Fine grain steels have good cold formability and toughness. They have fine grain structure due to the low carbon content and micro-alloying elements (e.g. titanium and niobium).
Fine grain structure and high purity guarantee excellent properties for various uses. The steels have outstanding weldability and bending possibilities with small radius.
Thyssenkrupp Steel Europe produces PERFORM® 650MC and 700MC steels by thermomechanical rolling. No other heat treatment is used. The higher yield strengths of PERFORM® steels can be achieved by rapid cooling after hot rolling.
Utilization of fine grain steels allows thinner plate thicknesses compared to conventional structural steels, and thus reduced structure weights and increased payloads. This means saving in material costs. Other advantages worth mentioning are the great machining properties.
Fine grain steels can be used in numerous applications where structural light weight is required, such as:
- Frame structures and axle constructions for vehicles
- Components for mobile cranes
- The hulls and booms of forest machinery and equipment
- Longitudinal and cross-beam structures
- Dimensions
- Welding
- Machining
- Bending
- More details
The most common fine grain steel plate thicknesses and sizes available in our stock:
| Grade | Thickness (mm) | Width x length (mm) |
|---|---|---|
| S355MC | 3–12 15–20 | 1500 x 3000 1500 x 3000 |
| S420MC | 3–12 | 1500 x 3000 |
| PERFORM® 650MC | 3 4–10 4–10 | 1250 x 3000 1500 x 3000 1500 x 6000 |
| PERFORM® 700MC | 3 4–10 4–10 | 1250 x 3000 1500 x 3000 1500 x 6000 |
Fine grain steels have excellent weldability and they can be welded by all standard methods.
Steel’s susceptibility to cold cracking can be estimated on the basis of its chemical composition. Particularly suitable for this is the carbon equivalent (CET).
CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 +Ni/40
Due to the low carbon equivalent value (CET) the risk of cold cracking is minimal. Therefore, pre-heating is not generally necessary.
The only exception is submerged-arc welding PERFORM®650/700 plates with Union S3NiMoCr wire electrodes when preheating and interpass temperature at least of 120 °c is recommended. In this case the CET in the weld metal is much higher than in the parent metal.
Welding conditions have a crucial effect on mechanical properties of welding joints. Thermal effects of welding are not allowed to weaken the steel properties in the way the construction would not meet the requirement set. Mechanical properties should be achieved both in the welding metal and heat-affected-zone (HAZ).
The steel properties in the heat-affected zone (HAZ) of the weld undergo a change as a result of the temperature time cycle. Rapid cooling of welded beads leads to a high hardness and the risk of cold cracking increases in the welding area. Too slow cooling, on the other hand, may result in poorer toughness and hardness.
PROWELD
ProWeld application is an effective assistant in selecting the correct welding parameters for PERFORM® steels. Order Proweld free of charge via e-mail: steel.valkeakoski@flinkenberg.fi
The drilling, turning and milling of micro-alloyed high-strength special structural steels can be compared to the chip-removing machining works of traditional structural steels.
The good forming behavior of the fine grain steels stems from the fine-grain microstructure and cleanliness.
Fine grain steels can be bent with small radius in spite of their strength.
Recommended minimum bending radius and die widths compared to the plate thickness (t)
| Min bending radius (mm) | Min die width (mm) | |
|---|---|---|
| S355MC | 0,25 t | 6,5 t |
| S420MC | 0,5 t | 7 t |
| PERFORM® 650/700MC | 1,5 t | 9 t |
Possible elongation of the plate’s edge is dependent on the quality of the plate and the quality of the cut. The cut edges should be flawless in order to achieve the minimum inner radius. In difficult cases, grinding the edges is recommended.
More information about fine-grain steels can be found from following pdf-files:
