Q235 Steel vs 45 Steel vs 40Cr Steel

In engineering practice, steel selection directly influences performance, hana ailihua, kūlia, and cost of components.

Three commonly referenced steels in Chinese and international standards — Q235, 45 Kukui Kekuhi, a 40Cr — cover a broad spectrum of design requirements, from basic structural support to high‑strength mechanical parts.

Although each is based on iron‑carbon metallurgy, their alloying strategies, microstructural behavior, ʻO ka hana mechanication, and optimal applications differ substantially.

This article provides a multi‑perspective, moo kakahtia, and in‑depth comparison to guide material selection and engineering decision‑making.

1. Metallurgical Identity and Classification

Q235 Steel

Q235 is a low-carbon structural steel widely used in general engineering and construction applications.

It is the most common Chinese ʻaihue kīwī Kumu, equivalent to Astm A36 a EN S235JR. Q235 offers a balance of strength, kumaikalua, a me ka wellingbility, making it suitable for bridges, Nā hale, ship structures, Poolali, and machinery frames.

Nā hiʻohiʻona

• Kinohi: Carbon ≤ 0.20–0.25%, Mn 0.30–0.70%, trace S and P.
• Nā Pīkuhi Propertinies: Yield strength ≈ 235 Mpa, tensile strength ≈ 375–500 MPa.
• Weldable and formable: Hiki keʻoki maʻalahi, welded, and cold-formed.
• Kumukūʻai-maikaʻi: Economical option for general structural applications.
• Noi: Construction beams, nā hana hana, shopbuilding, nā ipu koʻikoʻi.

45 Kukui Kekuhi (also known as C45 or 1.1191)

45 steel is a medium-carbon steel widely used in China and internationally for mechanical parts requiring higher strength and hardness than low-carbon steels.

It corresponds roughly to AISI 1045. It is suitable for shafts, Kauluhi, and fasteners that are mechanically loaded and can be heat-treated.

Nā hiʻohiʻona

• Kinohi: Carbon ≈ 0.42–0.50%, Mn 0.50–0.80%, S/P <0.05%.
• Nā Pīkuhi Propertinies (Anned): Tensile strength ≈ 570–700 MPa, yield strength ≈ 330–500 MPa.
• Heat-treatable: Can be quenched and tempered to achieve higher hardness and wear resistance.
• Good machinability and moderate toughness: Balances strength and processability.
• Noi: Nā papahele, Kauluhi, nā bolts, ankles, ka hoʻopiliʻana i nā rods, and mechanical parts under moderate loads.

40Cr Steel (Uaʻikeʻia e like me 1.7035)

40Cr is a medium-carbon, Chromium-alloyed steel widely used in applications requiring ʻoi nui ka ikaika, hālulu, a kau pale than ordinary medium-carbon steels.

Chromium improves hardenability, Ke kū'ē neiʻo Corrosionion, a me ka ikaika kaumaha. It is roughly equivalent to AISI 5140.

Nā hiʻohiʻona

• Kinohi: Carbon ≈ 0.37–0.44%, Chromium ≈ 0.80–1.10%, Mn 0.50–0.80%, S/P <0.035%.
• Nā Pīkuhi Propertinies (kūlohelohe): Tensile strength ≈ 745–930 MPa, yield strength ≈ 435–600 MPa.
• Excellent hardenability: Can be quenched and tempered to achieve high hardness (a i hrc 50) for wear-resistant parts.
• Good fatigue resistance and toughness: Suitable for critical mechanical components.
• Noi: Nā papahele, Kauluhi, lihao, Mea kaumaha-dram, Kuha wai, and other high-strength mechanical parts.

2. ʻO ke hoʻohālikelike o keʻano hoʻohālikelike: Q235 Steel vs 45 Steel vs 40Cr Steel

The chemical composition of steel directly determines its phase transformation behavior and mechanical properties.

The following table presents the standard composition ranges (per Chinese national standards) and the functional mechanisms of key elements for the three steels:

Key differences:

Q235 has low carbon and no intentional alloying elements, focusing on processability; 45 steel has higher carbon and stricter impurity control, enabling heat treatment;

40Cr adds chromium to optimize hardenability and mechanical properties, bridging the gap between carbon steel and high-alloy steel.

3. Nā hiʻohiʻona microstrucher: From As-Delivered to Heat-Treated States

Microstructure is the link between chemical composition and mechanical properties.

The three steels exhibit distinct microstructures in different states, directly affecting their performance:

As-Delivered State (Hot Rolled)

• Q235 Steel: Consists of ferrite (α-fe) + Puʻuʻupuʻu (lamellar mixture of ferrite and cementite). Ferrite is the main phase (70-80%), ensuring good ductility and weldability.
  Pearlite content (20-30%) provides moderate strength. The structure is coarse-grained due to low alloy content and simple hot rolling process.
• 45 Kukui Kekuhi: Ferrite + Puʻuʻupuʻu, with higher pearlite content (40-50%) than Q235 due to higher carbon content.
  The structure is finer and more uniform (kila kila kiʻekiʻe), with fewer inclusions, leading to better strength and toughness balance.
• 40Cr Steel: Ferrite + Puʻuʻupuʻu + trace chromium-rich carbides. Chromium refines the grain size, making the pearlite lamellae thinner than 45 Kukui Kekuhi.
  The presence of chromium carbides (Cr₃C) lays the foundation for subsequent heat treatment strengthening.

Heat-Treated State (Queech + Huhū, Q&T)

• Q235 Steel: Poor hardenability; Queech (wai waiʻunu wai) only forms martensite in the surface layer, with the core remaining ferrite-pearlite.
  Heat treatment is rarely used, as it cannot significantly improve overall performance and may cause deformation/cracking.
• 45 Kukui Kekuhi: Ma hope o ka haʻaleleʻana (840–860℃ water/oil cooling), the structure transforms into lath martensite (hard but brittle).
  Tempering at 200–300℃ (low tempering) produces tempered martensite, improving toughness while maintaining high hardness.
  Tempering at 500–600℃ (medium tempering) forms sorbite, achieving a balance of strength (σᵤ≥600 MPa) a me ka defility (δ≥15%).
• 40Cr Steel: Excellent hardenability; oil cooling (instead of water cooling) can achieve full martensite transformation even for workpieces with diameter ≤50 mm.
  After medium tempering (520–560℃), the structure becomes tempered sorbite (fine-grained sorbite + nā kāwele i laweʻia), with higher strength and toughness than 45 Kukui Kekuhi. Chromium stabilizes the martensite structure, reducing temper brittleness.

4. Mechanical Properties Comparison — Q235 Steel vs 45 Steel vs 40Cr Steel

5. Heat Treatment Characteristics: Hardenability and Process Adaptability

Heat treatment responsiveness (Kālā paʻakikī, temper stability) determines the scope of application of steel. The three steels differ significantly in this regard:

Hardenability

• Q235 Steel: Very poor hardenability. The critical cooling rate is high; only thin workpieces (≤5 mm) can form a small amount of martensite after water cooling, while thick workpieces remain ferrite-pearlite.
  Heat treatment is not economically viable, so it is used in the as-delivered state.
• 45 Kukui Kekuhi: Moderate hardenability. Workpieces with diameter ≤20 mm can achieve full martensite by water cooling; for thicker workpieces (20-40 mm), oil cooling leads to incomplete hardening (core is sorbite).
  It is suitable for medium-sized, medium-load parts requiring heat treatment.
• 40Cr Steel: Excellent hardenability. Chromium reduces the critical cooling rate, enabling full martensite transformation in workpieces with diameter ≤50 mm by oil cooling (avoiding water cooling-induced deformation/cracking).
  For workpieces up to 80 mm, water-oil quenching can achieve uniform hardening, making it suitable for large, heavy-load parts.

Common Heat Treatment Processes and Effects

• Annalile: Q235 annealing (600–650℃) relieves rolling stress; 45/40Cr annealing refines grains and reduces hardness for machining. 40Cr annealing also dissolves chromium carbides, preparing for quenching.
• Hana maʻamau: Q235 normalizing (880–920℃) improves structure uniformity; 45/40Cr normalizing enhances strength and toughness, used as a pre-treatment for complex parts.
• Queech + Huhū: The core process for 45/40Cr. 45 steel uses water quenching + medium tempering; 40Cr uses oil quenching + medium tempering, achieving better comprehensive performance and lower deformation.
• Eha hanona: 45/40Cr can undergo induction hardening or carburizing (45 Kukui Kekuhi) to improve surface hardness (HRC 50–60) for wear-resistant parts.
  40Cr’s chromium content enhances surface hardening effect and wear resistance.

6. Processing Performance: Kauhi, Kākau, Welding, a me ka machining

Processing performance directly affects manufacturing efficiency and cost, and is a key factor for material selection in mass production:

Casting Performance

• Q235 Steel: Poor castability. Low carbon and alloy content lead to poor molten fluidity and high shrinkage rate, prone to shrinkage cavities and porosity. Rarely used for casting; mainly for rolling and forming.
• 45 Kukui Kekuhi: Moderate castability. Higher carbon content improves fluidity compared to Q235, but still prone to hot cracking. Used for small to medium-sized cast parts with low precision requirements.
• 40Cr Steel: Better castability than 45 Kukui Kekuhi. Chromium refines the cast structure, reducing shrinkage and hot cracking tendency.
  Suitable for precision cast parts requiring heat treatment, but casting cost is higher than rolling.

Forging Performance

• Q235 Steel: Excellent forging performance. Forging temperature range (1150–850℃) is wide, with good plasticity and low deformation resistance. Suitable for hot forging of simple shapes (E.g., nā bolts, nā brackets).
• 45 Kukui Kekuhi: Good forging performance. Forging temperature (1100–800℃); requires uniform heating to avoid cracking. Forged parts have refined grains, improving heat treatment effect.
• 40Cr Steel: Moderate forging performance. Chromium increases deformation resistance, requiring higher forging force and stricter temperature control (1100–820℃).
  Post-forging annealing is necessary to eliminate internal stress and prepare for heat treatment.

Welding Performance

• Q235 Steel: Excellent welding performance. Low carbon content avoids martensite formation in the heat-affected zone (Haz), with no preheating or post-weld heat treatment (Pwht) required for thin workpieces. Compatible with all welding methods (Smaw, Kāmaʻa kikomua, Gtaw).
• 45 Kukui Kekuhi: Poor welding performance. High carbon content leads to hard martensite in the HAZ, prone to cold cracking.
  Manaihi (150–200℃) and PWHT (tempering at 600–650℃) are mandatory. Welding is only used for repair, not for load-bearing welds.
• 40Cr Steel: Worse welding performance than 45 Kukui Kekuhi. Chromium increases HAZ hardenability, making cold cracking and temper brittleness more likely.
  Strict preheating (200–300℃), low heat input welding, and PWHT are required. Welding is generally avoided; mechanical joining (bolting, riving) makemakeʻia.

Machimen Hana

• Q235 Steel: Excellent machining performance. Low hardness and good plasticity make cutting easy, with low tool wear.
  Suitable for high-speed machining and automated production lines (E.g., machining of brackets, Nā papa).
• 45 Kukui Kekuhi: Good machining performance in the as-delivered state (HBW 190–230). Ma hope o ka mālama wela (hardness ＞ HRC 30), machining difficulty increases, requiring hard alloy tools. It is a typical “machinable heat-treated steel”.
• 40Cr Steel: Moderate machining performance in the as-delivered state. Chromium increases cutting resistance, so tool wear is higher than 45 Kukui Kekuhi.
  After Q&T (HBW 280–320), machining requires higher cutting speed and feed rate control, with machining cost 15–20% higher than 45 Kukui Kekuhi.

7. Ke kū'ē neiʻo Corrosionion

All three steels are carbon/alloy structural steels without intentional corrosion-resistant alloying elements (Cr content in 40Cr is too low for passive film formation), so their corrosion resistance is generally poor, with slight differences:

• Q235 Steel: ʻO ke kū'ē kū'ē. High impurity content (S, P) and low alloy content accelerate atmospheric and freshwater corrosion, with a corrosion rate of 0.1–0.3 mm/year in industrial atmospheres. Must be protected (Kāleka, garvalirigigling) for outdoor service.
• 45 Kukui Kekuhi: Slightly better corrosion resistance than Q235. Lower impurity content and finer structure reduce corrosion initiation sites.
  Corrosion rate is 0.08–0.25 mm/year in industrial atmospheres, still requiring protection for long-term service.
• 40Cr Steel: Best corrosion resistance among the three. Chromium forms a thin oxide film on the surface, inhibiting corrosion.
  Corrosion rate is 0.05–0.20 mm/year in industrial atmospheres, and it has better resistance to mild acids/bases than Q235 and 45 Kukui Kekuhi.
  Akā naʻe,, it still suffers from pitting corrosion in high-chloride media, requiring anti-corrosion treatment (chromizing, Kāleka).

8. Application Scenarios Q235 Steel vs 45 Steel vs 40Cr Steel

The application of the three steels is strictly based on their performance and cost, covering different industrial fields:

Q235 Steel

Low-cost, general-purpose structural steel. Hoʻokomoʻia nā noi:

• Building and construction: Steel frames, beams, nā kolamu, steel plates, and reinforcement bars for ordinary buildings, Nā alahaka, and workshops.
• Mechanical manufacturing: Non-load-bearing parts (nā brackets, Nā Hale Kiʻi, uhiʻehā), nā bolts, Nā Kahu, and washers for low-load equipment.
• Pipeline and container: Low-pressure water pipelines, Nā pahu mālama, and brackets for non-corrosive media.

45 Kukui Kekuhi

Medium-strength, heat-treatable carbon steel. Hoʻokomoʻia nā noi:

• Mechanical parts: Nā papahele kāmaʻa, ka hoʻopiliʻana i nā rods, lihao, nā bolts, and nuts for medium-load equipment (E.g., small motors, Pumps, and agricultural machinery).
• Tool components: Nā Wili, Nā Punches, and dies for low-speed, low-wear tools (after surface hardening).
• Ka Hoʻolālā Wīwī: Non-critical parts (E.g., Nā Mō'ī Brake, ʻO nā alakaʻi alakaʻi) for low-end vehicles.

40Cr Steel

Ikaika-ikaika, alloy structural steel. Hoʻokomoʻia nā noi:

• Mechanical transmission parts: High-load gear shafts, Nā Kūlana, Kauluhi, and bearings for heavy machinery (E.g., engineering machinery, Hana Pūnaewele).
• Aitompetitive Aʻo Aerospace: Critical parts (E.g., engine crankshafts, pākuʻi nā mea kūʻai, transmission gears) for high-end vehicles and light aircraft.
• Petrochemical industry: High-pressure pipeline flanges, Nā Vilves, and pump shafts for medium-corrosion, high-load environments.

9. Cost and Cost-Effectiveness Comparison

Cost is a key factor in large-scale production. The relative cost (taking Q235 as the baseline) and cost-effectiveness of the three steels are as follows:

10. Hopena

The comparative analysis of Q235 steel, 45 Kukui Kekuhi, and 40Cr steel highlights how NA MANAOLO DOLIAMERA, AliLila, a me nā wela wela influence mechanical performance, hana ailihua, a me nā kūpono kūpono.

• Q235 steel he low-carbon structural steel with excellent ductility, wawahua, a me ka formability.
  Its cost-effectiveness makes it ideal for general structural and fabrication applications, but it has limited strength and requires corrosion protection.
• 45 Kukui Kekuhi he medium-carbon, heat-treatable steel offering higher strength and hardness than Q235.
  I ka wa ua pāʻia, it achieves significantly improved tensile strength and wear resistance, ke kūpono kūpono no mechanical parts such as shafts, Kauluhi, and axles.
• 40Cr steel he medium-carbon chromium-alloy steel Hoʻolālāʻia no high-strength and fatigue-resistant applications.
  Ia deep hardenability and wear resistance allow it to perform under heavy cyclic loads, e like me kaʻike lihao, ka hoʻopiliʻana i nā rods, and high-load machinery components.

Bottom line: Material selection should balance ikaika, paʻakikī, markinpalibility, wawahua, a me ke kumukuai against service requirements.
Q235 suits structural and low-load applications, 45 steel covers moderate-load mechanical parts, and 40Cr steel excels in high-strength, high-fatigue, and wear-critical components.

 

FaqS

What is the main difference between Q235, 45, and 40Cr steels?

• Q235 is low-carbon structural steel; 45 steel is medium-carbon and heat-treatable; 40Cr is a medium-carbon chromium-alloy steel with high strength and hardenability.

Can Q235 steel be heat-treated to improve strength?

• ʻAʻole, Q235’s low carbon content limits heat-treatment hardening. Strength improvements rely on cold working or design optimization.

Which steel is best for shafts and gears?

• 45 steel is suitable for moderate-load shafts and gears; 40Cr is preferred for high-strength, high-fatigue, and wear-resistant mechanical components.

Is 40Cr steel corrosion-resistant?

• Not inherently. Nā uhi pale, Wehe, or design considerations are needed for corrosive environments.

How does heat treatment affect 45 and 40Cr steels?

• Quenching and tempering significantly improve tensile strength, hālulu, a me kaʻehaʻeha, making them suitable for mechanically demanding components.