Q960E and Q690E are both domestic low-alloy high-strength structural steels with grade E, which means they both meet the impact toughness requirements at -40℃ and are suitable for low-temperature and harsh working conditions. However, there is a distinct gap in their strength levels. This gap further leads to obvious differences in chemical composition, production processes, processing requirements, and application scenarios.
Chemical Composition
Both steels rely on alloy elements to enhance performance, but Q960E has stricter control over carbon content to ensure ultra-high strength while avoiding excessive brittleness. The types and proportions of alloy elements are also more refined to balance the contradiction between strength and toughness. The specific composition comparisons are as follows:
| Element | Q960E | Q690E |
|---|---|---|
| Carbon (C) | ≤0.18% | ≤0.20% |
| Silicon (Si) | ≤0.5% | ≤0.60% |
| Manganese (Mn) | ≤1.5% | ≤2.00% |
| Phosphorus (P) | ≤0.015% | ≤0.025% |
| Sulfur (S) | ≤0.02% | ≤0.015% |
| Alloy elements | Contains ≤0.9% nickel, 0.04%-0.06% niobium, and the chromium content is as low as ≤0.01%. The precise proportion of micro-alloy elements ensures ultra-high strength and low-temperature toughness | Contains ≤0.80% nickel, ≤1.00% chromium, ≤0.30% molybdenum, and also adds micro-alloy elements such as niobium and titanium to enhance strength and welding performance |
Mechanical Properties
The most prominent difference between the two lies in the yield strength. Q960E is ultra-high-strength steel, and Q690E is high-strength steel. There are also corresponding differences in tensile strength, elongation and other indicators:
| Performance Indicator | Q960E | Q690E |
|---|---|---|
| Yield strength | ≥960MPa (for thickness ≤50mm) | ≥690MPa (for thickness ≤50mm); ≥630MPa when thickness >100mm) |
| Tensile strength | 980 - 1150MPa | 710 - 940MPa (varies with thickness) |
| Elongation | ≥12% | ≥14% |
| Impact toughness | Impact energy ≥27J (some standards require ≥34J) at -40℃ | Impact energy ≥47J at -40℃, with better low-temperature anti-fracture performance |
Production and Processing Requirements
To achieve different strength levels, the two steels have obvious differences in production process complexity and post-processing difficulty:
- Q960E: It adopts oxygen converter or electric furnace smelting, combined with vacuum degassing technology to achieve the standard of ultra-pure steel. After multi-pass rolling, it needs to go through quenching at 900 - 950℃ and tempering at 200 - 300℃. During welding, the preheating temperature must be controlled at 150 - 200℃, and the heat input should be limited to 15 - 25kJ/cm. When cutting and bending, the cold bending radius should be at least 6 times the plate thickness, and special tools are required for cutting.
- Q690E: It can be produced by conventional tempering process. Its welding performance is more outstanding, and it is suitable for common processes such as arc welding and gas shielded welding. There is no need for extremely strict preheating and heat input control during welding. The overall processing process is simpler, and the processing cost is much lower than that of Q960E.
Application Scenarios
The choice of the two in practical applications is mainly based on load-bearing requirements and cost budgets:
- Q960E: It is mainly used in high-end and high-demand fields. For example, it is used to make the booms of large-tonnage automobile cranes, which can reduce the weight of the boom by a large margin. It is also applied to the hulls of light armored vehicles, the supporting columns of 1000-meter skyscrapers, the pressure hulls of deep-sea drilling platforms and deep-sea lifeboats. Its ultra-high strength can meet the needs of extreme load-bearing and lightweight.
- Q690E: It is widely used in general heavy-duty projects with high cost performance. It is used for the pressure steel pipes of Baihetan Hydropower Station, some pipe sections of the China-Russia Eastern Route Natural Gas Pipeline, the bogie components of high-speed rail, and the hydraulic supports of coal mines. It can meet the strength requirements of most heavy-duty equipment and projects, and can significantly reduce costs compared with Q960E.
What do the "E" grades of Q960E and Q690E represent, and what impact does this have on their application scenarios?
The "E" in both steels indicates their quality grade, which means they both meet the impact toughness requirements under the condition of -40℃. This characteristic enables both steels to be applied in low-temperature and harsh environments, such as polar scientific research stations, alpine area projects and marine equipment. Unlike ordinary structural steels, they are not prone to brittle fracture in extreme low-temperature conditions, thus expanding their application scope in severe working conditions.
In terms of mechanical properties, what makes Q960E more suitable for manufacturing high-end equipment than Q690E?
The key advantage of Q960E over Q690E lies in its much higher yield strength. Its minimum yield strength of 960MPa is far higher than Q690E's maximum yield strength of 690MPa. Under the same load-bearing capacity, using Q960E can greatly reduce the thickness and weight of components. For example, when used to make crane booms, it can reduce the weight of the boom by more than 15%, which improves the operation efficiency and stability of the equipment. This lightweight and high-strength advantage is irreplaceable for high-end equipment with strict weight restrictions.
Are there significant differences in production costs and market prices between Q960E and Q690E?
Yes, there are huge differences. Q960E requires complex processes such as vacuum degassing and precise quenching and tempering during production, and the control of alloy elements is more stringent, which leads to high production costs. Its market price is about 2.5 times that of Q690E. Q690E has a mature and simple production process, low technical threshold, sufficient market supply, and stable prices. It is a cost-effective choice for general heavy-duty projects.
When constructing marine engineering projects, how to choose between Q960E and Q690E?
The choice depends on the specific components and load requirements. For key components that need to bear ultra-high pressure and heavy load, such as the pressure shell of deep-sea drilling platforms and the core load-bearing structure of large ships, Q960E should be selected for its ultra-high strength can ensure safety under extreme marine conditions. For conventional components such as general pipeline parts and ordinary deck structures of offshore platforms, Q690E is more appropriate. It can meet the basic strength and corrosion resistance requirements while controlling the overall project cost.
Why does Q960E have lower elongation than Q690E, and what impact does this have on its use?
Q960E sacrifices part of its elongation to achieve ultra-high strength. This is a common trade-off in the design of high-strength steels. Its elongation of ≥12% is lower than Q690E's ≥14%, which means its plastic deformation capacity is relatively weak. In practical use, Q960E is not suitable for components that need large plastic deformation. It is more used in load-bearing components with relatively fixed shapes and small deformation requirements, such as fixed supporting columns and crane booms, to avoid failure due to insufficient deformation capacity during use.