RAEX 400

RAEX AR 400 is a wear-resistant steel grade.  The number designation indicates the average Brinell hardness value: 400 HBW.  Despite its strength and hardness, weldability and formability of this grade is good.

Applications:

Ladles and lip plates of earth-moving machines, wearing parts of mining machines, concrete mixing plants and wood processing machines, platform structures, feeders and funnels.

Chemical Composition Content %, maximum (ladle analysis)

Aluminium (Al) and/or titanium (Ti) is used for binding nitrogen (N).

Supply Condition:  Hardened.

Abrasion Resistance & Hardness     

The microstructure of abrasion resistant steel is martensitic, which guarantees high hardness and tensile strength.  High hardness and tensile strength give a steel high resistance to abrasion.

Mechanical Properties

Carbon Equivalent (CEV)

CEV = C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15

Processing

Flanging

Despite their high strength RAEX AR 400 can still be formed by free bending or flanging.  However, the bending force, springback effect and the bending radius are greater than those for softer structural steels.  When bending or flanging, workshop practices, condition of the tools and exact design must be taken in to consideration.  Flangeability can be improved by raising the working temperature to 100°C - 200°C.

Welding

All the normal welding procedures can be used, provided that a professional welder pays special attention to the following factors:           

·         Use of correct working temperature.

·         Correct choice of welding consumables.

·         Suitable arc energy.

A reserved attitude to post-weld heat treatments should be taken because they have a tendency to weaken the most important property of these steels i.e. wear resistance.

Working Temperature

Increasing the working temperature slows the cooling of welded joints, which decreases the generation of a microstructure that is too hard and brittle and vulnerable to cracking in the heat affected zone (HAZ).  It is advisable to increase the working temperature of RAEX AR 400 steels when the combined plate thickness exceeds about 40mm.  Generally a good working temperature of 100°C is enough to ensure a good result. However, when heavy and complicated structures are welded and when welding takes place under difficult circumstances, a higher 150°C – 200°C, working temperature is recommended.  A higher working temperature than this may weaken the mechanical properties.

Welding Consumables

Either conventional, so called non-alloyed filler materials or so called alloyed materials that produce higher strength weld metals can be used as filler material.  Generally non-alloyed filler materials are silicon and manganese alloyed and the strength of the weld metal they produce remains lower than the strength of the hardened base material. 

An important advantage of non-alloyed filler material is that the softer weld metal they produce responds better to welding stresses.  This is due to the better elongation and deformation ability of the soft weld metal in comparison with high strength weld metal.  It is highly advisable to use low-hydrogen, basic filler materials so that the amount of hydrogen will remain safely low.

Heat-Treatment

The steels are not intended to be heat treated during or after fabrication.  Tempering at moderate temperatures, 150°C - 200°C, is the only heat treatment which will without fail allow the steel to retain its original wearing properties.

Flame Cutting

A heat affected zone (HAZ) will build up on a thermally cut surface which is similar to the HAZ on a fusion welded steel surface.  The surface hardens to a depth of 1mm-2mm during flame cutting and post heat results in a soft tempered layer below this.  When flame cutting, the pre-heating and working temperature instructions concerning welding can be used as a guideline.  In practice it is advisable to preheat when cutting plates, if the thickness is over 10mm.

The maximum allowable working temperature must be kept below 200°C in order that the wear resistance will meet requirements throughout the plate.  The cooling of a cut surface must not be accelerated under any circumstances, on the contrary, the cooling of the plate surface can be slowed down if necessary.  A plate brought in from cold outside storage must be allowed to warm up sufficiently before cutting.

Recommended working temperatures for flame cutting

Mechanical Cutting

The mechanical cutting of hardened wear-resistant steels is challenging, as the material to be cut is almost as hard as the cutting blade. RAEX AR 400 steels can be cut using heavy duty cutting machines.

Machining

AR steels can be machined using heavy-duty machines and hard metal tools.  It is even possible to drill holes using tools made of high-speed steel, given proper tool geometry and using suitable cutting fluids.