**Process Specification for the Heat Treatment of Nickel Alloys**

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| **Engineering Directorate**                                           |
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| **Structural Engineering Division**                                   |
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| **October 2006**                                                      |
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| ![](media/image1.png){width="1.3944444444444444in"                    |
| height="1.1458333333333333in"}                                        |
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| National Aeronautics and                                              |
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| Space Administration                                                  |
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| **Lyndon B. Johnson Space Center**                                    |
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| Houston, Texas                                                        |
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**Process Specification for the Heat Treatment of Nickel Alloys**

+-----------------+-------------------------------+--------+-----------+
| **Prepared      | # Signature on file           |        | ***10     |
| by:**           |                               |        | /04/06*** |
+-----------------+-------------------------------+--------+-----------+
|                 | ##### Daila Gonzalez,         |        | Date      |
|                 |                               |        |           |
|                 | Materials & Processes Branch  |        |           |
|                 | /ES4                          |        |           |
+-----------------+-------------------------------+--------+-----------+
|                 |                               |        |           |
+-----------------+-------------------------------+--------+-----------+

+-----------------+-------------------------------+--------+-----------+
| **Prepared      | # Signature on file           |        | ***10     |
| by:**           |                               |        | /04/06*** |
+-----------------+-------------------------------+--------+-----------+
|                 | ##### John D. Figert,         |        | Date      |
|                 |                               |        |           |
|                 | Materials & Processes Branch  |        |           |
|                 | /ES4                          |        |           |
+-----------------+-------------------------------+--------+-----------+
|                 |                               |        |           |
+-----------------+-------------------------------+--------+-----------+

+-----------------+-------------------------------+--------+-----------+
| **Approved      | # Signature on file           |        | ***10     |
| by:**           |                               |        | /04/06*** |
+-----------------+-------------------------------+--------+-----------+
|                 | Brad S. Files,                |        | Date      |
|                 |                               |        |           |
|                 | Chief, Materials & Processes  |        |           |
|                 | Branch /ES4                   |        |           |
+-----------------+-------------------------------+--------+-----------+

  ----------- --------------------------------------------- ---------------
  REVISIONS                                                 

  VERSION     CHANGES                                       DATE

  Baseline    Original version                              5/96

  A           Expanded sec. 3.0, furnace chart info.,       5/27/98
              tensile requirements                          

  B           Changed Training Requirements                 7/21/99

  C           Modified Training Requirements, Labeling      2/24/00
              Tensile Bars & Stock                          

  D           Included Information on Postweld Heat         8/24/00
              Treatment, Reduced Labeling Tensile Bars &    
              Stock Requirements                            

  E           Updated document due to reorganization from   1/20/04
              EM2 to ES4                                    

  F           Reviewed for accuracy and updated author.     10/04/06
  ----------- --------------------------------------------- ---------------

**1.0 [SCOPE]{.underline}**

This process specification establishes the engineering requirements for
the heat treatment of nickel and cobalt alloys.

**2.0 [APPLICABILITY]{.underline}**

This specification shall be applicable whenever the heat treatment of
nickel or cobalt alloys is invoked per section 3.0, "Usage".

**3.0 [USAGE]{.underline}**

The material to be heat treated shall be included in the parts list in
the heat treat condition in which the material is to be procured.
Availability of product forms and tempers may be obtained from the
manufacturing production controller or from the ES4 materials engineer.

This process specification shall be called out on the engineering
drawing by using an appropriate drawing note. The specific process or
combination of heat treat processes shall be noted, along with the final
temper. For example:

or

or

A description of the names for various heat treatments (e.g. S1750SDP)
and the heat treat temperatures may be found in AMS 2774.

**3.1 PROCESS SEQUENCE**

Unless otherwise specified on the engineering drawing, all parts shall
be heat treated before final machining to eliminate effects of
oxidation, alloy depletion, de-carburization, dimensional changes, and
to avoid placement of hardness

impressions on the final surface. Scale that is produced when nickel and
cobalt alloys are heat treated above 1550°F cannot normally be removed
by mechanical or chemical finishing techniques. After heat treatment, a
minimum of 0.010" will be removed during the final machining.

In some cases, it may be necessary to heat treat after final machining.
If heat treating will result in a heat tinted surface that will not be
removed by final machining, an appropriate finishing procedure to remove
the heat tint shall be called out on the engineering drawing. For
example:

Most postweld heat treat operations, when required, on nickel-based and
cobalt-based alloys are generally anneals or anneals plus aging. A
qualified welding procedure for the specific application needs to be
reviewed before making the postweld heat treat note. For example:

**3.2 NOTATIONS RELATED TO HARDNESS TESTS**

Normally, verification of heat treatment of nickel and cobalt alloys is
achieved by measuring hardness. When the hardness impressions are to be
made on the actual part, a site is chosen by the designer and ES4
materials engineer that will not be detrimental to the function of the
finished part. Special instructions must be included on the engineering
drawing, such as:

Sample parts may be used to verify heat treat instead of the actual
part. Sample parts shall be sketched and/or described on the engineering
drawing. They may have a simplified contour and may use nominal
dimensioning. Sample parts shall be made from the same raw material lot
and processed before heat treatment in an identical manner as the
production parts. When the heat treating process includes quenching, the
samples must be of similar thickness and mass as the production parts or
shall be parted from production parts after quenching. When a hardness
test is to be performed on a sample part, the following notation should
be included on the engineering drawing:

**3.3 NOTATIONS RELATED TO TENSILE TESTS**

For more critical parts, tensile testing may be warranted. Sample pieces
for tensile coupons shall be machined from the same raw material lot and
processed before heat treatment in an identical manner as the production
parts. When tensile testing is required, the number of coupons, grain
direction, and any special acceptance criteria shall be noted on the
drawing. For example:

**4.0 [REFERENCES]{.underline}**

All documents listed are assumed to be the current revision unless a
specific revision is listed.

AMS 2774 Society of Automotive Engineers Aerospace Materials
Specification, *Heat Treatment, Wrought Nickel Alloy and Cobalt Alloy
Parts*

ASTM E8 American Society for Testing and Materials Specification,
*Standard Test Methods of Tension Testing of Metallic Materials*

ASTM E18 American Society for Testing and Materials Specification,
*Rockwell Hardness and Rockwell Superficial Hardness of Metallic
Materials*

MMPDS Handbook, *Metallic Materials Properties Development and
Standardization*

TI-2000-01 Training Instruction: Training for Heat Treat Personnel

SAE ARP 1962 Training and Approval of Heat-Treating Personnel

The following references were used in developing this process
specification:

SOP-007.1 Preparation and Revision of Process Specifications

JSC 8500C Engineering Drawing System Requirements

**5.0 [MATERIALS REQUIREMENTS]{.underline}**

None identified.

**6.0 [PROCESS REQUIREMENTS]{.underline}**

All heat treatment of nickel and cobalt alloys shall comply with the
drawing requirements and AMS 2774, with the following modifications:

+--------------+-----------+----------------------+-------------------+
| Alloy        | Spec      | Heat Treat Variation | Acceptance Change |
+--------------+-----------+----------------------+-------------------+
| MP35N        | AMS 5844  | Use 1100°F           | Precipitation     |
|              |           | precipitation set    | heat treat shall  |
|              |           | temperature.         | be verified by    |
|              |           |                      | tensile testing.  |
+--------------+-----------+----------------------+-------------------+
| MP159        | AMS 5842  | Use 1225°F           | No change.        |
|              |           | precipitation set    |                   |
|              |           | temperature.         |                   |
+--------------+-----------+----------------------+-------------------+
| Alloy 718    | AMS 5662  | Use 100°F per hour   | Use 36 HRC        |
| Bar          |           | cool instead of      | instead of 331    |
|              | AMS 5596  | furnace cool during  | HB.               |
| S1750SDP     |           | precipitation heat   |                   |
|              | AMS 5889  | treatment.           |                   |
+--------------+-----------+----------------------+-------------------+
| Alloy 718    | AMS 5664  | No change.           | Use 38 HRC        |
| Bar          |           |                      | instead of 341    |
|              | AMS 5597  | No change.           | HB.               |
| S1950DP      |           |                      |                   |
+--------------+-----------+----------------------+-------------------+

Sample parts (e.g. for hardness and tensile measurements) shall be
processed before heat treatment in an identical manner as the production
parts. Sample parts must be heat treated simultaneously with the
production parts. If production parts have to be processed in more than
one batch, each batch must have its own set of sample bars.

Tools and equipment shall be as-specified in AMS 2774, with the
following exception. If a vacuum furnace is to be used to solution heat
treat nickel or cobalt alloys that require air cooling or rapid air
cooling, it shall be equipped with metal elements, metal shields and an
argon quench system capable of rapidly cooling parts from the annealing
temperature to below 1200°F.

Safety precautions and warning notes shall be as-specified in AMS 2774.

**7.0 [PROCESS QUALIFICATION]{.underline}**

Not required. However, work instructions shall be generated for
implementing this process specification. The work instructions shall
contain sufficient detail to ensure that the manufacturing process
produces consistent, repeatable products that comply with this
specification.

**8.0 [PROCESS VERIFICATION]{.underline}**

Verification of furnace temperatures shall be accomplished by recording
the furnace temperatures on strip charts or other suitable hard copy
recordings. Furnace charts for heat treatment shall be maintained with
the hardware\'s work order router package.

Verification of nickel and cobalt alloy heat treatment is normally
achieved by measuring hardness. Hardness impressions shall be made per
ASTM E18 on the actual part at the location specified on the engineering
drawing or on the samples heat treated together with the part.

When tensile tests are required on the drawing, specimens shall be
machined according to ASTM E8, using full-sized coupons whenever
possible. Testing shall be performed according to ASTM E8 by either the
JSC Structures Test Laboratory or an accredited mechanical testing
laboratory. Tensile test results for nickel and cobalt alloys shall meet
the minimum values listed in MMPDS. If no tensile values are available
in MMPDS for a specific alloy, acceptance values must be listed on the
engineering drawing.

Labeling of stock material prior to the heat treatment shall include the
material lot (certification #). Labeling of the stock material shall
either be done by stenciling or by using stainless tags and stainless
wire. Stainless tags shall be stenciled.

Tensile bars or tensile coupons shall be individually labeled
immediately after manufacture. Label information shall always include
material lot (certification #). If the tensile bars or tensile coupons
are made prior to heat treating, the tensile bars or tensile coupons
shall be labeled using austenitic stainless tags and austenitic
stainless wire. If the tensile bars or tensile coupons are made after
heat treating, cotton string and paper tags may be used instead of
stainless tags and wire. Paper tags shall include material type, the
material lot (certification #), and the work order router number.

**9.0 [TRAINING AND CERTIFICATION OF PERSONNEL]{.underline}**

All heat treatment of steel and stainless steel alloys used on flight
hardware shall be performed by qualified operators who have been
certified according to the requirements in TI-2000-01, Training for Heat
Treat Personnel. For vendors, a training program consistent with the
recommended practices in SAE ARP 1962 shall be required.

**10.0 [DEFINITIONS]{.underline}**

Age Harden A heat treatment process which consists of applying a
relatively low temperature for sufficient time to strengthen the alloy
to the desired temper.

Air Cooling The rate at which the parts, separated from one another
sufficiently to allow free air movement, would cool to room temperature
after being removed from the furnace and placed in shop air without
rapid motion of the air forced over the parts by a fan or blower.

Alloy Depletion Change in composition of an alloy near the surface when
one element, typically chromium, evaporates at high temperatures,
usually in a vacuum furnace.

Decarburization The loss of carbon from the surface of an alloy as a
result of heating in a medium (usually oxygen) that reacts with the
carbon.

Heat Tint A thin, tightly adhering oxide skin that forms when alloys are
heat treated at low temperatures, or for a short time, in air or in a
mildly oxidizing atmosphere. The color ranges from straw to light blue.

Precipitation An intermediate temperature heat treat process that causes
Heat Treat hardening and strengthening of the alloy by the precipitation

of intermetallic compounds and, in some cases, carbides

from supersaturated solid solutions.

Rapid Air Cooling The rate at which the parts, separated from one
another sufficiently to allow free air movement, would cool to room
temperature after being removed from the furnace and placed in shop air
with rapid motion of the air forced over the parts by a fan or blower.

Scale A heavy, penetrating oxide layer that forms when alloys are heat
treated at higher temperatures, or at longer times, in air or other
oxidizing atmospheres.

Stress Relief A thermal cycle to relieve residual stresses.