PC1570 vs PC1860 – Composition, Heat Treatment, Properties, and Applications

Introduction

PC1570 and PC1860 are two commonly encountered grades in the family of high-strength prestressing steels used for pre-tensioning and post-tensioning tendons, strands, and bars. Engineers, procurement managers, and manufacturing planners frequently weigh trade-offs between strength, toughness, weldability, fatigue performance, and cost when choosing between them — for example, specifying a higher nominal strength to reduce section size versus preferring a lower-strength but more ductile product to ease handling and reduce risk of brittle failure.

The principal technical distinction between these grades is their design intent for different levels of tensile capacity: one grade targets a lower specified ultimate strength and generally greater ductility and toughness for a given cross-section, whereas the other targets substantially higher specified ultimate strength (and corresponding prestress capacity), achieved through stronger alloying and processing. This makes the two grades complementary choices depending on structural demand, prestressing scheme, fatigue/wear environment, and fabrication constraints.

1. Standards and Designations

• Common international and regional standards where prestressing steels and high-strength wire/strand are specified include:
• ASTM/ASME (e.g., ASTM A416 for steel strands, ASTM A722 for high-strength steel wire)
• EN (e.g., EN 10080 for steel for the reinforcement of concrete — weldable reinforcing steel — and other EN standards for prestressing steels)
• JIS (Japanese Industrial Standards covering prestressing steels)
• GB (Chinese national standards for prestressing steels and wires)
• Classification:
• Both PC1570 and PC1860 are high-strength prestressing steels (specialty carbon/alloy steels tailored for prestress use).
• They are not stainless steels; they fall within the category of high-strength carbon or microalloyed steels for prestressing (some variants are thermomechanically processed or cold-drawn).

2. Chemical Composition and Alloying Strategy

The exact chemical analysis depends on the supplier and applicable standard, but the alloying philosophies are consistent: maintain low/controlled carbon to preserve ductility and weldability while adding controlled levels of Si and Mn for deoxidation and strength; microalloying additions (V, Ti, Nb) or small amounts of Cr/Mo are used in higher-strength grades to increase hardenability, temper resistance, and strength without excessively raising carbon.

Element	Typical role / presence in PC1570	Typical role / presence in PC1860
C (Carbon)	Controlled, relatively low to moderate to retain ductility and fatigue resistance	Slightly higher control or comparable; tight control needed to achieve higher tensile strength with acceptable toughness
Mn (Manganese)	Strengthening and deoxidation; moderate levels	Similar or moderately higher to improve hardenability
Si (Silicon)	Deoxidation and strength contribution; kept controlled	Controlled, sometimes slightly higher for strength
P (Phosphorus)	Kept to minimum; deleterious for toughness	Kept minimal
S (Sulfur)	Kept minimal; affects machinability and inclusions	Kept minimal
Cr (Chromium)	Usually low or absent; some grades may include small Cr for hardenability	May be present in small amounts in higher-strength variants
Ni (Nickel)	Not typical; used only in specialty chemistries	Rare; small additions possible in specialty steels
Mo (Molybdenum)	Rare but may be used in small amounts for temper resistance	May be used in trace amounts for high-strength variants
V, Nb, Ti (Microalloying elements)	Often present in trace amounts for grain refinement and strength	More likely or slightly higher additions to secure higher strength via precipitation strengthening
B (Boron)	If used, at ppm levels to improve hardenability	May be used in ppm to assist hardenability in high-strength grades
N (Nitrogen)	Controlled at low levels to avoid embrittlement	Controlled low

Notes: - Suppliers will publish exact chemical limits per product. The table above summarizes functional strategies rather than fixed compositions. - Higher nominal-strength grades typically rely more on controlled microalloying and processing to achieve strength without excessive carbon.

3. Microstructure and Heat Treatment Response

• Typical microstructures depend on production route:
• Cold-drawn prestressing wires historically develop a heavily drawn pearlitic or tempered microstructure with fine interlamellar spacing that supports high tensile strength and fatigue resistance.
• Thermomechanically processed bars or quenched-and-tempered products develop fine-grained bainitic or tempered martensitic structures with precipitate strengthening from microalloying elements.
• PC1570 (lower nominal strength):
• More readily attains required properties by controlled cold drawing and tempering or by lower-intensity quench/temper cycles that retain relatively more ductile microconstituents.
• Exhibits a favorable balance of ferrite/pearlite or tempered martensite/bainite with good toughness.
• PC1860 (higher nominal strength):
• Requires stronger hardenability and/or more severe deformation to reach the higher tensile level; microstructure often shows finer bainite or tempered martensite and a higher dislocation density plus precipitation strengthening.
• Heat treatments (e.g., quench + temper or controlled cooling) are optimized to achieve high ultimate strength while preserving required elongation and fatigue performance.
• Effect of processing:
• Normalizing improves uniformity and toughness by refining grain size.
• Quenching and tempering raise strength and can be tuned to optimize the strength–toughness trade-off.
• Thermo-mechanical controlled processing (TMCP) can produce fine-grained microstructures that improve both strength and toughness for high-strength variants.

4. Mechanical Properties

Quantitative values differ by standard and supplier; the table below highlights relative behavior and what engineers should expect.

Property	PC1570	PC1860
Tensile strength (ultimate)	Lower nominal category — designed for high strength but below the higher-grade counterpart	Higher nominal category — designed for significantly greater ultimate strength and prestress capacity
Yield strength (or proof)	Typically lower; provides more plastic reserve	Higher yield/proof levels to support higher prestressing forces
Elongation (ductility)	Generally higher ductility (greater elongation) for the same cross-section	Reduced elongation compared with PC1570 at the same strength level; still controlled to meet ductility requirements
Impact toughness	Usually better toughness, especially at lower temperatures, if alloying is conservative	Toughness can be lower if strength is prioritized; controlled alloying and processing mitigate embrittlement
Hardness	Lower to moderate hardness	Higher hardness reflecting higher tensile strength

Interpretation: - PC1860 achieves higher tensile and proof stresses but typically sacrifices some ductility and may have higher hardness and lower measured impact energy unless alloying and tempering are carefully controlled. - Selection should consider whether the structural design requires maximum prestress per tendon (favoring PC1860) or better ductility/toughness and handling margin (favoring PC1570).

5. Weldability

Weldability depends on carbon equivalent/hardenability and presence of microalloying elements. For assessment engineers often use indices such as:

$$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$

and

$$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$

Qualitative interpretation: - PC1570: Because of generally lower hardenability requirements and conservative microalloying, it tends to exhibit better intrinsic weldability and lower cold-cracking propensity than higher-strength variants. Preheat and controlled interpass temperatures are still often required for thick sections. - PC1860: Higher hardenability (from alloying or higher carbon equivalent) increases vulnerability to hard, brittle HAZ microstructures and hydrogen-assisted cold cracking. Welding procedures typically require stricter preheat/postheat and hydrogen control. For most prestressing applications, direct welding of wires or strands is limited and mechanical splicing or approved welding/joining methods are specified. - Practical note: For tendons, splicing/welding is often avoided in the prestressed zone unless explicitly qualified; mechanical couplers or factory-welded terminations are more common.

6. Corrosion and Surface Protection

• Neither PC1570 nor PC1860 are stainless steels; corrosion resistance is limited and depends on surface condition, coatings, and environment.
• Typical protections:
• Hot-dip galvanizing for bars/strands where sacrificial protection is acceptable.
• Epoxy coating, polymer sheathing, or grease/greased ducts for strands used in external, semi-exposed, or aggressive environments.
• Physical encapsulation (grout/injection) is standard practice in prestressed concrete tendons.
• PREN (pitting resistance equivalent number) is a stainless-steel index and is generally not applicable to non-stainless prestressing steels. For reference:

$$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$

but this index is relevant only for stainless alloys that intentionally include Cr, Mo and N at significant levels.

7. Fabrication, Machinability, and Formability

• Machinability:
• Higher-strength grades (PC1860) tend to be harder and more abrasive to tooling; cutting speeds and tool life must be adjusted.
• PC1570 is easier to machine and form due to lower hardness.
• Formability and bending:
• Ductility dictates allowable bending radii and cold forming processes; PC1570 will typically tolerate tighter bends and cold forming with lower risk of cracking.
• PC1860 may require larger bend radii, controlled heat treatments, or specialized forming processes.
• Surface finishing:
• Higher-hardness steels may develop microcracks during aggressive finishing operations; control of grinding and shot blasting is important.
• Installation and handling:
• Higher prestress levels in PC1860 impose stricter handling, anchorage, and tensioning equipment requirements because of higher stored elastic energy and risk during catastrophic failure.

8. Typical Applications

PC1570 — Typical Uses	PC1860 — Typical Uses
General prestressed concrete members where moderate-to-high prestress is required along with ease of installation and improved toughness (e.g., precast beams, slabs, smaller tendons)	High-capacity tendons where maximum prestress per tendon is needed to minimize section size, or for long-span/high-load bridges, post-tensioning of heavy slabs, and specialized applications
Elements where fatigue resistance and ductility are prioritized (bridges with many load cycles)	Applications where space or number of ducts must be minimized and higher proof stress per strand is economically advantageous
Situations with more complex field fabrication where higher weldability/formability is beneficial	Factory-manufactured high-strength elements and couplers where higher strength compensates for reduced ductility

Selection rationale: - Choose the grade whose balance of prestress capacity and ductility matches structural demand, tendon spacing, and construction constraints. Consider longevity and corrosion protection strategy as a co-factor.

9. Cost and Availability

• Relative cost:
• PC1860 is generally more expensive per unit mass due to additional alloying, more demanding processing and tighter quality control.
• PC1570 is typically less expensive and widely produced in common product forms (wire, strand, bar).
• Availability by product form:
• Both grades are commonly available as wire and strand; higher grades may be more commonly found in certain product forms (e.g., specially manufactured high-strength strands, bars or cold-drawn wire) and may have longer lead times for large quantities or special coatings.
• Procurement advice:
• Early engagement with suppliers is advisable for PC1860 to confirm lead time, heat-treatment route, and quality assurance for fatigue and fracture toughness, particularly for large projects.

10. Summary and Recommendation

Criterion	PC1570	PC1860
Weldability	Better (lower CE, easier to weld with standard precautions)	More challenging (higher CE/hardenability; stricter controls needed)
Strength–Toughness balance	More ductile, better toughness for many applications	Higher strength, but requires careful processing to retain toughness
Cost	Lower	Higher

Recommendation: - Choose PC1570 if: - The project prioritizes ductility, toughness, fatigue resistance and easier fabrication or field handling; where moderation of prestress per tendon is acceptable; and when cost or rapid availability is important. - Choose PC1860 if: - The design requires maximum prestress capacity per tendon to minimize tendon count or cross-section size, and the project can accommodate stricter welding/specification controls, potentially higher material cost, and close supplier qualification of heat treatment and toughness.

Final engineering note: Always confirm the exact chemical and mechanical limits with the supplier or the governing specification, review qualified welding and splicing procedures, and verify fatigue and fracture-critical performance by testing or supplier data for the chosen production route.