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High strength and abrasion-resistant steel can be oxyfuel cut like mild steel. However, like mild steel, the extremely high heat transforms and tempers the surrounding cold material. We speak of the surrounding area as the “heat affected zone” (HAZ). Flame cutting creates a risk of softening the steel in the HAZ.
In addition, flame cutting creates a risk of cut edge cracking. Cut edge cracks may take between 48 hours and two weeks to appear. To reduce the risk of cut edge cracking, steel mills recommend both preheating the steel prior to flame cutting and controlling the cut speed during the cutting process. Even where preheating is not recommended, it is necessary that the temperature of the steel be at least ambient room temperature prior to cutting. Keeping the steel warm prior to cutting is one of the major benefits of storing steel indoors.
Plasma arc cutting, laser cutting and waterjet cutting significantly reduce HAZ and reduce the risk of cut edge cracking. Underwater cutting will also minimize HAZ and reduce the risk of cracking. Our experience suggests that laser cutting can be slower than plasma cutting for high strength and abrasion-resistant steel, while waterjet cutting is often more expensive. We use plasma and oxyfuel cutting and a combination of preheating, controlled cut speeds, and underwater cutting to reduce HAZ and to reduce the risk of cut edge cracking.
Many steel mills provide their own guidelines on flame cutting and preheat temperatures. For example, specific technical information is available in these documents: Algoma 100 and AlgoTuf , Dillimax and Dillidur , durostat, alform, JFE EVERHARD, Quend and Quard.
All high strength HS 100 and abrasion-resistant HS 400, HS 450 and HS 500 steel plates can be welded by all the common processes provided low hydrogen weld material is used and the appropriate preheat temperatures are followed. Low heat input welding methods should be used, such as metal-arc, gas-shielded and multiple pass submerged arc welding. In this way, good mechanical properties can be retained in the heat affected zones. High heat input welding processes which generate heat input exceeding 90 KJ/in. (3.5 KJ/mm) should be avoided.
We have provided further information on welding below. Many steel mills provide welding guidelines and recommendations for their products. For example, specific technical information is available in these documents: Algoma 100 and AlgoTuf , Dillimax and Dillidur , durostat, alform, JFE EVERHARD, Quend and Quard, Swebor, Welding N-A-XTRA, Welding XAR, Preheat Temperatures N-A-XTRA, Preheat Temperatures XAR, Consumables N-A-XTRA, Consumables XAR
Carbon equivalent (CE) is a basis for evaluating weldability. A lower CE indicates better weldability. Less weldable (or more hardenable) steels have a higher risk of hydrogen induced cold cracking and therefore require precautionary steps such as preheating and low hydrogen practices to reduce that risk. There are various formulas for calculating carbon equivalent values. Producers of heat-treated plate generally recommend using the International Institute of Welding (IIW) formula (or the Dearden & O’Neil formula):
CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Working Temperature & Preheating
High strength and abrasion-resistant steel can sometimes be welded with the steel at room temperature without the risk of hydrogen cracking, particularly for thin plates. However, when single plate thickness is 0.75″ or above, some preheating above room temperature is generally required. Most mills provide detailed preheating recommendations for their products. When comparing recommendations, be sure to check the heat input. If the heat input is 25-30 KJ/in (0.9-1.1 KJ/mm), for example, the preheat temperature would typically be higher than if the heat input was 50-70 KJ/in. (1.9-2.7 KJ/mm), sometimes by as much as 100C (210F). When quenched and tempered steels are welded, a soft zone forms near the fusion limit. The width of the soft zone varies with heat input. If the heat input remains low, the soft zone should not affect the strength of the welded joint. For thicknesses below 0.375″ (9.5mm), heat input should generally not exceed 28 KJ/in. (1.1 KJ/mm).
Preheat and interpass temperatures should be maintained during welding by using a gas burner, heating blankets or, when the temperature is reached, by using the welding heat itself. Temperatures should be measured on both sides of the plate (for example, by using temperature crayons or heat guns). Under conditions of severe restraint, for tack welding, or in damp weather conditions, preheat temperatures would typically be increased
An undermatching weld metal is often desirable. Consumables that produce softer weld metal are cheaper and, because of their lower alloy content, are less hardenable than those producing a higher strength weld metal. In addition, consumables that produce softer weld metal are capable of deforming plastically more readily while the weld is cooling, thereby reducing the restraint on the joint. The filler material can be the same as for A572-50 or similar, such as AWS E7018 type. For butt welds where the joint strength must be equal to that of the parent plate, consider using electrodes such as AWS E11018.
Quenched and tempered steel can easily be welded together with other steels having a corresponding basic analysis. In such cases, consumables that match the softer steel grades should generally be chosen. However, only filler metals and processes that result in low hydrogen levels may be used. In addition, consumables must be stored in a manner that prevents the absorption of moisture. If there is any risk that moisture has been absorbed, the consumables must be discarded or redried in compliance with the manufacturer’s instructions. Covered electrodes should be thoroughly dried to ensure that the hydrogen content does not exceed 10mL/100 g weld metal.
For good welding results, it is important to keep crack-promoting hydrogens away from the weld joint. Make sure the joint is clean and use only dry consumables. The joints should be prepared in the same manner as for ordinary steels by means of gas cutting or machining. All impurities on or adjacent to the joint (such as scale, rust, oil, paint and moisture) must be removed prior to welding. These impurities contain hydrogen sources and may cause cracking. A good close fit between the members of the joint is essential to minimize the stresses and thereby reduce the risk of cracking. The risk is greatest for initial, often smaller, weld passes.
Many steel mills provide processing guidelines and recommendations for their products. For example, specific technical information is available in these documents: Algoma 100 and AlgoTuf , Dillimax and Dillidur , durostat, JFE EVERHARD, Quend and Quard.
In our experience, any high-speed steel drill can be used for drilling holes in HS 100 and HS 400. Our experience suggests that an 8% cobalt HSS-Co (m42 high speed steel) drill with a slow helix and heavy web construction can be used for HS 450 and HS 500. For production work, we recommend solid carbide or indexable carbide insert drills for a stable drilling machine. For a non-rigid machine where vibration could be a problem, we suggest cemented carbide drills. Because new drilling products are often developed, drilling charts for indexable carbide inserts, solid carbide and cemented carbide drills are best obtained from your tooling supplier or drill manufacturer.
When tapping in HS 100 any high-speed steel tap is suitable, whereas HS 400 requires a high quality HSS tap. For production work, tap life can be extended by using a coated HSS machine tap. Although it is possible to tap HS 500, this operation cannot be performed easily. We recommend a high-quality tap and a top end rigid machine. Expect a shorter tap life and possible tap failure by fracture from excessive torque inside the hole. Thread milling is a more reliable operation for threading holes in HS 500. When tapping in any grade, plenty of lubrication is required. We do not recommend hand tapping for any of the above steel types. Cutting speed is machine and tap dependent. We suggest a starting speed of 3 m/min (9 sfm), with adjustments to suit your particular machine and tap combination.
Countersinking and Counterboring
Countersinking and counterboring are best performed with replaceable insert tools. Counterboring is best performed with a revolving pilot to ensure hole accuracy and tool stability. Always ensure that the workpiece is secured properly to eliminate possible vibration. Cutting data will vary slightly from machine to machine. Charts for specific countersinking and counterboring tools are best obtained from your tooling supplier. In each case, we recommend plenty of coolant. Based on our experience, we recommend the following cutting values as general recommendations for a tool with replaceable inserts:
|STEEL GRADE (Drill Type)||CUTTING SPEED sfm||3/16" - 3/8" in /rev||3/8" - 3/4" in /rev||3/4" - 1-1/8" in /rev||1-1/8" + in /rev|
|A572 - 50W (HSS-E & HSS-co)||85 - 98||0.006||0.008||0.012||0.015|
|HS 100 QT (HSS-E & HSS-co)||52 - 65||0.004||0.004||0.009||0.014|
|HS 400 (HSS-Co w/slow helix)||26 - 33||0.002||0.004||0.009||0.014|
|HS 450 (HSS-Co w/slow helix)||19 - 26||0.002||0.004||0.009||0.014|
|HS 500 (HSS-Co w/slow helix)||13 - 19||0.002||0.003||0.007||0.010|
|STEEL GRADE (Drill Type)||CUTTING SPEED m/min||√∏ 5-10 mm Feed mm/rev||√∏ 10-20 mm Feed mm/rev||√∏ 20-30 mm Feed mm/rev||√∏ 30 mm + Feed mm/rev|
|A572 - 50W (HSS-E & HSS-co)||26 - 30||0.15||0.20||0.30||0.40|
|HS 100 QT (HSS-E & HSS-co)||16 - 20||0.10||0.10||0.23||0.35|
|HS 400 (HSS-Co w/slow helix)||8 - 10||0.05||0.10||0.23||0.35|
|HS 450 (HSS-Co w/slow helix)||6 - 8||0.05||0.10||0.23||0.35|
|HS 500 (HSS-Co w/slow helix)||4 - 6||0.05||0.05||0.08||0.25|
|Forming Radius (R) / Plate Thickness (t) @ 60º & 90º||Die Opening (W) / Plate Thickness (t) @ 60º||Die Opening (W) / Plate Thickness (t) @ 90º|
|GRADE||Transverse to the rolling direction R/t||Parallel to the rolling direction R/t||Transverse W/t||Parallel W/t||Transverse W/t||Parallel W/t|
|For bending to 90º in V-die die opening should "match" top tool radius to prevent impression in the plate.|
V-die and rollerbending are almost equivalent from a forming point of view. Increasing the die opening decreases the required bending force, but increases the springback. When forming to a 90º angle in a V-die, the value of the formula W/t – (1.4 x R/t) should be greater than 9 to prevent impression in the plate.
Bending a typical 3/8″ thick HS 100 plate with a W/t of 12.0 for forming transverse to the rolling direction, and an R/t recommended at 2 for a 90º bend, the formula shows.
Required bending force for rollerbending and V-die is calculated according to the following formula:
Bending Forces Needed in a Press Brake - Tons
|THICKNESS||WIDTH||HS 100||HS 400||HS 500|
|Bending force may vary due to die and shoulder design, surface condition and lubrication.|
The springback for different steel grades are illustrated in the table below. To compensate, overbending is necessary.
Typical Springback for Minimum Recommended Die Width Opening
|A572-50||80,000||3 - 5º|
|HS 100||125,000||6 - 10º|
|HS 400||181,000||9 - 13º|
|HS 500||225,000||13 - 16º|