The goal of this article is to provide a structure for communicating your heat-treating requirements to your commercial heat treater. It is written from the viewpoint of the company receiving the raw material stock or components for heat treatment, with the target audience being a manufacturer – big or small – who sends out steel products to be heat treated.



Commercial heat treaters spend much of their time trying to clarify what their customer’s expectations are on each order they process. Clearly defining the nature of the materials and the heat-treating requirements is the first step in making sure your heat treater will be able to meet or exceed your expectations. If possible, these requirements should be discussed with your heat treater before you start manufacturing the parts, not after they are final machined. It is also important to provide written documentation to the heat treater, including a duplicate copy sent with the materials/components, that represents the final agreed-upon treatments and specifications.

Fig. 1. Typical tool-and-die parts being prepared for heat treatment

Material Grade

The first piece of information you need to supply is the material grade, typically the AISI or SAE number. Examples of these designations include 4140, 1144, 1095, 52100, H11, M4. Other common material specification systems, such as ASTM, DIN and JIS, are also often used in today’s global marketplace. Cross-references to AISI grades should be supplied if possible.

To avoid confusion, listing trade names in place of these designations should be avoided. Examples of material trade names are Bearcat™, Airkool™ and Shock-Die™. If these are provided, the specific manufacturer’s data sheets should be included in the paperwork package.

The next most important document you can provide is the material certification sheet. This is provided to you by your material supplier and includes details such as the exact chemistry of the material being heat treated (including trace elements), grain size, cleanliness of the steel, prior processing and hardenability. These are invaluable aids for the heat treater to understand how to correctly process your material.

Condition Supplied

Most steels are supplied by the mill in the annealed condition. However, the material can also be supplied in other conditions such as normalized, normalized and tempered, or hardened. In addition, the material may have come to you from the mill as a sheet, bar, rod, forging or casting. It is critical that you notify the heat treater of the condition of the steel you are sending to them. If not, it is possible that the parts may not respond properly to the heat-treating process. For example, if you send parts made from 17-4PH to a heat treater to be processed to condition H-900 and the material was purchased in condition H-1150, it will not respond properly to the standard H-900 process. Your material supplier should notify you of the “as-supplied” condition in their material certification.

Fig. 2. Heat-treating purchase order checklist

Instructions and Specifications

There are three types of instructions (purchase orders) heat treaters receive from their customers:
  • Commercial practices
  • Customer specifications
  • Industry specifications
Examples of each of these are as follows:
  • Commercial: 440C material, heat treat to 58-60 HRC
  • Customer: 440C material, process per BPS-4602 (Bell Process Specification)
  • Industry: 440C material, process per AMS 2759/5 (Aerospace Material Specification)
For a commercial purchase order, the heat treater is able to choose their own process (process temperatures, equipment type, atmosphere, soak durations, etc.). This often gives heat treaters the ability to combine orders and reduce processing time and cost. It is fair to argue that this type of purchase order gives the heat treater too much freedom.

Purchase orders that call out specific customer or industry specifications are usually much more stringent. They may also bring other specifications and requirements into play as well. It is important for customers to realize that calling out a customer or industry specification on your purchase order may increase your heat-treating cost and lead time significantly.

For example, on a commercial order, 440C may only require two processes (hardening and tempering) in order to meet a given hardness requirement. If the same 440C order is required to be processed per a customer or industry specification, it may require that the parts be subjected to multiple tempers and deep-freeze operations. It may also bring additional requirements into play (backfill gas dew point, furnace atmosphere, furnace pyrometry, instrument calibration, intergranular attack, decarburization, surface contamination, special documentation, additional destructive testing, larger hardness-testing sampling sizes, training, cooling rates, process-temperature setpoints, soak durations, etc.).

Prints

It is extremely useful for your heat treater to have a copy of the current part drawing so that he can verify dimensions; note critical dimensions; understand the geometry of the part with respect to radii, sharp corners, ruling (thickest) section, the location of thin sections; surface-finish requirements and the like. Many customers also provide copies of their routers so that the heat treater can see how his processing fits into the overall scheme of the part manufacturing process. It is not uncommon for the heat treater to raise questions based on his experience and what he sees on the print. Remember, your heat treater has seen and dealt with literally thousands of shapes and sizes, and his opinions are invaluable.

Fig. 3. Process control of steel coils in a vacuum furnace using thermocouples inserted into the load in order to monitor actual part temperature

Approvals

Customers often require that their work be sent to heat treaters who have certain approvals in place. These approvals may include:

ISO9001:2000, AS9100, TS16949, CQI-9
In order to gain these types of approvals, the heat treater must have an effective quality system in place, and it must be verified by an outside service. ISO9001:2000, AS9100, TS16949 quality approvals are usually general in nature (quality management system, management responsibility, product realization, etc.) and are not heat-treating process specific.

Nadcap
This aerospace approval is the highest industry-wide accreditation a heat treater can achieve. Not only does it cover the quality systems above, it also includes audits on specific heat-treating processes. A portion of the weeklong audit also includes the witnessing of actual heat-treat runs. The process-related portion of the audit confirms compliance with aerospace and aerospace-prime specifications. PRI is the accrediting body for this program. More information on Nadcap can be found at www.pri-network.org.

Prime Approval
Even if a heat treater is ISO9001 and AS9100 approved as well as Nadcap accredited, they still may not be able to process work for certain aerospace primes. These include Boeing, Pratt & Whitney, Airbus, etc. These companies also require that your heat treater pass their site audits. If the parts you are sending out are related to the companies above, they can only be processed at heat-treating facilities approved by the aerospace prime.

Testing Requirements

Your purchase order or request for quotation should clearly state your testing requirements. If you are asking the heat treater to process the order to a certain AMS specification, these requirements may already be defined. Otherwise, you need to communicate what your requirements are (or what exceptions you will allow). A few examples of typical testing requirements include surface hardness, microhardness, tensile strength, surface carbon content, IGO/IGA and microstructure. Be aware that test coupons may be required to facilitate these types of tests. Also, keep in mind the consequences of the tests. For example, if an order is to be 100% Rockwell hardness tested, all of your parts are going to be returned with hardness dents or indentations on them.

Dimensional Requirements

To some degree, all materials will change size and shape during heat treatment. You need to plan your manufacturing process to accommodate these changes. Stating “Keep Flat” or “Keep Straight” on your purchase order is not realistic. However, there are materials and processes that can be chosen to minimize these changes. Putting a flatness or straightness callout on your purchase order is good practice, but only if it is realistic and achievable. Involving your heat treater early in the project can help in this regard. The heat treater will be able to assist in specifying the most suitable material and process sequence that will get results that meet your expectations.

Cosmetic Requirements

If your parts require special handling, please inform your heat treater of that fact. Keep in mind that individual handling and racking of parts can add significant cost. In most cases, heat treaters will handle your parts with care. However, if you require that a certain surface remain free of hardness indentations, for example, please note that instruction on your purchase order. Other cosmetic requirements may include glass beading after heat treatment, vacuum processing to keep parts clean and bright, and keeping sharp corners of parts free from nicks and dings.

Documentation Requirements

There are several levels of documentation that can be supplied by the heat treater.
  • Shipping ticket only
  • Product certifications (hardness, microstructure, mechanical properties, etc.)
  • Process certifications
  • Furnace chart-recorder data
The shipping ticket is signed by the customer and used as the proof of delivery document. Product certifications typically show the number of parts tested and their range of values. It should also state the specification the testing complied with. The process certification usually shows the process that was run (soak times, temperature setpoints, quenchants used, etc.). It will also state what specifications the process was in compliance with. For commercial work, only the first two are usually supplied.

For aerospace work, the first three are typically supplied. The furnace chart-recorder data is usually kept on file by the heat treater for a predetermined number of years. It can be made available to the customer on request. If the heat treater is running a proprietary process, however, he may be unwilling to hand this intellectual property over to the customer.

Summing Up

In conclusion, a true partnership needs to exist between the customer and heat treater in order to optimize the performance of the end-product. Heat treaters have their customer’s best interest at heart, but they are not mind readers and have limitations that are best overcome by mutual information flow and good planning combined with knowledge and experience.IH

For more information:Contact Patrick McKenna, Nevada Heat Treating, Inc.; e-mail: patm@nevadaheattreating.com; web: www.nevadaheattreating.com; or Dan Herring, The HERRING GROUP, Inc.; e-mail: dherring@heat-treat-doctor.com; web: www.heat-treat-doctor.com; or Craig Darragh, AgFox LLC; e-mail: agfox@att.net

Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: normalized, ISO, Nadcap, dew point, pyrometry, IGO/IGA