Wear Resistant Steel

Wear-resistant steel is characterized by outstanding weldability.  Steel can be welded by means of all prevalent methods, preferably the MAG and manual arch processes. Due to the low carbon equivalent wear-resistant steels possess a low risk for cold cracking. Besides the cold cracking behavior during welding attention should be paid to the mechanical properties of the weld joint. The right working temperature and the cleanliness of the surfaces are both crucial when achieving the best quality.

Cold cracking is a time-delayed phenomenon in the heat-affected zone (HAZ) or in the weld metal that can occur during under conditions of hydrogen and stress exposure. The cold cracking behavior is governed by the plate thickness, the hydrogen content of the weld metal, the heat input during welding, the residual stress state in the weld region and the chemical composition of the parent metal and weld metal.

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

Typical carbon equivalents (CET) % for wear-resistant steel:

Thickness (mm)	≤ 8	10	15	20	25	30	35	40	50	60	70	80	90	100
XAR®400	0.28	0.32	0.32	0.32	0.33	0.33	0.33	0.37	0.37	0.37	0.37	0.37	0.37	0.37
XAR®450	0.30	0.35	0.35	0.35	0.35	0.35	0.35	0.41	0.41	0.41	0.41	0.41	0.41	0.41
XAR®500	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.41	0.44	0.44	0.44	0.44	0.46	0.46
XAR®600	0.54	0.54	0.54	0.54	0.54	0.54	0.54	0.54	0.54	-	-	-	-	-

Wear-resistant steels have been optimized with regards to lowest possible carbon equivalents and are therefore excellent to weld. An effective means for avoiding cold cracking is preheating. It delays the cooling of the weld region and id thereby conductive to hydrogen effusion. Preheating is generally necessary if the CET is over 0,32 %.

Preheat temperatures for MAG-welding of wear-resistant steel: (heat input 1kJ/mm, hydrogen content 2ml/100g)

Thickness (mm)	≤ 5	≤10	≤15	≤20	≤25	≤30	≤35	≤40	≤45	≤50	≤55	≤60	≤65	≤70	>70
XAR®400	-	-	-	-	75	75	75	125	125	125	150	150	150	150	175
XAR®450	-	-	-	75	75	125	125	150	150	175	175	175	175	175	175
XAR®500	-	100	100	125	125	150	150	175	175	200	200	200	200	200	200
XAR®600	150	175	200

The risk of cold cracking occurring in the weld metal is at its lowest when using austenitic welding filler metals. In this case the need for preheating decreases. If ferritic welding filler metals are used preference should be given to the MAG welding method, as it offers comparatively low hydrogen content in the weld metal.

The properties in the heat-affected zone of the weld undergo a change as a result of the temperature time cycle during welding. The parameter of optimal cooling time t8/5 tells how long does it take for a weld bead to cool from 800 °c to 500 °c.

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.

Recommended cooling time range for wear-resistant steels:

	Cooling time t8/5
XAR®400, XAR®450	5-20 s
XAR®500	6-15 s
XAR®600	8-15 s

When machining HB400 and HB450 wear-resistant steels HSS E twist drills are recommended. Carbide-tipped drills are necessary for the HB500 and HB600 steels.

When drilling the vibrations should be minimized by following steps:

• Clamping the workpiece firmly as close as possible to the drill
• Placing the workpiece and the drilling head as close to the machine column as possible
• Using short drills and spindle
• Cooling with heavy duty special oil
• For countersinking and boring piloted tools should be used to prevent any additional horizontal movement

Guide values for drilling of wear-resistant steel:

	Cutting speed (m/min)	D = 6 mm Rpm / mm/R	D = 8 mm Rpm / mm/R	D = 10 mm Rpm / mm/R	D = 12 mm Rpm / mm/R
XAR®400	3–5	210/0,05	160/0,08	130/0,10	100/0,15
XAR®450	3–5	210/0,05	160/0,08	130/0,10	100/0,15
XAR®500	20–25	1300/0,05	1000/0,05	800/0,08	670/0,08

XAR®HT, XAR®400 and XAR®450 are the most suitable wear-resistant steel grades for cold forming.

When forming wear-resistant steels it is necessary to make allowance for two additional factors: a greater force is required and the springback is stronger. Greater forces are needed because of the higher deformation resistance. The bending force can be reduced as much as 25 % by lubricating the die edges.

Best bending results are achieved by notch-free and de-burred plate edges, high-quality tools and the lubrication of the die and bending punch.

Minimum bending radii and die widths for cold bending and press brake bending of XAR®:

	Thickness (mm)	Bending radius (mm)		Die width (mm)
		I	II	I	II
XAR®400	t ≤ 8 8 < t ≤ 20 t > 20	2,5 t 3 t 4,5 t	3 t 4 t 5 t	8,5 t 10 t 12 t	10 t 10 t 12 t
XAR®450	t ≤ 8 8 < t ≤ 15 t > 15	4 t 4,5 t 5 t	4,5 t 5 t 6 t	10 t 12 t 12 t	12 t 12 t 14 t
XAR®500	t ≤ 8 t > 8	5 t	6 t	12 t	13 t

 I = Bending line transverse to the rolling direction
II = Bending line parallel to the rolling direction

More information about wear-resistant steels can be found from following pdf-files:

• XAR® wear resistant steels for longer service and reduced costs in special vehicles
• XAR® wear-resistant steels – Processing recommendations
• Datasheet XAR® 400
• Datasheet XAR® 450
• Datasheet XAR® 500
• Datasheet XAR® 600
• Datasheet XAR® HT