Stress Relieving

During the manufacturing process of the tool, considerable machining stresses are generated on the surface. These stresses are known as induced residual stress raisers. Thus, the more the tooling is machined, the more induced mechanical stresses are generated.

The induced residual stresses will only emerge with the application of heat. Thus, at final heat treatment, if the induced residual stresses have not been dealt with, then the residual stress will emerge at the final heat treatment. The next illustration shows a fishbone sketch of generated stress raisers during the manufacturing of the tooling.

In addition to the induced stresses, there may be the effect of potential cracking as a result of the induced stress in the steel. In some instances, and where surface compressive stress generated the compressive stress could have the potential to reduce the cracking.

In tooling manufacture, it is not uncommon to introduce residual stress relieving treatments during the machining and grinding operations during the manufacture of the particular tool.

It is also not uncommon to experience crack occurrences during the final grinding operations that are being applied to hardened and tempered tool steels with martensitic microstructures, or even to tooling that may have been work hardened during its operational life.

Those types of induced mechanical stress as the possibility of being the root cause of cracking during service. The Stress Relieve Temperature selection will be below the Indicted Red Horizontal Line 

• Plain Carbon/Low Alloy Steels
• 550°C to 650°C

Do not underestimate the value if prior stress relieving before continuing to the final heat treatment procedure. It will reduce the potential for serious distortion.

Hardening of Tool Steels

This section will discuss the principles of heat treatment which will be followed by the principles of heat treatment of specific tool steel grades.The principal considerations that should be considered when preparing to harden and temper the particular tool steel grade and component for the final heat treatment is based upon;

Steel chemistry.

• Selection of the appropriate processing temperature in relation to the metallurgical requirement of the tool steel.
• The time of residence at the selected temperature.
• The events that occur when the steel transitions from room temperature to the selected process temperature, which determines the structure that the steel will orient itself into, and its phases, are known as transformation.
• The cooling rate must also be considered from the specifically selected process temperature.
• The final temperature (known as the tempering temperature) to enable the steel to be ‘fit for service’.

 Basic Principles of Hardening the Steel

 A very simple description of steel is that it is simply a mixture of iron, plus a very small amount of carbon. That is as simple a description as can be made of steel.

In order to make the steel become hard, it is necessary to add small amounts of carbon. Carbon is the magic ingredient (so to speak) that will make the steel hard. However, the maximum hardness that the steel will accomplish will be approximately 62 HRC.

That will of course depend on the amount of carbon present in the steel. But it is necessary to make the steels do other things other than just become hard, and it is at this point that we will start to discuss the principles of making the steel become hard.

Basic Principles of Hardening the Steel

In this section you will gain an understanding of the Iron Carbon Equilibrium Diagram, the phases that the steel will transition through (depending on the amount of carbon present in the steel), its mechanical properties and the causes of these transformations.

At Room Temperature the Iron exists in a 9-atom structure which is one on each corner and one located in the centre of the cube. This is known as a Body Cantered Cubic Lattice and will exist in this form up to approximately 720°C.  as shown below.

This Illustration below displays the phase changes that occur in the Iron.

As you can observe the are three distinctive phase transformation occurrences. It should also be noted (as a very important observation) that each of the phases have a different volumetric size change. This simply means, that no matter what or how you heat up the iron, there WILL BE a size change. You have NO CONTROL over that phenomena.

Origin of Names of Phases

Ferrite is an area below the lower critical line of the Iron Constitution diagram and has a magnetic property.  It comprises 9 atoms and is a BCC. (Body Cantered Cubic Lattice structure)

We now have added carbon (in controlled amounts at the steel making process), so now we have made steel!!!  Depending how much carbon we add to the iron (in its molten condition), we can now determine what happens to the phase structure at various temperatures, with various carbon contents in relation the phase which will occur.

The following illustration shows the Iron Carbon Equilibrium Diagram. (Please be aware, that the diagram does not consider the addition of various alloys, only Iron and Carbon. For simplicity, one can make an equilibrium diagram with ordinary waters plus salt and noting the freezing point and boing point with different additions of salt into the water.)

Hypo-eutectoid steels: Steels having less than 0.8% carbon are called hypo-eutectoid steels (hypo means “less than”).  Consider the cooling of a typical hypo-eutectoid alloy along line y-y‘.

At high temperatures the material is entirely austenite. Upon cooling it enters a region where the stable phases are ferrite and austenite. The low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon. Hyper-eutectoid steels (hyper means “greater than”) are those that contain more than the eutectoid amount of Carbon.

The Eutectoid line is that vertical line that separates hypo from hyper. It is generally found at a point of 0.77% on the horizontal carbon axis line. When such a steel cools, as along line z-z’ , the process is similar to the hypo-eutectoid steel, except that the primary or pro-eutectoid phase is now cementite instead of ferrite.

Various phases that appear on the Iron-Carbon equilibrium phase diagram are as under:

• Austenite
• Ferrite
• Pearlite/Cementite
• Martensite

Ferrite

Ferrite is known as α (Alpha) solid solution. It is an interstitial solid solution of a small amount of carbon dissolved in α (Alpha) (BCC) iron. It is a stable form of iron below 912°C. The maximum solubility is 0.025 % C at 723°C and it dissolves only 0.008 % C at room temperature. It is the softest structure that appears on the diagram.

Ferrite Properties:

Tensile strength = 40,000 psi;

Elongation = 40 % in 50mm;

Hardness  > Rockwell C 0 or Rockwell B 90

Cementite

Cementite or iron carbide, is a very hard, brittle intermetallic compound of iron & carbon, as Fe₃C, contains 6.67 % C. It is the hardest structure that appears on the diagram, exact melting point unknown. Its crystal structure is orthorhombic. It is/has;

• A low tensile strength (approx. 5,000 psi).
• A high compressive strength.

This week we start off with a news item from Mexico about captive/Commercial heat treater Kern Liebers in Queretaro adding some more vacuum nitriding capacity.  “Rohde Installs New Vacuum Nitriding Furnace at Kern Liebers Mexico Plant; In these pictures we see a brand new Rohde furnace that has been installed at the Kern Liebers plant located in Queretaro, Mexico. This is the 3rd Rohde furnace at this plant. It is a vacuum nitriding pit furnace with working dimensions of 160/350. Over the years Rohde has delivered several furnaces to Kern Liebers‘ plants worldwide. This new furnace will start production in January 2020 at the Queretaro plant.  In the one picture below we see from left to right: Luis Andrade (Kern Liebers, Mexico), Tim Lotz (Rohde), Emmanuel Cabrera (Kern Lievbers, Mexico) and Stefan Braun (Rohde).”

Mike Arnold, Heat Treat Engineer at ALD Thermal Treatment in Port Huron, MI., USA has parted ways with the company to try new challenges. ALD in Port Huron is one of the largest single location heat treats in North America and specializes in vacuum carburizing of automotive transmission components. While we don’t have a photo of Mike we do have these picture of the facility which were taken earlier this year by Jordan Montgomery.

Down in the US Southeast Braddock Metallurgical are the “big boys” on the block when it comes to heat treating-we have this people news from the company; “Braddock Metallurgical Aerospace Services congratulates Steve Hutchinson, General Manager – Boynton Beach, FL facility on his retirement. We thank Steve for all the years of dedicated service and commitment to Braddock Metallurgical. His contributions, knowledge, and passion have been integral to the success and growth of the company. He will be greatly missed but his retirement is well deserved. We hope Steve is blessed in his retirement with much joy, rest, and many successful fishing trips.”

For reasons completely unknown to us there appears to be a significant number of auctions featuring used heat treat equipment coming up in the near future. The details of two of these auctions can be found in the “Hilco” banner ad. The one auction features an enormous Abar Ipsen vacuum furnace which is located at a closed Aerojet Rocketdyne facility in California. The second covers all of the equipment at the Bluewater Thermal facility in Canada which recently shut down. These by the way are only two of several auctions to be held in the next few months featuring heat treat equipment.

We have been told that commercial heat treater Valley Metal Treating Inc., in Pomona, California, USA will be closing their doors within the next two weeks. We know little about the company beyond the fact that it is a small to medium sized operation which offers a wide variety of processes. We always find it upsetting to see any company having to close their doors but particularly so in this case as the company is over 70 years old. While we don’t know the details behind the closing we did run across this posting from a customer which appears to put the blame on the stringent California environmental regulations. 

“Established in 1936, Valley heat treat is forced to close its doors because of California air quality control management. The upgrades required were not feasible and so yet another company closes here in SoCal. Regulations are getting out of hand and affecting 1000’s of local business. Plating companies have been hard hit here as well. After using Valley for decades, we are now forced to look elsewhere and that sucks.”

“Solar Manufacturing has shipped a vacuum furnace for processing additive manufactured parts to a large science and technology laboratory. The lab requires the furnace to further their research and development work. Built with Solar Manufacturing’s SolarVac® Polaris control system and a graphite-insulated hot zone, the furnace is designed to accommodate loads up to 36” wide x 36” high x 48” deep, with a maximum weight of 5,000 lbs. Operating at a vacuum level of 10-5 Torr, with maximum temperatures up to 2400 °F, and quench pressure of two bar, the furnace will be commissioned by year’s end.

“Solar Manufacturing was awarded the order because we offered the best solution for this customer’s vacuum furnace needs,” comments Dan Insogna, Solar Manufacturing’s Southeast Sales Manager. “Our knowledge and experience of the Additive Manufacturing market set us apart from the competition. We are pleased to provide a solution to the growing research and development efforts within the Additive Manufacturing Industry, and we know our Solar Manufacturing vacuum furnace is the right tool for job.”

Solar Manufacturing designs and manufactures a wide variety of vacuum heat treating, sintering, and brazing furnaces and offers replacement hot zones, spare parts, and professional service. To learn more about Solar Manufacturing contact Pete Reh, VP of Sales, at 267-384-5040 x1509, or via email [email protected] or visit us at www.solarmfg.com.”

South-Tek is becoming a fairly well known name in the business of on site nitrogen generating systems for the heat treating industry making this a rather interesting news item.

“South-Tek Systems LLC, a leading designer and manufacturer of nitrogen generators for a diversified worldwide marketplace, will move into an existing 66,000-sq.-ft. building on US Highway 421 in Wilmington as part of an enhanced growth strategy that includes additional hiring and new products. Established in Wilmington in 1997, the company was privately held until its November 2018 acquisition by Pfingsten Partners LLC, a Chicago-based private equity group. South-Tek began quietly considering a move to larger space three years ago, according to Alan Norman, the company’s vice president of operations. “At that time, there wasn’t much space in Wilmington larger than 40,000 square-feet,” Norman says. With the acquisition by Pfingsten last year, the company stepped up its site search with a call to WBD. “In receiving additional resources for growth, we knew we needed to move,” he says. With its vast contacts in Greater Wilmington’s industrial real estate market, WBD had heard of an available building that could fit the company’s growing needs. “Scott [Satterfield] connected us with the right agent and got the ball rolling,” says Norman. The company hopes to relocate to its new facility next month, a move that will take its operations from 28,000 square-feet to 66,000 square-feet. “We’re expecting tremendous growth in the next five years – people, revenue, products, everything,” says Scott Bodemann, president of South-Tek Systems. A major wave of reinvestment in marketing, R&D and product development is behind the wave of growth. Thus far in 2019, for example, South-Tek has added 17 jobs to its workforce, bringing its headcount to 64. “In considering both office and manufacturing space, we’ve reached the maximum capacity of South-Tek’s current facility,” says Bodemann. “We are excited to transition into the larger building as it will increase our efficiencies as well as allow us to better plan for the future needs of our customers.”

  Greg Pope and Paul Cairney of South Tek along with Aaron Ackerman an established rep in the Michigan area.

“Since 1989 the first generation of ALD’s single-chamber vacuum furnaces has been running reliably in the production facility of Oerlikon Metco Coatings GmbH in Salzgitter, Germany. In September of this year, a purchase order for another state-of-the-art furnace, a type ALD MonoTherm®. This furnace also meets Nadcap and AMS requirements. With the existing ALD system and the new unit, Oerlikon Metco Coatings will be able to double their heat treatment capacity for vacuum heat treatment of critical aerospace components.”