 Reduction and Elimination of Quench Distortion by CRB method
A new practical method and its explanations about quench distortion and its prevention were reported in this paper. A curve which relates hardness and cooling rate (HCRC) was derived from the end quench (Jominy test ) curve. The HCRC was divided into four parts£ºI rapid cooling rate zone, ¢òadequate cooling rate zone, ¢ó insufficient cooling rate zone, ¢ô too slow cooling rate zone, which characterize the different quench effect. A cooling rate band (CRB) of the distortion participating region (DPR) in the workpiece was defined by hardness measurement. And the location of the CRB relative to that of the HCRC of different parts was determined according to the quench distortion and the measured hardness of the workpiece. Quench distortion can be reduced only if the location of CRB of the workpiece is controlled totally within the range of the cooling rate zone ¢ò. The role and effect of the heat treating technological parameters, chemical compositions of the steels, other conventional methods and measures to reduce quench distortion by adjustment of the position of CRB related to the HCRC were discussed. How to select and utilize these factors to make the CRB totally within the cooling rate zone II so as to solve the quench distortion problems were illustrated. More details
Selection of Quench Media Based on Their Cooling Characteristics
Based on the cooling characteristics of quench media, principles for selection of quench media to meet the quality requirements for the heat treated components were discussed in this paper. An area enclosed between the minimum and the maximum cooling rate distribution curves was introduced as the criterion for selection of suitable quench media. This criterion is in agree with the CRB idea illustrated in the previous paper. All the principles suggested in the paper were exercised and exemplified by case analyses which occurred in heat treating workshops in China. How to select a quench medium which can be used in common for a variety of workpieces was also discussed. More details
Investigation on Two Main Shortcomings of Tap Water as a Quenching Medium
Based on the facts that workpieces are prone to quenching crack and spotty hardness and large distortion when quenched in tap water, two shortcomings are attributed to tap water: 1. the cooling rate is too fast in low temperature range, 2. the cooling characteristics is too sensitive to the variation of water temperature. The causes for the inhomogeneity in hardness and distortion originated from the second shortcoming of tap water were analyzed. By comparison with gaseous quenchant medium, it is pointed out that there are two shortcomings shared in common by all liquid quenching media: 1. the adjustable range of cooling rate for any given liquid quenching medium is so limited that ordinary quenching oil, modest rate quenching oil and rapid rate quenching oil must be provided in one workshop. 2. Larger quenching distortion may result from abrupt increase in cooling rate when the workpiece experiences the transformation from the vapor blanket cooling stage to the blanket transport cooling stage. Seven kinds of technical measures to overcome the defects derived from the second shortcoming of liquid quenchant were suggested. More details
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