S890QL1 Chemical Composition and Carbon Equivalent (CEV) Explained

1. Ladle Chemical Composition (Castings Analysis, Maximum Percentage)

Note:

1) The combined alloying element limits apply to EN 10025-6;

2) Actual values are subject to specific mill certificates.

2. Role of Each Element

Carbon (C ≤ 0.20%): The primary strength-contributing element; however, it must be kept at a low level to maintain weldability and toughness. Although excessively high carbon content can increase tensile strength, it significantly reduces toughness in the heat-affected zone (HAZ) and increases the risk of cracking.

Manganese (Mn ≤ 1.70%): Improves hardenability and strength through solid solution strengthening and controlled MnS formation (S must be kept ≤ 0.010% to avoid MnS segregation bands).

Nickel (Ni ≤ 0.20%): A key toughening element that significantly improves low-temperature impact toughness. Grade L1 steels rely on controlled nickel addition to achieve performance at -60°C.

Chromium and Molybdenum (Cr, Mo): Provide hardenability and resistance to temper softening, ensuring that the steel can be fully hardened even in thick sections during the QT treatment process.

Boron (B ≤ 0.005%): A trace element that strongly enhances hardenability, allowing full-thickness hardness to be maintained while reducing carbon content.

Niobium, Vanadium, and Titanium (Nb, V, Ti): Microalloying elements that precipitate carbonitrides and pin the austenite grain boundaries, forming the fine-grained microstructure required for strength and toughness.

3. Carbon Equivalent (CEV) and Weldability

Carbon equivalent is a standard indicator for evaluating the weldability of alloy steels. The commonly used formula is as follows:

CEV (IIW/ISO formula):

CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

For a typical S890QL1 composition, the CEV typically ranges from 0.50% to 0.65%. Although this value is moderate, the high base strength means that hydrogen-induced cold cracking (HICC) remains a real risk. Therefore, the welding process must meet the following requirements:

Use low-hydrogen filler metal (Class H5 or H4);

Preheat when plate thickness or CEV meets the specified criteria;

Control heat input and interpass temperature.

4. FAQ

Q1: What is the typical CEV for S890QL1?

Most factory certificates indicate that for plate thicknesses ≤ 50 mm, CEV ranges from 0.50% to 0.60%. As plate thickness increases, hardenability improves, and CEV tends toward the upper limit of the range.

Q2: Is S890QL1 a low-alloy steel?

Yes. This steel grade is classified as a high-strength low-alloy (HSLA) quenched and tempered steel. The total alloy content (Cr + Mo + Ni + Cu + B + microalloying elements) is kept below typical alloy steel levels to maintain good weldability.

Q3: What is the difference between ladle analysis and product analysis?

According to EN 10025-6, product (inspection) analysis allows for slightly wider tolerances. When performing welding evaluations and CEV calculations, the ladle analysis values reported in the factory certificate should always be used.