Application of high strength steels may offer many advantages. Today, high strength steels are

increasingly applied in pipelines, cranes, offshore construction, bridges, minesweepers, etc. In order to meet market requirements for a wider range of steel grades, consumables for applicable processes need to be available, whether it is for manual or mechanized welding.

Initially, weldability is the feature to be met. Next, chemical composition and mechanical properties in the as welded and/or post weld heat treated condition need to be demonstrated,followed by a consumable classification according to AWS, EN or other. Influence of individual elements (like Mn,Ni, Mo, Ti or B) on weld metal toughness and strength level is discussed.

An important issue for end-users is the working range of a consumable that still delivers required

properties. Restrictions in operability, heat input, welding position, joint configuration or heat

treatment, do limit the application of a specific consumable and should be minimized. Consistency in obtained mechanical properties is an essential development criterion.

Finally, welding procedures will be discussed using consumables that demonstrated fitness for purpose.

In European Standards, construction steel grades are classified according to method of production.

Normalized fine grain steel grades (EN 10113)

TMCP fine grain steel grades (EN 10113)

Q&T high strength steel grades (EN10137)

The application of these steel grades is sub-divided in two main groups:

EN 10113 & EN 10137

Steels in these groups are used in more severe constructions like offshore, bridges, cranes,

storage tanks, minesweepers, etc. Application can be at low temperatures.

Classification of steel grades

EN standard "Current" Classification "Old" Classification---EN 10113:

Normalized fine grain steel grades

S 275 N,S 355 N,S 420 N,S 460 N, StE 285, StE 355, StE 420, StE 460

TMCP fine grain steel grades:

S 275 M,S 355 M,S 420 M,S 460 M,StE 355 TM,StE 420 TM,StE 460 TM

EN10137 Q&T high strength steel grades:

S 460 Q,S 500 Q,S 550 Q,S 620 Q,S 690 Q,S 890 Q,S 960 Q, StE 500 V, StE 550 V

StE 620 V, StE 690 V, StE 890 V,StE 960 V

The excellent mechanical properties of these grades are obtained by a well-balanced chemical

composition in combination with a well-controlled heat treatment. Within one chemical composition, it is possible to supply different strength levels.

With quenched and tempered steel grades, the high tempered martensite will result in good ductility and high yield and tensile strength. When welding these steel grades, the heat input needs to be such that forming of ferrite and perlite is avoided, because of lower strength and toughness level.

At a particular plate thickness, the cooling time t800-500, is a function of heat input.When cooling too fast, the presence of some alloying elements could result in high HAZ hardness. An optimal t800-500 needs to be established.

Recent advances in thermo-mechanical controlled processing of steel have resulted in low carbon

equivalent, higher strength pipe steel, with limited the risk of HAZ cracking. The predominant

strengthening mechanism in the weld metal, however, is through alloy additions. The weld metal thus becomes the “weakest link" with increased susceptibility to hydrogen cracking. Consumables for welding high strength steels have been developed parallel with base material. Optimization of these consumables has been a continuous process. With this background, defining the limits of consumables becomes relevant.

Empirical carbon equivalent expressions have been developed that weigh the relative effects of alloying elements on material hardenability.

In general, consumables are selected on strength and toughness, which is normally a "matching"

consumable. The yield strength of the deposited weld metal in that case is slightly higher than the

specified minimum yield strength of the steel applied. In some applications, an overmatching of 15-20% is prescribed, which means a significant higher yield strength than the base metal. For instance steel grade S500, with a minimum yield strength of 500MPa would require a minimum yield of the welded joint of 580MPa.

With increasing yield strength, the elongation will decrease. In order to handle shrinkage and distortion, this elongation is important. Preheat, in combination with a "softer" weld metal for the root, could be beneficial.

However when using Q&T steel grades, the high tempered martensite will result in high yield- and tensile strength. It will also result in good toughness and low susceptibility to brittle fracture. The formation of relatively soft ferrite and perlite should be avoided in order to maintain a higher strength level.Typically, Q&T steel grades do not require overmatching to an extend as the TMCP steel grades.