Nitrex Communicator September/October 2011 - Visit us at ASM HT booth 1623

MUST-ATTEND PRESENTATIONS
Jack Kalucki, Heat Treating Projects Manager, will offer new information on the "Effect of Process Time on Low-temperature Nitrided Austenitic Stainless Steels Layer Structure" in his speech on Tuesday, November 1 at 4:30pm. Click here for a summary.
For the complete conference program click ASM Heat Treat 2011 Program.

And switching over to Gear Expo, our commercial services team is conducting a short but idea-packed session called "Challenges in Nitriding of Gears". The session is scheduled on Thursday, November 3 at 10:30am. It will cover challenges frequently encountered with nitriding gears of various sizes and suggests possible ways of minimizing quality risks.
For the complete program click Gear Expo Solution Center.
Nitrex Commercial Services welcomes you to their booth #1310.

AERO-ENGINE COMPANY ORDERS SECOND NITRIDING SYSTEM

Nitrex Metal received a follow-on order from Xi'An Aero-Engine Group, a manufacturer of turbojet and turbofan engines and gas turbines. The Nitreg®-S type nitriding system will be used for processing stainless steel aero parts as well as Nitralloy and alloy steel components. The furnace, with a work zone measuring 32 x 59 inches (800 x 1500 mm), has a maximum load weight of 3300 lbs (1500 kg) and is equipped with an Ammonia Dissociator for delivery of process gases only as needed and a Neutralizing System to meet emission standards.
The system, which will be delivered in the second half of 2011, complements a previous system delivered to Xi'An nine years ago and will support the company’s production expansion efforts. With this order, Nitrex will have shipped 20 systems to China since its first sale in 2002.

OTHER NEWS : The European subsidiary of U.S. tube-bending tools manufacturer OMNI-X placed an order for the model NXK-409 furnace with a 660-pound capacity. It will be used to nitride tube-bending tooling such as bend dies, clamp dies and pressure dies. The preassembled, plug-and-play system includes integrated automation and Nitreg® control technology, which will ultimately result in improved tool durability and bending quality. The system was recently installed at the Brno, Czech Republic facility.

SURFACE IMPROVEMENT TECHNOLOGIES
Part 7 - ONC®
by Chris Morawski

Chrome and military black are the perennial favorite choices for surface finishes on products such as cars, audio systems, rifles, golf clubs, or other toys. While Nitreg® is the heat treater's equivalent of the former, the latter is sometimes produced by ONC®.
The term originated as an abbreviation of "oxy-nitro-carburizing". The treatment is applied most frequently to low-alloyed structural steels, exposed to particularly intense corrosion hazards, while requiring improved wear resistance. All ferrous alloys can be treated, including stainless steels. The ONC® part of the treatment, which follows Nitreg®, Nitreg®-C or Nitreg®-S processing, provides a substantial enhancement of the corrosion resistance of nitrided and nitrocarburized surfaces. Such surface hardening treatments are an attractive choice. They are applicable to virtually all ferrous alloys, with new breakthroughs in technology permitting a great deal of control over the properties. The challenge remains, however, in that the improvement of corrosion resistance due solely to the nitriding process is in most cases insufficient. Corrosion properties of nitrided materials are so tightly related to nitriding itself that some of its aspects must be emphasized up front, particularly with regard to high alloy and stainless steels. A Nitreg® process produces a white layer composed of two phases. The γ' contains approximately 6% nitrogen (by weight) while ε is anything over 8%. These numbers mean two things for the purpose of this description: (a) depending on the nitrogen concentration in the surface layer we will form a particular structure of the compound layer, and (b) if the upper limit of the e range is locally exceeded, the "surplus" nitrogen will form "bubbles" of gas that will cause porosity near the surface, a phenomenon significantly affecting the corrosion properties of such a surface. The bubbles are of course of microscopic size, significantly less than 0.1 µm (0.000004") in diameter.

However, that porosity can be seen! The figure below shows a typical microstructure of a relatively thick white layer produced on 4140 steel. The presence of a significant amount of porosity is clearly visible. Even though the white layer itself will not corrode easily, it is intuitively obvious that microcracks and excessive porosity in the layer will allow a corrosive attack on the substrate, over time. Presence of oil or corrosion inhibitors on the surface and in the pores will enhance the resistance of the layer.

ONC® is a process that can be successfully applied to all ferrous materials, including cast iron and stainless steels, therefore it would be pointless to list the materials individually. However, this does not mean that all materials develop identical properties when treated in the same process. Tests show that optimum corrosion resistance is achieved with white layers in the 20 µm-30 µm (0.0008"-0.0012"), and porosity around 30% to 40% range. However, it must be noted that a thick white layer on 440 stainless steel may be too brittle and a compromise should be made with a layer of perhaps as little as 10 µm (0.0004"). On the other hand a layer as deep as 40 µm (0.0016") may be perfectly appropriate for certain materials, e.g., low carbon steel.

Techniques of nitriding stainless steels without diminishing their inherent corrosion resistance are an exciting new development; the Nano-S™ process was described in our previous newsletter. However, they are not similar to ONC® in any way, hence they are not the subject of this article.
ONC® is a process that takes advantage of surface porosity observed in most compound layers after nitriding. It is a simple concept but the process is not easy in that the amount of porosity generated during the nitriding stage must be properly controlled. Too much, and it will actually enhance the progress of corrosion by creating easy channels for electrolytes to travel down to the substrate material. On the other hand, if the porous zone is too thin, one will not get the maximum out of it when the oxidizing medium is introduced. When brought in contact with the nitrided surface the oxidizing medium easily penetrates the pores, partly transforming the nitride phases into an oxide phase.

Meanwhile some of our customers are also interested in the esthetics of the parts. The adjacent figures show the typical appearance. Nitrex is capable of performing the ONC process on parts weighing up to 55,000 lb and up to 16.5 feet in length.

References:

1. Technical Report 110620 - ONC® Testing - Nitrex-Nevada internal report filed June 20, 2011.
2. Nitreg® & ONC® - Where Corrosion Resistance and Wear Requirements Finally Meet - 2003.

FOLLOW USE ON

WORTH THE READ

Principles of Gas Nitriding (Part 1) by Dr. Dan Herring

Principles of Gas Nitriding (Part 2) by Dr. Dan Herring

Principles of Gas Nitriding (Part 3) by Dr. Dan Herring

HANDY TOOLS

Nitriding Potential Calculator

Hardness Reference Chart

ASM Heat Treating Event
Cincinnati, OH, USA
October 31-November 2

Gear Expo 2011
Cincinnati, OH, USA
November 1-3

NITREX METAL INC. | 3474 Poirier Boulevard, Montreal, QC H4R 2J5 | Telephone +1.514.335.7191 | nitrex@nitrex.com




MUST-ATTEND PRESENTATIONS Jack Kalucki, Heat Treating Projects Manager, will offer new information on the "Effect of Process Time on Low-temperature Nitrided Austenitic Stainless Steels Layer Structure" in his speech on Tuesday, November 1 at 4:30pm. Click here for a summary. For the complete conference program click ASM Heat Treat 2011 Program. And switching over to Gear Expo, our commercial services team is conducting a short but idea-packed session called "Challenges in Nitriding of Gears". The session is scheduled on Thursday, November 3 at 10:30am. It will cover challenges frequently encountered with nitriding gears of various sizes and suggests possible ways of minimizing quality risks. For the complete program click Gear Expo Solution Center. Nitrex Commercial Services welcomes you to their booth #1310. AERO-ENGINE COMPANY ORDERS SECOND NITRIDING SYSTEM Nitrex Metal received a follow-on order from Xi'An Aero-Engine Group, a manufacturer of turbojet and turbofan engines and gas turbines. The Nitreg®-S type nitriding system will be used for processing stainless steel aero parts as well as Nitralloy and alloy steel components. The furnace, with a work zone measuring 32 x 59 inches (800 x 1500 mm), has a maximum load weight of 3300 lbs (1500 kg) and is equipped with an Ammonia Dissociator for delivery of process gases only as needed and a Neutralizing System to meet emission standards. The system, which will be delivered in the second half of 2011, complements a previous system delivered to Xi'An nine years ago and will support the company’s production expansion efforts. With this order, Nitrex will have shipped 20 systems to China since its first sale in 2002. OTHER NEWS : The European subsidiary of U.S. tube-bending tools manufacturer OMNI-X placed an order for the model NXK-409 furnace with a 660-pound capacity. It will be used to nitride tube-bending tooling such as bend dies, clamp dies and pressure dies. The preassembled, plug-and-play system includes integrated automation and Nitreg® control technology, which will ultimately result in improved tool durability and bending quality. The system was recently installed at the Brno, Czech Republic facility. SURFACE IMPROVEMENT TECHNOLOGIES Part 7 - ONC® by Chris Morawski Chrome and military black are the perennial favorite choices for surface finishes on products such as cars, audio systems, rifles, golf clubs, or other toys. While Nitreg® is the heat treater's equivalent of the former, the latter is sometimes produced by ONC®. The term originated as an abbreviation of "oxy-nitro-carburizing". The treatment is applied most frequently to low-alloyed structural steels, exposed to particularly intense corrosion hazards, while requiring improved wear resistance. All ferrous alloys can be treated, including stainless steels. The ONC® part of the treatment, which follows Nitreg®, Nitreg®-C or Nitreg®-S processing, provides a substantial enhancement of the corrosion resistance of nitrided and nitrocarburized surfaces. Such surface hardening treatments are an attractive choice. They are applicable to virtually all ferrous alloys, with new breakthroughs in technology permitting a great deal of control over the properties. The challenge remains, however, in that the improvement of corrosion resistance due solely to the nitriding process is in most cases insufficient. Corrosion properties of nitrided materials are so tightly related to nitriding itself that some of its aspects must be emphasized up front, particularly with regard to high alloy and stainless steels. A Nitreg® process produces a white layer composed of two phases. The γ' contains approximately 6% nitrogen (by weight) while ε is anything over 8%. These numbers mean two things for the purpose of this description: (a) depending on the nitrogen concentration in the surface layer we will form a particular structure of the compound layer, and (b) if the upper limit of the e range is locally exceeded, the "surplus" nitrogen will form "bubbles" of gas that will cause porosity near the surface, a phenomenon significantly affecting the corrosion properties of such a surface. The bubbles are of course of microscopic size, significantly less than 0.1 µm (0.000004") in diameter. However, that porosity can be seen! The figure below shows a typical microstructure of a relatively thick white layer produced on 4140 steel. The presence of a significant amount of porosity is clearly visible. Even though the white layer itself will not corrode easily, it is intuitively obvious that microcracks and excessive porosity in the layer will allow a corrosive attack on the substrate, over time. Presence of oil or corrosion inhibitors on the surface and in the pores will enhance the resistance of the layer. ONC® is a process that can be successfully applied to all ferrous materials, including cast iron and stainless steels, therefore it would be pointless to list the materials individually. However, this does not mean that all materials develop identical properties when treated in the same process. Tests show that optimum corrosion resistance is achieved with white layers in the 20 µm-30 µm (0.0008"-0.0012"), and porosity around 30% to 40% range. However, it must be noted that a thick white layer on 440 stainless steel may be too brittle and a compromise should be made with a layer of perhaps as little as 10 µm (0.0004"). On the other hand a layer as deep as 40 µm (0.0016") may be perfectly appropriate for certain materials, e.g., low carbon steel. Techniques of nitriding stainless steels without diminishing their inherent corrosion resistance are an exciting new development; the Nano-S™ process was described in our previous newsletter. However, they are not similar to ONC® in any way, hence they are not the subject of this article. ONC® is a process that takes advantage of surface porosity observed in most compound layers after nitriding. It is a simple concept but the process is not easy in that the amount of porosity generated during the nitriding stage must be properly controlled. Too much, and it will actually enhance the progress of corrosion by creating easy channels for electrolytes to travel down to the substrate material. On the other hand, if the porous zone is too thin, one will not get the maximum out of it when the oxidizing medium is introduced. When brought in contact with the nitrided surface the oxidizing medium easily penetrates the pores, partly transforming the nitride phases into an oxide phase. Meanwhile some of our customers are also interested in the esthetics of the parts. The adjacent figures show the typical appearance. Nitrex is capable of performing the ONC process on parts weighing up to 55,000 lb and up to 16.5 feet in length. References: 1. Technical Report 110620 - ONC® Testing - Nitrex-Nevada internal report filed June 20, 2011. 2. Nitreg® & ONC® - Where Corrosion Resistance and Wear Requirements Finally Meet - 2003.		FOLLOW USE ON WORTH THE READ Principles of Gas Nitriding (Part 1) by Dr. Dan Herring Principles of Gas Nitriding (Part 2) by Dr. Dan Herring Principles of Gas Nitriding (Part 3) by Dr. Dan Herring HANDY TOOLS Nitriding Potential Calculator Hardness Reference Chart ASM Heat Treating Event Cincinnati, OH, USA October 31-November 2 Gear Expo 2011 Cincinnati, OH, USA November 1-3

NITREX METAL INC. \| 3474 Poirier Boulevard, Montreal, QC H4R 2J5 \| Telephone +1.514.335.7191 \| nitrex@nitrex.com Copyright© 2011 NITREX METAL INC. All rights reserved.