Microstructural Design for High Strength Steel Welds: The Concept of Duplex Microstructure

2005 ◽  
Author(s):  
Stephen Liu
Keyword(s):  
Weld Metal ◽  
High Strength Steel ◽  
Lath Martensite ◽  
High Strength ◽  
Low Carbon ◽  
Duplex Microstructure ◽  
Weld Metal Microstructure ◽  
Steel Welds ◽  
Metal Microstructure ◽  
Welding Processes

In the past three decades, Colorado School of Mines researchers have investigated flux-related welding processes for pipeline applications and systematically characterized the fundamental behavior of welding fluxes. They also established the relationships between flux ingredients, weld metal microstructure, and weld joint mechanical properties. These studies clarified for high strength steel welds the importance of the bimodal nature of weld metal inclusions, related to weld metal transformations. As strength and toughness levels of the steels continue to increase, new generations of consumables must be developed. Two novel consumables design concepts are being investigated at the CSM. The first one is based on a duplex microstructure consisted of lath martensite and ferrite, and the second is based on low carbon, high alloy martensite.

Effect of Ti on the Microstructures and Toughness of TMCP-600 Steel Weld Metals

2013 ◽  
Vol 746 ◽  
pp. 462-466
Author(s):  
Jin Hyun Koh ◽  
Bok Su Jang
Keyword(s):  
Weld Metal ◽  
Impact Energy ◽  
Acicular Ferrite ◽  
Gas Metal Arc Welding ◽  
Control Process ◽  
High Strength ◽  
Weld Metal Microstructure ◽  
Metal Microstructure ◽  
The Impact ◽  
Ti Content

The Ti addition effect on the characteristics of weld metal, such as impact energy, microstructure and nonmetallic inclusions, was investigated to develop a suitable gas metal arc welding wire for the high strength of TMCP (Thermo Mechanical Control Process)-600 steel. The fraction of acicular ferrite which was known to be a favorable weld metal microstructure for toughness was increased with Ti content from 0.002% to 0.025%, The impact energy of weld metal was increased whereas the ductile to brittle transition temperature was decreased with increasing Ti content. The size of nonmetallic inclusion was decreased while the density of inclusions was decreased with increasing Ti content. It was found that Ti content on the weld metal toughness had a plus effect by increasing the fraction of acicular ferrite in the weld metal microstructure.

Martensitic Transformation in a Low-Alloy Ultra-High-Strength Steel

2011 ◽  
Vol 295-297 ◽  
pp. 1470-1473 ◽  
Author(s):  
Zhi Xia Qiao ◽  
Dan Tian Zhang ◽  
Yong Chang Liu ◽  
Ze Sheng Yan
Keyword(s):  
Martensitic Transformation ◽  
High Strength Steel ◽  
Lath Martensite ◽  
High Strength ◽  
Transformation Rate ◽  
Low Carbon ◽  
High Carbon ◽  
Process Characteristics ◽  
Ultra High Strength Steel ◽  
Carbon Martensite

Martensitic transformation is the most important phase transformation strengthening the 30CrNi3MoV ultra-high-strength steel during heat treatment process. Characteristics of the martensitic transformation in the 30CrNi3MoV steel were investigated by means of dilatometric measurements and microstructural observations. The results showed that the starting and finishing martensitic transformation temperatures of the 30CrNi3MoV explored steel are 317°C and 167°C respectively, which are hardly influenced by the cooling rate from austenite region. Such a wide temperature range of martensitic transformation in the 30CrNi3MoV steel results into the diversity of martensite microstructures. The microstructures in all the quenched 30CrNi3MoV samples are composed of mixture of lath and acicular martensite, corresponding to low-carbon and high-carbon martensite respectively. The transformation rate of acicular martensite is much slower than that of lath martensite, which can be attributed to the stabilization of the rest high-carbon austenite after the formation of lath martensite.

The Influence of Zirconium and Boron on Low Carbon Steel Weld Metal Microstructure

1994 ◽  
Vol 116 (1) ◽  
pp. 26-31 ◽  
Author(s):  
D. W. Oh ◽  
D. L. Olson ◽  
R. H. Frost
Keyword(s):  
Carbon Steel ◽  
Weld Metal ◽  
Low Carbon Steel ◽  
Steel Weld ◽  
Low Carbon ◽  
Weld Deposit ◽  
Steel Weld Metal ◽  
Weld Metal Microstructure ◽  
Metal Microstructure

By substituting zirconium-boron additions for titanium-boron additions in the weld deposit, further understanding of the role of specific microalloying additions on the suppression of grain boundary ferrite and the promotion of the intragranular formation of acicular ferrite in low carbon steel weld metal is achieved.

Experimental Study on the Effect of CGHAZ Microstructure on CTOD of High-Strength Steel EQ56

2011 ◽  
Vol 117-119 ◽  
pp. 1874-1879
Author(s):  
Zi Yu Xia ◽  
Zhang Mu Miao ◽  
Tao Ma ◽  
Gang Chen ◽  
Sheng Peng
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Strength Steel ◽  
Lath Martensite ◽  
Microstructural Analysis ◽  
High Strength ◽  
Low Carbon ◽  
Welding Joints ◽  
The Relationship ◽  
Scanning Electron

The CGHAZ Microstructure has great effect on the toughness of welding joints and CTOD. This paper discussed the relationship between the CGHAZ and CTOD .The samples, carried out on high-strength steel EQ56, were observed by scanning electron microscopy. The Microstructural analysis result shows CGHAZ microstructure of EQ56-5, presenting high CTOD with 0.272mm, is low-carbon lath martensite and little M-A constituent, which contribute to the better toughness of EQ56-5. CGHAZ microstructure of EQ56-4, presenting the low CTOD with 0.082 mm, contains M-A constituent. The M-A constituent makes the CGHAZ brittle. The crack would grow easily along the M-A grain boundaries.

Microstructure of resistance spot welding of maraging steels

1990 ◽  
Vol 48 (4) ◽  
pp. 900-901
Author(s):  
I. Neuman ◽  
S.F. Dirnfeld ◽  
I. Minkoff
Keyword(s):  
Maraging Steel ◽  
Spot Welding ◽  
Lath Martensite ◽  
Base Material ◽  
Aging Treatment ◽  
High Strength ◽  
Maraging Steels ◽  
Heat Treated ◽  
Current Cycle ◽  
Welding Processes

Experimental work on the spot welding of Maraging Steels revealed a surprisingly low level of strength - both in the as welded and in aged conditions. This appeared unusual since in the welding of these materials by other welding processes (TIG,MIG) the strength level is almost that of the base material. The maraging steel C250 investigated had the composition: 18wt%Ni, 8wt%Co, 5wt%Mo and additions of Al and Ti. It has a nominal tensile strength of 250 KSI. The heat treated structure of maraging steel is lath martensite the final high strength is reached by aging treatment at 485°C for 3-4 hours. During the aging process precipitation takes place of Ni3Mo and Ni3Ti and an ordered solid solution containing Co is formed.Three types of spot welding cycles were investigated: multi-pulse current cycle, bi-pulse cycle and single pulsle cycle. TIG welded samples were also tested for comparison.The microstructure investigations were carried out by SEM and EDS as well as by fractography. For multicycle spot welded maraging C250 (without aging), the dendrites start from the fusion line towards the nugget centre with an epitaxial growth region of various widths, as seen in Figure 1.

scholarly journals Comprehensive Analysis of the Microstructure and Mechanical Properties of Friction-Stir-Welded Low-Carbon High-Strength Steels with Tensile Strengths Ranging from 590 MPa to 1.5 GPa

2021 ◽  
Vol 11 (12) ◽  
pp. 5728
Author(s):  
HyeonJeong You ◽  
Minjung Kang ◽  
Sung Yi ◽  
Soongkeun Hyun ◽  
Cheolhee Kim
Keyword(s):  
Mechanical Properties ◽  
Tensile Test ◽  
Joint Strength ◽  
Solid Phase ◽  
Welding Process ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Friction Stir ◽  
Welding Processes

High-strength steels are being increasingly employed in the automotive industry, requiring efficient welding processes. This study analyzed the materials and mechanical properties of high-strength automotive steels with strengths ranging from 590 MPa to 1500 MPa, subjected to friction stir welding (FSW), which is a solid-phase welding process. The high-strength steels were hardened by a high fraction of martensite, and the welds were composed of a recrystallized zone (RZ), a partially recrystallized zone (PRZ), a tempered zone (TZ), and an unaffected base metal (BM). The RZ exhibited a higher hardness than the BM and was fully martensitic when the BM strength was 980 MPa or higher. When the BM strength was 780 MPa or higher, the PRZ and TZ softened owing to tempered martensitic formation and were the fracture locations in the tensile test, whereas BM fracture occurred in the tensile test of the 590 MPa steel weld. The joint strength, determined by the hardness and width of the softened zone, increased and then saturated with an increase in the BM strength. From the results, we can conclude that the thermal history and size of the PRZ and TZ should be controlled to enhance the joint strength of automotive steels.

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