SUP9 vs SUP10 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SUP9 and SUP10 are closely related structural carbon-steel grades frequently considered in heavy fabrication, machinery components, and heat-treated parts. Engineers, procurement managers, and manufacturing planners commonly weigh trade-offs between weldability, toughness, machinability, and achievable strength when selecting between them. The principal practical distinction is a deliberate, modest increase in carbon content in SUP10 compared with SUP9, which shifts performance toward higher hardenability and strength at the expense of some ductility and weldability. These two grades are often compared where designers must balance component load-carrying capacity and wear resistance against ease of fabrication and heat treatment cost.
1. Standards and Designations
- Typical standards where similar grade families appear: ASTM/ASME (carbon and low-alloy steels), EN (European structural and quenched-tempered steels), JIS (Japanese Industrial Standards), GB/T (Chinese standards).
- Classification: both SUP9 and SUP10 are non-stainless carbon or low-alloy steels (not tool steels or austenitic stainless). They are generally positioned as carbon steels or low-alloy steels intended for parts that may be normalized, quenched & tempered, or otherwise heat-treated to control strength/toughness. They are not high-nickel stainless grades nor HSLA with significant microalloying by default, although specific mill variants may include microalloy additions.
2. Chemical Composition and Alloying Strategy
| Element | SUP9 (typical strategy) | SUP10 (typical strategy) |
|---|---|---|
| C (Carbon) | Lower carbon relative to SUP10; targeted for balance of toughness and weldability | Higher carbon than SUP9 to increase strength/hardenability |
| Mn (Manganese) | Moderate — deoxidizer and strength contributor | Similar or slightly adjusted to maintain hardenability and strength |
| Si (Silicon) | Deoxidizer; typically low-to-moderate | Similar — primarily deoxidation role |
| P (Phosphorus) | Controlled low impurity level | Controlled low impurity level |
| S (Sulfur) | Kept low; machinability sulfide additions may be present in free-machining variants | Kept low; similar approach |
| Cr (Chromium) | Often minimal or absent; when present, small amounts for hardenability | May have similar small amounts; not a principal strengthening alloy |
| Ni (Nickel) | Usually absent or trace | Usually absent or trace |
| Mo (Molybdenum) | Usually trace if any; used to increase hardenability in alloyed variants | Could be present in small amounts in some suppliers to boost hardenability |
| V, Nb, Ti (Microalloying) | Often not specified; may be present in microalloyed variants | Possible low-level additions in some variants to refine grain and improve toughness |
| B (Boron) | Not typically specified | Not typically specified |
| N (Nitrogen) | Low; controlled | Low; controlled |
Notes: Rather than radical differences in alloy suite, the design approach for SUP10 is to increase the carbon content to raise achievable hardness and tensile strength after heat treatment while retaining a relatively simple alloy recipe. Mn and Si are used conventionally for deoxidation and strength control. Microalloying (V, Nb, Ti) may appear in specific mill products to tailor toughness without excessive carbon.
How alloying affects properties: - Carbon: primary determinant of hardness and quenched martensite fraction; higher carbon increases strength but reduces ductility and weldability. - Manganese and molybdenum: increase hardenability and strength; they moderate the sensitivity to cooling rate. - Microalloying elements (V, Nb, Ti): refine grain, increase precipitation strengthening, and can improve toughness without large carbon increases.
3. Microstructure and Heat Treatment Response
Typical microstructures: - SUP9 (lower carbon): in normalized condition, tends to form a ferrite–pearlite matrix with relatively coarser pearlite depending on cooling. After quench & temper, a tempered martensite / bainite microstructure is expected at moderate hardening levels. - SUP10 (higher carbon): more pearlite in as-rolled or normalized condition; when quenched, a higher proportion of martensite forms at comparable cooling rates, producing higher hardness and strength.
Heat treatment routes: - Normalizing: refines grain and produces ferrite–pearlite; SUP10’s higher carbon yields a harder normalized structure than SUP9 for the same cooling path. - Quenching & tempering: both grades respond by forming martensite on rapid cooling. SUP10 attains higher as-quenched hardness and requires tempering schedules that reduce brittleness while preserving higher strength. Tempering recipes must account for increased carbon to avoid temper embrittlement zones. - Thermo-mechanical processing: controlled rolling or TMCP with accelerated cooling can produce fine bainitic or martensitic-ferrite mixes. Microalloyed variants of either grade can gain improved toughness with finer grain sizes.
Metallurgical implications: - Higher carbon increases the Ms (martensite start) temperature sensitivity and raises potential hardness post-quench, but also increases the risk of brittle martensitic microstructures if tempering is inadequate. - Alloying elements that increase hardenability (Mn, Mo) reduce the need for extremely fast cooling but must be balanced to maintain weldability.
4. Mechanical Properties
| Property | SUP9 (general expectation) | SUP10 (general expectation) |
|---|---|---|
| Tensile strength | Moderate — good balance with ductility | Higher — increased maximum tensile capacity after heat treatment |
| Yield strength | Moderate | Higher |
| Elongation (ductility) | Higher ductility compared to SUP10 | Lower elongation owing to increased carbon and martensite fraction |
| Impact toughness | Better notch toughness at comparable strength due to lower carbon | Reduced impact toughness at equal heat treatment level unless tempered or alloyed to compensate |
| Hardness (as-quenched potential) | Lower maximum achievable hardness | Higher achievable hardness; increased wear resistance potential |
Explanation: The carbon-driven increase in SUP10 raises the potential tensile and yield strengths under similar heat-treatment conditions. The trade-off is decreased ductility and toughness unless tempering, microalloying, or post-weld heat treatments are used to mitigate brittleness. Material selection must therefore consider the required balance between static strength and dynamic toughness.
5. Weldability
Weldability considerations emphasize carbon content, hardenability, and ppm-level microalloying.
Useful indices: - Carbon Equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (for steels that include other alloying effects): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - SUP10’s higher carbon increases $CE_{IIW}$ and $P_{cm}$ relative to SUP9, signaling higher susceptibility to cold cracking, greater preheat requirements, and the need for controlled interpass temperatures. - If Mn/Mo are raised alongside carbon to maintain hardenability balance, the effect on weldability can be amplified because these elements further raise the carbon-equivalent metrics. - Practical mitigation: preheat and controlled interpass temperatures, lower hydrogen welding processes, post-weld heat treatment (PWHT), and filler metals designed to match toughness requirements.
Overall: SUP9 is generally easier to weld and requires less stringent preheating/PWHT than SUP10 for comparable component geometries.
6. Corrosion and Surface Protection
- Both SUP9 and SUP10 are non-stainless carbon steels; they rely on surface protection for corrosion resistance.
- Typical protection strategies: hot-dip galvanizing, zinc electroplating, organic coatings (paints, epoxies), and specialized conversion coatings. For components requiring long-term exposure resistance, duplex systems (galvanize + paint) are common.
- PREN (pitting resistance equivalent number) is not applicable to plain carbon steels: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index applies to stainless alloys; since Cr and Mo contents are low or absent in SUP9/SUP10, corrosion resistance must be supplied by coatings rather than intrinsic alloying.
7. Fabrication, Machinability, and Formability
- Machinability: SUP10’s higher hardness and carbon content increase tool wear and may require slower feeds or tougher tooling grades. SUP9 will generally machine easier, especially in annealed or normalized conditions.
- Formability: SUP9’s higher ductility makes it better for forming operations (bending, deep drawing) without cracking. SUP10 is less forgiving in forming and may require intermediate anneals.
- Cutting and finishing: abrasive wear resistance is higher for SUP10 when heat-treated to higher hardness, making it preferable for wear-prone parts but more challenging for finishing operations.
- Overall: choose supply condition (annealed, normalized, quenched & tempered) to suit the downstream forming and machining processes.
8. Typical Applications
| SUP9 — Typical Uses | SUP10 — Typical Uses |
|---|---|
| Structural components where weldability and toughness are prioritized (fabricated frames, general machine parts) | Components requiring higher strength/hardness and wear resistance (gears, pins, shafts subjected to higher loads) |
| Parts that need good formability or complex fabrication before heat treatment | Heat-treated parts where higher tensile strength is required after quench & temper |
| Medium-duty fasteners, brackets, supports where cost and fabrication ease matter | Bearing housings, medium-wear mechanical interfaces, tempered quenched components |
Selection rationale: - Choose SUP9 when fabrication complexity, weldability, and notch toughness are critical and the design does not demand the absolute highest hardened strength. - Choose SUP10 when design calls for higher post-heat-treatment strength, wear resistance, or smaller component sizes where higher strength reduces section size or weight.
9. Cost and Availability
- Cost: SUP10 typically carries equal or slightly higher material cost driven by additional heat treatment and tighter control needed for higher carbon variants. If SUP10 requires more stringent PWHT or special filler metals for welding, lifecycle fabrication cost rises.
- Availability: both grades are commonly available in standard product forms (bars, plates, forgings) from general steel suppliers. SUP9 variants may be more widely stocked for general structural applications; SUP10 may be produced to order in specific heat-treated conditions or require longer lead times if special chemistries or microalloying are requested.
- Procurement note: request mill certificates and heat-treatment records to confirm chemical composition, hardness, and heat treatment condition when specifying either grade.
10. Summary and Recommendation
| Attribute | SUP9 | SUP10 |
|---|---|---|
| Weldability | Better — lower carbon equivalent | Moderate to lower — higher CE, needs preheat/PWHT |
| Strength–Toughness balance | Balanced — better ductility and notch toughness | Higher strength potential — reduced ductility unless tempered |
| Cost (material + processing) | Lower to moderate | Moderate to higher (processing/heat treatment/welding) |
Recommendation: - Choose SUP9 if you need a steel that is easier to weld and fabricate, requires good toughness and formability in the finished component, or when minimizing fabrication cost and complexity is a priority. - Choose SUP10 if the design requires higher quenched-and-tempered strength or higher surface hardness for wear resistance and you can accommodate stricter welding controls and appropriate tempering/PWHT treatments.
Final practical guidance: - Specify the required supply condition (annealed, normalized, quenched & tempered) and target mechanical properties rather than only the grade name. Ask vendors for certified composition and hardness/impact test records. If welding is required, include preheat and PWHT instructions in the fabrication specification and consider specifying filler metal and hydrogen controls to mitigate cracking risk.