Q355B S355JR Structural Steel: Cutting & Processing Methods and Performance Parameters

1. Basic Standard & Material Introduction

Applicable Standard: EN 10025-2, European standard low-alloy high-strength structural steel Domestic Equivalent Grade: Q355B; Former Grade: St52-2
Grade Code Definition:

• S = Structural Steel
• 355 = Minimum yield strength of 355 MPa for plates ≤16 mm thick
• JR: Charpy V-notch impact test at 20°C with minimum impact energy of 27 J, delivered in hot-rolled condition

2. Complete Performance Parameters of S355JR

2.1 Chemical Composition (Ladle Analysis, wt%)

表格

Element	Maximum Content	Remarks
C (Carbon)	≤0.22	Low carbon content, excellent weldability; Carbon Equivalent: 0.42~0.47
Si (Silicon)	≤0.55	Deoxidizer, improves tensile strength
Mn (Manganese)	≤1.60	Matrix strengthening, enhances toughness
P (Phosphorus)	≤0.025	Harmful impurity, strictly controlled to avoid cold brittleness
S (Sulfur)	≤0.025	Tightly limited to prevent hot cracking
N (Nitrogen)	≤0.012	Restricts free nitrogen to avoid aging embrittlement
Cu (Copper)	≤0.55	Trace addition improves atmospheric corrosion resistance

2.2 Mechanical Properties (Hot-rolled, Room Temperature 20°C)

(1) Minimum Yield Strength ReH, Tensile Strength Rm & Elongation A5

表格

Plate Thickness t	Min Yield Strength (MPa)	Tensile Strength Rm (MPa)	Elongation A5 ≥
3＜t≤16 mm	355	470~630	22%
16＜t≤40 mm	345	470~630	22%
40＜t≤63 mm	335	470~630	21%
63＜t≤80 mm	325	470~630	21%
80＜t≤100 mm	315	470~630	20%

(2) Impact Toughness

• JR Grade: Charpy V-notch impact test at 20°C; Single specimen impact energy ≥27 J, average value ≥34 J

(3) Fundamental Physical Properties

• Density: 7.85 g/cm³
• Hardness (Hot-rolled): HB 140~180
• Elastic Modulus E: 206 GPa
• Thermal Conductivity: 46 W/(m·K)
• Linear Thermal Expansion Coefficient: 12×10⁻⁶ /°C

2.3 General Machining Characteristics

1. Weldability: Excellent low carbon equivalent. Thin plates require no preheating; preheating is mandatory for thick plates to prevent cracking.
2. Cold Forming: Bendable and stampable. Minimum bending radius ≥2t, larger springback than Q235 steel.
3. Cutting Compatibility: Fully compatible with flame cutting, plasma cutting, laser cutting and waterjet cutting. Preheating is required for thermal cutting of thick plates.

3. Four Main Cutting & Processing Methods for S355JR

(Applicable thickness, process parameters, advantages, disadvantages and operational key points)

3.1 CNC Flame Cutting (Oxy-propane / Oxy-acetylene)

Applicable Thickness: 10~300 mm extra-thick plates (max cutting thickness up to 1000 mm)

Core Process Parameters

• Oxygen pressure: 0.7~1.0 MPa; Fuel gas pressure: 0.05~0.12 MPa
• Plates ≥40 mm: Preheat to 100~150°C to avoid hydrogen-induced cracks at cutting edges
• Cutting speed: 180~220 mm/min for 20 mm plate; 80~120 mm/min for 100 mm thick plate
• One-step bevel forming: 30°~45°, suitable for blanking before welding

Advantages

Low equipment cost; the most economical solution for extra-thick plates; mass production of heavy-duty bases, flanges and bearing housings.

Disadvantages

Wide heat-affected zone (5~10 mm); dross adheres to cutting surface; dimensional tolerance ±1~3 mm; thin plates prone to burn-through; workpieces suffer severe thermal deformation.

Exclusive Operation Notes for S355JR

Cover cut workpieces with thermal insulation cotton and cool slowly to room temperature after cutting. If ambient temperature ＜5°C, raise preheating temperature to 150~200°C to prevent microcracks at edges within 48 hours post-cutting.

3.2 Fine Plasma Cutting (High-precision)

Applicable Thickness: 3~40 mm medium & thin plates, mass production of special-shaped parts

Process Parameters

• 10 mm S355JR: Current 160~190 A, cutting speed 300 mm/min, compressed air / oxygen auxiliary gas
• 20 mm S355JR: Current 200~240 A, cutting speed 240~280 mm/min

Advantages

Much faster cutting speed than flame cutting; good verticality of cutting surface; dimensional tolerance ±0.5 mm; capable of complex holes and special contours.

Disadvantages

Sharp cost increase for plates over 40 mm; thin hardened layer forms on cutting surface, which must be ground off before welding for thick plates.

3.3 Fiber Laser Cutting (High-precision Finishing)

Applicable Thickness: 0.5~25 mm thin plates for precision components (gears, machine casings, thin-plate construction machinery accessories)

Process Parameters

• 3~6 mm: 2000 W laser power, cutting speed 2~4 m/min, oxygen auxiliary for burr-free cross-section
• 10~16 mm: 6000 W laser power, cutting speed 0.6~1.2 m/min
• 16~25 mm: 12000 W high-power laser with low cutting speed

Advantages

Highest dimensional accuracy (±0.05~0.2 mm); minimal heat-affected zone; narrow kerf; negligible thermal deformation; smooth cutting surface with no secondary grinding required.

Disadvantages

High initial equipment investment; low efficiency and high cost for plates thicker than 25 mm compared with flame cutting.

3.4 Waterjet Cutting (Thermal-stress-free Cutting)

Applicable Thickness: 0~200 mm, parts requiring zero thermal deformation and no hardened layer

Process Parameters

Water pressure: 360~420 MPa; 80~120 mesh garnet abrasive

Advantages

Zero heat-affected zone; no cutting hardening or cracks; workpieces can be bent or machined directly after cutting, ideal for precision pressure-bearing structural parts.

Disadvantages

Slowest cutting speed; highest processing cost; poor cost performance for large-size blanking.

4. Process Selection Table for S355JR by Plate Thickness

表格

Plate Thickness	Recommended Cutting Method	Application Scenarios
≤10 mm thin plate	Fiber Laser Cutting	Precision machinery, thin-plate construction machinery parts, mass small-hole components
10~30 mm medium plate	Fine Plasma Cutting	Flanges, special-shaped connecting plates, standard steel structure parts
30~300 mm thick plate	CNC Flame Cutting	Bearing housings, equipment bases, thick flanges, bridge auxiliary components
All thicknesses, zero thermal deformation required	Waterjet Cutting	Precision molds, pressure-bearing structural parts, parts requiring subsequent cold working

5. General Quality Control Points for S355JR Cutting

1. Crack Prevention for Thick Plates: Preheat plates ≥40 mm to over 100°C; increase preheating temperature in low-temperature environments and adopt slow cooling after cutting.
2. Hardened Layer Treatment: A 1~3 mm hardened layer exists on edges cut by plasma or flame. Grind it completely before welding to avoid brittle welds.
3. Blanking Sequence: Cut internal holes first, then outer contours to release internal stress and prevent plate warpage.
4. Z-direction Performance Steel (S355JR-Z15/Z25/Z35): Adopt low cutting speed and avoid rapid quenching to prevent cross-section lamination and tearing.
5. Post-cutting Procedures: Remove burrs and molten slag; inspect dimensional tolerances; high-stress components may undergo stress relief annealing at 530~580°C to 580°C.

6. Typical Application Fields

Heavy machinery bases, steel plant building beams and columns, crane arms, bridge auxiliary parts, flange plates, bearing housings, construction machinery boxes, non-pressure-bearing shells for pressure vessels, etc.