NEWS&CASES
Time：2026-02-02
Class：News
Carbon Steel Bar Selection Technical Guide: Accurately Matching Working Conditions for Efficient Procurement
I. Core Definition and Key Advantages
Carbon steel bars are based on iron with a carbon content of 0.03%~2.0% and extremely low alloy element content, belonging to basic steel categories. Their core advantages are based on stable composition and mature production processes:
- Excellent machinability: Adaptable to multiple processing procedures such as turning, forging, welding, and cutting. Low-carbon steel and medium-carbon steel can be directly subjected to secondary processing without complex pre-treatment, improving production efficiency.
- Wide performance adaptability: Through carbon content adjustment, it achieves performance coverage from flexible forming to high strength and wear resistance, adapting to mechanical requirements of various scenarios such as fasteners, structural parts, and tooling components.
- Sufficient supply guarantee: Stable market inventory, mainstream suppliers can provide services such as retail cutting, fixed-length processing, and fast delivery to ensure project progress.
II. Core Selection Process: Three-Step Accurate Matching
The core of carbon steel bar selection is "matching performance to working conditions, locking grade to performance, and corresponding specification to grade", forming a closed-loop, accurate and efficient process.
Step 1: Lock Carbon Content Grade According to Working Conditions
Carbon content is the core indicator determining the strength, hardness, plasticity, and machinability of carbon steel bars. It is divided into three categories according to content, adapting to different working conditions:
Technical Tip: Medium-carbon steel (35#, 45#) is preferred for mechanical manufacturing; low-carbon steel (20#) is preferred for construction and welding scenarios; high-carbon steel (such as T12) is used for tool products.
Step 2: Determine Specifications and Forms According to Processing Requirements
After locking the carbon content grade, match specifications and forms with processing equipment and product dimensions to reduce waste and processing costs.
1. Form Selection (Adapting to Processing and Working Conditions)
- Round Steel: Mainstream form, diameter 5.5mm~220mm (theoretical weight 0.186kg/m~298kg/m), suitable for turning and forging, used for shafts, gears, fasteners, etc., with strong versatility.
- Square Steel/Hexagonal Steel: Square steel is used for brackets and bases; hexagonal steel has high precision, suitable for fasteners such as nuts and bolts, no additional positioning required during processing.
- Flat Steel: Thin with large surface area, used for frames and connectors, adapting to construction and equipment manufacturing scenarios.
2. Core Specification Parameters (Mandatory Inspection Items)
- Dimensional Tolerance: Implements GB/T 702-2008 standard, the diameter tolerance of round steel is controlled within ±0.02mm to ensure processing precision.
- Length: Standard length 6m, 9m, 12m, supporting fixed-length cutting to reduce material loss.
- Processing Technology: Hot-rolled (low cost, large batch); forged (dense structure, excellent impact toughness, suitable for high-strength parts, such as 45# forged round steel).
Step 3: Screen Grades and Suppliers According to Quality Standards
The quality of carbon steel bars directly determines the reliability of end products, focusing on controlling quality grades and supplier qualifications.
1. Quality Grade Classification
- Ordinary Carbon Steel: High sulfur and phosphorus impurity content, low price, suitable for extensive scenarios such as temporary supports.
- High-Quality Carbon Steel: Low impurity content, stable performance, mainstream grades 20#, 35#, 45#, suitable for machinery and automotive industries.
- High-Grade High-Quality Carbon Steel: Extremely low impurity content, excellent performance, suitable for precision machinery and high-end equipment.
2. Supplier Screening Standards
To avoid risks such as shoddy products and inconsistent specifications, focus on verifying three core qualifications:
- Qualifications and Testing: Supports material inspection, can provide MTC (Mill Test Certificate) to ensure that composition and mechanical properties meet national/industry standards.
- Inventory and Services: Sufficient inventory, supporting retail cutting and fixed-length processing, delivery cycle 3~7 days to ensure supply timeliness.
- Reputation and Cases: With cooperation cases of well-known enterprises, priority is given to established special steel suppliers in regions such as Wuxi and Handan with sufficient technical reserves.
III. Recommended Mainstream Grades: High-Adaptability Selection Reference
Three mainstream grades are recommended, covering more than 80% of procurement needs, adapting to core application scenarios:
1. 20# Carbon Steel Bar (Benchmark of Low-Carbon Steel)
Carbon content 0.17%~0.23%, excellent plasticity and weldability, low processing difficulty, market price about 3850 RMB/ton, a general-purpose high-cost-performance grade. Suitable for building structures, mechanical blanks, pipe fittings and other scenarios, with sufficient inventory and fast delivery.
2. 45# Carbon Steel Bar (Core of Medium-Carbon Steel)
Carbon content 0.42%~0.50%, balanced comprehensive performance, can be strengthened by heat treatment, suitable for core mechanical parts such as gears and shafts (corresponding to ASTM 1045). Supporting forged round processing with better performance, it is the preferred grade for mechanical manufacturing.
3. 35# Carbon Steel Bar (Flexible Medium-Carbon Steel)
Carbon content 0.32%~0.39%, between 20# and 45#, better weldability than 45#, higher strength than 20#, suitable for auto parts, mold bases and other scenarios. Market price about 4150 RMB/ton, supporting customized cutting and inspection.
IV. Procurement Control Points: Four Core Anti-Pit Measures
1. Strictly control quality and cost: Avoid low-cost and inferior products, prioritize suppliers that can provide test reports and reasonable prices to reduce rework risks.
2. Match welding requirements: For welding working conditions, prioritize low-carbon steel or special medium-carbon steel (such as 35# welding type), and pre-evaluate the weldability of high-carbon steel.
3. Clarify specification details: Confirm diameter, length, tolerance and surface state (pickling, bare wire) in advance to ensure compatibility with processing equipment and product design.
4. Sample before bulk procurement: Before bulk procurement, conduct sample processing tests and composition inspections, and place bulk orders after passing the tests.
V. Summary
The core of carbon steel bar selection is "determine grade by working conditions, select specification by grade, and control quality by specification": 20# for construction and welding, 45# for mechanical parts, 35# for balancing welding and strength. Combined with high-quality suppliers and comprehensive testing, efficient and accurate procurement can be achieved.
If there are doubts about grade identification and working condition matching during procurement, detailed requirements can be provided to suppliers, and professional and technical personnel will issue customized selection plans.