The objective of this study was to investigate the influence of softening in the heat-affected zone of welds and the constraint effect on the transverse tensile strength of a microalloyed, thermomechanically controlled processed (TMCP) high-strength steel grade. The welding was performed with three different levels of energy input to establish soft zones with varied extensions to investigate the dimension of softening and to determine the constraint effect on various widths of the soft zone. The results showed that the tensile strength was not significantly compromised by softening in the HAZ. The reason for this is the constraint effect of the base metal and the high strength of the weld metal. In conclusion low heat input welding processes keep the soft zone small and the strength high.

/pdf/influence-of-the-soft-zone-on-the-strength-of-welded-modern-3rivj2j5i8.pdf

Influence of the soft zone on the strength of welded modern hsla steels

Softening in the heat-affected zone (HAZ) may occur at welding of high-strength low-alloy steels and might have a negative effect on the static strength of welded joints. This study investigates the influence of HAZ softening in combination with different filler metal strength classes, weld seams, and hot rolled strips on static performance of a GMA-welded joints. The results of these welding experiments were compared and discussed with a numerical investigation on factors influencing the static strength of HSLA steel welds. At the numerical investigation, a systematical study on potential strength influencing factors and a Pareto analysis based on a multiple regression was done and the potential strength influencing factors were ranked according their degree of influence. The comparison of the results of this experimental and numerical study showed a good accordance.

Evaluation of the factors influencing the strength of HSLA steel weld joint with softened HAZ

The ongoing need to reduce the weight of products while increasing strength has resulted in new generation steel manufacturing using special heat treatments to produce High Strength Steels (HSS) and Ultra High Strength Steels (UHSS) with up to 1700 MPa tensile strength. The high strength level of these steels makes it possible to produce structures with a considerable weight and cost reduction, and such steels have been adopted in the automotive industry and for mobile heavy equipment. Welding of UHSS is, however, not without its complications and welding processes for these steels need careful attention. For instance, their high susceptibility to cracking and Heat Affected Zone (HAZ) softening are risks that need to be borne in mind when choosing welding parameters. This research work discusses the difficulties and challenges of successful welding of UHSS. Common welding methods used in welding of UHSS are briefly reviewed to gain a better understanding of the effects of different welding parameters and methods. The paper finds that UHSS can be satisfactorily welded with laser welding, electron beam welding, resistance welding, and conventional arc welding methods, but the quality of the weld is dependent on appropriate control of several parameters and variables of the welding processes.

Welding of Ultra High Strength Steels

https://dr.ntu.edu.sg/bitstream/10356/142816/2/Welding%20effect%20on%20tensile%20strength%20of%20grade%20S690Q%20steel%20butt%20joint.pdf

Welding effect on tensile strength of grade S690Q steel butt joint

This study investigates the influence of the soft zone on the static tensile strength of welded joints. A micro-alloyed, thermo-mechanically controlled processed (TMCP) high strength low alloy steel grade (HSLA) was joined with electron beam welding at different energy input levels. The welded joints were investigated by means of light optical microscopy, FE-SEM (field emission scanning electron microscopy) analyse, hardness measurement and quasi- static tensile test. The results of this investigation were compared with the mechanical properties of GMAW welded joints of same base metal.

Electron Beam Welding Of Atmcp Steel With 700 Mpa Yield Strength

In all application fields for hot rolled strip products for direct processing, e.g. construction and engineering but also crane and truck industry, there is a strong customers demand for grades with increased strength levels and well balanced formability. At voestalpine Stahl GmbH these requirements were met with the development of the high strength microalloyed steel grade ALFORM700M and the ultra high strength steel grade ALFORM900M with a minimum yield strength (YS) of 700 MPa and 900 MPa, respectively. In the present paper investigations on the steel grades ALFORM700M and ALFORM900M are introduced. To explain the evolution of the obtained complex microstructures consisting of bainitic ferrite, bainite and martensite alloy design and industrial production process is discussed on the base of dilatometric experiments and TEM investigations. The formation of precipitates is studied by using a numerical model, chemical methods and mechanical testing after heat treatment. Mechanical and mechanic-technological properties of the two steel grades are compared. Furthermore, some processing aspects as weldability an bending behaviour are highlighted. Finally, some typical applications for this high and ultra high strength steel grades are presented.

R. Rauch

Papers

Thermomechanically Hot Rolled High and Ultra High Strength Steel Grades - Processing, Properties and Application