Tecnologia em Metalurgia, Materiais e Mineração
https://tecnologiammm.com.br/article/doi/10.4322/2176-1523.20212297
Tecnologia em Metalurgia, Materiais e Mineração
Artigo Original

Análise via microscopia óptica de um aço bainítico DIN 18MnCrSiMo6-4 austenitizado e resfriado em diferentes meios

Optical microscopic analysis of a DIN 18MnCrSiMo6-4 bainitic steel austenitized and quenched with different coolants

Cristiano José Turra, Pedro José de Castro, Antonio Figueiredo Silveira, Alexandre da Silva Rocha

Downloads: 2
Views: 86

Resumo

mo Aços bainíticos de baixo carbono e baixa liga produzidos por resfriamento contínuo apresentam formidável combinação de resistência mecânica e tenacidade para uma série de aplicações. O ponto chave desta interessante combinação está relacionado à microestrutura multifásica, a qual é influenciada principalmente pela composição química e parâmetros de tratamentos térmicos ou termomecânicos. O modo e a velocidade de resfriamento são parâmetros essenciais nas transformações microestruturais, e impactam no tipo, proporção e refino da microestrutura, determinando o desempenho do material. O objetivo deste trabalho foi avaliar a influência de diferentes meios de resfriamento sobre a microestrutura do aço bainítico DIN 18MnCrSiMo6-4. Amostras do material na condição de recebimento foram submetidas à austenitização e posteriormente ao resfriamento em água e óleo (têmpera), ao ar (normalização), em forno (recozimento) e em banho aquecido (austêmpera). As amostras tratadas foram caracterizadas por microscopia óptica e medições de dureza Vickers. Os resultados mostraram que o resfriamento em forno favorece a formação de ferrita, reduzindo a dureza do material, enquanto que o resfriamento ao ar não modifica significativamente a microestrutura e dureza. Já o resfriamento em banho isotérmico produz bainita granular e bainita em ripas, aumentando ligeiramente a dureza. Os resfriamentos em água e óleo formam martensita com dureza de 436 e 424 HV, respectivamente.

Palavras-chave

Aço bainítico; Bainita; Microestrutura multifásica; Resfriamento.

Abstract

Low carbon and low alloy bainitic steels produced by continuous cooling present a formidable combination of strength and toughness for various applications. The key point of this interesting combination is related to their multiphase microstructure, which is mainly influenced by chemical composition and heat treated or thermomechanical parameters. Cooling conditions and rate are the most predominant factors when regarding microstructural transformation, and impact on the resulting phases, quantity and refinement of microstructure, determining the material performance. This work aims at evaluating the influence of different cooling media over the microstructure of DIN 18MnCrSiMo6-4 steel. Steel samples in as received condition were submitted to austenitizing and subsequently cooled in water, oil (quenching), air (normalizing), in the furnace (annealing), and in heated bath (austempering). The treated samples were analyzed by Optical Microscopy and Vickers microhardness measurements. Results showed that cooling from furnace benefits ferrite formation, reducing the material hardness, while air cooling doesn’t change the microstructure and hardness significantly. In addition, cooling in heated bath produces granular bainite and lath-like bainite, slightly hardness increasing. Water and oil cooling forms martensite with hardness 436 and 424 HV, respectively.

Keywords

Bainitic steel; Bainite; Multiphase microstructure; Cooling

Referências

1 Lan HF, Du LX, Misra RDK. Effect of microstructural constituents on strength–toughness combination in a low carbon bainitic steel. Materials Science and Engineering A. 2014;611:194-200.

2 Wang K, Tan Z, Gao G, Gao B, Gui X, Misra RDK, et al. Microstructure-property relationship in bainitic steel: the effect of austempering. Materials Science and Engineering A. 2016;675:120-127.

3 Kyung Sung H, Ho Lee D, Yong Shin S, Lee S, Yong Yoo J, Hwang B. Effect of finish cooling temperature on microstructure and mechanical properties of high-strength bainitic steels containing Cr, Mo, and B. Materials Science and Engineering A. 2015;624:14-22.

4 Liang J, Zhao Z, Tang D, Ye N, Yang S, Liu W. Improved microstructural homogeneity and mechanical property of medium manganese steel with Mn segregation banding by alternating lath matrix. Materials Science and Engineering A. 2018;711:175-181.

5 Qian L, Zhou Q, Zhang F, Meng J, Zhang M, Tian Y. Microstructure and mechanical properties of a low carbon carbide-free bainitic steel co-alloyed with Al and Si. Materials & Design. 2012;39:264-268.

6 Zhu K, Mager C, Huang M. Effect of substitution of Si by Al on the microstructure and mechanical properties of bainitic transformation-induced plasticity steels. Journal of Materials Science and Technology. 2017;33(12):1475-1486.

7 Hofer C, Bliznuk V, Verdiere A, Petrov R, Winkelhofer F, Clemens H, et al. High-resolution characterization of the martensite-austenite constituent in a carbide-free bainitic steel. Materials Characterization. 2018;144:182-190.

8 Wang JP, Yang ZG, Bai BZ, Fang HS. Grain refinement and microstructural evolution of grain boundary allotriomorphic ferrite/granula bainite steel after prior austenite deformation. Materials Science and Engineering A. 2004;369:112-118.

9 Sourmail T. Bainite and superbainite in long products and forged applications. HTM Journal of Heat Treatment and Materials. 2017;72(6):371-378.

10 Zhao MC, Yang K, Shan Y. The effects of thermo-mechanical control process on microstructures and mechanical properties of a commercial pipeline steel. Materials Science and Engineering A. 2002;335:14-20.

11 Caballero FG, Chao J, Cornide J, García-Mateo C, Santofimia MJ, Capdevila C. Toughness deterioration in advanced high strength bainitic steels. Materials Science and Engineering A. 2009;525:87-95.

12 Zhou Y, Jia T, Zhang X, Liu Z, Misra RDK. Investigation on tempering of granular bainite in an offshore platform steel. Materials Science and Engineering A. 2015;626:352-361.

13 Morales-Rivas L, Roelofs H, Hasler S, Garcia-Mateo C, Caballero FG. Detailed characterization of complex banding in air-cooled bainitic steels. Journal of Mining and Metallurgy, Section B: Metallurgy. 2015;51(1):25-32.

14 Kozeschnik E, Bhadeshia HKDH. Influence of silicon on cementite precipitation in steels. Materials Science and Technology. 2008;24(3):343-347.

15 ASM Handbook Commitee. ASM Handbook. Heat Treating. Vol. 4. 10th ed. Materials Park, Ohio: ASM International; 1991.

16 Long X, Zhang F, Yang Z, Lv B. Study on microstructures and properties of carbide-free and carbide-bearing bainitic steels. Materials Science and Engineering A. 2018;715:10-16.

17 Kong X, Qiu C. Continuous cooling bainite transformation characteristics of a low carbon microalloyed steel under the simulated welding thermal cycle process. Journal of Materials Science and Technology. 2013;29(5):446-450.

18 Garcia-Mateo C, Caballero FG, Bhadeshia HKDH. Development of hard bainite. ISIJ International. 2003;43(8):1238-1243.

19 Chang LC. Microstructures and reaction kinetics of bainite transformation in Si-rich steels. Materials Science and Engineering A. 2004;368:175-182.

20 Zhang P, Chen Y, Xiao W, Ping D, Zhao X. Twin structure of the lath martensite in low carbon steel. Progress in Natural Science: Materials International. 2016;26(2):169-172.

21 Luo Z, Shen J, Su H, Ding Y, Yang C, Zhu X. Effect of substructure on toughness of lath martensite/bainite mixed structure in low-carbon steels. Journal of Iron and Steel Research International. 2010;17(11):40-48.


Submetido em:
18/03/2020

Aceito em:
16/10/2020

611ffee1a953957b1c75c003 tmm Articles
Links & Downloads

Tecnol. Metal. Mater. Min.

Share this page
Page Sections