2Cr13 Stainless Steel Seamless Pipe Production Process
Published: December 22, 2025 | Category: Blog | By FUSHUN METAL
Table of Contents
1. Introduction to 2Cr13 Stainless Steel
2Cr13 stainless steel is a martensitic stainless steel grade that has gained significant importance in industrial applications. Cold-rolled and cold-drawn pipes made from this material are primarily used in demanding environments requiring specific mechanical and chemical properties.
2Cr13 stainless steel offers excellent corrosion resistance, thermal strength, weldability, and superior vibration damping properties, making it ideal for defense applications and valve manufacturing.
Many countries have established specialized production lines for large-scale manufacturing of this material. However, domestic production volumes remain relatively low, with production processes still requiring optimization. The main challenges are concentrated in the pickling, lubrication, cold rolling, and cold drawing procedures.
Historical production attempts in the late 1970s achieved only approximately 30% yield rate from billet to finished product, primarily due to poor pickling quality, susceptibility to cracking during rolling and drawing, and difficulties in implementing slow cooling after hot piercing.
Product Specifications Developed
Through systematic process development, over a dozen specifications have been successfully produced, including various diameter and wall thickness combinations. By mid-production period, more than 10 tons of finished pipes were delivered to inventory, meeting requirements from petroleum instrumentation, electric motor, and valve manufacturing industries.
2. Billet Preparation Process
2.1 Main Process Flow
The billet preparation follows two primary routes depending on the starting material:
| Route | Process Steps |
|---|---|
| Route A (Ingot) | Ingot Casting → Annealing → Forging → Slow Cooling → Billet Rolling → Annealing → Cutting → Peeling |
| Route B (Continuous Casting) | Electric Arc Furnace Melting → LF Refining → Continuous Casting → Slow Cooling → Billet Rolling |
| Subsequent Processing | Heating → Piercing → Pickling → Lubrication → Cold Rolling/Drawing → Annealing → Straightening → Pickling → Inspection → Storage |
2.2 Key Process Parameters
Process Route A:
- Electric arc furnace melting with return material and flux
- Temperature control at 1580-1600°C for oxygen blowing and desulfurization
- Slag removal and composition adjustment before tapping
- Annealing at 860±10°C with furnace cooling at 30°C/hour
Process Route B:
- LF refining with composition adjustment
- Argon stirring and wire feeding (CaSi)
- Cover agent addition before continuous casting
- Square billet production with covered slow cooling
2.3 Forging and Billet Rolling
| Parameter | Forging | Billet Rolling |
|---|---|---|
| Heating Temperature | 1150-1180°C | 1150-1180°C |
| Starting Temperature | 1100-1150°C | – |
| Finishing Temperature | ≥850°C | – |
| Post-Processing | Pit slow cooling | Controlled cooling |
3. Hot Working Process
3.1 Process Flow
Billet Inspection → Cutting to Length → Peeling → Inspection → Heating → Piercing → Slow Cooling
3.2 Billet Preparation Before Piercing
The piercing quality of the billet is crucial for determining whether cold working can proceed normally. To ensure piercing quality, emphasis must be placed on billet peeling inspection and complete elimination of billet defects.
3.3 Billet Heating
Critical Control Points: In addition to controlling furnace atmosphere and temperature in each zone, frequent observation and turning of billets is essential to ensure uniform heating.
The heating process follows a carefully designed curve with staged temperature increases and adequate soaking time to achieve uniform temperature distribution throughout the billet cross-section.
3.4 Piercing Operation
To produce shell tubes meeting specifications, the following key aspects are controlled during hot piercing:
- Temperature Control: Piercing mill entry temperature controlled at 1100-1150°C
- Rolling Rhythm: 40-50 seconds between pieces, with roll speed adjusted as needed
- Tool Inspection: Regular checking of piercing tool surface condition
- Roll Gap: Maintained at 85-100mm
- Plug Position: 35-50mm ahead of roll centerline
3.5 Slow Cooling
Based on the characteristics of 2Cr13 steel, implementing slow cooling can produce a combined microstructure of fine pearlite lamellae plus martensite, which is more favorable for cold working than pure martensite.
Slow cooling after piercing is achieved using slow cooling pits. When pits are unavailable, aluminum silicate fiber blankets are used to seal and slowly cool the red-hot shell tubes. Through these measures combined with careful operation, shell tube surface quality and dimensional accuracy reached normal piercing levels, with hot-rolled shell tube qualification rates achieving approximately 95%.
4. Cold Working Process
Due to the lack of mature production experience, small batch trial production was organized first. Based on finished product specifications and existing equipment capabilities, the production process employs either cold rolling to finished size or cold rolling for wall sizing followed by cold drawing for OD sizing.
4.1 Main Process Flow
Shell Tube Inspection → Grouping → Annealing → Pickling → Inspection → Lubrication → Cold Rolling → Degreasing → Annealing → Straightening → Cutting → Pickling → Lubrication → Cold Drawing to Finished Size → Inspection → Storage
4.2 Sample Deformation Schedule
| Pass | Dimensions (OD×WT) | Cross-Section Area (mm²) | Area Reduction (%) | Elongation Ratio |
|---|---|---|---|---|
| Shell | φ70×8.5 | 1642.4 | – | – |
| 1 | φ48×5.5 | 734.4 | 55.3 | 2.24 |
| 2 | φ32×3.5 | 313.4 | 57.3 | 2.34 |
| 3 | φ21×2.5 | 145.3 | 53.6 | 2.16 |
| 4 | φ14×1.5 | 58.9 | 59.5 | 2.47 |
4.3 Alternative Deformation Routes
| Route | Deformation Sequence |
|---|---|
| Route 1 | Roll φ70×8.5 → Roll φ48×5.5 → Roll φ32×3.5 → Roll φ16×1.5 |
| Route 2 | Roll φ70×8.5 → Roll φ45×4.5 → Draw φ32×4.5 |
5. Production Problems and Solutions
5.1 Cracking During Rolling and Drawing
2Cr13 stainless steel exhibits unique heat treatment characteristics:
Self-Quenching Phenomenon: When heated to high temperature to form austenite and then cooled, 2Cr13 transforms to martensite. Due to chromium’s effect of significantly reducing the critical quenching rate, air cooling after high-temperature heating produces martensite structure. This is also called “self-hardening steel.”
Causes of Cracking:
- When FCC austenite transforms to BCC martensite, volume expansion occurs due to specific volume differences, creating significant internal stress that reduces plasticity
- Overheating at excessively high temperatures with prolonged holding produces coarse grains with poor plasticity
- Incomplete annealing above Ac1 significantly reduces corrosion resistance; complete annealing dissolves carbides in austenite, forming martensite on cooling which increases strength and hardness, unfavorable for cold working
Solution: Recrystallization annealing should be used for cold working to eliminate work hardening. Initial trials using 860°C heating with 2-hour hold and furnace cooling to 500°C resulted in head cracking during rolling. Modified heat treatment at 780±10°C with 1.5-2 hour hold significantly reduced head splitting and longitudinal cracking. Further optimization at 760-780°C with 2-hour hold and furnace cooling to 500°C produced marked improvement.
5.2 Pitting Corrosion and Pickling Difficulties
When 2Cr13 stainless steel is pickled with sulfuric acid, surface quality is poor—some areas are over-pickled while oxide scale remains on others. In trial production, some shell tubes experienced corrosion depths of 0.3mm while local oxide scale remained.
Causes:
- Like austenitic stainless steel, chromium forms stable oxide film at high temperature. Spectral analysis of 2Cr13 oxide layer shows Cr₂O₃ content of 22.45%, FeO at 51.28%, Fe₂O₃ at 23.07%, with Cr₂O₃ in spinel form that is insoluble in single acids
- Failure to degrease before annealing allows soap and oil lubricants on pipe surface to cause uneven oxide scale during annealing
5.3 Surface Scratches and Scoring During Drawing
2Cr13 steel has thermal conductivity similar to austenitic stainless steel—much lower than carbon and alloy structural steels. Phosphate treatment produces poor quality coating. After saponification, drawing causes severe scratching as lubricant film breaks down under high pressure and temperature, resulting in uneven friction and die sticking.
6. Improved Process Parameters
6.1 Optimized Heat Treatment
| Parameter | Specification |
|---|---|
| Treatment Type | Recrystallization Annealing |
| Heating Temperature | 760-780°C |
| Holding Time | 1.5-2 hours |
| Cooling Rate | 30-50°C/hour (furnace cooling) |
| Exit Temperature | Below 500°C, then air cool |
6.2 Improved Pickling Solution
| Component | Concentration |
|---|---|
| Nitric Acid (HNO₃) | 10-15% |
| Hydrofluoric Acid (HF) | 2-5% |
| Solution Temperature | 40-60°C |
| Pickling Time | 15-30 minutes (until scale removed) |
6.3 Enhanced Straightening Process
Due to pickling difficulties, shell tubes undergo pre-straightening to loosen oxide scale and facilitate pickling. Shell tubes shorter than 1.5m create straightening difficulties. Billet cutting length is specified at 370-420mm to ensure both bore quality and straightener length requirements. Cold-worked semi-finished and finished products must be straightened 2-3 passes after annealing before pickling.
6.4 Improved Lubrication
- Cold Rolling: Chemical copper plating with high-temperature sodium-based grease applied to inner surface
- Cold Drawing: High-temperature sodium-based grease : lime = 0.5-0.8 : 1 ratio
- Pre-heating: Pipes heated to 80-150°C before warm drawing
- Post-drawing: Immediate heating after drawing to prevent cracking
6.5 Cold Rolling Parameters
- Feed rate: 2-3mm per stroke
- Saponification solution flow strictly controlled
- Frame stroke rate: 50-60 strokes/minute
Quality Requirement: Cold-drawn 2Cr13 pipe mechanical properties should be maintained at tensile strength 550-650 N/mm² with elongation ≥18%. Deviation from these values tends to produce defective products.
7. Technical Discussion
7.1 Cold Rolling Challenges
Despite continuous heat treatment improvements, head splitting and longitudinal cracking still occur during rolling. Production measures include:
- Paraffin solution lubrication for plug and inner surface
- Controlled saponification solution flow
- Reduced frame stroke rate
- “Start-close” saponification technique: solution off during bite-in, on after initial rolling engagement
Notably, cracking is significantly reduced when using forged billets compared to continuous cast or rolled billets. This suggests that besides intermediate heat treatment, pickling, and rolling control, pass design optimization specifically for 2Cr13 characteristics (plasticity, thermal conductivity, elastic modulus, lubrication quality) is needed, as current pass designs are based on parameters for other steel grades.
7.2 Copper Plating Issues
Pickling with H₂SO₄ + HCl solution produces unsatisfactory results. Using HNO₃ + HF solution basically resolves pickling issues but creates extreme difficulty in copper plating. The difference between these approaches requires further investigation.
8. Conclusion
The successful development of 2Cr13 stainless steel pipe production using established processing techniques has achieved the following:
- Dimensional tolerances and mechanical properties meeting technical agreement specifications
- Production specifications ranging from φ6×1.5 to φ32×4.5mm across more than ten sizes
- Mature production processes capable of supporting batch production requirements
- Addition of a new member to the stainless steel pipe product family
The key to successful 2Cr13 stainless steel seamless pipe production lies in understanding its unique metallurgical characteristics—particularly its self-quenching tendency—and implementing appropriate heat treatment, pickling, and lubrication processes tailored to these properties.
9. Frequently Asked Questions
Q: What is 2Cr13 stainless steel used for?
A: 2Cr13 stainless steel is widely used in defense applications, valve components, petroleum instrumentation, and motor manufacturing due to its excellent corrosion resistance, thermal strength, weldability, and vibration damping properties.
Q: Why does 2Cr13 stainless steel crack during cold working?
A: 2Cr13 stainless steel has self-quenching characteristics. When heated to high temperatures and air-cooled, it forms martensite structure, which significantly reduces plasticity and causes internal stress, leading to cracking during cold rolling or drawing.
Q: What heat treatment is recommended for 2Cr13 stainless steel pipes?
A: Recrystallization annealing is recommended at 760-780°C with holding time of 1.5-2 hours, followed by furnace cooling at 30-50°C/hour to below 500°C, then air cooling.
Q: What pickling solution works best for 2Cr13 stainless steel?
A: A mixed solution of HNO₃ (10-15%) + HF (2-5%) at 40-60°C is recommended for effective oxide scale removal, as chromium oxide is not soluble in single acids like sulfuric acid, hydrochloric acid, or nitric acid alone.
Q: How to prevent surface defects during cold drawing of 2Cr13 pipes?
A: Use high-temperature sodium-based grease with lime as lubricant, preheat pipes to 80-150°C before drawing, ensure smooth pipe heads without shoulders or visible cracks, and maintain tensile strength between 550-650 N/mm² with elongation ≥18%.
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