Amstrong® Ultra 650MCT: High-Strength, Low-Carbon Steel for Superior Weldability

Its very high yield strength contributes to a solution that increases the payload capacity and gives higher strength structures.

Typical applications include telescopic cranes, aerial platforms, concrete pumps, telescopic handlers, tippers and truck trailers, where the emphasis is on strength and weight reduction potential.

The above chemical properties are based on cast analysis data.

Weight reduction

The grade in this data sheet combines outstanding mechanical properties (very high strength, fatigue resistance and toughness) with good formability and weldability. Its guaranteed high yield strength makes it possible to achieve substantial weight reduction through downgauging, whilst maintaining overall performance and safety. This steel grade is therefore frequently used to replace conventional structural steel grades when weight reduction is required.

Thickness reduction brings additional savings when processing the material, since it is easier to weld, and reduces transport costs. Further savings are also achieved in service, in the form of lower energy consumption, improved mechanical performance, safety etc.

Estimation of the possible thickness reduction

When switching from grade 1 (with low yield strength) to grade 2 (proposed in this data sheet), an estimation of the thickness reduction that can be achieved is given by the following formula:

t2 = t1 (Re1/Re2)½ where t = thickness and Re = yield strength

Please note that other issues, such as fatigue resistance, need to be checked before reducing thickness.

Fatigue resistance

The fine grain size and low sulphur content improve the fatigue resistance of the steel. Fatigue performance is measured by uniaxial tests at different stress levels. These values are used to plot the Wöhler curve and determine the endurance limit of the steel grade.

This grade is available in "A - Unexposed" finish only.

This grade is suitable for oxygen, plasma and laser cutting.

Abrasion/wear resistance

In some applications (conveying devices, earth-moving or transportation vehicles etc), the steel surface can be subject to wear. Wear is a complex physical phenomenon that depends not only on the presence of abrasive materials but also on the conditions under which it occurs (pressure, temperature, impact, corrosion etc).

Compared with standard structural steel grades, Ultra High Strength Steel grades allow a significant improvement in wear resistance. In many cases, they can be more economical and easier to process than steel grades specifically designed for wear resistance.

Weldability and cold crack susceptibility of this grades are more accurately assessed using the PCM formula (parameter crack measurement), which was developed for low carbon steels (< 0.11%).

Due to its typical low carbon equivalent value (PCM < 0.25), this ArcelorMittal grades does not need to be pre- or post-heated when welding. It is not prone to excessive hardening due to its low carbon and low alloy content, is totally insensitive to cold cracking and is suitable for all types of arc welding.

Heat-affected zone softening - welding recommendations

If special care is not taken, softening may occur in the heat-affected zone (HAZ), particularly in the intercritical heat-affected zone (ICHAZ), which is typical behaviour of thermomechanically rolled steel grades with yield strength above 500 MPa. The extent of softening and the width of the softened zone increases with heat input applied during welding.

In order to preserve the high mechanical properties of the base material after welding, the recommendation is to limit the welding energy to about 1.5 kJ/cm per millimetre of thickness, as shown in the figure below, which corresponds to the following maximum cooling times (between 800°C and 500°C):