Applied Process and others to begin doing business as Aalberts surface technologies
April 5, 2022 Source: ASM International
Applied Process and other U.S. based thermal processing, surface treatment businesses will begin doing business as Aalberts surface technologies.
Continue readingOne Minute Mentor: Crevice Corrosion Testing
January 22, 2018 Source: ASM International
In crevice corrosion testing, treated 316 stainless steel compares favorably with alloy 625, as shown in the figure with three images. This figure shows three specimens at the end of a weeklong crevice corrosion test in natural seawater, at room temperature, under an applied potential of 300 mV.
Continue readingOne Minute Mentor: Low-Temperature Carburization of Stainless Steels
December 11, 2017 Source: ASM International
The combination of hardness and ductility achieved by low-temperature carburization also enhances resistance to erosion. The graph shows the results of cavitation testing of treated and nontreated 316 stainless steel specimens.
Continue readingOne Minute Mentor: Maps of Wear Resistance
November 27, 2017 Source: ASM International
The images show wear maps for (a) treated and (b) nontreated 316 stainless steel. The T316 stainless steel was treated by low-temperature carburization.
Continue readingOne Minute Mentor: Diffusivity of Nitrogen in Austenite
May 26, 2017 Source:
The diffusivity of nitrogen in γN was determined from the stepwise denitriding kinetics of initially fully nitrided homogenous (stress-free) expanded austenite coupons. From the average diffusion coefficient for a series of narrow composition intervals, the composition-dependent diffusivity of nitrogen was reconstructed. The graph shows the diffusion coefficient of nitrogen in expanded austenite as a function of the nitrogen occupancy of the interstitial sites of the face-centered cubic lattice. Models based on the growth kinetics of the expanded austenite zone should take into consideration that the diffusivity of interstitials in expanded austenite is (strongly) concentration dependent and driven not only by a composition gradient but also by the presence of a (huge) compressive residual stress gradient over the thickness of the zone.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Low-Temperature Surface Hardening of Stainless Steel ⇒ Physical Metallurgy of Expanded Austenite
The diffusivity of nitrogen in ?N was determined from the stepwise denitriding kinetics of initially fully nitrided homogenous (stress-free) expanded austenite coupons.
Continue readingOne Minute Mentor: High-Temperature Nitriding for Deeper Case
March 2, 2017 Source:
High-temperature nitriding or solution nitriding at temperatures of 2010 ± 90°F is a new treatment available to produce cases with nitrogen concentrations in the range of 0.4 to 0.9 wt%, which is low compared to plasma nitriding treatments at low temperature (up to 16.9wt% N), but the resulting case is up to 100 times deeper (2 mm, or 0.08 in.). The lower nitrogen concentration implies a lower surface hardness (360 HV for solution nitriding of austenitic steels).
The graph shows a time-temperature transformation (TTT) curve for the precipitation of Cr2N, from which it can be estimated that, to avoid CrN precipitation, the temperature must drop from 2010°F to below 1650°F in approximately 20 seconds. That is feasible only in relatively thin parts (large area/volume ratio) that cool sufficiently to cope with the TTT curve time limitations to avoid precipitates, and only for a small number of parts at a time.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Nitriding of Stainless Steels ⇒ Thermochemical Nitriding Treatments
High-temperature nitriding or solution nitriding at temperatures of 2010 ± 90°F is a new treatment available to produce cases with nitrogen concentrations in the range of 0.4 to 0.9 wt%, which is low compared to plasma nitriding treatments at low temperature (up to 16.9wt% N), but the resulting case is up to 100 times deeper (2 mm, or 0.08 in.).
Continue readingOne Minute Mentor: Plasma Nitriding
January 3, 2017 Source:
Plasma nitriding is a surface-hardening process in which glow-discharge technology introduces nascent (atomic) nitrogen into the surface of a metal part for subsequent inward diffusion. The process takes place in a vacuum chamber, with the workpiece as the cathode (negative potential) in a nitrogen/hydrogen atmosphere at pressures between 100 and 1000 Pa (0.015 and 0.15 psi).
A voltage in the range of 500 to 1000 volts is applied between the metal part and the chamber wall, resulting in the formation of a plasma through which positive nitrogen ions are accelerated against the negative-biased part to be treated. This ionic bombardment heats the piece to the treatment temperature, cleans the surface by sputtering, and provides active nitrogen species for the nitriding process.
The diagram shows the schematic of a device used for glow-discharge plasma nitriding. 1 and 2, gas introduction; 3, thermocouple; 4, cathode; 5, pressure sensor, 6 to 8, needle valve; 9, diaphragm valve; 10, solenoid; 11, vacuum pump; 12, sample holder; 13, sample; 14, anode; 15, sealing ring; 16, stainless tube; 17, window and 18, insulator.
Volume 4D, Heat Treating of Irons and Steels ⇒ Nitriding of Stainless Steels ⇒ Thermochemical Nitriding Treatments
Plasma nitriding is a surface-hardening process in which glow-discharge technology introduces nascent (atomic) nitrogen into the surface of a metal part for subsequent inward diffusion
Continue readingOne Minute Mentor: The Passive Layer in Stainless Steels
December 1, 2016 Source:
The presence of chromium causes the buildup of a chromium oxide layer that is impermeable and adherent to the alloy substrate, protecting it from any further oxidation or corrosion. Any scratch on this protective layer exposes the substrate to oxygen, and a new protective oxide layer is produced.
One important aspect of this layer is that it must be homogeneous throughout the surface of the alloy. Any differences from place to place could generate a difference of electrochemical potential, which could trigger a corrosion process.
Under normal conditions, the thickness of the protective passive layer is in the range of 1.5 to 2.5 nm, composed mostly of chromium oxide/hydroxide and iron/iron oxide. The strong affinity of chromium for oxygen promotes a very stable compound (Cr2O3) that suppresses any other reactions and thus stops corrosion.
The chemical stability of the passive layer depends on the type of surface-finishing treatment. Processes such as electrochemical polishing increase the surface concentration of chromium, promoting a thicker and more stable passive layer when compared to mechanically processed surfaces
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Nitriding of Stainless Steels ⇒ Stainless Steels
The presence of chromium causes the buildup of a chromium oxide layer that is impermeable and adherent to the alloy substrate, protecting it from any further oxidation or corrosion.
Continue readingOne Minute Mentor: Heat Treating of Martensitic Stainless Steels
October 10, 2016 Source:
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.
Continue readingChromium Nitride in Duplex Stainless Steels
September 9, 2016 Source:
Because of the use of nitrogen as an alloying element in these stainless steels, chromium nitrides (CrN) may be present on α/α grain boundaries, on γ/α boundaries, and within the α grains. If formed in large quantities and under conditions in which the chromium-depleted areas do not have time to repair themselves during annealing, the presence of CrN may adversely affect corrosion resistance.
However, because higher nitrogen promotes more γ- phase, which has a high solubility for nitrogen, most modern DSS steels seldom contain significant amounts of CrN. Furthermore, duplex stainless steels are made with very low carbon content, so that carbide formation to a detrimental extent is not usually a concern. The only exceptions to this are the very lean grades, such as S32101, S32022, and S82011, which can lose corrosion resistance and toughness due to carbide and nitride formation. This is most likely to occur in the 1130 to 1475°F range.
With these very lean grades, the rate of formation of intermetallic compounds is sufficiently slow that the phases most likely to cause a loss of properties are the carbides and nitrides. The kinetics of carbide and nitride formation is similar to that of σ/χ precipitation in the 2205 grade.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Austenitic and Duplex Stainless Steels ⇒ Duplex Stainless Steels
Because of the use of nitrogen as an alloying element in these stainless steels, chromium nitrides (CrN) may be present on ?/? grain boundaries, on ?/? boundaries, and within the ? grains. If formed in large quantities and under conditions in which the chromium-depleted areas do not have time to repair themselves during annealing, the presence of CrN may adversely affect corrosion resistance.
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