H13 Steel Acceptance and Heat Treat Criteria — 2003 • i



H13 Steel Acceptance and Heat Treat Criteria — 2005 • i

i • H13 Steel Acceptance and Heat Treat Criteria — 2005

Special Premium and Superior Quality Die H13 Steel and Heat Treatment Acceptance Criteria for Pressure Die Casting Dies

NADCA #207-200X3 (Premium and Superior)

Contents Page

Abstract 1

Statement of Purpose 1

I. Material Quality Requirements 2

II. Material Quality Certification of Conformance 5

III. Heat Treatment Quality Requirements 6

IV. Heat Treatment Quality Testing Requirements 8

V. Heat Treatment Quality Certification of Conformance 10

Acknowledgements 12

Appendix 1: Guide to Sample Preparation Techniques 13

Appendix 2: Practical Guide to Steel and Heat 16

Treatment Quality

Appendix 3: Welding Die Casting Die Materials 28

by:

NADCA DIE MATERIALS COMMITTEE

ASTM Standards referred to in this document may be obtained from:

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North American Die Casting Association

Wheeling Rosemont, Illinois 60018-4733

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Neither the North American Die Casting Association, nor the authors of this work:

• Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document;

• Assumes any liability with respect to the use of, or for damages resulting from the use of, any information, method, process or equipment described in this document.

ABSTRACT

An agreement has been reached with NADCA member firms that are major material suppliers and/or heat treaters of H13 die steel to the die casting industry. Acceptance criteria, restrictive specifications as noted, and a certification plan have been developed for both the Material Quality and the Heat Treatment Quality of Special Premium and Superior Quality Grade H13 die steels. By specifying die H13 steels produced to these specifications, improved levels of cleanliness, a reduction in micro and macro banding, and impact toughness capabilities are certified. These This steels will respond more uniformly and predictably to heat treatment, thus reducing the risk of excessive distortion and cracking during heat treatment and giving longer and more consistent die life.

When dealing with premium grade H13 neither the steel making process nor the forging practices are stipulated by this specification, provided that all quality requirements in this specification are met.

When dealing with superior grade H13 With the exception of Grade A (“Premium H13”) die steel, the steel making process shall include secondary refining, either ESR (electro-slag remelt) or VAR (vacuum arc remelt). However, small round stock less than 3” diameter may not be available by these remelt process. Regardless of the steel making process or the forging practices, material covered by this specification must meet all quality requirements in this specification.

The heat treatment quality requirements in this specification pertain to the vacuum hardening and high-pressure gas quenching process. While NADCA recognizes the viability of other heat treatment methods, the scope of the procedures within this specification are exclusively vacuum austenitizing and pressurized gas quenching.

STATEMENT OF PURPOSE

These acceptance criteria and specifications are not intended for all die casting applications. They apply where high volume production or critical performance is required. Die casters and tool builders should insist that certification of the Material Quality accompany each piece of Special Quality Premium or Superior H13 die steel purchased for use in die casting dies and that certification of the Heat Treatment Quality accompany each furnace load of Special Quality die H13 steel hardened in accordance with this protocol.

For certain applications requiring a higher level of Material Quality and Heat Treatment Quality, Superior Grade H13 is a variety of Special Quality die steels are listed in this specification as Grades B - H that are commercially available and should meet the appropriate specification requirements of NADCA #207-200 3 Superior.

For applications requiring a lesser level of Material Quality and/or Heat Treatment Quality, Grade A (“Premium H13”) die steel Premium Grade H13 is is available and should meet the appropriate specification requirements of NADCA # 207-200X 3 Premium.

It should be noted that die performance is a complex combination of many factors including die size & design, casting alloy, operational procedures, steel composition, austenitizing temperature, impact toughness and hardness. Other factors such as temper resistance, hot strength, and fatigue resistance also effect die performance and should be considered when specifying steel grade, heat treatment parameters. Final hardness should be selected based upon steel grade, size, and die design. Consult your steel supplier and/or heat treater for guidance.

NOTE: Every effort has been made to assure information contained in these procedures is correct. However, NADCA does not accept responsibility for damage, injury or costs incurred by using these procedures.

Check the suppliers’ instructions for specific directions on products used. Be sure to comply with all applicable safety codes and regulations.

I. Material Quality Requirements

A. Chemical composition (% by weight) of Critical Alloying Elements & Impurities

Special Quality Both Premium and Superior grades of die H13 steel must conform to the Chemical Requirements of Table 1 ASTM A681 (latest revision) Section 6 with the following modifications, or emphasis.

| | |PREMIUM GRADE A | |SUPERIOR ALL OTHER GRADES |

|ELEMENTS | |MIN. |MAX. | |MIN. |MAX. |

|Carbon | |0.37 * |0.42 * | |0.37 |0.42 |

|Manganese | |0.20 |0.50 | |0.20 |0.50 |

|Phosphorus | |— |0.025 * | |— |0.015 ‡ |

|Sulfur | |— |0.005 * | |— |0.003 ‡ |

|Silicon | |0.80 |1.20 | |0.80 |1.20 |

|Chromium | |5.00 * |5.50 * | |5.00 |5.50 |

|Vanadium | |0.80 |1.20 | |0.80 |1.20 |

|Molybdenum | |1.20 * |1.75 * | |1.20 |1.75 |

|* Modifications from ASTM A681 for premium quality |‡ Modifications from NADCA Premium Quality for Superior Quality |

B. Hardness

1. Both Premium and Superior Qualities: Annealed hardness of Special Quality steel, as received, shall not exceed 235 HBW.

C. Microcleanliness

The permissible limits of microcleanliness (severity levels of non metallic inclusion content) shall be determined by ASTM E45, Method A (latest revision). Plate I-r should be used to obtain rating increments of 0.5. The maximum allowable limits are as follows.

| | |GRADE A PREMIUM | |ALL OTHER GRADES SUPERIOR |

|INCLUSION TYPE | |THIN |HEAVY | |THIN |HEAVY |

|A (sulfide) | |1.0 |0.5 | |0.5 ‡ |0.5 |

|B (aluminide) | |1.5 |1.0 | |1.5 |1.0 |

|C (silicate) | |1.0 |1.0 | |0.5 ‡ |0.5 ‡ |

|D (globular oxides) | |2.0 |1.0 | |1.5 ‡ |1.0 |

|‡ Modifications from NADCA Premium Quality for Superior Quality |

D. Ultrasonic quality (ASTMA-681 S1.1)

Appropriate ultrasonic inspection techniques shall be performed to assure soundness. All blocks shall be free from internal defects such as stringers, oxides, porosity, bursts, heavy segregation, etc., as indicated by ultrasonic testing. Ultrasonic examination of the original steel stock shall be conducted in accordance with ASTM recommended practices A388 and E114 (latest revision). Acceptance criteria are as agreed upon between supplier and vendor.

E. Impact Capability Testing

Impact capability testing pertains to all mill product forms with a thickness greater or equal to 2-1/2 inches. Specimen blanks shall be removed from the short transverse orientation corresponding to the center location of the parent block of steel (see Fig. 1 and 2). A minimum of one set of 5 impact specimens shall be tested per lot of material produced. A lot shall consist of all the product of a single ingot, which is forged or rolled via a common procedure to one size and annealed in a single furnace charge. Multiple starting ingots, variations in forging or rolling size or procedure, or variations in annealing furnace charge are defined as a multiple lots and shall require additional sets of tests.

Fig. 1. Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the short transverse orientation corresponding to the center location of a parent block of steel that has a rectangular/square cross-section.

NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent block or slab, See Charpy V-notch samples per ASTM A370, latest revision.

Fig. 2 Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the transverse (radial) orientation corresponding to the center location of a parent bar of steel that has a circular cross-section.

NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent bar. See Charpy V-notch samples per ASTM A370, latest revision.

Individual specimens shall be machined oversize to be nominally 1/2” x 1/2” x 2-1/2”each. Specimens are to be hardened and tempered before machining to final dimensions. Specimens shall be heat treated, machined, and tested as follows (see Table 2 for designated autenitizing / tempering temperatures and final hardness):

1. Austenitize at 1885°F (1030°C) for 30 minutes;

2. Oil quench. Oil temperature 120°F (50°C) maximum;

3. Minimum double temper at a temperature of at least 1100°F (590°C) for 2 hours minimum each temper to achieve a final hardness of 44/46 HRC;

4. Air cool to room temperature between each temper;

5. Following the preceding laboratory hardening process, the samples shall be machined to final size and finish ground. See Charpy full size test impact specimen per ASTM A370, Fig. 11a:

• adjacent sides shall be at 90 degrees ±10 minutes

• cross section dimensions shall be ±0.100 mm (±0.004 in.)

• length of specimen shall be 55 ±1 mm (2.165 ± 0.040 in.)

• surface finish shall be 63 micro inch (1.6 micro meter) max. on the 55 x 10 mm faces.

6. Five impact specimens shall be tested at room temperature on test machines that meet the calibration requirements of ASTM E23 or ISO 148/R442 (latest revision). The values of the highest and lowest specimens shall be discarded and the average of the remaining three results shall be computed. Testing shall yield the following specified values.

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7. Acceptance Criteria:

a) Premium Quality is 8 ft. lbs. (11 J) average with 6 ft. lbs. (8 J) single minimum value.

b) Superior Quality is 10 ft. lbs. average (14 J) with 8 ft. lbs. (11 J) single minimum value.

see Table 2 for capability impact toughness acceptance criteria

NOTE: These impact toughness values apply only to impact specimens that are individually heat treated prior to final machining in accordance with the method prescribed above. Charpy impact specimens are to be notched after final machining. Ground notches are preferred and shall be used for referee purposes. EDM notches are not allowed.

F. Grain Size:

Grain size shall be developed using the Direct Quench method per ASTM E112 by austenitizing at 1885°F (1030°C) for 30 minutes, quench at a moderate or rapid rate and temper at 1100°F minimum. Hardening should be in a protective media or by using an appropriately oversize sample in a non-protective media. Grain size to be measured by using the ASTM comparative method and shall be predominately ASTM No. 7 or finer.

An alternative method to rate the grain size may be used. The Shepherd Fracture Grain Size shall be predominantly No. 7 or finer when made on a hardened (air cooled after heating for 30 minutes at 1885° F (1030° C), in a protective media or using an appropriately oversize sample in a non protective media) and untempered specimen taken from a representative sample.

G. Annealed Microstructure:

The annealed microstructure of the as-received steel shall consist essentially of a ferritic matrix with a homogeneous distribution of spheriodized carbides when examined at 500X, after being polished and etched with 5% Nital. Acceptable microstructures for annealed die steels H13 steel are shown in the NADCA Annealed Microstructure Reference Chart.

H: Banding Segregation:

The annealed microstructure shall be free of excessive banding by conformance with the NADCA Banding Segregation Reference Chart for levels of microbanding or microchemical segregation. For sizes 4” and below, banding segregation shall not be cause for rejection unless excessive primary carbides are present.

II. Material Quality - Certification of Conformance:

|Material that has been designated as NADCA Special Premium Quality or |A. |NADCA Grade (A – H) |

|Superior Quality H13 die steel in accordance with this specification shall be | | |

|accompanied by a Certificate of Conformance from the steel supplier that |B. |Supplier Heat Designation |

|includes the following data and information: | | |

| |C. |Annealed Brinell Hardness |

| | | |

| |D. | |

| | |Chemical Analysis |

| |E. |Microcleanliness levels |

| |F. |Confirmation that Ultrasonic Inspection has been |

| | |performed |

| |G. |Grain Size Number |

| |H. |Annealed Microstructure Rating Number |

| |I. |Microbanding Designation Levels |

| |J. |Impact capability test results: shall include three|

| | |individual results of specimens and average result,|

| | |heat treatment and final hardness. |

| | | |

| |NOTE |The laboratory capability austenitizing temperature|

| | |must be stated |

| | | |

III. Heat Treatment Quality Requirements

Vacuum Heat Treatment Process Requirements

The most critical parameters in the heat treatment of Special Premium and Superior Quality H13 die steels are the austenitizing treatment and the quench rate from the austenitizing temperature. The quench rate must be controlled to provide optimum metallurgical properties while minimizing distortion and risk of cracking. A more detailed discussion of the heat treatment process is included in Appendix 2: Practical Guide to Steel and Heat Treatment Quality.

NOTE for SUPERIOR QUALITY: Except for Premium H13 Grade A, a test coupon must be attached to the workpiece prior to hardening. See Section IV-L for details.

NOTE: ALL Special Quality Die Steels can be certified as either “Class 1” or “Class 2” Heat Treatment Quality. Certification as Class 1 Heat Treatment Quality requires that a test coupon must be attached to the workpiece prior to hardening. See Section IV-L for details.

A. Equipment

Premium

• Vacuum furnace with a minimum 2 bar backfill capability and a programmable furnace controller linked to multiple load thermocouples.

• Sufficient cooling capability to cool die surface from 1885° F (1030 °C) at a minimum rate of 50°F/min. (28°C/min.). See Section III F.

• Furnace must be capable of isothermal hold during quench based on input from surface and core thermocouples where interrupted quench is required.

Superior

• Vacuum furnace with high-pressure gas quenching capability and a programmable furnace controller linked to multiple load thermocouples.

• Sufficient backfill pressure and cooling capability to cool die surface from the designated austenitizing temperature 1885°F (1030°C) at a minimum rate of 50°F/min. (28°C/min.). See Section III F.

• Furnace must be capable of isothermal hold during quench based on input from surface and core thermocouples where interrupted quench is required.

‡ Modifications from NADCA Premium Quality for Superior Quality

B. Furnace Loading

• Pieces in the load shall be placed and distributed to allow for uniform heating and quenching.

• The geometry of the pieces must be considered to insure uniform heat treatment and crack prevention.

• The furnace must not be overloaded, so that the minimum quench rate can be achieved.

C. Thermocouple Placement

• A dedicated thermocouple hole for placement of the surface thermocouple (Ts) is recommended. Hole should typically be 1/8” to 1/4” (3.175mm to 6.35mm) diameter, depending on thermocouple wire used and should be 0.625” ± 0.125” (15.87mm ± 3.175mm) deep.

• The surface thermocouple (Ts) hole should be located in the center of the largest area of the die in the backside and should be at least 1/4T x 1/4W or mid-radius from the nearest corner.

• The core thermocouple (Tc) should be placed as close to the center of mass as possible using existing coolant holes. In cases where core thermocouple placement is not possible, the furnace load shall be controlled from a load block that represents the maximum thickness of the die with a thermocouple at the center of mass.

• All thermocouple holes shall be packed with a fiber refractory material to prevent direct contact with quenchant.

• Thermocouple wires must be secured to prevent movement during quenching.

• If multiple blocks are hardened in the same load, thermocouples should be placed in the block with the largest cross section.

D. Preheating Practice

• Load work into cold furnace and heat at a rate not to exceed 400°F/hour (220°C/hour) as measured by Tc.

• Heat to 1000°F to 1250°F (540°C to 675°C) furnace temperature and hold until Ts-Tc ................
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