Forged steel valves are similar to cast steel valves, but their essence is very different! The forged steel is formed by high-pressure plastic forming, with dense grains, and is suitable for the ultra-high pressure working conditions of PN320. Cast steel relies on liquid casting and is suitable for complex structural valve bodies below PN40. Choosing the wrong valve = burying the hidden danger of bursting – this article will use 15 hard-core data to reveal the rules of accurate selection.

The Core Difference: How the Manufacturing Process Determines Valve Performance

Forged steel valve: the principle of high-pressure plastic forming

Pressure is applied to the metal billet by forging machinery (hydraulic hammer/press) to cause plastic deformation above or below the recrystallization temperature (hot forging) or below (cold forging). This process forces the metal grains to flow in the direction of force, eliminating defects such as casting pores and shrinkage, and forming a dense fibrous structure. Key benefits:

• Grain refinement: Grain size is 30%-50% smaller than cast steel
• Defect elimination: welded holes with a density close to theoretical (7.85 g/cm³)
• Strength jump: 25%-30% increase in tensile strength

Typical application scenarios: supercritical steam valves for power stations, hydrogen high-pressure filling valves

Cast steel valves: the essence of the liquid casting process

Molten molten steel (temperature ≥ 1600°C) is poured into the prefabricated sand mold/metal cavity and cooled and solidified. The core of the process lies in the liquid flow filling complex cavities, but cooling shrinkage is prone to internal defects:

• Inherent defects: up to 3%-5% shrinkage (X-ray inspection required)
• Tissue segregation: uneven distribution of carbon/alloying elements (marginal and core hardness difference≥ 15HB)
• Stress concentration: Cooling stress leads to micro-crack risk

Typical application scenarios: DN300 or above butterfly valve body, special-shaped ball valve shell

Process comparison table

• Pursuing high-pressure safety (PN≥100) → Forged steel is a must
• Special-shaped structures (multi-channel/thin-walled) are required→ Cast steel is preferred

Performance Hard-Core Comparison: The Basis for Data-Based Decision-Making

Comparison of pressure capacity

Pressure grade comparison table

Note: The bursting pressure of PN320 forged steel valve ≥ 480 MPa, which is equivalent to the pressure of the base of the Eiffel Tower!

Mechanical properties differences

Case: Under -46°C LNG conditions, the impact toughness of cast steel valves plummets to 15 J/cm² (forged steel maintains 70 J/cm²), and the wrong selection will cause low-temperature brittleness!

Size Limitations and Affordability

Dimensional boundary

• Forged Steel Valve:
  • Advantage diameter: DN6~DN50 (monopoly in the field of high-pressure micro valve)
  • Limit size: die forging DN200 (requires 10,000 ton hydraulic press)
• Cast Steel Valve:
  • Advantage diameter: DN80~DN1200
  • Largest record: DN4000 Butterfly Valve for Hydropower Station (85 tons)

Cost comparison formula:

• Forged steel cost ≈ 1.8× material cost + complex processing fee
• Steel casting cost ≈ 1.2× material cost + post-processing fee

(For reference only, compare the approximate ratio of the two)

• High pressure valves below DN50: Forged steel is expensive but irreplaceable
• Atmospheric pressure valve above DN300: the cost of cast steel is only 1/5 of that of forged steel

Fatal Shortcomings: These Scenes Must not be Chosen Wrong

3 types of high-risk working conditions for cast steel valves are prohibited

Authoritative basis: ASME B16.34 standard stipulates:

• Under the temperature drastication condition (ΔT>100°C/h), carbon cast steel valves are prohibited
• Impact load > 50J/cm² scene requires forged steel or special casting

There are two major application limitations of forged steel valves

Limitation 1: The cost of large size diameter is out of control

• Root cause:
  • DN>80 10,000-ton hydraulic press (single equipment investment > $20 million)
  • Material utilization < 50% (60% of the forging billet is turned away)
• Economic tipping point:
  • DN50 forged steel valve cost = $1000
  • DN80 Forged Steel Valve Cost = $6500 (↑550%)
  • DN80 cast steel valve cost = $900
    (For reference only, compare the approximate ratio)

Limitation 2: Difficult processing of complex runners

• The tee/multi-chamber valve body needs to be forged and welded in sections → welds are weak points
• Comparison: Cast steel can be formed with multiple runners (e.g. Y-type filter body)

Compromise:

• Medium pressure working condition (PN40) → It adopts cast steel + forged valve cover composite structure
• Ultra-complex valve body → Precision casting + hot isostatic pressure (HIP) reinforcement

Key experience summary table

“Cast steel is afraid of sudden changes, forged steel is afraid of deflection” – temperature/pressure drastic changes kill cast steel, and the medium flows to parallel forged steel grains will accelerate corrosion!

Four Steps to Lock in the Best Solution

Step 1: Pressure level screening

If the working pressure is ≥ PN100 (or American Standard 1500LB), the forged steel valve is mandatory.
If the pressure is ≤ PN40 (or American Standard 900LB), proceed to the second step of judgment.
If it is in the PN40~PN100 transition area, the forged steel is preferred; Cast steel valves are optional when economically constrained, but must be supplemented with radiographic detection (RT).
*Note: ASME B16.34 standard stipulates that the main material of valves above PN64 must meet the SA-105/SA-182 standard for forgings*

Step 2: Medium impact assessment

• Temperature drastication condition (ΔT>80°C/h): Forged steel must be selected (cast steel thermal fatigue life < 1 year)
• Solid particles/high-velocity fluids: selected forged steel with a surface hardness ≥ HRC35 (40% lower erosion resistance of cast steel)
• Corrosive medium (Cl⁻>50ppm): choose special forged steel such as duplex steel (200% higher corrosion rate at the grain boundary of cast steel)
• Static Pure Fluid: Optional Cast Steel (Cost Advantage)

Step 3: Diameter and structural complexity

• Bore ≤ DN50:
  • Simple structure (straight-through type): direct selection of forged steel
  • Complex structure (angle valve/tee): using die forging process
• DN50 < bore ≤ DN200:
  • High pressure/impact working conditions: select sectional forging + welded forged steel valves
  • Atmospheric pressure static working conditions: cast steel valves
• Bore > DN200: mandatory choice of cast steel (forging costs increase exponentially)
  *Structural limitations: It is difficult to achieve multi-chamber/asymmetrical runner/thin wall (<8mm) in forged steel; Cast steel should be used with caution with neck butt weld (WN) and threaded connection (SW)*

Step 4: Cost life cycle calculation

Total Cost of Ownership (TCO) Formula:
TCO = Acquisition cost + installation fee + Σ (maintenance cost × years) + lost downtime

DN80 ball valve cost comparison case (working condition: PN40 water medium):

• Purchase price: Forged steel $6,500 | Cast steel $900 → forged steel high $5,600
• Setup fee: $800 → no difference
• 10-year maintenance fee: forged steel $1,200 | Cast steel $4,800 → Forged steel saves $3,600
• Expected downtime loss: Forged steel $0 | Cast steel $15,000 → Forged steel saves $15,000
• 10-year TCO total: Forged steel $8,500 | Cast steel $21,500 → Forged steel saves $13,000
  *Key parameters: cast steel failure rate 2.3 times/year (forged steel 0.2 times/year), single downtime loss of $5,000 (chemical industry average)*

The ultimate decision tree logical chain

1. Pressure≥ PN100? → is the end of → selected forged steel →
2. The media has upheaval/corrosion/particles? → is the end of → selected forged steel →
3. Diameter≤ DN50? → is the end of → selected forged steel →
4. Bore > DN200? → is the → cast steel → ends
5. Calculating TCO: Cast steel TCO >1.5× Forged steel TCO? → is → selected forged steel | No → Cast steel is selected

Analysis of Forging Process Technology

Closed die forging vs open forging

Closed Die Forging (Die Forging)

• Process principle: The heated metal billet is placed in a closed mold cavity, and the metal filling mold is forced to form by high pressure (≥ 800 ton hydraulic press).
• Precision control: dimensional tolerance ±0.25mm, surface roughness Ra≤1.6μm.
• Core Benefits:
  • Fiber streamlines are distributed along the part contour→ Stress corrosion resistance is increased by 40%
  • It is suitable for precision parts such as high-pressure ball valve spools and needle valve cones
• Limitations: High mold cost ($50,000~$200,000), only suitable for mass production.

Open Forging (Free Forging)

• Process principle: The metal billet is freely deformed between the upper and lower anvils, and there is no closed cavity constraint.
• Accuracy range: dimensional tolerance ±2.5mm, subsequent cutting is required.
• Core Benefits:
  • Low equipment investment (less than $500,000)
  • It is suitable for the production of large gate valve bodies (> 1 ton) and other single parts

Core differences:

• The flow line of die-forged valve fittings is distributed along the contour→ and stress corrosion resistance ↑40%
• Free forging costs are 30% lower, but material utilization is < 50%

Applicable scenarios of hot forging/warm forging/cold forging

Temperature Critical Point Warning:

• Austenitic stainless steel hot forging needs to be controlled at 850°C~1200°C (to prevent σ phase embrittlement)
• When the deformation of cold forging > 75%, intermediate annealing is required (to avoid cracking)

The effect of forging ratio (3:1~5:1) on quality

Forging ratio formula: Forging ratio K = cross-sectional area before deformation / cross-sectional area after deformation

Quality correlation law:

1. K=1~2：
   • Only casting defects are eliminated, and the grain is not refined
   • Only suitable for non-supportive parts of the bracket type
2. K=3~4：
   • The grain size is reduced by 30% and the anisotropy is reduced
   • PN160 Valve Minimum Requirements (ASME SA-105 Standard)
3. K≥5：
   • Continuous fiber streamline, impact toughness ↑50%
   • Mandatory for ultra-high pressure valves (PN320).

Forging process selection guide

1. Selection criteria for high-pressure valves

For valves with pressure class ≥ PN160 or if the media contains corrosive components:

• Closed die forging process must be used
• The forging ratio needs to be ≥5
• Material Selection:
  • Austenitic stainless steel is hot forged (1100-1250°C)
  • Martensitic stainless steel is warm-forged (650-950°C)

2. Large parts selection criteria

When the weight of the part > 500kg:

• Open free forging process is adopted
• The forging ratio needs to be ≥3
• Hot forging process is adopted

3. Selection criteria for mass production

When production batches > 10,000 pieces:

• Prioritize cold forging processes
• Only suitable for materials with an elongation > 35%
• Intermediate annealing is required (when the deformation > 75%)

4. General selection criteria

Other cases:

• Warm forging process is recommended
• The best choice for balancing cost and performance

Industry norms requirement

• ASME SA-105 standard: minimum forging ratio of pressure-bearing forgings K=3
• NACE MR0175 standard: Acid service valves must meet:
  • Forging ratio K≥4
  • 100% ultrasonic testing

Analysis of Casting Process Technology

Sand casting vs specialty casting

Sand casting (ordinary casting)

• Process characteristics:
  • Use natural quartz sand + binder (such as bentonite) to make the mold
  • Low cost, suitable for single-piece/low-volume production
  • Surface roughness Ra 12.5~50μm, dimensional tolerance ± 1.5mm
• Applicable valve types:
  • DN80~DN2000 gate valve, butterfly valve body
  • Low pressure (PN16~PN40) ball valve housing

Special Casting (Precision Casting)

• Main methods:
  • Investment casting (lost wax method): dimensional accuracy ± 0.3mm, Ra 3.2~6.3μm
  • Metal casting: finer grains, 20% higher mechanical properties
  • Centrifugal casting: suitable for symmetrical rotary bodies (e.g. valve sleeves)
• Applicable valve types:
  • Complex flow channel control valves (e.g. Y-filters)
  • Corrosion-resistant special alloy valves

Comparison conclusion:

Three types of cast steel (carbon steel/low alloy steel/special steel)

Key figures:

• WCB Cast Carbon Steel: -29°C Impact ≥ 20J (Heat Treatment Required)
• CF8M stainless steel: Cl-resistant concentration > 10000ppm

Casting defect prevention program

Casting process selection decision logic

Step 1: Assess the pressure level

If the valve pressure ≤ PN40 → go to step 2

If the pressure > PN40 → forcing the selection of forged steel

Step 2: Determine the production batch

Single/small batch (<100 pieces) → Sand casting

Medium batch (100~500 pieces) → metal mold casting

Large batches (> 500 pieces) → Go to step 3

Step 3: Analyze the structural complexity

Simple structure (pass-through) → Metal casting

Complex structures (multi-channel/thin-walled) → investment casting

Step 4: Verify corrosion resistance requirements

Corrosive media (Cl⁻>50ppm) → special casting + HIP treatment

Non-corrosive media → Maintain step 3 selection

There is No Best, Only the Most Suitable

Three core scenarios that are irreplaceable for forged steel valves

1. Ultra-high pressure extreme working conditions
   • Key words: PN320 high pressure valve/3500LB forged steel valve
   • Typical Applications:
     • Ultra-high pressure pipeline system of hydrogen energy refueling station
     • Deep sea drilling blowout preventer control valve manifold
     • The main steam shut-off valve of supercritical thermal power unit
2. strong impact vibration environment
   • Key words: impact resistant forged steel valves/high toughness valves
   • Typical Applications:
     • Compressor inlet and outlet pulsating buffer valves
     • Military ship shock absorbing pipeline system
     • Oil drilling wellhead control valve
3. Extreme temperature conditions
   • Key words: -196°C cryogenic valve/650°C high-temperature valve
   • Typical Applications:
     • LNG ultra-low temperature shut-off valve
     • Nuclear power plant main steam isolation valve
     • High temperature control valve for molten salt energy storage system

Technical support: Forged steel grain size up to ASTM 8-10, impact toughness super cast steel 200%

4 typical working conditions with the best cost performance of cast steel valves

1. Large diameter low pressure system
   • Key words: DN1000 or above valves/water supply and drainage cast steel valves
   • Typical Applications:
     • Butterfly valve of municipal water supply pipe network
     • Gate valve of the power station circulating water system
     • Sewage treatment plant control valve
2. Complex structural components
   • Key words: special-shaped cast steel valve/multi-channel valve body
   • Typical Applications:
     • Y-filter body
     • Tee control valve housing
     • Worm gear drive box
3. Conventional corrosive environments
   • Key words: CF8M stainless steel valve/acid and alkali resistant cast steel valve
   • Typical Applications:
     • Chemical media ball valve
     • Stopcock valves for desalination systems
     • Acid-alkali tank bottom valve
4. Deliver projects quickly
   • Key words: short delivery valves/spot cast steel valves
   • Typical Applications:
     • Emergency repair replacement valves
     • Temporary piping system
     • Batch matching equipment valve manifold

Economic data: DN300 cast steel gate valve costs only 1/5 of forged steel, and the delivery time is 3 weeks faster

As a leading valve supplier in the industry, JH Valve Manufacturing Factory strictly follows the national API, EN, ISO standard system, has a complete forged steel valve and cast steel valve production line, whether it is high-pressure forged steel valves or complex cast steel valves can be customized production, we provide full-process solutions from selection consultation to after-sales service, immediately send your product requirements or consult customized services, professional engineers will provide you with the best selection plan and technical guidance for free