1、DEUTSCHE NORM October 1994 Heat treatment of ferrous products I I 17022-1 Hardening and tempering ICs 25.200 Descriptors: Ferrous products, heat treatment, steel. Wrmebehandlung von Eisenwerkstoffen; Verfahren der Wrmebehandlung; Hrten, Bainatisieren, Anlassen und Vergten von Bauteilen In keeping wi
2、th current practice in standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker. Contents Page 1 Scope and field of application 2 2 Terminology 2 3 Brief description of heat treatment procedures . 2 3.1 Quench hardening 2
3、 3.1.1 Austenitizing . 2 3.1.2 Cooiing/quenching . 3.2 Tempering . 2 3.3 Quench hardening followed by tempering 2 3.4 Austernpering 2 3.4.1 Austenitizing . 2 3.4.2 Cooling and isothermal transformation . 2 4 Identification of heat treatment condition 2 5 Heat treatment procedures . 2 5.1 Preparatory
4、 treatment and conditioning 2 5.1.1 Preparatory treatment . 2 5.1.2 Conditioning . 3 5.1.2.1 Stress relieving 5.1.2.2 Normalizing 3 5.2 Quench hardening 3 5.2.1 Austenitizing . 3 5.2.2 Cooiing/quenching 3 5.3 Subzero cooling 4 5.4 Tempering . 4 5.5 Quench and tempering 4 Page 5.6 Austempering 4 5.6.
5、1 Austenitizing . 4 5.6.2 Cooling and isothermal transformation . 4 6 Heat treatment media . 4 6.1 Heating media 4 6.1.1 Liquid heating 4 6.1.2 Gaseous heating media 5 6.2 Cooling and quenching media 5 6.2.1 Liquid cooling media 5 6.2.2 Gaseous cooling media 5 6.2.3 Subzero cooling media 5 7 Selecti
6、ng heat treatment units . 5 7.1 Units for heat treatment and isothermal holding 5 7.2 Units for cooling and quenching 5 7.3 Units for subzero cooling 7 8 Testing and inspection of heat treated products 7 9 Straightening distorted products 7 10 Designing for heat treatment 7 11 Defects in heat treate
7、d products . . Standards and other documents referre Other relevant standards . 15 Explanatory notes . 15 Continued on pages 2 to 15. ?uth Verlag GmbH, Berlin, has the exclusive right of sale for German Standards (DIN-Normen). DIN 17022-1 Engl. Price group 1 12.96 Sales No. O1 12 Page2 DIN 17022-1 1
8、 Scope and field of application This standard describes methods for the heat treatment of ferrous products. Particular regard is given to quench hard- ening, austempering, tempering, or quench hardening and tempering procedures. The following specifications also cover the heat treatment of semi-fini
9、shed products, such as steel bars. 2 Terminology This standard is based on the heat treatment terminology specified in DIN EN 10052. 3 Brief description of heat treatment procedures 3.1 Quench hardening Quench hardening is achieved by cooling a ferrous product in such way that previously obtained au
10、stenite transforms partially or totally to martensite imparting a specific hard- ness to the product. 3.1.1 Austenitizing During austenitizing the ferrous product is brought to and maintained at the specific temperature range at which its structure totally or partially transforms to austenite. The a
11、ustenitizing temperature, which may be attained step by step, is the highest temperature at which the ferrous product is held during austenization. It is usually identical with the temperature at which the cooling procedure be- gins. The quality of austenite widely depends on the composition and ini
12、tial structure of the material, the form and size of the product, and the intended heat treatment condition. The initial and final stages of transformation of a ferrous product to austenite under isothermal conditions are shown in the isothermal diagrams in subclause 5.2.1 (cf. figures 1,2 and 5). 3
13、.1.2 Cooling/quenching Following austenitizing, cooling/quenching is carried out in one or several stages at a rate suitable for bringing the hardness of the product to the required level. The cooling schedule depends on the composition of the material, the design and size of the product, and the mi
14、crostructure desi red. In order to achieve complete austenitizing, cooling may be carried out below ambient temperature (cf. subclauses 5.2 and 5.3). 3.2 Tempering In order to compensate for a reduction in toughness of the material occurring as a result of hardening, the products (except austempered
15、 products) may be tempered. Tempering consists in heating the product to a specific temperature, holding it at that temperature and then cool- ing to ambient temperature at a suitable rate. The behaviour of the material during tempering is determined by the com- position of the material and its init
16、ial microstructure. The specific time-temperature (TT) cycle is to be selected as a function of the desired level of hardness and other proper- ties required. For further information, refer to relevant standards for steel. vourable relationship between the toughness and strength of ferrous products.
17、 It aims at obtaining a particularly good ductility and high toughness and consists in quench hard- ening and subsequent tempering to a temperature ranging between 540 and 680 “C. 3.4 Austempering Austempering is a heat treatment procedure involving austenitizing followed by step quenching at a rate
18、 fast enough to avoid formation of ferrite or pearlite, and holding at a temperature just above Ms), ensuring partial or total transformation of austenite to bainite. Austempering is applied to bring both the toughness and hardness to a high level and to reduce the risk of distortion during subseque
19、nt martempering. This objective requires cooling to the lowest possible transformation temperature and isothermal holding. 3.4.1 Austenitizing For a description of this type of heat treatment, see sub- clause 3.1.1. 3.4.2 Cooling and isothermal transformation After austenitizing, the product is cool
20、ed at a rate fast enough to ensure that the bainite transformation range is attained. For further information regarding holding times, refer to the time-temperature-transformation WT) diagram illustrated in figure 8b. 4 Identification of heat treatment condition On drawings, the heat treatment condi
21、tion shall be indi- cated as specified in DIN 6773-2. Refer to DIN 17023 as a guideline for giving any further instructions on heat treat- ment. Symbols used to designate the type of heat treatment ap- plied shall be given as specified in DIN 17014-3. 5 Heat treatment procedures 5.1 Preparatory trea
22、tment and conditioning Prior to heat treatment, the product shall undergo prepara- tory treatment and conditioning to ensure that its surface and initial microstructure are suitable, and that residual stresses do not interfere with the heat treatment proce- dure. 5.1.1 preparatory treatment Dependin
23、g on how badly the surface of the product has been soiled, it may have to undergo cleaning, blast clean- ing, drying, deburring, machining, or pickling. The products shall be free from burrs, scale, rust, shot, skin, and from oil, fat or paint residues, so that the effi- ciency of the heat treatment
24、 medium is not impaired. Make sure the products are dry to avoid unintended evaporation, such as may result in sait bath eruptions, which would in- terfere with the heat treatment procedure. The surface layer of ferrous products shall not be decarbu- rized in order to prevent cracking and the format
25、ion of soft skin, or soft spots. 3.3 Quench hardening followed by tempering*) Quench hardening followed by tempering (quench and tempering, for short) is carried out to produce a more fa- *) Translators note: As there is no English equivalent for I) Temperature at which the austenite begins to trans
26、form vergten, the concept has been paraphrased. into martensite. DIIN 17022-1 Page3 Furthermore, the products shall be uncoated and free from residues to prevent foreign elements (such as phosphorus particles originating from phosphate layers) from being in- corporated into the surface layer by diff
27、usion. For safety reasons, any bolts and screws are to be removed from the product prior to cleaning or heat treatment. 5.1.2 Conditioning 5.1.2.1 Stress relieving If residual stresses are likely to cause distortion during heat treatment, the product shall be stress relieved. Stress re- lieving may,
28、 however, lead to changes in size and to surface deterioration (e.g. decarburization). The size of the product should be selected in such way that any dimensional changes or surface deterioration may be compensated for by machining. Care shall be taken that no further residual stresses are induced b
29、y heating or cooling. During stress relieving the temperature attained should be slightly below temperature A, .e. the temperature at which austenite begins to form during heating. In this case, isothermal holding may not be necessary. Cold worked products should not be stress-relieved but rather no
30、rmalized to prevent grain coarsening during recrystallization. For further information regarding stress relieving, refer to relevant standards. 5.1.2.2 Normalizing Residual stresses may also be relieved by normalizing the product. This procedure homogenizes the microstructure and helps prevent grain
31、 coarsening in critical areas. For further information regarding normalizing, refer to relevant standards and documentation. 5.2 Quench hardening 5.2.1 Austenitizing An isothermal diagram, illustrating the time-temperature relationship at the surface and core of a product with a simple cross section
32、, is shown in figure 1. Products with a varying cross section require different time-temperature cycles for the various cross sections. For information regarding specific austenitizing tempera- tures, refer to relevant standards and documentation. The austenitizing time includes both the time during
33、 which a product is heated to a given temperature and the time during which it is held at that temperature. During the heating process, different temperatures are achieved at the surface and core of the product. The differ- ence in temperature increases as a function of the cross- sectional dimensio
34、n and heating rate, and in an inverse proportion to the thermal conductivity of the material. The resulting thermal stresses may lead to distortion. There- fore, large-size products as well as products with a varying cross section, particularly alloyed steel products, are to be brought to the specif
35、ic austenitizing temperature by heat- ing in stages (see figure 2). Figure 3 illustrates a thermal cycle (.e. heating-up time as a function of cross-sectional dimensions) for products with a circular or rectangular cross section which are treated in a salt bath. Reference values regarding heat treat
36、ment in forced air furnaces and retort furnaces are given in figure 4. The lT diagram in figure 5 illustrates the microstructural changes which annealing steel (grade 34CrMo4) undergoes in the course of the continuous heating process leading to the formation of austenite. It shows that as the heatin
37、g rate raises the point of austenitization and carbide dissolution is shifted upwards. The diagram gives a rough idea of the microstructure obtained as a function of heating rate and temperature. Austenitization and carbide dissolution depend on the type and quantity of alloying elements. A complete
38、 dissolution of carbide is generally not required. However, carbide disso- lution should be sufficient to produce the carbon content required for a specific hardness. Once the product has been heated to transformation temperature, it is to be held at the critical point so that by allowing sufficient
39、 dissolution of carbide the desirable microstructure is produced. The isothermal time for steel products usually does not exceed 30 minutes. If, after forging, products are to be hardened while still hot, care should be taken that fine grain austenite has formed prior to cooling. 5.2.2 Coolinglquenc
40、hing As occurs during heating, differences in temperature may also arise throughout the thickness of the product during cooling. In order to reduce the effect of residual stresses resulting from differences in temperature, sensitive prod- ucts may be step quenched. However, step quenching should onl
41、y be performed on products with sufficient hardenability. For specifications regarding hardenability, refer to relevant standards and documentation. Uniform cooling is ensured by stacking the units of a batch in such way that they are fully exposed to the quenching medium. This allows hardening to t
42、ake place to a full extent and minimizes the risk of distortion and thermal cracking. Various cooling curves are shown in figure 6. In step quenching, the cooling procedure is interrupted at a temperature just above the Ms temperature range. At this point, a uniform temperature, reducing the effect
43、of residual stresses, should be achieved throughout the structure of the product without pearlite and/or bainite forming. Once the product has reached the desirable temperature, it is cooled to ambient temperature at an appropriate rate. Figure 7 shows reference cooling rates for circular or rec- ta
44、ngular cross sections which are air-cooled to ambient temperature. Scale or salt residues on the surface of the product may interfere with the cooling process. The TTT diagram in figure 8 illustrates the microstructural changes which annealing steel (grade 34CrMo4) undergoes in the course of continu
45、ous cooling beginning at austenitizing temperature. The TT depends on the steel composition of the product and the austenitizing condi- tions. The continuous cooling transformation (CCT) dia- grams show the microstructure and hardness achieved at ambient temperature. The objective of quench hardenin
46、g (.e. the greatest possi- ble transformation of austenite to martensite) can only be achieved if the specific critical cooling rate, K, has been maintained for all cross sections of the product (see fig- ure 8). If the required quenching efficiency is not attained, or if large-size products, or pro
47、ducts with insufficient har- denability are involved, this may lead to the unintended formation of bainite, pearlite, or ferrite. Furthermore, hyper- eutectoid steels may contain retained austenite, as well as undissolved or proeutectoid carbides. Depending on size, design and hardenability, the pro
48、duct may be quenched in water, in an aqueous medium, in oil, or molten salt, or may be cooled in a fluidized bed, in air, or in inert gas. Move the product about, or circulate the cooling medium, to achieve sufficient and uniform cooling. During the cooling procedure, austenite is fully transformed
49、to martensite once the M, temperature has been reached. Depending on the ferritic composition and the carbon con- Page4 DIN 17022-1 tent in austenite, theM, temperature may lie below ambient temperature. The amount of retained austenite is a function of the dis- solved carbon content in austenite and may increase as a result of rapid cooling. 5.3 Subzero treatment The amount of retained austenite found in the final micro- structure, once the product has been quenched and has reached ambient temperature, may be reduced by subzero treatment. Subzero treatment is recommended in
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