Effect of Niobium on the Microstructure and Mechanical Properties of Low Carbon Steel Plate with Intercritical Quenching

The microstructure and mechanical properties of the low carbon steel plates containing Niobium content of 0.038%, 0.063% and 0.082% with intercritical quenching were studied by SEM, TEM, tensile and impact tests. The results showed that the intercritical quenching steel with high Niobium content can gain the fine microstructure , but also easily obtain the martensite, which made the strength very high but low temperature toughness very low, however, the steel with low Niobium content can not reach enough austenitization level, which caused both low temperature and yield ratio high relatively. So in the given rolling and heat treatment process, there was suitable Niobium content can contribute to obtain the optimal austenization level resulting in the good combination of strength, yield ratio, elongation and low temperature toughness after intercritical quenching in the low carbon steel.

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Microstructure and Mechanical Properties of Cooled and Tempered Cu and Nb-Bearing Ultra-Low Carbon Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.3242 ◽

2010 ◽

Vol 638-642 ◽

pp. 3242-3247 ◽

Cited By ~ 1

Author(s):

Hui Guo ◽

Zhi Qiang Yao ◽

Shan Wu Yang ◽

Xin Lai He

Keyword(s):

Mechanical Properties ◽

Carbon Steel ◽

Low Carbon Steel ◽

Carbon Steels ◽

Steel Plates ◽

Low Carbon ◽

Niobium Content ◽

Low Carbon Steels ◽

Microstructure And Mechanical Properties ◽

Ultra Low Carbon Steel

To improve the toughness and weldability, the carbon content of the steels has to be deduced, and more and more attention has been attracted to the low carbon and ultra-low carbon steels. To strengthen the microstructure Cu and Nb-bearing steels are developed. However, the knowledge on influence of combined addition of Cu and Nb is still in lack. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The experimental results show that if niobium is added without copper, the increase of niobium addition does not have a significant influence on the phase transformation and mechanical properties before tempering. The strength and toughness of those copper-free niobium steels do not vary significantly after tempered at different temperatures, while the strength of niobium steels with 1.8% copper added increases after tempered in the range of 450-650°C and reaches a peak at 500-550°C. If combined with 1.8% copper, the increase of niobium addition from 0.08% to 0.16% improves the hardenabililty and strength significantly, and the strength peak after tempering moves to a lower temperature. The strength of air-cooled niobium steels with 1.8% copper added is usually higher than those water-cooled, while after tempered at a proper temperature, the strength of the latter becomes higher than the former.

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