Effect of Intercritical Quenching on Microstructure and Mechanical Properties of Ultra Low Carbon Heavy Steel Plate

2010 ◽  
Vol 152-153 ◽  
pp. 1371-1376
Author(s):  
De Hui Zou ◽  
Zhi Fang Peng ◽  
Ping He Li ◽  
Ai Min Guo
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
Ambient Temperature ◽  
Steel Plate ◽  
Cold Water ◽  
Annealing Treatment ◽  
Low Carbon ◽  
Comprehensive Properties ◽  
Microstructure And Mechanical Properties ◽  
Low Temperature Toughness

The Effect of intercritical quencing on microstructure and mechanical properties of ultra low carbon heavy steel plate were studied by utilizing SEM, TEM, tensile and impact tests. The specimens were firstly subjected to an annealing treatment at 930 oC followed by quenching to ambient temperature, then were repeatedly annealing at the temperatures being varied in the range of 600~870 oC, and then repeatedly quenched to ambient temperature in cold water. When the intercritical quenching was just slightly above Ac1, the strength and low temperature toughness were remarkably deteriorated attributing to the massive grain and some twins in the bainite islands. However, the more when the annealing temperature increased higher than Ac1 but still below Ac3, the more regions can be austenized, which cause the average of carbon content in the austenized regions to be relatively low. So it was difficult that these austenite regions changed into twin martensites after interctitical quenched. Then the comprehensive properties including low temperature toughness became good again.

Effect of Tempering on Microstructure and Mechanical Properties of Ultra Low Carbon Heavy Steel Plate with Intercritical Quenching

2010 ◽  
Vol 152-153 ◽  
pp. 1276-1283 ◽  
Author(s):  
De Hui Zou ◽  
Zhi Fang Peng ◽  
Ruo Min Wang ◽  
Shan Wang
Keyword(s):  
Mechanical Properties ◽  
Steel Plate ◽  
Secondary Phase ◽  
Slight Variation ◽  
Low Carbon ◽  
Tempering Temperature ◽  
Microstructure And Mechanical Properties ◽  
The Matrix ◽  
Mixed Fracture ◽  
Low Temperature Toughness

The Effect of tempering on microstructure and mechanical properties of ultra low carbon heavy steel plate with intercritical quenching were studied by utilizing SEM, TEM, tensile and impact tests. Mobile dislocations decreased, plenty of carbides and secondary phase particles precipitated dispersedly in the matrix, and then some dislocations were pinned by these precipitations, which made the YS increase when tempered from 180 to 450 oC. However, the bainite islands, formed after intercritically quenched, were still existed, the boundaries of which were clear but just laths broadening in the interior, so the UTS had a slight variation. With increasing tempering temperature from 450 to 630 oC, carbides became coarse, the bainite islands were gradually polygonized, even the boundary of which became fuzzy, dislocations transferred and formed the cellular sub-grain, which caused synthetically both YS and UTS decreasing evidently, the low temperature toughness gradually increasing, and the mixed fracture of impact specimens converting into ductile fracture.

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

2010 ◽  
Vol 152-153 ◽  
pp. 1382-1386
Author(s):  
De Hui Zou ◽  
Zhi Fang Peng ◽  
Ping He Li ◽  
Ai Min Guo
Keyword(s):  
Mechanical Properties ◽  
Carbon Steel ◽  
Low Temperature ◽  
Low Carbon Steel ◽  
Yield Ratio ◽  
Steel Plates ◽  
Low Carbon ◽  
Niobium Content ◽  
Microstructure And Mechanical Properties ◽  
Low Temperature Toughness

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.

Mechanical Properties and Bending Behaviors of Low Temperature Toughness Linepipe Steels

2007 ◽  
Author(s):  
Seong Soo Ahn ◽  
Woo Yeon Cho ◽  
Tae-Yang Yoon ◽  
Jang-Yong Yoo
Keyword(s):  
Mechanical Properties ◽  
Transition Temperature ◽  
Low Temperature ◽  
Axial Compression ◽  
Large Scale ◽  
Steel Plate ◽  
Compressive Strain ◽  
Compression Force ◽  
X80 Steel ◽  
Low Temperature Toughness

API-X70 and X80 steel with good low temperature toughness were developed. The microstructure and mechanical properties of API-X70 steel plate and pipe were investigated and the buckling behavior of X80 steel pipe was evaluated through large scale deformation tester. API-X70 steels with 30 mm thickness were manufactured by finished rolling below Ar3. The microstructure was composed of polygonal ferrite with subgrain network, degenerated pearlite and bainite. The yield strengths of API-X70 pipes were lower than those of plates, while the tensile strengths were similar in both states. The Charpy upper shelf energy of API-X70 steel plate was about 350 J and the energy transition temperature was below −100 °C. The separations were observed on the DWTT fracture surface of API-X70 steel plate. The DWTT 85 SA% transition temperature of plate was below −30 °C. It was conjectured that the separation associated with the low temperature rolling might increase the strength without deterioration of DWTT properties. API-X80 steels with 19mm thickness were fabricated with finished rolling above Ar3 and pipes with 30” diameter were made with R/B process. The deformation capacity of X80 linepipe was evaluated by large scale deforming machine operating under the loading of bending and axial compression force. It was showed that 2nd moment term should be calculated more correctly to measure the accurate critical compressive strain of pipe in the loading of bending and axial compression force. The compressive axial force had a little effect on the peak moment but changed the deformation pattern and state of critical compressive strain of linepipe. It was found that X80 linepipe used in this study was within the specification of DNV and API codes in terms of buckling capacity.

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