共查询到20条相似文献,搜索用时 17 毫秒
1.
2.
3.
M. T. Miglin J. P. Hirth A. R. Rosenfield 《Metallurgical and Materials Transactions A》1983,14(10):2055-2061
Fracture toughness and ductile-brittle transition behavior were measured for a copper-bearing HSLA steel. The value ofK
lc for cleavage failure was independent of heat treatment, whileJ
lc for ductile failure decreased monotonically with increasing strength level. With both failure modes, fracture appears to
be controlled by cracking of sulfide inclusions. The decrease in ductile-failureJ
lc is caused by decreased work-hardening rates that suppress cleavage and facilitate void coalescence. Both higher austenitizing
temperature and quenching rate after austenitization influence the ductile/brittle transition temperature, either through
grain-size and precipitate refinement or through an increase in the resistance of the steel to shear failure.
Formerly Graduate Student, The Ohio State University 相似文献
4.
Sangho Kim Byoungchul Hwang Sunghak Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2003,34(6):1275-1281
This study is concerned with the analysis of fracture toughness in the transition region of an Mn-Mo-Ni low-alloy steel, in
accordance with the ASTM E1921 standard test method. Elastic-plastic cleavage fracture toughness (K
Jc
) was determined by three-point bend tests, using precracked Charpy V-notch (PCVN) specimens, and relationships between K
Jc
, the critical component of J (J
c
), critical distance (X
c
), stretch-zone width (SZW), local fracture stress, and plane-strain fracture toughness (K
Ic
were discussed on the basis of the cleavage fracture behavior in the transition region. The master curve and the 95 pct confidence
curves well explained the variation in the measured K
Jc
, and the Weibull slope measured on the Weibull plots was consistent with the theoretical slope of 4. Fractographic observation
indicated that X
c
linearly increased with increasing J
c
, and that the SZW had a good correlation with K
Jc
, irrespective of the test temperature. In addition, the local fracture stress was independent of the test temperature, because
the tempered bainitic steel used in this study showed a propagation-controlled cleavage fracture behavior. 相似文献
5.
Mechanism of detrimental effects of carbon content on cleavage fracture toughness of low-alloy steel
The variation in fracture toughness of low-alloy base steels and weld steels with carbon contents of 0.08 and 0.21 wt pct
was investigated using notched and precracked specimens tested at low temperatures. The attention is focused on the mechanism
associated with detrimental effects on cleavage fracture toughness resulting from increasing carbon content. Analyses reveal
that, in the case of constant ferrite grain sizes with increasing carbon content, the yield stress σ
y
increases and the local fracture stress σ
f
remains constant for notched specimens. For precracked specimens, the σ
y
increases, whereas the σ
f
decreases. In both cases, the ratio σ
f
/σ
y
decreases; this ratio is one of the principal factors inducing the deterioration in the cleavage fracture toughness of the
higher carbon steels. Analyses also reveal that the critical strain for initiating a crack nucleus, which decreases with increasing
carbon content and impurity elements, appears to be another principal factor that has a negative effect on the fracture toughness
in both notched and precracked specimens. The results of the fracture toughness measured for weld metal with various grain
sizes further support the predominant effect of grain size on the toughness of notched specimens. 相似文献
6.
7.
Tensile prestrains of various levels were applied to blank steel specimens. Four-point bend tests of notched specimens at
various temperatures revealed an appreciable drop in the notch toughness of the specimens, which experienced 3 pct tensile
prestrain. Further prestrains of up to 20 pct had a negligible effect on the notch toughness despite additional increases
in the yield strength. Microscopic analyses combined with finite element method (FEM) calculations revealed that the decrease
in toughness resulted from a change of the critical event controlling the cleavage fracture. The increase in yield strength
provided by prestraining allowed the normal tensile stress at the notch tip to exceed the local fracture stress σ
f
for propagating a just-nucleated microcrack. As a result, for the coarsegrained steel with low σ
f
tested presently, the critical event was changed from tensile stress-controlled propagation of a nucleated microcrack to
plastic strain-controlled nucleation of the microcrack at the notch tip. A reduction of toughness was induced as a result
of this. The increase in yield strength provided by decreasing the test temperature acted in the same way. 相似文献
8.
9.
10.
Sunghak Lee Byung Chun Kim Dongil Kwon 《Metallurgical and Materials Transactions A》1993,24(5):1133-1141
This study is concerned with a correlation of fracture toughness with microstructural factors in heat-affected zones (HAZs)
of a normalized high-strength low-alloy (HSLA) steel. In order to explain weld joint performance, tensile and plane strain
fracture toughness tests were conducted for the simulated coarse-grained HAZ microstructures. The micromechanisms of fracture
processes involved in void and microcrack formation are identified byin situ scanning electron microscopy (SEM) fracture observations and void initiation study. The fracture toughness results are also
interpreted using simple fracture initiation models founded on the basic assumption that a crack initiates at a certain critical
strain or stress developed over some microstructurally significant distance. The calculated KIc values are found to scale roughly with the spacing of the stringer-type martensite islands associated with voids, confirming
that martensite islands play an important role in reducing the toughness of the coarse-grained HAZs. These findings suggest
that the formation of martensite islands should be prevented by controlling the chemical compositions and by using the proper
welding conditions to enhance fracture toughness of the welded joints of the HSLA steel.
Formerly Research Assistant with the Department of Materials Science and Engineering, Pohang Institute of Science and Technology 相似文献
11.
Effect of alloying elements on the microstructure and properties of a hot-rolled low-carbon low-alloy bainitic steel 总被引:1,自引:0,他引:1
P. L. Mangonon 《Metallurgical and Materials Transactions A》1976,7(8):1389-1400
A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct
cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2
pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular
bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite.
Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation
of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained
to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than
nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The
results illustrate the short-coming of a pure statistical approach to the design of alloys. 相似文献
12.
P. L. Mangonon 《Metallurgical and Materials Transactions A》1976,7(9):1389-1400
A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct
cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2
pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular
bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite.
Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation
of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained
to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than
nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The
results illustrate the short-coming of a pure statistical approach to the design of alloys. 相似文献
13.
14.
15.
Effect of decreased hot-rolling reduction treatment on fracture toughness of low-alloy structural steels 总被引:2,自引:0,他引:2
Yoshiyuki Tomita 《Metallurgical and Materials Transactions A》1990,21(9):2555-2563
Commercial low-alloy structural steels, 0.45 pct C (AISI 1045 grade), 0.40 pct C-Cr-Mo (AISI 4140 grade), and 0.40 pct C-Ni-Cr-Mo
(AISI 4340 grade), have been studied to determine the effect of the decreased hot-rolling reduction treatment (DHRRT) from
98 to 80 pct on fracture toughness of quenched and highly tempered low-alloy structural steels. The significant conclusions
are as follows: (1) the sulfide inclusions were modified through the DHRRT from a stringer (mean aspect ratio: 16.5 to 17.6)
to an ellipse (mean aspect ratio: 3.8 to 4.5), independent of the steels studied; (2) the DHRRT significantly improvedJ
Ic
in the long-transverse and shorttransverse orientations, independent of the steels studied; and (3) the shelf energy in the
Charpy V-notch impact test is also greatly improved by the DHRRT, independent of testing orientation and steels studied; however,
(4) the ductile-to-brittle transition temperature was only slightly affected by the DHRRT. The beneficial effect on theJ
Ic
is briefly discussed in terms of a crack extension model involving the formation of voids at the inclusion sites and their
growth and eventual linking up through the rupture of the intervening ligaments by local shear. 相似文献
16.
采用FeV与VN两种钒微合金化方式,对两种实验钢板进行显微组织分析,主要讨论了含钒微合金钢的强韧性能,研究结果表明V-N微合金钢具有良好的性能,优越于V钢. 相似文献
17.
对钢结构而言,诸如海洋平台、船舶、桥梁、建筑和油气管线等,焊接后的性能直接决定了其服役寿命和安全性,重要性不言而喻.在针对焊接相关问题的研究中,焊接热影响区的韧性提升一直是重点和难点.焊接热影响区会经历高达1400℃的高温,从而形成粗大的奥氏体晶粒,如果焊接参数控制不当,不能通过后续冷却过程中的相变细化组织,就会造成韧性的降低.而多道次焊接的情况更为复杂,前一道次形成的粗晶区还会在后续焊接过程中经历二次热循环,从而形成链状M-A,造成韧性的急剧下降.本文旨在对一些现有焊接热影响区的相关研究结果进行总结,探讨母材的成分、第二相及焊接工艺等因素对热影响区微观组织和性能的影响,为低温环境服役的大型钢结构的焊接性能改善提供一些设计思路. 相似文献
18.
19.
20.
Upset testing of cylindrical specimens generates circumferential tensile stresses at the barreled surfaces. These stresses
can be utilized in the same manner as the tensile stresses in the tension test to evaluate the ductility of materials. Using
the upset test method, the anisotropy of ductile fracture in AISI 1045 hot-rolled steel plates was determined. Ductility parallel
to the plane of inclusions is found to be ≈ 50 pet higher than that perpendicular to the inclusions. It is shown that the
local surface strains at fracture in upset testing correlate well with the true zero-gage-length fracture strain in tension
testing, provided the tensile stresses in the respective tests are in the same direction relative to the inclusion orientation.
Thus, compression tests parallel to the inclusion direction, which generate tensile stresses perpendicular to the inclusions,
can be utilized to measure ductility transverse to the fiber of wrought materials. This is particularly useful in determining
the short transverse or through-thickness ductility in hot-rolled or forged materials having thin sections. 相似文献