QML_revision_052720.pdf

NIST Charpy V-notch Standard Reference Materials

Machining Qualification Program Policy

Background:

The purpose of this qualification procedure is to identify and qualify machine shops and producers capable of machining and/or supplying Charpy V-Notch Specimens according to the NIST specification.

Qualified Vendors will be placed on the Qualified Manufacturers List (QML).

NIST has manufacturers produce reference-grade Charpy Impact Specimens in batches. The process has 3 major steps:

1) Rough machining, where the bar is cut to length and machined into “blanks”. The blanks are not notched and have over-sized dimensions suitable for heat treating. This step eliminates surface defects that can induce quench cracks during processing and the oversized dimensions of the blanks allow for re-processing when necessary.

2) Heat treating the blanks so that the final machined specimens meet NIST acceptance criteria.

3) Final machining of heat-treated specimens to final dimensions.

It is also acceptable for a qualified manufacturer to just fulfill step 3) above, i.e., supply already heat-treated and finally-machined reference specimens.

There are 2 levels of qualification: (1) machining only, and (2) full qualification. To qualify for machining only, proficiency in machining needs to be demonstrated. For full qualification, a Vendor must demonstrate the ability to rough machine blanks of NIST steel, then heat treat the blanks, and finally machine the specimens so that all dimensional and performance criteria are met for the energy level under consideration. Alternatively, a qualified Vendor shall demonstrate the ability to supply NIST with reference Charpy specimens that are acceptable from the point of view of both machining quality and performance criteria.

Application:

Test specimen lots for the Charpy V-notch Machining Qualification Program will be accepted throughout the calendar year. The Vendor must be on the QML list prior to issuance of the procurement action.

Successful completion of the program places the applicant on the Qualified Manufacturers List (QML), the list of Vendors authorized to compete for contracts to machine Charpy specimens SRMs.

Qualification does not guarantee a contract. Those Vendors that fail qualification will be promptly notified and furnished specific reasons why qualification was not attained.

The Charpy Coordinator will maintain the Machining QML. The Vendor shall not be charged a fee for submitting test specimens to be evaluated, nor shall the Vendor be reimbursed for any test specimens submitted.

Inclusion on this list does not constitute endorsement of any product, source, or manufacturer by the National Institute of Standards and Technology.

Period of Qualification:

Qualification is valid for five years starting with approval of the initial qualification test. Approval of a pilot lot of material renews this approval for another five years. Thus, production of acceptable lots of material within a five-year span will result in remaining on the QML indefinitely.

A Vendor wishing to remain on the QML after its five-year period has expired must requalify. If a Vendor fails to perform adequately during the five-year period or if for some other reason the Vendor is deemed unable to perform adequately, the Vendor shall be promptly notified, removed from the QML, furnished specific reasons for removal, and asked if they wish to requalify after taking corrective actions.

Qualification Requirements

Documentation Required:

The Vendor shall supply a company description, including all personnel involved in the specimen production process. This information will be used to evaluate the technical competence of the Vendor, and assist NIST in answering any technical questions that may arise. All information agreed upon as proprietary shall be held in the strictest confidence. NIST reserves the right to visit the Vendor's facilities to audit the procedures and equipment.

Specimen Dimensions and Marking:

All specimens submitted shall conform to the dimensional specifications listed in Appendix A. The specimen identification marking scheme is outlined in Appendix B.

Stage 1: Machining The Vendor shall first supply a Stage 1 test lot consisting of 50 specimens from any steel supplied by the Vendor to the dimensions in Appendix A and marked/identified in accordance with Appendix B.

The aim of Stage 1 is to confirm the Vendor's ability to machine samples that meet NIST requirements and maintain tolerances in a production mode.

Stage 2: Full Qualification Following successful completion of Stage 1, the Vendor has the option to fully qualify for the production of NIST Charpy SRMs. To complete stage 2, the Vendor shall heat treat and machine a Stage 2 test lot. The lot consists of 300 specimens machined and heat treated from steel purchased from NIST or supplied by the Vendor (based on NIST approval on the type and properties of the steel). In the event that a first test lot does not qualify, the Vendor may submit additional test lots. The Vendor is limited to submitting a reasonable number of test lots per year, to be determined by NIST, on the basis of the Vendor's capability to show progress in delivering an acceptable lot. In no case is the number of Stage 2 test lots submitted to exceed 4 per year for any energy level. Test lots for each energy level will be qualified individually (low, high, super-high, etc.) to the NIST acceptance criteria, outlined in Appendix C. Failure to comply with any part of the acceptance criteria can result in rejection of the test lot.

Mail all test lots and documentation to:

National Institute of Standards and Technology Charpy Coordinator, Raymond Santoyo Division 647 325 Broadway Boulder, Colorado 80305-3328

Questions may be directed to:

Enrico Lucon, Charpy Project Leader Phone: (303) 497-4750 E-mail: enrico.lucon@nist.gov

Raymond Santoyo, Charpy Coordinator Phone: (303) 497-3351 Fax: (303) 497-5939 E-mail: charpy@nist.gov mailto:enrico.lucon@nist.gov mailto:charpy@nist.gov

Appendix A

The Vendor shall manufacture Charpy V-notch specimens to the following dimensions and specifications:

Specimen Dimensions and Specifications:

1. The material shall be out and ground to the finished length of 55 mm 0.00 𝑚𝑚𝑚𝑚 −0.30 𝑚𝑚𝑚𝑚 (2.165 in. 0.00 𝑖𝑖𝑖𝑖.

−0.012 𝑖𝑖𝑖𝑖.).

2. One end of each specimen shall be stamped with the lot number and the serial number, the other end shall be stamped with the letters: NIST, See Appendix B: Marking Test Lots, for the details.

3. The Vendor shall determine the exact heat treatment needed to produce the required energy level.

4. The specimen cross section dimensions shall be 10 mm ± 0.03mm (0.394 ± 0.001 in.) ground square;

any two adjacent sides shall be square to 90° ± 9’.

5. The surface roughness shall be 1.6 µm (47 µin.) or less on the notched surface and opposite surface, and 3.2 µm (100 µin.) or less on the other two longitudinal surfaces, plus both ends.

6. Notch and Side-Groove Specifications:

a. Centering of the notch shall be at 27.5 mm ± 0.20 mm (1.083 in. ± 0.008 in.)

b. The ligament size below the notch shall be 8.0 mm ± 0.025 mm (0.315 in. ± 0.001 in.).

c. The notch shall be perpendicular to the longitudinal axis of the specimen to 90° ± 9’.

d. The notch opening angle shall be 45° ± 1°, with a notch root radius of 0.25 mm ± 0.025 mm

(0.010 in. ± 0.001 in.).

e. If side-grooves are required (e.g. for super-high-energy specimens), specimens shall be side-grooved for a total reduction of 10 % of the original thickness, corresponding to 0.5 mm ±

0.05 mm (0.02 in. ± 0.002 in.) per side (unless otherwise specified). Side-grooves shall have an included angle ≤ 90° and a root radius of 0.25 mm ± 0.05 mm (0.01 in. ± 0.002 in.).

f. Specimen notches and side-grooves shall be ground on a surface grinder or cut with an electrical discharge machining (EDM) process (machining with a fly cutter, multitooth cutter or broach is not acceptable). Overheating or cold working the material adjacent to the notch or side-groove shall be avoided. For grinding, the next to last cut shall be more than 0.25 mm (0.010 in.) and less than 0.38 mm (0.015 in.). Appropriate machining oil shall be used during all grinding or machining operations. Notches and side-grooves shall be deburred.

Permissible variations shall be as follows:

Notch length to edge: 90o ± 9’

Adjacent sides shall be at: 90o ± 9’

Cross-section dimensions: 10 mm ± 0.03 mm (0.394 in. ± 0.001 in.)

Length of specimen (L): 55 mm + 0.00 _ 0.30 mm (2.165

in. + 0.00 in. –0.012 in.)

Centering of notch (L/2): 27.5 mm ± 0.20 mm (1.083 in. ± 0.008 in.)

Opening angle of notch: 45o ± 1o

Radius of notch 0.25 mm ± 0.025 mm

(0.010 in. ± 0.001 in.)

Ligament size under the notch 8.0 mm ± 0.025 mm (0.315 in. ± 0.001 in.)

Side-groove depth 0.5 mm ± 0.05 mm (0.02 in. ± 0.002 in.)

Side-groove angle ≤ 90°

Side-groove root radius 0.25 mm ± 0.05 mm (0.01 in. ± 0.002 in.)

Finish requirements: The surface roughness shall be 1.6 µm (47 µin.) or less on the notched surface and opposite surface, and 3.2 µm (100 µin.) or less on the two longitudinal surfaces, plus both ends.

Appendix B Marking Test Lots

1. The Vendor name and lot number shall be placed on or adjacent to all exterior mailing or shipping labels of test lot shipments.

2. Individual specimens shall be stamped or etched on one end with one of the following lot numbers:

Low Energy: LL NNN

High Energy: HH NNN

Super-High Energy: SH NNN where ‘NNN’ is the lot number. These numbers will be assigned by the Charpy Coordinator, Raymond Santoyo.

3. The serial number shall be stamped or etched below the lot number. Serial numbers shall begin with the number 1 and end with the last number produced within the lot.

4. The opposite end shall be stamped or etched with the letters: NIST.

Appendix C

1. For SRM 2092 Low Energy Specimens and SRM 2096 High Energy Specimens, the microstructure shall be 100% tempered martensite. No ferritic, austenitic or bainitic structures shall be visible when polished sections are examined at 1000 X.

2. For all specimens, dimensions (length, width, notch configuration, etc.) shall be within the stated tolerances.

3. The hardness of each specimen shall be within ± 1 HRC of the average of the pilot lot. This applies to low, high, and super-high energy level pilot lots.

4. The average hardness of low energy specimens shall not be less than HRC 44.

5. The acceptable ranges for the average energies of pilot lots are as follows:

a. Low energy specimens shall produce an average energy between 14.0 J to 20.0 J (10.0 ft-lbf to

15.0 ft-lbf) at -40 °C ± 1 °C.

b. High energy specimens shall produce an average energy between 88.0 J to 136.0 J (65.0 ft-lbf to

100.0 ft-lbf) at -40 °C ± 1 °C.

c. Super-High energy specimens shall produce an average energy between 175.0 J to 275.0 J (129.0 ft-lbf to 202.8 ft-lbf) at 21 °C ± 1 °C.

Any lot whose average energy lies outside the ranges above shall be subject to final approval by the

Charpy Program coordinator and the Charpy Project Leader.

6. Specimens at all energy levels should meet the requirements below:

a. If the variance of the reference machines is acceptable (k is less than 1.25), then the sample size shall not exceed 5. The sample size (n) is calculated as follows:

𝑖𝑖 = �

3𝑆𝑆𝑝𝑝

𝐸𝐸

where E is equal to 1.4 J or 5 % of the average energy for the 3 machines (whichever is the greater), and Sp is the pooled standard deviation of the 3 reference machines. The standard deviation (s), pooled standard deviation (Sp), and the kn variance values are calculated as follows:

𝑠𝑠 = �(𝑥𝑥1 − �̅�𝑥)2 + (𝑥𝑥2 − �̅�𝑥)2+⋯+ (𝑥𝑥𝑛𝑛 − �̅�𝑥)2 𝑖𝑖 − 1

𝑆𝑆𝑝𝑝 = �𝑠𝑠1

2 + 𝑠𝑠22 + 𝑠𝑠32 𝑘𝑘1 = 𝑠𝑠1

𝑆𝑆𝑝𝑝

,𝑘𝑘2 = 𝑠𝑠2

𝑆𝑆𝑝𝑝

,𝑘𝑘3 = 𝑠𝑠3

𝑆𝑆𝑝𝑝

where s1, s2, and s3 are the standard deviations of the machines.

b. The number of outliers shall not exceed 10 % of the number of specimens tested in the pilot lot (8 is the maximum for a pilot lot of 75). The outlier analysis is performed using box-and whiskers plots to provide a graphical summary of the data and identify outliers. Outliers are defined as values that are lower than the first quartile or higher than the third quartile by more than 1.5 times the absolute difference between the first and third quartiles. An alternative outlier analysis can be performed by means of Grubbs’ test (extreme studentized deviate) with α = 0.05.

An outlier will not be removed from analysis unless it shows physical evidence of jamming, material flaws, or other reason for atypical behavior.