Process Specification for the Heat Treatment of Steel Alloys

+-----------------------------------------------------------------------+
| **Engineering Directorate**                                           |
|                                                                       |
| **Structural Engineering Division**                                   |
|                                                                       |
| **October 2006**                                                      |
|                                                                       |
| ![](media/image1.png){width="1.301388888888889in"                     |
| height="1.082638888888889in"}                                         |
|                                                                       |
| National Aeronautics and                                              |
|                                                                       |
| Space Administration                                                  |
|                                                                       |
| **Lyndon B. Johnson Space Center**                                    |
|                                                                       |
| Houston, Texas                                                        |
+-----------------------------------------------------------------------+

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

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

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

+----------------+---------------------------------+-----+-----------+
| **Approved     | ***Signature on file***         |     | 10/04/06  |
| by:**          |                                 |     |           |
+----------------+---------------------------------+-----+-----------+
|                | 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, Updated to SAE 7/21/99
              AMS-H-6875A                                   

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

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

  E           Changed sec. 6.0 on aging requirements for    6/06/02
              A286. Updated document due to reorganization  
              from 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 steel and stainless steel alloys.

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

This specification shall be applicable whenever the heat treatment of
steel or stainless steel 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 a
manufacturing production controller or from an 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:

For Class A Carbon and Low Alloy Steels:

For Class B Martensitic Corrosion Resistant Steel (CRES):

For Class C Austenitic CRES:

For Class D Precipitation Hardening CRES and Maraging Steel

**3.1 PROCESS SEQUENCE**

Unless otherwise specified on the engineering drawing, all parts shall
be heat treated before final machining to remove scale and
decarburization, as well as to avoid changes in dimensions. Scale and
decarburization, typically produced at temperatures above 1200°F, are
normally detrimental to the finished part and cannot be removed by
mechanical or chemical finishing techniques. After heat treating, a
minimum of 0.020" will be removed from all scaled or decarburized rough
machined surfaces 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:

Class A (Carbon and Low Alloy Steels) and B (Martensitic Corrosion
Resistant Steel) items often require stress relief after welding
operations. Postweld stress relief should be performed as soon as
possible after the welding operation---typically within 2 hours. Except
for rare exceptions, hardness testing and tensile testing are not
required for postweld stress relief operations. A qualified welding
procedure for the specific application needs to be reviewed before
making the stress relief note. For example:

**3.2 NOTATIONS RELATED TO HARDNESS TESTS**

Verification of heat treat of steel and stainless steel parts is
typically achieved by measuring hardness. Unless otherwise specified on
the engineering drawing, the hardness measurement will be made on the
actual or rough machined part. For most parts, the hardness impression
will be machined away during subsequent machining. When the hardness
measurements must be made on the finished part, a test location shall be
chosen by the designer and the 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 shall be 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 cross section as the production parts or
shall be parted from the production part after quenching.

When a hardness test is to be performed on a sample part, special
instructions shall be included on the engineering drawing, such as:

or

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 necessary, the number of coupons, grain
direction (when applicable), and any special acceptance criteria shall
be noted on the engineering drawing. For example:

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

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

ASTM A370 American Society for Testing and Materials Specification,
*Standard Test Methods and Definitions for Mechanical Testing of Steel
Products*

SAE AMS-H-6875A Society of Automotive Engineers, Inc., Aerospace
Material Specification, *Heat Treatment of Steel Raw 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

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

None identified.

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

All heat treatment of steel and stainless steel alloys shall comply with
SAE AMS-H-6875A and the drawing requirements. All parts shall be heat
treated before final machining, unless otherwise specified on the
engineering drawing. Except for A286, specific times and temperatures
for heat treatment are given in Tables 1A, 1B, 1C, and 1D of SAE
AMS-H-6875A. For A286, the aging cycle required in the material
specification shall be used to age harden the metal.

Sample parts (for hardness and/or tensile tests) 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
and sample bars are needed, each batch must have its own set of labeled
sample bars.

Tools and equipment shall be as-specified in SAE AMS-H-6875A. Safety
precautions and warning notes shall be as-specified in SAE AMS-H-6875A.

# Stress relief after welding shall be done as-specified in section 3.2.4.4 in SAE AMS-H-6875A. Please note that the post stress relief cycles on austenitic stainless steel and pH stainless steel notes may not be necessary for specific cases. 

**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 (or equivalent documentation).

Verification of heat treat of steel and stainless steel is typically
achieved by measuring hardness. Sample parts shall be used for hardness
verification only if specified by the engineering drawing. When hardness
tests are to be performed on the stock material or rough machined actual
parts, the hardness impressions shall be placed in a location that will
be machined off during machining. Hardness impressions on finished parts
shall be made only at the location specified on the engineering drawing.

When tensile tests are required by the drawing, specimens shall be
machined according to ASTM A370, using full-sized coupons whenever
possible. Testing shall be performed according to ASTM A370 by either
the JSC Structures Test Laboratory or an accredited mechanical Testing
laboratory. Tensile test results for Class A steels shall meet the
drawing requirements. The yield strength and elongation shall meet the
appropriate values listed in MMPDS, with maximum strengths 20 ksi above
the minimums. Tensile tests are not required to verify annealed
condition of Class C steels. Tensile test results for Class B and D
steels shall meet the minimum values listed in MMPDS, with maximum
strengths 20 ksi above the minimums.

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.

Decarburization Loss of carbon from the surface of a carbon-containing
alloy from reaction with chemical substances (usually oxygen) during
heat treating.

Heat Tint A thin, tightly adhering oxide skin that forms when steels 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.

Material Lot A single batch (bar, forging, extrusion, etc.) of material
that is produced by the vendor and is documented by a certificate of
compliance.

Scale A heavy, penetrating oxide coating that forms when steels 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.