A STUDY CRYOGENIC TREATMENT OF TOOL STEELS TO IMPROVE WEAR RESISTANCE

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1 International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN Vol. 3, Issue 2, Jun 2013, TJPRC Pvt. Ltd. A STUDY CRYOGENIC TREATMENT OF TOOL STEELS TO IMPROVE WEAR RESISTANCE P. SEKHAR BABU Professor, Vijaya Krishna Institute of Technology & Sciences, Palamakula(V), Shamshabad(M), Andhra Pradesh, India ABSTRACT In this work we studied the improvement in wear resistance of some tool and die steels by Cryogenic Treatment. Five different materials are tested for improvement in abrasive wear resistance by treating cryogenically at different temperatures below 0 0 C. All the samples are first heat treated as per standard norms and re tempered after Cryogenic treatment. The samples are treated at 0 0 C, C, C, C and at C. It is observed that the wear resistance has been improved for all the samples from 300% to 700% depending on the material. KEYWORDS: NASA, Cryogenic Treatment, ASM Standards, ASTM INTRODUCTION NASA engineers are the first to notice the effects of cold temperatures on materials. They noticed that many of the metal parts in the aircraft that had returned from the cold vacuum of space came back stronger than they were before flight. Since then sub zero treatment (-80 0 C) has been used for many years, but with inconsistencies in their results. Many of the inconsistencies had been reduced by longer soaking periods and with deep cryogenic treatment ( C). Tool steels are high quality steels made to close compositional and physical tolerances. They are used to make tools for cutting, forming or shaping a material into a part or component adapted for a specific use. In Service most tool steels are subjected to extremely high loads that are applied rapidly. They must withstand these loads a great number of times with out breaking and without undergoing excessive wear or deformation. The performance of a tool in service depends on 1,2 Proper tool design Accuracy with which the tool is made Selection of proper tool steel Application of proper heat treatment A tool can perform successfully in service only when all four of these requirements have been full filled. All tool steels must be heat treated to develop specific combinations of wear resistance, resistance to deformation or breaking under high loads and resistance to softening at elevated temperatures. For a given tool steel at a given hardness, wear resistance may vary widely depending on the wear mechanism involved and the heat treatment used. It is important to note also that among tool steels with widely differing compositions but identical hardness, wear resistance may vary widely under identical wear conditions. In the heat treatment of tool steels the problem of retained austenite after heat treatment has prevailed since the development of tool steels. The retained austenite is soft and unstable at lower temperatures that it is likely to transform into martensite. It should be noted that freshly formed martensite is brittle and only tempered martensite is acceptable. The

2 132 P. Sekhar Babu transformation of austenite in to martensite yields 4% volume expansion causing distortion, which cannot be ignored 3. Therefore the retained austenite should be transformed to the maximum possible extent before any component or tool is put into service. Treating the material after heat treatment at sub zero or cryogenic temperatures transforms the retained austenite into martensite. Meng and etal 4 proposed that greater wear resistance can be obtained with longer soaking periods (~24hour) because of the formation of Eta carbides which improves the wear resistance to the maximum possible extent. Notations M1 H13 EN19 - Molybdenum high speed steel - Chromium/molybdenum hot die steel - Chromium molybdenum (constructional) steel Standard steel o C In Wt - Degree Centigrade - Initial Weight in grams Fn Wt - Final weight in grams HT - Heat Treatment % WT Lost - Percent weight lost Deg. - Degree MATERIALS USED IN THIS STUDY The materials tested for the present study is listed in table: 1. Three tool steels and two other steels are selected. The chemical composition of these materials is given in table: 2 One High Speed steel (M1) which is used for Lathe tools, milling cutters, cutter blades, boring tools, twist drills, metal cutting saws etc, One constructional steel (EN19) used for axle shafts, gears, connecting rods, studs, bolts and propeller shaft joint etc, One high carbon high chromium steel (D3) used for thread rolling dies, hobs, cold extrusion tools, reaming tools and blanking etc. One chromium hot work steel (H13) used for making cutters and one standard steel (52100) is selected to observe the improvements in various materials. EXPERIMENTATION Standard bar stock of 8-12mm diameter available in the market was procured and samples of 50mm length were made (the samples made are shown in figure: 2). The samples are heat treated separately as per the prescribed ASM standards. All the samples are divided in to six groups. First group of the samples are kept aside after heat treatment and tempering to help as a reference for measuring the improvements in wear resistance at different temperature treatments. Second group of the samples are cooled down to 0 0 C slowly at a rate of 0.9 K/min. Third group of the samples are cooled to C, Fourth group of the samples are cooled down to C, Fifth group of the samples are cooled down to C and the sixth group of the samples are cooled down to C. All the samples are soaked at the respective temperatures for 24 hours and slowly warmed back to the room temperature and retempered. The wear test apparatus is shown in schematically in Figure 3. Each sample is abraded for 3 min against a fine grinding wheel of outer diameter 200mm,

3 A Study Cryogenic Treatment of Tool Steels to Improve Wear Resistance 133 running at 288 rpm under a load of 20N. The sample is weighed before and after every abrasion period. The analyses are presented in table 3-7, the results summery is plotted in Figure 1. RESULTS It is observed that the wear resistance of the materials tested is improved with redduction in temperature. The improvement shown has steady growth upto C, but the improvement is substantial for specimens treated at C Table 1: Materials Selected S.No AISI # Description of the Material 1 M1 Molybdenum high speed steel 2 H13 Chromium/molybdenum hot die steel 3 D3 High carbon high chromium die steel 4 EN19 Chromium molybdenum (constructional) steel Standard steel Table 2: Composition AISI C Mn Si Cr V Mo W M H D EN Table 3: M1 Samples Analysis HT C C C C C Table 4: D3 Samples Analysis HT C C C C C Table 5: H13 Samples Analysis HT C C C C C

4 134 P. Sekhar Babu Table 6: EN19 Samples Analysis HT C C C C C Table 7: Samples Analysis HT C C C C C Figure 1: Graphical Representation of Wear Resistance Analysis Figure 2: Samples after Heat Treatment

5 A Study Cryogenic Treatment of Tool Steels to Improve Wear Resistance 135 Figure 3: Abrasive Wear Test Apparatus REFERENCES 1. ASTM Volume 3, page no ASM handbook volume 4 page no Cryogenic treatment to augment wear resistance of tool and die steels D.Mohan Lal, S. Ranganarayan, A. Kalanidhi, Cryogenics International Journal Volume 41(2001) pp Meng, Fanger, etal, Role f Eta-carbide precipitations in the wear resistance Improvement of Fe-12Cr-MoV-1.4C tool steels by cryogenic treatment ISIJ international, Volume 34(1994) No.20, pp R. F. Barron, Cryotreatment to Improve Wear resistance, Cryogenics, Vol. 22, Issue No. 5, (1982) pp A Bensely, A Prabhakaran, D Mohan Lal and G Nagarajan, Enhancing the wear resistance of case carburized steel (En 353) by cryogenic treatment. Cryogenics International Journal Volume 45, Issue 12, December 2005, pp

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