What Are The Differences Among The Four Types Of Materials, Q235A, Q235B, Q235C And Q235D?

Q235 series is the most widely used carbon structural casting steel in China. Its naming rule is “Q + number + quality grade symbol”, where “Q” stands for yield strength, “235” indicates the yield strength value of 235 MPa, and A, B, C, and D represent different quality grades. These four materials have significant differences in chemical composition, mechanical properties, smelting process, and application scenarios. The following is a detailed comparison of five dimensions.

I. Chemical composition: The content of sulfur and phosphorus decreases gradually at each level.

The core differences among Q235A, B, C, and D lie in the control of impurity elements such as sulfur (S) and phosphorus (P). According to the national standard GB/T 700-2006:

1.1 Q235A: Carbon content 0.14% – 0.22%, sulfur content ≤ 0.050%, phosphorus content ≤ 0.045%. It has relatively loose control over impurity elements and is suitable for scenarios where corrosion resistance requirements are not high.

1.2 Q235B: Carbon content ≤ 0.20%, sulfur content ≤ 0.045%, phosphorus content ≤ 0.045%. Compared with Q235A, it has stricter requirements for sulfur content and more stable mechanical properties.

1.3Q235C: Sulfur content ≤ 0.040%, phosphorus content ≤ 0.040%. Further reduce impurity content and enhance low-temperature toughness.

1.4 Q235D: Sulfur content ≤ 0.035%, phosphorus content ≤ 0.035%. It has the lowest impurity content among the four materials, ensuring excellent performance even in extremely cold environments.

1.5 Impact: Sulfur is prone to causing hot brittleness (cracking during high-temperature processing), and phosphorus is likely to cause cold brittleness (brittle fracture at low temperatures). As the grade increases, the purity of the steel improves, and its corrosion resistance and toughness are significantly enhanced. For instance, Q235D can maintain impact toughness at -20℃, while Q235A may experience brittle fracture at low temperatures.

2. Mechanical properties: Impact toughness increases step by step.

The tensile strength, yield strength and elongation requirements for the four materials are the same, but there are significant differences in impact toughness.

2.1 Q235A: Impact tests are not required, and its performance under impact loads cannot be guaranteed. It is suitable for structural components subjected to static loads, such as simple building frames and temporary steel structures.

2.2 Q235B: It is required to undergo a 20℃ room temperature impact test, with the V-notch impact energy ≥ 27J. It is suitable for the manufacturing of bridges, ships and vehicles in normal temperature environments.

2.3 Q235C: Impact tests at 0℃ are required, with impact energy ≥ 27J. It is suitable for steel structure projects and low-temperature mechanical equipment in northern winter construction.

2.4 Q235D: Impact tests at -20℃ are required, with impact energy ≥ 27J. It is specifically designed for extremely cold regions, such as high-latitude bridges and polar scientific research equipment.

III. Smelting Process: The density of the microstructure is gradually enhanced.

All four materials are processed with calm steel technology (fully deoxidized and dense structure), but Q235D may use special calm steel (TZ), which has more stable performance.

3.1 Q235A/B: Conventional mild steel, meeting general engineering requirements.

3.2 Q235C/D: Special deoxidation processes may be adopted to further reduce gases and inclusions and enhance low-temperature toughness.

3.3 Process differences: Calming steel eliminates bubbles in the molten steel by adding deoxidizers (such as aluminum), making the structure more compact. Special calming steel (TZ) reduces non-metallic inclusions through stricter deoxidation control and is suitable for scenarios with extremely high requirements for toughness.

IV. Four application scenarios: Full coverage from normal temperature to extreme cold.

Based on the working environment and performance requirements, the application scenarios of the four materials are clearly distinguished:

4.1 Q235A: It has the lowest cost, but its impact toughness cannot be guaranteed. It is suitable for structural components with low quality requirements and subject to static loads, such as factory trusses, simple mechanical casings, rivets, and welded parts.

4.2 Q235B: It offers the best cost performance and is widely used in general engineering structures and mechanical manufacturing. For instance, it is applied in bridges, ships, vehicles, steel structure workshops, common bolts, and sprockets.

4.3 Q235C: It is suitable for applications where there are certain requirements for low-temperature impact performance, such as cold storage equipment, winter construction machinery, and steel structures in northern regions.

4.4 Q235D: Specifically designed for extremely cold environments. Such as outdoor steel structures in Northeast China, high-latitude bridges, low-temperature cold storage facilities, and polar scientific research equipment.

V. Future Trends: Dual Drive of High Performance and Environmental Protection

With the development of industry, the Q235 series of materials is evolving towards higher strength and better toughness.

5.1 Microalloying technology: 

By adding elements such as Nb and V, it enhances strength while maintaining cost advantages.

5.2. Controlled rolling and controlled cooling process: Optimize hot rolling parameters, refine grains, and enhance comprehensive performance.

5.3. Environmental requirements: Reducing sulfur and phosphorus content not only enhances performance but also decreases pollutant emissions during the smelting process.

Supplier

Luoyang Fonyo Heavy Industries Co., Ltd,founded in 1998,is a manufacturer in railway casting parts.Our factory covers an area of 72,600㎡, with more than 300 employees, 32 technicians, including 5 senior engineers, 11 assistant engineers, and 16 technicians.Our production capacity is 30,000 tons per year. Currently, we mainly produce casting, machining, and assembly for locomotive, railcar, high-speed trains, mining equipment,wind power,etc.
We are the railway parts supply to CRRC(including more than 20 branch companies and subsidiaries of CRRC),Gemac Engineering Machinery,Sanygroup, Citic Heavy Industries,etc. Our products have been exported to Russia, the United States, Germany, Argentina, Japan, France, South Africa,Italy and other countries all over the world.