Why Chinese Steel Grade Names Matter
Chinese steel grades follow a logical naming system that packs the most important information about a material into a short designation. Once the rules are understood, a grade name such as Q235B or 12Cr1MoVG tells you the yield or carbon level, the main alloying elements and sometimes the delivery state or the intended service. This article explains the system step by step, using the grades most frequently encountered in pipe and structural steel orders.
The Q-Series Structural Steels: Q235B and GB/T 700
Q235B is the most common general structural steel in China. The letter Q is the pinyin initial of the Chinese word for yield, the number 235 is the minimum yield strength in MPa, and the trailing letter B is the quality grade. Grades run from A to D; the higher the letter, the better the guaranteed impact toughness, with Grade D typically tested at -20°C.
The deoxidation method can be added as another suffix. F means rimmed steel, b means semi-killed steel, Z means killed steel and TZ means special killed steel. Grade B and above are usually supplied killed. Per GB/T 700, Q235B plate and sections up to 16 mm guarantee a yield strength of at least 235 MPa, tensile strength of 370–500 MPa and elongation of at least 26%, with Charpy impact energy of at least 27 J at +20°C.
Carbon Steels Named by Carbon Content: 20# and GB/T 699
High-quality carbon structural steels are named by their average carbon content in hundredths of a percent. Grade 20 therefore contains about 0.20% carbon, grade 45 about 0.45%, and so on. When manganese is present as a deliberate alloying element, the letter Mn is added, as in 20Mn, and its mass fraction is stated separately in the standard.
Quality designations may follow: A means high-quality steel and E means special high-quality steel, as in 50MnA. These grades are used for machine parts, shafts, couplings and pressure-processing components, and grade 20 pipe is a standard material for boiler and heat-exchanger tubing at moderate temperatures.
Pipeline Steels: L245 and GB/T 9711
Line-pipe grades begin with L, the initial of Line, followed by the minimum yield strength in MPa. L245 guarantees at least 245 MPa yield, L290 at least 290 MPa, and L415 at least 415 MPa. The standard GB/T 9711 is the Chinese equivalent of API 5L.
Delivery condition letters follow the number: R for rolled, N for normalized, Q for quenched and tempered, and M for thermomechanically rolled. The letter S is added for pipes intended for sour service, where the material must resist sulfide stress cracking. An example such as L415QS therefore identifies a thermomechanically rolled, sour-service line pipe with a 415 MPa minimum yield strength.
Alloy and Special-Purpose Steels
| Grade | Standard | Meaning of the designation |
|---|---|---|
| 12Cr1MoVG | GB 5310 | About 0.12% carbon, about 1% chromium, molybdenum and vanadium alloying; G means boiler steel |
| 16MnDG | GB/T 18984 | About 0.16% carbon with manganese; DG means low-temperature pipeline steel |
| 15CrMoR | GB 713 | About 0.15% carbon with chromium and molybdenum; R means boiler and pressure vessel steel |
These designations are used for high-temperature boiler tubes, low-temperature pipelines and pressure vessels respectively. The letter system is consistent: G for boiler, DG for low-temperature pipeline, and R for pressure vessel.
Reading Numbers in Chinese Steel Names
Two- or three-digit numbers at the start of a designation usually indicate the carbon content in hundredths of a percent. The value is the target or best-controlled content, not a strict maximum, and the real permitted range is given in the corresponding standard table. In alloy grades such as 12Cr1MoVG, the same convention applies: 12 means roughly 0.12% carbon.
FAQ
Q1: What does the letter B in Q235B mean?
B is the quality grade of the steel. Grades A, B, C and D differ mainly in guaranteed Charpy impact energy: Grade B is tested at +20°C, Grade C at 0°C and Grade D at -20°C. Higher grades also allow slightly lower phosphorus and sulfur limits.
Q2: Does the number 235 in Q235 mean the actual yield strength?
It is the minimum guaranteed yield strength in MPa for thickness up to 16 mm. For thicker sections the guaranteed value steps down, and the governing tables of GB/T 700 must be used.
Q3: What does 20 in 20# steel mean?
It means the steel has an average carbon content of about 0.20%, expressed as a percentage. The two-digit number is the carbon content in hundredths of a percent.
Q4: What is the difference between L245 and Q235B?
L245 is a line-pipe grade defined in GB/T 9711 for oil and gas pipelines, with a minimum yield of 245 MPa and tight control of ductility and weldability for pipe service. Q235B is a general structural steel from GB/T 700, intended for buildings and machinery rather than pressurized pipeline service.
Q5: What do the suffixes R, N, Q and M after pipeline grades mean?
They describe the delivery condition: R is rolled, N is normalized, Q is quenched and tempered, and M is thermomechanically rolled. The condition affects the microstructure and hence the toughness of the pipe.
Q6: How should I interpret 12Cr1MoVG?
12 indicates about 0.12% carbon, Cr1 indicates about 1% chromium, Mo and V indicate molybdenum and vanadium additions, and G identifies the grade as a boiler steel under GB 5310, used for high-temperature superheater and header tubing.