In the study of oxy-acetylene gas cutting of low alloy high strength steel, the relation between crack sensitivity of heat affected zone and following subjects are researched applying bending tests. ...Gas cutting speed Pre-heating temperature Post-heating temperature Hardness of mother steel Condition of cutting surface Composition of steel etc. Experiments are made in this study, in order to know the metallergical nature of heat affected zone and its effect for weldability of mother steel. Following results are shown by these experiments. 1. Increase of bending angle in bending test and decrease of maximum hardness at heat affected zone show that 100°C pre-heating gives remarkable effect to improve the crack sensitivity of steel. 2. 200°C or over 400°C post-heating gives effect for the decreasing of crack sensitivity value, through 100°C pre-heating gives better effect. 300°C post-heating which belongs to the range of temper brittleness should be avoidable. 3. Less cutting speed gives better bending effect generally. 4. Less hardness by high tempering temperature gives better bending effect to mother steel, just same as the effect of post-heating temperature. 300°C tempering gives less bending effect. 5. Removing of cutting carf makes bending effect a little better, despite removing of heat affected zone gives remarkable effect. 6. Value of bending test of rolled steel is far higher than cast steel. 7. X-ray spectrochemical analysis and michro-structure proof the increase of Ni, Cu, Mo content and the decrease of C, Cr, Mn content on the gas cutting surface. 8. It is suposed that the cementite zone and the high carboned zone inside made by carbon defusion out of mother steel. 9. It became clear that the application of suitable gas cutting is quite effective for the welding edge of low alloy high strength steel.
Past experimental report shows that Slit Test, C.T.S. Test, Maximum Hardness Test of Weld Heat-Affected Zone, Single Bead Bending Test, V-Notched Charpy Impact Test are available to infer the weld ...crack sensitivity of low alloy high strength steel, except C.T.S. Test. In order to determine the weldability on this report, above four testing methods are applied for 25 mm thick Ni-Cr-Mo low alloy high strength steel plates which have different hardness with dissimilar heat treat conditions. Following results is given about low alloy high strength steel by this comparative weldability test. (1) Cast steel plate shows far inferrior weld crack sensitivity than rolled steel plate. (2) Original hardness of base steel shows almost no effect for the crack sensitivity of weld heataffected zone. (3) Slit Test shows excellent effect as the way to determine the weld crack sensitivity. (4) Maximum Hardness Test of Weld Heat-Affected Zone is effective to infer the weld crack sensitivity to certain extent.
Following five Testing Methods which were slected out of about twently Weldability Tests being made during past several years, are utilized for Low Alloy High Strength Ni-Cr-Mo Steel on this Study. ...Slit Typie Crack Senstivity Test. C.T.S. Crack Sensitivity Test. Maximum Hardness Test of Heat Affected Zone. Single-Bead Bending Test. V-Notch Charpy impact Test. Utilized Rolled Steel Plates which have 10, 16 and 37 mm thickness respectively and 50 mm Casted Steel Plates were given by ten Japanese steel manufacturers. The nature of Coated Electrode NCM-T was reported in the Report (I) and the Report (II) already. The Result on this Study is suinmerized as follows. (1) Slit Type Test is quite Effective to resurch the Crack Sensitivity of Low Alloy High Strength Steel. (2) Serious relation is seen between Crack Sensitivity Ratio in Slit Type Test and Maximum Hardnes in the heat affected zone. (3) Certain relation is seen between V-Notch Charpy Value and Crack Sensitivity Ratio in Slit Type Test. (4) Crack Sensitivity Ratio in Single-Bead Bending Test or Slit Type Test has certain relation with the Maximum Hardness in the heat effected zone. (5) C.T.S. Test can be effective for the Crack Sensitivity Test in the case of austenitic welding of Low Alloy High Strength Steel.
We have compared with welding workability, mechanical properties and crack sencitivity of deposited metals, for trial production and market austenitic electrodes. The results are as follows : 1. ...Titania type coated austenitic electrodes has good welding workability compared with lime type. 2. Low ratio of silicon content to manganese content, low ratio of sulphur content to manganese content and low phosphorous content in deposited metals is desirable to prevent the weld metal hot cracking. 3. Trial production fully austenitic Ni-Cr-Mn (12-20-8) electrode has good welding workability, mechanical properties and crack free welds. 4. Trial production austenitic. Mn-Cr-Ni (17-17-5) electrode has good weldability too. 5. Tezuka type slit test has excellent characters for the crack test of welding electrodes.
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