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International Journal of Metallurgical & Materials Science and Engineering (IJMMSE) ISSN Vol. 3, Issue 2, Jun 2013, TJPRC Pvt. Ltd. EFFECTS OF CRYOGENIC TREATMENT ON H13 TOOL STEEL AN EXPERIMENTAL
International Journal of Metallurgical & Materials Science and Engineering (IJMMSE) ISSN Vol. 3, Issue 2, Jun 2013, TJPRC Pvt. Ltd. EFFECTS OF CRYOGENIC TREATMENT ON H13 TOOL STEEL AN EXPERIMENTAL INVESTIGATION P SEKHAR BABU Professor, Department of Mechanical Engineering, Vijaya Krishna Institute of Technology & Sciences, Andhra Pradesh, India ABSTRACT Cryogenic treatment is the supplementary process to conventional heat treatment process in steels, by deep freezing materials at cryogenic temperatures to enhance the mechanical and physical properties of materials being treated. Cryogenic treatment of materials has shown significant improvement in their properties like increase in hardness, increase in wear resistance, reduced residual stresses, fatigue Resistance, increased dimensional stability, increased thermal conductivity, toughness, by transformation of retained austenite to martensite. KEYWORDS: Tool Steel, Heat Treatment, Wear Resistance, Cryogenic Treatment INTRODUCTION Cryogenic process is one of the most exciting fields in material science today. Longevity of tools and equipment are important factors in any Industry in the manufacturing process and the product itself. Since the inception of the machine tool industry, cutting tool life and tool wear remain a subject of deep interest to study its failure and improvement. One of the new methods to enhance the characteristics of tool and equipment are to treat at cryogenic temperature known as cryogenic treatment. Cryogenic treated tools are the latest in machine/cutting tool treatment technology. The effects of low temperatures in retained austenite, increases hardness and toughness which leads to increase product life more economical than any of the surface treatments (Bowers R.G, 1974). Cryogenic treatment refers to the post-heat treatment process, where the mass of products to be treated are slowly cooled to very low temperatures, usually the liquid nitrogen temperature, held at that temperature for a specific period of time and warmed back to room temperature at a specific rate (A Bensely, A Prabhakaran, D Mohan Lal and G Nagarajan, 2005). The mechanism for the improvement was attributed to transformation of retained austenite (Moore K, Collins DN,1993), formation of fine carbides (R. F. Barron,1982) and also depends on long soaking period(d. Mohanlal, S. Renganarayanan and A. Kalanidhi 2001). The transformation of retained austenite to martensite is not the only reason for prolonging tool life but the precipitation of small finely dispersed carbides in the martensite is one among the main reasons (Vaccari JA,1986) The material selected for the present study is chromium hot work steel (AISI H13), H13 Tool Steel is a versatile chromium-molybdenum hot work steel that is widely used in hot work and cold work tooling applications. The hot hardness (hot strength) of H13 resists thermal fatigue cracking which occurs as a result of cyclic heating and cooling cycles in hot work tooling applications. Because of its excellent combination of high toughness and resistance to thermal fatigue cracking (also known as heat checking) H13 is used for more hot work tooling applications than any other tool steel. 54 P Sekhar Babu Because of its high toughness and very good stability in heat treatment, H13 is also used in a variety of cold work tooling applications. In these applications, H13 provides better hardenability (through hardening in large section thicknesses) and better wear resistance than common alloy steels such as The composition of H13 steel is given in Table-1. H13 steel is generally used for making aluminum extrusion dies, bolt dies, bulldozer dies, die casting dies, forging dies, forming punches, heavy duty compression tools, hot forging tools with deep recesses, hot piercing punches and components that require high toughness and excellent polishability. METHOD Steps Involved in Experimentation of Cryogenic Processing of Metals Specimen preparation. Heat treatment of specimens. Cryogenic Treatment of the specimens at different temperatures. Wear resistance testing of the specimens. Standard bar stock available in the market is procured and specimens of about 5 mm diameter and length 50mm are prepared. The picture of the specimens is presented as picture 1 in the appendix. All the specimens are subjected to heat treatment as per the standards prescribed by ASM standards. The details of the pre heat temperature, hardening temperature, quenching medium and tempering temperatures of the selected materials are presented in the table 2. After heat treatment, the specimens are divided into five groups. The first set of the specimens is kept aside for wear resistance comparison as a standard to compare with the wear resistance of the specimens subjected to different temperature treatments. Second set of the specimens is subjected to C treatment, third set of the specimens is subjected to C treatment, fourth set of the specimens is subjected to C treatment and the fifth set of the specimens is subjected to C treatment respectively. All the sets of specimens are tempered again after treatment. During cryogenic treatment the specimens are cooled with a slow cooling rate of 1 K per min. Once the aimed temperature is reached the specimens are soaked for 24 hours at the same temperature and then warmed back to the room temperature slowly. RESULTS In the present study abrasive wear of three selected materials is studied using Pin-on-disk test and the results are quantified for improvement in wear resistance among conventional heat treated specimen and cryogenically treated specimens at different temperature treatments. Pin-on-disk tests were conducted using approximately 5.00 mm diameter metal sample pins, at three different speeds of 130rpm, 200rpm and 280rpm, at three different loads of 20N, 30N and 50N and for three different periods of abrasion of 5min, 10min and 15min.It is observed that the wear resistance of H13 material also is improved progressively for every stage of cryogenic treatment. The improvement is progressively higher for treatment temperatures 40 0 C, C, C and C compared to normal heat treatment for operating speeds of 130rpm and 200rpm. The difference of improvement obtained between C and C treatment is very less while operating at 280rpm. In some occasions no further improvement is obtained. CONCLUSIONS The difference of improvement obtained for H13 material between C and C treatment is very less, the Effects of Cryogenic Treatment on H13 Tool Steel An Experimental Investigation 55 improvement is maximum at C itself. Further lowering the temperature did not show any improvement in wear resistance. Therefore it maybe concluded that the deep cryogenic treatment improves the wear resistance of many materials. But for materials like H13 while working at higher speeds treatment at C would be sufficient. Treating to further lower temperature may not be justified because of the very small or no percentage improvement. REFERENCES 1. Bowers R.G., Theory and Practice of Sub-Zero Treatment of Metals, Heat treatment of Metals, Vol. 1, No. 1, (1974) 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 R. F. Barron, Cryotreatment of metals to Improve Wear resistance, Cryogenics, Vol. 22, Issue No. 5, (1982) pp D. Mohanlal, S. Renganarayanan, A. Kalanidhi, Cryogenic treatment to augment wear resistance of tool and die steels, Cryogenics, 41, (2001) pp Vaccari JA, Deep freeze improves products, American machinist Automated Manufacturers,Vol. 130, Issue No. 3, March (1986) pp (Also published in M. M. Schwartz (ed) Machining source Book, ASM International, 1988) 6. ASM, Tool steels Properties and selection metals hand book, Vol.3,(1990), pp ASM, Principles and practices for iron and steel, heat treaters guide, 2 nd edition(1995) 8. ASTM, Standard test methods for wear test with a Pin-on-disk apparatus, G99-95 Vol , (1996) pp Randall F Barron - Cryogenic Systems 2 nd edition, Oxford University Press, New York (1985) 10. Avener SH. Introduction to Physical metallurgy, Newyork, McGraw-Hill, (1982) 11. Moore K, Collins DN, Cryogenic treatment of three heat treated tool steels, Key Engineering Materials, Vol. 86 & 87; (1993) pp APPENDICES Table 1: Composition of Tool Steel (H 13) Selected for Study S.No. Material C % Mn % Si % Ni % Mo % Cr % V % 1 H Material Table 2: Heat Treatment Temperatures Pre Heat Temperature, 0 C Hardening Temperature, 0 C Quenching Medium Tempering Temperature, 0 C H Air 56 P Sekhar Babu Table 3: Wear Resistance Analysis of H13 at 130 rpm 5min 10min 15min AVG C C C C Figure 1: Wear Resistance of H13 at 130rpm Table 4: Wear Resistance Analysis of H13 at 200 rpm 5min 10min 15min AVG C C C C Figure 2: Wear Resistance of H13 at all Loads, 200rpm Table 5: Wear Resistance Analysis of H13 at 280 rpm 5min 10min 15min AVG C C C C Effects of Cryogenic Treatment on H13 Tool Steel An Experimental Investigation 57 Figure 3: Wear Resistance of H13 at all Loads, 280rpm Picture 1: Specimens of H13 Material
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