Abstract
Studies are carried out on the microstructure and micro-hardness distribution of structural steel 30HN3А samples hardened by laser quenching by means of continuous radiation from a multi-channel 48 rays CO2 laser system CLT-Yu-5. To provide the formation of a uniform structure, hardness and depth distribution in the hardened material layer a laser emitter was used with four plug-in radiating tubes arranged one into another in an octahedral configuration (patent RF № 2580350). An important role of a high uniformity of the integral heat input across the hardening zone width on the uniformity of properties of the hardened layer is demonstrated. It was found that in the hardened area a finely dispersed martensite structure was formed. The carbides contained in the initial structure of sorbite dissolve not completely during laser hardening. They are characterized by a globular form and size of 0.2...0.3 µm. The microhardness of steel in the hardened area was about 6800 MPa. The thickness variation of the hardened layer, which is characterized by the ratio between minimal, hmin, and maximal, hmax, depths, is equal to 0.76 at hmax = 1050 µm. A reduction in microhardness in a tempering zone formed between two successive hardened bands down to the values of 5500...6000 MPa was found. The width of this tempering zone is about 1.8 mm. The decrease of microhardness in this zone is due to a dissociation of the martensite and formation of tempering troostite structure. Lamellar carbides are formed during this process. Steel in the laser hardened area has a favorable structure in terms of the strength and durability. Thus, hardening of steel by means of multi-channel CO2 laser systems provides wide opportunities in improving of material properties and is recommended for hardening of expensive machine parts increasing their service lifetime.
References (8)
1. Patent RF № 2580350, 05.11.2014 (in Russian) [Патент РФ № 2580350, 05.11.2014].
2. V. I. Yugov. Fotonika (2012). 4, Р. 12 - 20. (in Russian) [В. И. Югов Фотоника. (2012). 4, C. 12 - 20.].
3. L. E. Afanasieva, I. A. Barabonova Laser and cryogenic treatment of high speed steel. Tver, TvSTU. (2014). 96 p. (in Russian) [Афанасьева Л. Е., Барабонова И. А. Лазерная и криогенная обработка быстрорежущей стали / . Тверь, ТвГТУ, 2014. 96 c.].
4. Ashby M. F., Easterling K. E. //Acta Metallurgica. (1984). V. 32 (11). P. 1935 - 1948.
5. Na S. J., Yang Y. S. //Surface and Coatings Technology. (1988). V. 34 (3) / . P. 319 - 330.
6. Qingbin L., Hong L. //Journal of materials processing technology. (1999). V. 88 (1). P. 77 - 82.
7. Komanduri R., Hou Z. B. //Int. J. of Machine Tools and Manufacture. (2004). V. 44 (9). P. 991 - 1008.
8. Arzamasov B. N., Makarova V. I., Mukhin G. G., et al. Materials Science: textbook / Moscow, Bauman MGTU. (2005). 646 pp. (in Russian) [Б. Н. Арзамасов, В. И. Макарова, Г. Г. Мухин и др. Материаловедение: учебник для вузов / М.: МГТУ им. Н. Э. Баумана, 2005. 646 с.].