1、GM DAEWOO Auto & Technology EDS Engineering, GM DAEWOO Auto & Technology Standards METHODSOFDECARBURIZEDDEPTHMEASUREMENTFORSTEEL EDS-T-7109 ISSUED DATE: 1990. 11. 13 REVISED DATE: 2006. 06. 19 VERSION: 3 EDS-T-7109METHODSOFDECARBURIZEDDEPTHMEASUREMENTFORSTEEL PAGE: 1/3 ISSUED DATE: 1990. 11. 13 REVI
2、SED DATE: 2006. 06. 19 VERSION: 3 GM DAEWOO Auto & Technology 1. PURPOSE This standard aims at evaluating the product quality by measuring decarburized depth which affects severely mechanical properties of steels, especially fatigue strength. 2. SCOPE This standard specifies the method of decarburiz
3、ed depth measurement for steel. 3. DEFINITIONS 3.1. Decarburized layer The surface layer of steel where the carbon content is reduced by hot working or heat treating. 3.2. Total decarburized depth Distance from the surface of the decarburized layer to the position where the difference in chemical or
4、 physical properties between the decarburized layer and the core material is no longer determinable. Remark: Chemical properties shall be determined by the microscopic structure and physical properties from the hardness. 3.3. Ferrite decarburized depth Distance from the surface of steel to the posit
5、ion where is exclusively made of ferrite formed by decarburization. 3.4. Decarburized depth specified by residual carbon ratio Distance from the surface to the position where the residual carbon ratio, i.e. the residual carbon content per carbon content of the core material, has a specified value. 3
6、.5. Practical decarburized depth Distance from the surface to the position where practically permissible hardness has been obtained. 4. CLASSIFICATION OF MEASURING METHODS 4.1. Measuring method by microscope Method of measuring decarburized depth by microscope on the section of the test piece after
7、etched. This method shall, in general, be applicable mainly for as cast, as forged, or as rolled, normalized or annealed state. 4.2. Measuring method by hardness test This method shall be applicable mainly for as quenched and quenched-tempered state. Method of measuring the decarburized depth by the
8、 hardness test along the cross sectional plane of the test piece. EDS-T-7109METHODSOFDECARBURIZEDDEPTHMEASUREMENTFORSTEEL PAGE: 2/3 ISSUED DATE: 1990. 11. 13 REVISED DATE: 2006. 06. 19 VERSION: 3 GM DAEWOO Auto & Technology 5. MEASURING METHOD BY MICROSCOPE 5.1. Test piece shall be cut at right angl
9、e to the surface and the plane shall be finished by polishing for testing. Care shall be taken in cutting and polishing that these processes may not blunt the edges of the test plane. 5.2. After etching the test plane by an appropriate method for the specific steel, the decarburized depth shall be d
10、etermined under the microscope through the measurement of the decarburized state which shall be decided from the area ratio of ferrite, pearlite or carbide. 5.3. The magnification of the microscope shall range from 100 to 500 and the decarburized depth shall be measured by employing an eye-piece wit
11、h a scale attached. 6. MEASURING METHOD BY HARDNESS TEST 6.1. The test piece shall be cut at right angle to the surface and the plane shall be finished by polishing for testing. Care shall be taken in cutting and polishing that these processes may not affect the hardness and not blunt the edges of t
12、he surface to be tested. 6.2. For the determination of the total decarburized depth, Vickers hardness test shall be applied to the test plane to measure the hardness along the plane from the surface to the point where the hardness approaches the value at the core material. In this case, it is prefer
13、able to draw the hardness transition curve. For hypereutectoid steel, the method specified in paragraph 5 shall be applied. 6.3. For the determination of the practical decarburized depth, measure the distance from the surface to the position where the specified hardness is measured. 6.4. Unless spec
14、ified otherwise, in measuring decarburized depth by hardness test, sampling and measuring shall follow the instructions in drawings. For coil springs and leaf springs, test shall be conducted as follows: 6.4.1. Sampling : coil spring and leaf spring Take samples along either transverse or longitudin
15、al direction. (1) Coil spring : Get the mean of four measurements at right angle at points with severe decarburization. Decarburized depth = (A + B + C + D) / 4 (2) Leaf spring : Take samples at the center of either transverse or longitudinal direction. Observation shall be possible for at least 20m
16、m portion along the length at each section. Note. TRANS:X, LONGI:Y EDS-T-7109METHODSOFDECARBURIZEDDEPTHMEASUREMENTFORSTEEL PAGE: 3/3 ISSUED DATE: 1990. 11. 13 REVISED DATE: 2006. 06. 19 VERSION: 3 GM DAEWOO Auto & Technology (COIL SPRING) (LEAF SPRING) Figure 1. Collecting method of coil spring & le
17、af spring test piece 7. INDICATION 7.1. The decarburized depth shall be expressed in mm, down to second decimal point for the microscopic observation, and down to first decimal point for the hardness test. 7.2. The symbols for the indication of decarburized depth shall be as shown in the following T
18、able 1 Table 1. Indication Symbols of Decarburized Depth Measuring method Decarburized depth Measuring method by microscope Measuring method by hardness test Total decarburized depth Ferrite decarburized depth Decarburized depth specified by residual carbon ratio Practical decarburized depth DM-T DM
19、-F DM-S - DH-T - - DH-P Ex) 1. DM-T 0.28 means that the total decarburized depth is 0.28 mm measured by microscope. 2. DH (0.3)-T 0.2 means that the total decarburized depth is 0.2 mm measured by Vickers Hardness Test using Vickers Hardness Testing Machine with a load of 0.3 kgf 2.9N. 3. DM-F 0.05 m
20、eans that the ferrite decarburized depth is 0.05 mm measured by microscope. 4. DM-S (70) 0.10 means that the decarburized depth specified as residual carbon ratio 70% is 0.10 mm measured by microscope. 5. DM-F 0.05-S (50) 0.15-T 0.28 means that the ferrite decarburized depth is 0.05 mm, specified de
21、pth of 50% residual carbon ratio is 0.15 mm, and the total depth is 0.28 mm measured by microscope. 6. DH (0.3)-P (450) 0.2 means that the practical decarburized depth of Hv 450 is 0.2 mm measured by Vickers Hardness Test using Vickers Hardness Testing Machine with a load of 0.3 kgf 2.9N . 7. DHC-P (0.2) 45 means that HRC45 was obtained at specified depth 0.2 mm, measured on C scale using the Rockwell Hardness Testing Machine.8. RELATED STANDARDS KS D 0216 Methods of measuring decarburized depth for steel
