Author details

mechanism for dislocation to pass through carbides. On the other hand, in steels B and C, the measured ΔHv values were far from the calculated data. This could be because of the misfit dislocations that were produced around the carbides to reduce the misfit strain between carbides and matrix, since the misfit parameter (ε) of NbC and TiC is very large. Hence, precipitation hardening in steels B and C would not be understood simply by the cutting mechanism only presumably because of the loss of coherency between the coarsen carbides and matrix. Reduction of ΔHv, therefore, took place because of a loss of coherency at the carbide/matrix interface [15]. Loss of coherency at the interface is well known to appear by coarsening [24, 25] and large lattice misfit strain [26]. Hence, complicated dislocation-bypass mechanisms could be activated depending on the size of precipitates in

Figure 6. Relationship between the measured precipitation hardening (ΔHv) and estimated parameter G|ε|1.5 (fr/b)0.5 using experimental data of the present steels, which are exhibited by symbols. For comparison, the relationship derived

The precipitation hardening due to complex carbides in medium carbon bainitic steels was

1. Small amount of additional elements can cause drastic change in the structures and chemical compositions of nanocarbides dispersed in steels, which induce conversion in

dislocation bypass mechanisms to improve mechanical properties.

steels B and C.

34 New Uses of Micro and Nanomaterials

5. Conclusions

investigated. The yielded results are as follows:

from Eq. (9) is also shown by dotted lines with k constants of 1 and 3.

Makoto Okonogi<sup>1</sup> , Takuya Hara<sup>2</sup> and Hiromi Miura3 \*

\*Address all correspondence to: miura@me.tut.ac.jp

1 Kimitsu R&D Lab., Nippon Steel and Sumitomo Metal Corporation, Kimitsu, Chiba, Japan

2 Pipe and Tube Research Lab., Steel Research Laboratories, Nippon Steel and Sumitomo Metal Corporation, Amagasaki, Hyogo, Japan

3 Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan
