1、lAND SEA AIR SPACE AEROSPACE MATERIAL Society of Automotive Engineers, Inc. SPECIFICATION 400 COMMONWEALTH DRIVE. WARRENDALE, PA. 15096 HEAT TREATMENT Carbon, Low-Alloy, and Specialty Steels AMS 2760 Issued 1-15-76 Revised 1. SCOPE: This specification covers the procedure for through-hardening and r
2、elated heat treat ments of carbon, low-alloy, and specialty steel parts to produce specified mechanical properties within the capability of each respective steel. 1.1 Heat treating processes such as induction hardening, flame hardening, carburizing, nitriding, austempering, and martempering are reco
3、gnized processes but are not covered by this speci fication. 2. APPLICABLE DOCUMENTS: The following publications form a part of this specification to the extent specified herein. The latest issue of Aerospace Material Specifications (AMS), Aerospace Standards (AS), and Aerospace Recommended Practice
4、s (ARP) shall apply. The applicable issue of other documents shall be as specified in AMS 2350. 2.1 SAE Publications: Available from Society of Automotive Engineers, me., 400 Commonwealth Drive, Warrendale, PA 15096. 2.1. 1 Aerospace Material Specifications: AMS 2350 -Standards and Test Methods 2. 1
5、. 2 Aerospace Standards: AS 1260 -Equivalent Sections of Certain Shapes to Round Bars 2.1. 3 Aerospace Recommended Practices: ARP 1341 -Determining Decarburization and Carburization in Finished Parts of Carbon and Low-Alloy Steels 2. 2 ASTM Publications: Available from American Society for Testing a
6、nd Materials, 1916 Race Street, Philadelphia, PA 19103. ASTM A255 -End-Quench Test for Hardenability of Steel ASTM A370 - Mechanical Testing of Steel Products ASTM Ell2 -Estimating the Average Grain Size of Metals 2. 3 Government Publications: Available from Commanding Officer, Naval Publications an
7、d Forms Center, 5801 Tabor Avenue, Philadelphia, PA 19120. 2. 3.1 Military Standards: MIL-STD-105 - Sampling Procedures and Tables for Inspection by Attributes MIL-STD-794 - Parts and Equipment, Procedures for Packaging and Packing of Copyright 1976 by Society of Automotive Engineers, Inc. All right
8、s reserved. AMS 2-;-2-3. GENERAL REQUIREMENTS: 3. 1 Equipment: 3. 1. 1 Furnaces: 3.1.1.1 The design and capacity of the heating equipment shall be such that the temperature at any point in the working zone shall not vary from the set heat treating temperature, after the charge has been brought up to
9、 temperature, by more than_2:15F (_2:8.3C) for temperatures not over 1200F (649C), and by more than_2:25F (_2:14C) for temperatures over 1200F (649C). 3.1.1. 2 Thermocouples shall be located in the working zones and shall be adequately protected from furnace atmosphere contamination. 3.1. 2 Heating
10、Media: Protective atmospheres shall be used when heat treating parts with finish machined surfaces at temperatures over 1200F (649 C). Atmospheres shall be of a type which will not react objectionably with the steel being treated and shall be essentially neutral to the carbon con tent of the steel b
11、eing heat treated. Protective atmospheres may be omitted for parts which will have at least 0. 020 in. (0. 51 mm) of metal removed from the surfaces after heat treatment, for parts with non-machined surfaces permitted by part drawing, or for furnace operating temperatures of 1200 F (649 C) or lower.
12、 3. 1. 2. 1 Atmospheric furnaces shall be supplied with precisely controlled atmospheres or equipped with precision atmospheric generators and controls as appropriate. Ducts and working zones shall be sealed to prevent contamination by outside gases. 3.1. 2. 2 Forced circulation is recommended to eq
13、ualize temperatures within the working zone. 3.1. 2. 3 Precautions should be taken when using celtai.n plotective atmospheres below 1400 F (760 C because of potential explosive characteristics. 3. 1. 2. 4 A suitable vacuum may be used in lieu of protective atmosphere, when permitted by purchaser. 3.
14、1. 2. 5 Salts used in salt-bath furnaces shall not react objectionably with the steels being heat treated within the respective working temperature ranges. 3.1. 2. 6 Adequacy of heating media shall be determined as in 3. 5. 2. 3.1. 3 Temperature Controllers: Suitable automatic temperature controllin
15、g and recording instruments, preferably of the potentiometer type, shall be provided on all heat treating equipment to assure adequate control of temperatures in all working zones. 3.1. 4 Quenching Equipment: 3.1. 4.1 Quenching Baths: Means shall be provided for adequate circulation of the cooling m
16、edia, for in dicating the temperature of the media, and for cooling or heating the media, as applicable. Quenching baths shall be of a size and design that the heat transferred by the most massive part to be quenched together with the necessary fixtures to limit warpage will cool the parts at a rate
17、 equal to or exceeding the critical cooling rate for the respective composition and will not significantly increase the temperature of the bath. Effectiveness of the quench shall be deter mined as in 3. 1. 4. 4. 3.1. 4. 2 Water quenching baths employed in cooling steel parts which have been heated i
18、n salt-bath fur naces shall be provided with an inflow of fresh water. During or immediately following quench ing, all salt residues shall be removed from work processed in salt-bath furnaces. - 3-AMS 271“ 3.1. 4. 3 Location of Quenching Equipment: Quenching equipment shall be located in such a mann
19、er and handling facilities shall function with sufficient speed to assure the effectiveness of the quench. 3.1. 4. 4 Effectiveness of Quench: The effectiveness of the transformation shall be ascertained by making hardness tests on the cross-section of representative round specimens of size comparabl
20、e to the maximum cross section of the parts being heat treated after quenching with a production batch. The mid-point as-quenched hardness shall be not lower than the hardness of the end quench hardenability specimen at a distance from the quenched end specified in Table I as cor responding to the d
21、iameter of the specimen. This end-quench hardness shall be taken from the actual hardenability curve determined in accordance with ASTM A225. TABLE I Equivalent Hardness Locations on End-Quench Bars Midpoints of Quenched Bars Distance in Sixteenths of an Inch From Quenched End When Round is Diameter
22、 of Round Water Oil Inches (Millimetres) Quenched Quenched 0.50 ( 12. 7) 1 3 1.00 ( 25. 4) 3 6 1. 50 ( 38.1) 5 9 2.00 ( 50. 8) 8 11 2.50 ( 63. 5) 10 14 3.00 ( 76.2) 13 17 3.50 ( 88. 9) 15 21 4.00 (101. 6) 18 26 3.1. 4. 4. 1 For example, the midpoint hardness of a specimen 1. 50 in. (38. 1 mm) in dia
23、meter quenched in water shall be not less than the hardness found 5/16 in. (7. 9 mm) from the quenched end of an end-quenched hardenability test specimen of the same heat of steel. If the 1. 50-in. (38. 1-mm) specimen were oil quenched, the midpoint hardness shall be not less than the hard ness 9/16
24、 in. (14. 3 mm) from the quenched end of the end-quench specimen. 3.1. 4. 4. 2 The actual material used for testing need not be the same composition as that of the steel from which the parts being treated are made but shall be of comparable hardenability. The length of the cylinder for this test mus
25、t be at least 3 times the diameter. After cutting to obtain ac cess to the midpoint of the sample, the following test shall be used to check for possible tem pering during the cutting or grinding operation: 3. 1. 4. 4. 2. 1 Wash specimen in hot water and etch, in a solution containing 5% by volume c
26、oncentrated nitric acid and 95% by volume water, until black. Wash in hot water. Immerse for approx imately 3 sec in a solution containing 50% by volume concentrated hydrochloric acid and 50% by volume water. Wash streaks indicate that the structure has been overheated at the surface by the cutting
27、or grinding operation. This change in structure shall be removed before hardness testing. 3.1. 5 Refrigeration Units: The design and capacity of the refrigeration equipment shall be such that the temperature at any point in the working zone shall not vary from the desired sub-zero temperature, after
28、 the charge has been brought down to temperature, by more than 2:10o F (2:5. 6 C). Refrigera tion units shall be equipped with temperature recording instruments having an accuracy of 2:2 F (2:1.1oC). AMS z-, -v -4-3. 2 Qualification and Calibration of Equipment: 3. 2.1 Temperature Uniformity of Batc
29、h Furnaces: A temperature survey in furnace working zones shall be performed on each new furnace at the maximum and minimum temperatures for which each furnace is to be used if the maximum and minimum are more than 200 F (111 o C) apart. There shall be at least one thermocouple test location for eac
30、h 25 cu ft (0. 7 m3) of furnace air volume up to a maximum of 40 test locations, with a minimum of 9 test locations, one at each corner and one at the center. For furnaces of less than 10 cu ft (0. 28 m3) furnace air volume, the temperature survey may be made with a minimum of 3 thermocouples locate
31、d at the front, center, and rear or at top, center, and bottom of the furnace. For salt bath furnaces, one test is required for each 40 cu ft (1.12 m3) of volume with a minimum of 5 test locations. The survey shall be performed in such manner as to reflect the normal operating characteristics of the
32、 furnace. 3. 2.1.1 After insertion of the temperature-sensing elements, readings should be taken frequently enough to determine when the temperature of the hottest region of the furnace approaches the bottom of the temperature range being surveyed. From that time until thermal equilibrium is reached
33、, the temperature of all test locations should be determined at intervals not greater than 2 min. in order to detect any overshooting. After thermal equilibrium is reached, read ings should be taken at approximately 5 min. intervals for sufficient time to determine the re current temperature pattern
34、, but not less than 30 minutes. Before thermal equilibrium is reached, none of the temperature readings shall exceed the maximum temperature of the range being surveyed. After thermal equilibrium is reached, the maximum temperature variation of all elements shall not exceed the limits of 3. 1. 1. 1.
35、 After the initial survey, each furnace shall be surveyed at least semi-annually at the maximum operating temperature except that annual surveys are sufficient for furnaces employed for annealing, normalizing, or stress relieving operations only, and for salt bath furnaces regularly used in producti
36、on and having printed records of three successive satisfactory performances during semi-annual surveys. 3. 2. 2 Te:tnpe:cature Uniformity of Continuous Furnaces: The type. of initial and semi-annual survey and the procedures for performing the survey should be established for each particular furnace
37、 in volved. The types of continuous heat treating furnaces may vary considerably depending upon the product and sizes involved. For some types and sizes of furnaces, the only practical way to sur vey the furnace is to perform an extensive mechanical property survey of the limiting product sizes to v
38、erify conformance to the specified mechanical properties for such items. Specimens shall be cut from the center and immediately below the surface of samples representing the most massive sections of the parts to be heat treated in production. The variation in properties of test specimens, after temp
39、ering to the maximum strength at which the respective steel is used in production, shall be within the limits of 3. 5. 1. 2. 3 and the maximum variation of austenitic grain size shall not exceed two sizes, determined in accordance with ASTM El12. During all periodic surveys, at least two load thermo
40、couples shall be attached to a part of maximum section thickness which will be processed, one thermocouple being located at the center of the section and the other at a surface exposed to the heat source. The test part shall be run, as part of a normal furnace load, in such manner as to reflect the
41、normal operating characteristics of the furnace. The indi cated temperatures shall be monitored as the part moves through the furnace at the maximum speeds used in production. The uniformity of temperature and holding time after reaching tem perature shall comply with 3.1.1.1 and Table IV requiremen
42、ts and metal temperatures shall not exceed Table III limits. - 5-AMS27 -3. 2. 3 Accuracy of Furnace Control Instruments: The accuracy of temperature measuring and controlling instruments shall be checked at regular intervals by comparison test with precision potentiometer type instruments of known a
43、ccuracy used with a calibrated thermocouple. Tests shall be rerun following each redesign or reconstruction of the furnace. The test thermocouple shall be located within 3 in. (76 mm) from the furnace control thermocouple. The check shall be made at a normal working temperature and with or without a
44、 production load in the furnace or both. If instruments are replaced or not used during a 3-month interval, they shall be checked before use. The inter vals at which the temperature measuring instruments are checked are dependent upon the type of thermocouple, working temperature, frequency of opera
45、tion, and furnace atmosphere but should be at regular intervals not exceeding one month. Chromel-alumel thermocouples shall be replaced whenever testing shows they are no longer within calibration. 3. 2. 3. 1 Temperature readings shall be within 1. O% or 10 F (5. 6 C), whichever is smaller, of the t
46、emperature indications of the calibrating equipment. 3. 2. 4 Processes: For each furnace, specimens representative of the maximum section size of material to be heat treated in that furnace shall be processed and tested periodically to determine conform ance to the requirements of this specification
47、. Pertinent details such as type of bath or furnace atmosphere employed, atmosphere controls, and furnace and auxiliary controls shall be recorded. Processed specimens shall be examined for surface contamination due to heat treatment, tested for mechanical properties as indicated by 3. 5. 1, and the
48、 microstructures of zones immediately below specimen surfaces examined metallographically for contamination by atmospheric gases, bath impurities, or absorption of other undesirable elements. 3. 2. 4. 1 Tests shall be made whenever production of parts changes to compositions of steel not pre viously
49、 heat treated in the respective equipment. The results of tests made to determine con formance of heat-treated material to the requirements of the respective material specification are acceptable in lieu of the periodic test as evidence of the properties being obtained with the equipment and procedures employed. 3. 3 Preparation of Parts: Dirt, welding flux, shot peening residues, die pick-up, and similar contami nation that could detrimentally affect parts shall be removed before placing the parts in the furnace. Cleaners shall be compatible with the alloy and
