad for four hours at temperature given; air cooled.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Martensitic Stainless Steels ⇒ Tempering
The effect of tempering temperature on hardness and tensile properties of high-alloy steels appears to have the same general form as those of low-alloy steel.
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One Minute Mentor: Tempering Corrosion-Resistant Tool Steels
May 6, 2016
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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: Tempering Temperature and Corrosion Properties
March 31, 2016
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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
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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: Effects of Different Cooling Rates on Corrosion-Resistant Tool Steels
March 18, 2016
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The graph shows the effects of different cooling rates on the toughness properties (un-notched samples) of AISI 420 and nitrogen-alloyed M333 tool steels.
The cooling parameter λ8/5, which is the cooling time from 1470° to 930°F in seconds, divided by 100, is used. Besides the general trend of falling toughness with rising cooling time, it is clearly evident that the nitrogen-alloyed steel grade M333 (420Mod), which has a lower carbon content, shows significantly higher toughness values. These can be further improved by lowering the austenitizing temperature. This behavior correlates well with the reduced tendency to form proeutectoid carbides at grain boundaries. A similar correlation can be found for the steel grades AISI 440B and the nitrogen-alloyed M340 (440Mod).
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 effects of different cooling rates on the toughness properties (un-notched samples) of AISI 420 and nitrogen-alloyed M333 tool steels.
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One Minute Mentor: Tempering Characteristics of P20 Mold Steel
March 11, 2016
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Tempering characteristics for P20 mold steels carburized at two different temperatures are shown in the graphs. In (a), the upper curve represents steel carburized in hardwood charcoal at 1675 to 1700°F for eight hours, air cooled in pack, reheated at 1725 to 1750°F, cooled in air, and tempered. The middle curve represents steel carburized in cast iron chips at 1725 to 1750°F, removed from pack, cooled in air, and tempered. Graph (b) shows surface hardness after heating at temperature for two hours in a 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
Tempering characteristics for P20 mold steels carburized at two different temperatures are shown in the graphs.
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One Minute Mentor: Tempering Tool Steels
February 26, 2016
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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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