Further study on the mechanism of the ductile-to-brittle fracture transition in C-Mn base and weld steel
- Gansu Univ. of Technology, Lanzhou, Gansu (China). Welding Research Inst.
- Xian Jiaotong Univ. (China). Mechanics Dept.
In the present study, the crack opening displacement (COD) tests of specimens of C-Mn base and weld steel were carried out in the ductile-brittle transition temperature region. The majority of the specimens were fractured and others were unloaded prior to fracture after ductile fracture initiated and extended. The cavities and cleavage microcracks located in the vicinities of tips of fibrous cracks of the unloaded specimens were observed in detail. The finite element method (FEM) calculations of the stress and strain distribution ahead of the tip of an extending fibrous crack were completed. The mechanism of the ductile-to-brittle fracture transition was further investigated. It was revealed that in the ductile-brittle transition temperature region, the ductile fracture process was independent of temperature. The ductile-to-brittle fracture transition was triggered by initiating a catastrophic extension of a cleavage crack ahead of the fibrous crack tip, which occurred in a condition satisfying a combined criterion composed of three items, i.e., {var_epsilon}{sub p} {ge} {var_epsilon}{sub pc} for initiating a crack nucleus; {sigma}{sub m}/{bar {sigma}} {ge} {Tc} for preventing the crack nucleus from blunting; and {sigma}{sub yy} {ge} {sigma}{sub f} for propagating the crack nucleus. For a specimen in which a fibrous crack occurred and propagated, the critical event for initiating a brittle cleavage fracture was the propagation of a ferrite grain-sized crack into neighboring grains. With extension of a fibrous crack, the behavior of the ductile-to-brittle fracture transition could be analyzed by the effect of the size of an active zone on the initiation of the brittle cleavage fracture.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 540995
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 8 Vol. 28; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Fracture process of a low carbon low alloy steel relevant to Charpy toughness at ductile-brittle fracture transition region
Further study on the mechanism of cleavage fracture at low temperatures