1、UDC 621.785.6/.7: 669.1 : 621.9.02: 620.1 DEUTSCHE NORM June 1986 I I Heat treatment of ferrous materials Heat treatment methods Hardening and tempering of tools - DIN 17 022 Part 2 Wrmebehandlung von Eisenwerkstoffen; Verfahren der Wrmebehandlung; Hrten und Anlassen von Werkzeugen In keeping with c
2、urrent practice in standards published by the International Organization for Standardization (/SO), a comma has been used throughout as the decimal marker. Contents Page 1 Scope and field of application . 1 2 Concepts 1 3 Principle of heat treatment . 1 3.1 Hardening 1 3.1.1 Austenitizing . 1 3.1.2
3、Cooling . 1 3.2 Tempering 2 4 Indicating the heat-treated condition 2 5 Hardening and tempering procedure . 2 5.1 Preparation and pretreatment 2 5.1 .I Stress relieving 2 5.1.2 Hardening and tempering (pretreatment) 2 5.1.3 Tool preparation . 2 5.2 Hardening 2 5.2.1 Austenitizing . 2 5.2.2 Cooling .
4、 .: 4 5.2.3 Deepfreezing . 5 5.3 Tempering 5 5.4 Hardening and tempering of unalloyed steel tools 8 5.4.1 Hardening . 8 5.4.2 Tempering . 8 5.5 Hardening and tempering of tools made from cold work and hot work alloy steels 9 1 Scope and field of application This standard describes heat treatment pro
5、cedures and provides information on the hardening and tempering of tools made from tool steels, e.g. from those specified in DIN 17 350. 2 Concepts The terminology associated with heat treatment as used in this standard has been adopted from DIN 17014 Part 1 which also gives the relevant definitions
6、. 3 Principle of heat treatment 3.1 Hardening Hardening consists of austenitizing and cooling at a rate suitable for the intended application. 3.1.1 Austenitizing Austenitizing is effected by heating and soaking at austenitizing temperature, the hardening temperature Page 5.5.2 Deep freezing . 10 5.
7、5.3 Tempering . 10 5.6 Hardening and tempering of high speed steel tools. 10 5.6.1 Hardening . 10 5.6.2 Tempering . 10 6 Heat treatment media 1 O 6.1 Heating media 10 6.1.1 Liquid heating media 12 6.1.2 Gaseous heating media . 12 6.1.3 Vacuum 12 6.2 Cooling/quenching media 12 6.2.1 Liquid cooling me
8、dia 12 6.2.2 Gaseous cooling media . 12 6.2.3 Deep freezing media 12 7.1 Heat treatment furnaces . 12 7.3 Deep freezing equipment. 14 8 Defects caused by errors in the heat treatment of tools 14 9 Design criteria for proper heat treatment . 14 10 Notes on straightening . 18 11 Inspection of heat-tre
9、ated tools . 18 5.5.1 Hardening . 9 7 Notes on heat treatment equipment . 12 7.2 Cooling/quenching equipment . 14 being generally identical with the austenitizing temper- ature. Heating may be effected in stages, this being the usual procedure for alloy steel tools. The austenitizing conditions are
10、primarily governed by the chemical composition and the required final condition of the material by the shape and dimensions of the tool being hardened and by the initial condition of the material. The interrelationship of the material-related factors is illustrated by time-temperature austenitizing
11、diagrams (see subclause 5.2.1). 3.1.2 Cooling Austenitizing is followed by cooling at a rate suitable for imparting the required hardness. Cooling may be carried out with the temperature lowered in stages, this being the usual procedure for alloy steel tools. The cooling process is a function of the
12、 chemical composition of the steel, the austenitizing conditions, the shape and dimensions of the tool being hardened and by the required final condition of the material. Cooling may be continued below ambient temperature (see subclause 5.2.3). Continued on pages 2 to 19 Beuth Verlag GmbH. Berlin. h
13、as the exclusive right of sale for German Standards (DIN-Normen). 01.88 Sales No. O1 12 DIN 17022 Part2 Engl. Pricegroup I, Page 2 DIN 17 022 Part 2 3.2 Tempering After hardening, the tools shall be tempered either once or several times. The tempering temperature and duration of tempering are functi
14、ons of the required hardness and other functional properties of the tool, the tempering behaviour being governed by the chemical composition of the material and the prevailing structure condition. 4 Indicating the heat-treated condition On drawings, the heat-treated condition shall be indicated as s
15、pecified in DIN 6773 Part 2. Detailed specifications of the heat treatment procedure may require the provision of a heat treatment instruction as specified in DIN 17 023, or a heat treatment schedule. For denoting details of the heat treatment procedure, the symbols given in DIN 17 014 Part 3 shall
16、be used. 5 Hardening and tempering procedure 5.1 Preparation and pretreatment The preparation and conditioning of tools is intended to eliminate any undesirable influence of internal stresses on distortion, or of the surface condition on the final condition, and to ensure that heat treatment is not
17、interrupted by workpiece failure. 5.1 .I Stress relieving Stress relieving is necessary if internal stresses present in the material influence its susceptibility to distortion to an unacceptable extent, the resulting changes in size and shape being taken into account b!t the provision of an adequate
18、 machining allowance. The temperature shall lie below the transformation temperature Ac1 , but should be as close to this temperature as possible. This being the case, soaking after heating is not required. Heating and cooling shall be performed so as to prevent additional internal stresses arising.
19、 In the case of cold-formed tools, normalizing is to be preferred if stress relieving is likely to result in grain coarsening due to recrystallization. 5.1.2 Hardening and tempering (pretreatment) The internal stresses present in the tool blank may also be reduced by heating to austenitizing tempera
20、ture instead of stress relieving, this also making the material more homogeneous. If the tool blank is then cooled as in the case of hardening, the changes in dimensions and shape likely to result during subsequent hardening of the machined tool can be reduced, and the extent and direction of the li
21、kely changes can be estimated. Following this, the tool blank shall be tempered so as to allow further machining and correction of the changes in size and shape that have occurred. This so-called “Pretreatment“ of the blank including intermediate machining prior to hardening of the tool has proved i
22、ts value, particularly when exacting demands have to be met in respect of behaviour in terms of changes in size and shape. 5.1.3 Tool preparation Depending on the level of surface impurities dnd the quality requirements to be met, it will be necessary for tools to be prepared, prior to hardening, by
23、 washing, drying, pickling, sand-blasting, flash-trimming, machining or other suitable measures to ensure that, for example, salt baths are not contaminated by flash, adherent chips, rust, scale or skin due to rolling, forging or casting; no eruptions occur in salt baths due to sudden evapora- tion
24、of water; soft skin, soft spottiness and cracks do not occur as a result of decarburized surface layers. Bolts or screws used for closing bores or tapped holes shall be removed prior to heat treatment or even prior to cleaning. 52 Hardening 5.2.1 Austenititing The temperature in the surface zone and
25、 in the core of a tool of simple geometry and of more or less uniform cross section, when it is brought to austenitizing temper- ature, is shown as a function of time in a graph in figure 1. Tools of non-uniform cross section, however, yield different heating curves for surface zone and core in each
26、 cross section. The hardening temperature to be applied as a function of the material shall be taken from DIN 17 350 or corresponding documentation provided by the steelmakers. The sum of heating and soaking time is the holding time of a tool in a furnace. During heating, temperature differences ari
27、se between the surface zone and the core of the tools. The bigger the cross sections of the tools to be heated, the higher the rate of heating and the lower the thermal con- ductivity of the material, the more pronounced are these temperature differences. These differences and the resulting structur
28、al transformations at different points in time are the cause of stresses occurring. Distortion may result. Tools with big differences in cross section and/or large dimensions, particularly when made of alloy steel, shall therefore be heated slowly or in stages (see figure 2). Guidance on the heating
29、 time for various thermal cycles is given in figure 3, which also gives guideline values for circular, square or rectangular tool cross sections and for heating procedures using salt baths. Corresponding guideline values for heating in air-circulating furnaces and chamber furnaces can be taken from
30、figure 4. The time-temperature austenitizing diagram shown in figure 5 illustrates, for X 38 CrMoV 5 1 hot work steel, the structural transformation occurring during heating to austenitizing temperature. Figure 5 shows that, as the heating rate increases, both austenite formation and carbide dissolu
31、tion are displaced towards more elevated temperatures. With the aid of the different heating rate curves the temperature or time required to achieve a given structure condition can be estimated. As the alloy content increases, the austenite formation and carbide dissolution are delayed and shifted t
32、owards more elevated temperatures, both these processes being also dependent on the initial condition. Complete dissolution of the carbide is not generally desirable. Austenitizing of tools should take place in salt baths, in a controlled atmosphere or inert gas or in a vacuum furnace (see subclause
33、 6.1). lustenitizing temperature or hardening First-stage heating time *) DIN 17022 Part 2 Page 3 2mperature rn Heating ti me Hold ing ti me Second-stage heating time *) Figure 1. Thermal cycle for austenitizing (schematic) Austenitizing temperature or hardening temperature 3rd preheating stage 2nd
34、preheating stage 2 3 4- n + $ Ist preheating stage Time - Figure 2. Thermal cycle for austenitizing with preheating in three stages (schematic) 20 m: .- E 10 $5 ci m C .- I. 0 10 20 30 40 50 60 70 80 90 100 mm Diameter or thickness of square or rectangular cross sections - !O Figure 3. Heating time
35、for heating in salt baths, with and without preheating (guideline values based on tests carried out on specimens made from S 6-5-2 steel) *) Translators note. As there is no English equivalent for the German terms Anwrmdauer and Durchwrmdauer, the terms used in this translation have been derived fro
36、m the definitions given in EURONORM 82 - 1983 corresponding to the German terms. 170 min 150 140 130 120 t 2 90 00 E 70 60 50 40 30 20 10 .- C - Heating rate 1300 OC 1200 1100 t lOoo p! 2 900 E 3 4- 5 c 800 7 O0 OJ 1 10 io2 io3 io4 io5 Time - 522 Cooling During cooling, as with heating, temperature
37、differences occur between the surface zone and the core of tools. With regard to the magnitude and effect of such differ- ences, similar considerations apply as in the case of heating. Therefore, in order to keep the internal stresses assmall as possible after cooling, tools that are susceptible to
38、cracking or distortion shall be cooled in stages. In this case it is necessary, from the aspect of the hardness required, to use materials possessing adequate harden- ability. Information on hardenability shall be taken from DIN 17 350 or corresponding documentation provided by the steelmakers. To e
39、nsure that the hardening is not unacceptably impaired at critical points in the surface zone, and to keep distortion and the risk of cracking as small as possible, the batch shall be so stacked and the material to be heat-treated introduced into the cooling medium so that the entire surface zone is
40、covered. In figure 6, possible cooling curves are shown sche- matically. When cooling is effected in stages, the process is inter- rupted at a temperature that lies between the pearlite and martensite stage and is preferably just above theM, temperature. This is intended to effect the maximum temper
41、ature equalization in the tool possible, thereby preventing the occurrence of stresses, or reducing any stresses present through plastic deformation. Following temperature equalization, the tools undergo further cooling in air, in oil or in salt water. To reduce the risk of cracking, tools should no
42、t be cooled to ambient temperature prior to tempering, except for those made of high speed steels (see subclauses 5.4.1 to 5.6.1 and figures 12, 13,14 and 15). Figure 5. Time-temperature austenitizing diagram for continuous heating of X 38 CrMoV 5 1 steet (material number 1.2343) (from Atlas zur Wrm
43、ebehandlung der Stahle (Steel heat treatment atlas) DIN 17022 Part 2 Page 5 1 Slow cooling / (e.g. in air) Cooling in stages (e.g. in a sait bath, “i;,;. , subsequently in air) Time - Figure 6. Cooling curves (schematic) Figure 7 gives guideline values of cooling time for tools having circular, squa
44、re or rectangular cross section when quenching in a hot bath (550C) or cooling in air to ambient temperature. The transformation processes during cooling from austenitizing temperature are illustrated, taking the X 38 CrMoV 5 1 hot work steel as an example, in figure 8 in the form of a time-temperat
45、ure-transformation (TTT) diagram for continuous cooling. The TTT diagrams show for each steel the ranges within which structural changes occur. Their position and the progress of the transformation processes are subject to the influence of the steel composition and the austenitizing conditions. From
46、 the TTT diagrams for continuous cooling it is possible, on the basis of the cooling curves, to assess the structure condition likely to be obtained at ambient temperature and the associated hardness. The aim during hardening is to effect transformation at the martensite stage, this only being possi
47、ble if the critical cooling rate, K, which is characteristic to each steel, can be achieved (see figure 8). 170 min I I I r I/ 140 )I; The transformation of austenite does not end until the so-called Mf temperature has been reached, which, for the majority of tool steels, is below ambient temperatur
48、e. M, decreases as the amounts of carbon and alloying elements dissolved in the austenite increase. The proportion of retained austenite is all the higher the larger the amount of carbon and alloying elements dissolved in the austenite; it varies with the cooling rate (see subclause 6.2). After cool
49、ing, the structure consists of martensite and retained austenite, and possibly includes bainite components. Hypereutectoid steels may also contain proeutectoidally separated carbides in addition to the undissolved carbides. 5.2.3 Deep fraezing The retained austenite present at ambient temperature may be reduced by subsequent deep freezing. In this connection, it has to be borne in mind that stabilization of the retained austenite may occur as a result of pro- longed holding at ambient temperature or tempering at low temperatures (e.g. 2OOOC) .*) For guidance on deep freezing
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