Standard Specifications

ASTM A194 Specification covers Carbon and Alloy Steel Nuts most popular grade 2H, 2HM, 3, 4, 6, 7, 7M, 8, 8M, 8T, 16, etc., to be used with ASTM A193 Bolts for High Pressure or High Temperature Service, or both.

This specification covers a variety of carbon, alloy, and martensitic stainless steel nuts in the size range 1 ⁄ 4 through 4 in. and metric M6 through M100 nominal. It also covers austenitic stainless steel nuts in the size range 1 ⁄ 4 in. and M6 nominal and above. These nuts are intended for high-pressure or high temperature service, or both. Grade substitutions without the purchaser’s permission are not allowed.
Bars from which the nuts are made shall be hot-wrought. The material may be further processed by centerless grinding or by cold drawing. Austenitic stainless steel may be solution annealed or annealed and strain-hardened. When annealed and strain hardened austenitic stainless steel is ordered in accordance with Supplementary Requirement S1, the purchaser should take special care to ensure that 8.2.2, Supplementary Requirement S1, and Appendix X1 are thoroughly understood.

Nut Grades

Manufacture (Process)

Stainless steels for all types of Grade 6 and 8 nuts shall be made by one of the following processes:
Electric-furnace (with separate degassing and refining optional),
Vacuum induction furnace, or
Either of the above followed by electroslag remelting, or consumable-arc remelting.
The steel producer shall exercise adequate control to eliminate excessive unhomogeneity, nonmetallics, pipe, porosity, and other defects.
Grades 1 and 2 nuts shall be hot or cold forged, or shall be machined from hot-forged, hot-rolled, or cold-drawn bars.
All Grade 1 and 2 nuts shall be stress-relieved at a temperature of at least 1000 °F [538 °C] after forming or machining from bar with the following exceptions:
Nuts made by hot forging.
Nuts machined from hot-forged or hot-rolled bar.
Nuts machined from hot-forged/hot-rolled and coldfinished (max 10 % reduction in area) bar.
Nuts machined from cold-drawn and annealed (min 1000 °F [538 °C]) bar.
Grade 1 and 2 nuts made by hot forging or by machining from hot-forged or hot-rolled bars need not be stress relieved.
Grades 2H, 2HM, 3, 6, 6F, 7, 7M, and 16 nuts shall be hot- or cold-forged or shall be machined from hot-forged, hot-rolled, or cold-drawn bars and shall be heat treated to meet the required mechanical properties. These grades shall be uniformly reheated to the proper austenitizing temperature (a group thus reheated being known as a quenching charge) and quenched under substantially uniform conditions for each quenching charge and tempered as shown below. Grades 2H, 2HM,3, 7, and 7M shall be liquid quenched. Grades 6 and 6F shall be quenched in liquid or inert gas. Grade 16 shall be heated to a temperature range from 1700 to 1750 °F (925 to 955 °C) and oil quenched.

Nuts machined from bar heat treated in accordance with this specification need not be reheat-treated. For Grade 2HM and 7M nuts, a final stress relief shall be done at or above the minimum tempering temperature after all forming, machining, and tapping operations. This final stress relief may be the tempering operation.
Grade 6 and 6F nuts shall be tempered for a minimum of 1h at the temperature.
Grades 8, 8C, 8CLN, 8M, 8T, 8F, 8P, 8N, 8MN,8R, 8S, 8LN, 8MLN, 8MLCuN, 8ML4CuN, and 9C nuts shall be hot or cold forged, or shall be machined from hot-forged, hotrolled or cold-drawn bars.
Grades 8A, 8CA, 8CLNA, 8MA, 8TA, 8FA, 8PA, 8NA, 8MNA, 8RA, 8SA, 8LNA, 8MLNA, 8MLCuNA, 8ML4CuNA, and 9CA nuts shall be hot- or cold-forged or shall be machined from hot-forged, hot-rolled, or cold-drawn bars and the nuts shall subsequently be carbide-solution treated by heating them for a sufficient time at a temperature to dissolve chromium carbides followed by cooling at a rate sufficient to prevent reprecipitation of the carbides.

Chemical Composition

Note:
^A The internal addition of Bi,Se,Te, and Pb is not permitted except for Grades 6F, 8F, and 8FA, in which Se is specified and required.
^B Total aluminum, soluble and insoluble.
^C Maximum unless minimum or range is indicated.
^D Where ep ses(...) appear in this table there is no requirement ad the element need not be determined or reported.
^E Because f the degree to which sulfur segregates,product analysis for sulfur over 0.060% max is not technologically appropriate.
^F As described in Specification A276/A276M.
^G Typical se l compositions used for this grade include 4140,4142,4145,4140H,4142H, and 4145H.
^H Niobium (Nb) and Columbium (Cb) are alternate names for element 41 in the Periodic Table of the Elements.
^I Product Analysis-Individual determinations sometimes vary from the specified limits as shown in the tables.The several determinations of any individual element in a heat may not vary both above and below the specified range.Product variation limits are over for maximums,over or under for ranges, and under for minimums,unless otherwise indicated.

Mechanical Properties

Hardness Test:
Requirements:
All nuts shall meet the hardness requirements specified in Table 2. Sample nuts of Grades 1, 2, 2H, 2HM, 3, 7, 7M, and 16 which have been given the treatment described in 8.1.5 shall meet the minimum hardness specified in Table 2.
Number of Tests— (Grades 1, 2, 2H, 3, 7, and 16 and all types of Grade 6):
Tests on the number of sample nuts in accordance with the following table shall be performed by the manufacturer following all production heat treatments:

In addition, a hardness test shall be performed by the manufacturer in accordance with 8.1.5 on one sample nut selected from each nominal diameter and series from each grade and heat number following completion of all production heat treatments.
Number of Tests, Grades 2HM and 7M:
Each nut shall be tested in accordance with either Specification A962/A962M or with Test Methods F606/F606M to ensure product conformance. The use of 100 % electromagnetic testing for hardness as an alternative to 100 % indentation hardness testing is permissible when qualified by sampling using indentation hardness testing. Each lot tested for hardness electromagnetically shall be 100 % examined in accordance with Practice E566. Following electromagnetic testing for hardness, a random sample of a minimum of 100 pieces in each purchase lot (as defined in 3.1.3) shall be tested by indentation hardness methods. All samples must meet hardness requirements to permit acceptance of the lot. If any one sample is outside of the specified maximum or minimum hardness, the lot shall be rejected and either reprocessed and resampled, or tested 100 % by indentation hardness methods.
In addition, shall be met.
Number of Tests, All Types of Grade 8 — Tests on the number of sample nuts in accordance with shall be performed by the manufacturer.
Test 2— In addition to the testing required by the manufacturer shall also perform hardness tests on sample nuts after the following test heat treatment. After completion of all production heat treatments heat the specimen nuts to the temperatures indicated below for 24 h, then slow cool. Test at room temperature.

^A Nuts intended to be coated with zinc or cadmium (marked in accordance with the requirements of Supplementary Requirement S8) are not subjected to the requirements of (See Appendix X2).

Special Requirement, Grades 2HM and 7M Preparation of Grades 2HM and 7M nuts for hardness test and the hardness test itself shall be performed with consideration to (1) protect legibility of markings; (2) minimize exterior dimensional changes; and (3) maintain thread fit.
Proof Load Test:
Requirements— The nuts listed in Tables 3 and 4 shall be capable of withstanding the proof loads specified therein. Proof load testing of nuts manufactured to dimensions and configurations other than those covered in Table 3 or Table 4 is only required when S9 is specified in the order or inquiry otherwise the nuts shall be cross-sectional hardness tested per Annex A3 of Test Methods and Definitions A370. Nuts that would require a proof load in excess of 160 000 lbf or 705 kN shall, unless Supplementary Requirements S1 or S4 are invoked in the purchase order or contract, be proof load tested per Section 8, or cross sectional hardness tested per Annex A3 of Test Methods and Definitions A370.
Number of Tests:
The manufacturer shall test the number of nuts specified in following all production heat treatments. Proof Load tests prevail over hardness tests in the event a conflict exists relative to minimum strength.
Test Method— The test shall be run using a threaded mandrel or a test bolt in accordance with Specification A962/A962M.
Cone Proof Load Test:
Requirements— This test shall be performed only when visible surface discontinuities become a matter of issue between the manufacturer and the purchaser. Nuts in the size range 1 ⁄ 4 to 1 1 ⁄ 2 in. inclusive and M6 to M36 inclusive shall be proof load tested. Nuts not in this size range and all types of Grade 8 nuts are not subject to this test. Also, nuts manufactured to dimensions and configurations other than those covered by Specification A962/A962M, ASME B1.1, ASME B1.13M, ASME B18.2.2, ASME B18.2.4.6M, and ISO 4033 are not subject to the cone proof load test. The cone proof load applied shall be determined in accordance with the Cone Proof Load requirements in Specification A962/A962M (tables or formulae or both) based upon the proof stresses shown in Table 5 and Table 6 of Specification A194/A194M.
Number of Tests — The manufacturer shall sample and test the number of nuts specified. The lot shall be considered acceptable if the sample nut(s) withstand(s) application of the cone proof load without failure.

Hardness Requirements ^A

Proof Load Using Threaded Mandrel — Inch Series

Note:Proof loads are not design loads.

Note:
^A See limit for proof load test. The proof load for jam nuts shall be 46 % of the tabulated load.
^B Based on proof stress of 130 000 psi.
^C Based on proof stress of 120 000 psi.
^D Based on proof stress of 150 000 psi.
^E Based on proof stress of 135 000 psi.
^F Based on proof stress of 175 000 psi.
^G Based on proof stress of 150 000 psi.
^H Based on proof stress of 80 000 psi.
^I Based on proof stress of 75 000 psi.

Proof Stress Using 120° Hardened Steel Cone — Inch

Dimensions

Nuts shall be hexagonal in shape, and in accordance with the dimensions for the hex or heavy hex series, as required, by ASME B18.2.2, ASME B18.2.4.6M, and ISO 4033. Unless otherwise specified, the American National Standard Heavy Hex Series shall be used and nuts shall be either double chamfered or have a machined or forged washer face, at the option of the manufacturer, and, conform to the angularity requirements of ASME B18.2.2, ASME B18.2.4.6M, and ISO 4033.
Unless otherwise specified, threads shall be in accordance with ASME B1.1 or ASME B 1.13M, and shall be gauged in accordance with ASME B1.2 and ASME B1.13M as described.
Nuts up to and including 1 in. nominal size shall be UNC Series Class 2B fit. Metric nuts up to and including M24 nominal size shall be coarse thread series tolerance 6H.
Nuts over 1 in. nominal size shall be either UNC Series Class 2B fit or 8 UN Series Class 2B fit. Unless otherwise specified, the 8 UN series shall be furnished. Metric nuts over M24 nominal size shall be coarse thread series tolerance 6H.
Note: Modification of thread dimensions may result in loss of load carrying ability

Nut Marking

In addition to the requirements of Specification A962/A962M, nuts shall be legibly marked on one face with marking representing the grade, type, and applicable manufacturing process shown in Table 7. Marking of wrench flats or bearing surfaces is not permitted unless agreed upon between manufacturer and purchaser.

Note:
^A Where ellipses (...) appear in this table there is no requirement.
^B The letters H and M indicate heat-treated nuts (see Section 6)
^C An underline as a marking requirement for grades 2HM and 7M has been removed but is permitted.
^DSee Supplementary Requirement S3.

S1. Strain-Hardened Austenitic Steel Nuts

Strain hardened Grades 8, 8C, 8T, 8M, 8F, 8P, 8N, or 8MN nuts may be specified. When Supplementary Requirement S1 is invoked in the order, nuts shall be machined from cold drawn bars or shall be cold forged to shape. No subsequent heat treatment shall be performed on the nuts. Nuts made in accordance with this requirement shall be proof load tested in accordance with and shall withstand the proof load specified in Table S1.1 and Table S1.2. Testing nuts requiring proof loads over 160 000 lbf or 705 kN is only required when Supplementary Requirement S4 is invoked. The hardness limits of Table 2 do not apply to strain hardened nuts. Nuts made in accordance with this requirement shall be marked with the Grade symbol underlined.

S2. Retests by Purchaser’s Representative

The purchaser’s representative may select two nuts per keg (200-lb unit [90-kg]) for sizes 5 ⁄ 8 in. and M16 and smaller, one nut per keg for sizes over 5 ⁄ 8 in. and M16 up to and including 11 ⁄ 2 in. and M36, and one nut per every two kegs for sizes larger than 11 ⁄ 2 in. and M36, which shall be subjected to the tests specified in Section 8.

S3. Low-Temperature Requirements for Grade 7 or Grade 7M Nuts

When low-temperature requirements are specified for Grade 7 nuts, the Charpy test procedures and requirements as defined in Specification A320/A320M for Grade L7 shall apply. When low-temperature requirements are specified for Grade 7M nuts, the Charpy test procedures and requirements as defined in Specification A320/A320M for Grade L7M shall apply. Charpy specimens may be taken from a sample nut, nut blank, or may be taken from separate test samples of the same heat processed through heat treatment with the nuts for which the test is to apply. Impact testing is not required when the bar stock or nut is smaller than 5 ⁄ 8 in. [16 mm] in diameter. S3.2 An “L” shall be added to the marking, as shown in Table 7, for nuts so tested.

Proof Load Testing of Strain Hardened Nuts Using Threaded Mandrel — Inch Series

Proof loads are not design loads.

Note:
^A The proof load for jam nuts shall be 46 % of the tabulated value.
^B Based on proof stress of 110 000 psi up to 3 ⁄ 4 in.; 100 000 psi 7 ⁄ 8 to 1 in.; 95 000 psi 1 1 ⁄ 8 to 11 ⁄ 4 in.; 90000 psi 13 ⁄ 8 to 11 ⁄ 2 in.
^C Based on proof stress of 125 000 psi up to 3 ⁄ 4 in.; 115 000 psi 7 ⁄ 8 to 1 in.; 105 000 psi 1 1 ⁄ 8 to 11 ⁄ 4 in.; 100000 psi 13 ⁄ 8 to 11 ⁄ 2 in.

S4. Proof Load Tests of Large Nuts

Proof load testing of nuts requiring proof loads of over 160 000 lbf or 705 kN is required. Testing shall be performed in accordance with 8.2 to the loads required in Table S4.1 and Table S4.2. The maximum load will be based entirely on the equipment available.

S5. Control of Product by Heat Number

When control of nuts by actual heat analysis is required and this supplementary requirement is specified, the manufacturer shall identify the completed nuts in each shipment by the actual heat number. When this supplementary requirement is specified, a certificate including the results of the actual production tests of each test lot together with the heat chemical analysis shall be furnished by the manufacturer.

S6. Grain Size Requirements for Non H Grade Austenitic Steels Used Above 1000 °F

For design metal temperatures above 1000 °F [540 °C], the material shall have a grain size of No. 7 or coarser as determined in accordance with Test Methods E112. The grain size so determined shall be reported on the Certificate of Test.

S4.1 Proof Load for Large Heavy Hex Nuts — Inch ^A

Note:
^A ASME B18.2.2 in the size range over 1 1 ⁄ 2 in. provides dimensions only for heavy hex nuts.
^BProof loads for nuts of larger dimensions or other thread series may be calculated by multiplying the thread stress area times the proof stress in the notes to Table 3 or Table S1.1. The proof load for jam nuts shall be 46% of the tabulated load.

S7. Coating on Nuts

It is the purchaser’s responsibility to specify in the purchase order all information required by the coating facility. Examples of such information may include but are not limited to the following:
Reference to the appropriate coating specification and type, thickness, location, modification to dimensions, and hydrogen embrittlement relief.
NOTE S7.1 — Modification of thread dimensions may result in loss of load carrying ability.
Reference to Specifications A153/A153M, B633, B695,B696, B766,F1941/F1941M, F2329/F2329M, or Test Method F1940, or other standards.

S8. Marking Coated Nuts

Nuts coated with zinc shall have ZN marked after the grade symbol. Nuts coated with cadmium shall have CD marked after the grade symbol.
As an example the marking for zinc-coated 2H bolting components will now be 2HZN rather than 2H.

S9. Proof Load Testing

Proof load tests of nuts made to dimensions, thread pitch, and configurations other than those covered in Table 3 or Table 4 shall be made using loads agreed upon between the manufacturer and the purchaser.

S10. 100 % Hardness Testing of Grade 2HM and 7M

Each nut shall be tested for hardness by indentation method and shall meet the requirements specified in Table 2.

Other Information

1. STRAIN HARDENING OF AUSTENITIC STEELS

Strain hardening is the increase in strength and hardness that results from plastic deformation below the recrystallization temperature (cold work). This effect is produced in austenitic stainless steels by reducing oversized bars to the desired final size by cold drawing or other process. The degree of strain hardening achievable in any alloy is limited by its strain hardening characteristics. In addition, the amount of strain hardening that can be produced is further limited by the variables of the process, such as the total amount of crosssection reduction, die angle and bar size. In large diameter bars, for example, plastic deformation will occur principally in the outer regions of the bar, so that the increased strength and hardness due to strain hardening is achieved predominantly near the surface of the bar. That is, the smaller the bar, the greater the penetration of strain hardening. Thus, the mechanical properties of a given strain hardened bolting compdependent not just on the alloy, but also on the size of bar from which it is machined.

2. COATINGS AND APPLICATION LIMITS

Use of coated bolting components at temperatures above approximately one-half the melting point (Fahrenheit or Celsius) of the coating is not recommended unless consideration is given to the potential for liquid and solid metal embrittlement, or both. The melting point of elemental zinc is approximately 780 °F [415 °C]. Therefore, application of zinc coated bolting components should be limited to temperatures less than 390 °F [210 °C]. The melting point of cadmium is approximately 600 °F [320 °C]. Therefore, application of cadmium coated bolting components should be limited to temperatures less than 300 °F [160 °C].