Edmund Tasak

Cracking of High-Strength Steel Welded Joints

ABSTRACT Fracture evaluation of welded joints in high-strength steels, with bainitic and martensitic structures, is presented and cracking mechanisms discussed. Hot cracks or microcracks formed during welding are further expanded as cold cracks on cooling. The cause of cracking is shown to be low temperature of weld solidification and deformation-induced contraction. Hydrogen can also be an important factor in this cracking.

The influence of pulsation of the MIG arc on the structure of aluminium alloy welds

In this article, trends in the development of welding equipment in Japan were discussed. Results of examinations of the influence of MIG welding with both single and double arc pulses on a macrostructure of aluminium welds were presented. It was stated that, because of lower line energy (the so-called cold weld pools), welding with a double pulse has the most disintegrated crystalline structure. Welding with a single pulse results in a crystalline structure in weld reinforcement only, whereas welding without an arc pulse causes formation of very adverse columnar crystals, which increases susceptibility to hot cracking.

The role of hydrogen in weld cracking processes – a new look at the problem

Hydrogen’s effect on steel properties has already been described in many publications and monographs. Usually in these publications, only hydrogen’s effect on properties and cracking at near ambient temperatures and minus temperatures is analysed. For example, similar effects of hydrogen on properties and weld cracking are described in detail in Refs. 3–7. Until now, the common belief was that hydrogen causes:

Technology of welding and properties of welded joints of new bainitic and martensitic steels with creep-resistant steels

This paper shows the results of welding tests used so far on high-temperature creep resistant steels and new bainitic and martensitic steels. The positive results of this research allowed the elaboration of a welding procedure specification that was ultimately approved by TÜV. This then allowed the SEFAKO Company to attempt welding of the latest generation boiler steels for use under heavy conditions.

Influence of post-weld heat treatment (PWHT) on the structure and properties of welded joints of chromium–nickel stainless steel with soft martensite

This paper reviews the results of investigations on how post-weld heat treatment (PWHT) influences the hardness and microstructures of welded joints in stainless steel X3Cr-NiMo 13-4. It is known that welding leads to high segregation of components in the solidification process, which has an influence on phase transitions in PWHT. The investigated steel has a very narrow PWHT range, about 600–620°C, which provides optimum levels of hardness and toughness. Excessive annealing temperature leads to decreased toughness, which in turn causes exceeding of the Ac1 temperature in the segregation range, which then leads to increased ‘fresh’ martensite content.

Metallurgical problems in the welding process of selected construction steels

Selected problems with the weldability of higher-strength steels, high-strength steels and martensitic copper-precipitation-hardened stainless steels, which were solved by the Physical Metallurgy and Powder Metallurgy Department at the AGH University of Science and Technology, are presented in the article. It was pointed out that the formation of M-A islands in welded structures results from too-slow cooling after the welding process, and is the reason why the welds and the heat affected zones (HAZs) have such a low impact. Testing of copper-based precipitation hardening of martensitic stainless steel demonstrated that fractures occurring in the HAZ were of the hot fracture type, and result from the steels surface having been enriched with copper.