Zhuojin Pipe Fitting Co., LtdSurfacing of GQ40-B Steel Bar Cutting Machine Blade Edges
Literature Overview
This paper by Yan Jun from the Fuyang District Boiler Inspection Institute in Anhui Province, published in Welding journal (1997, Vol. 6, pp. 28–29), describes a practical engineering solution for the manufacturing of cutting blades for the GQ40-B steel bar cutting machine. The GQ40-B cutting machine is designed to cut round steel bars with tensile strength up to 450 MPa and diameter 6–40 mm, deformed steel bars with tensile strength up to 650 MPa and diameter 6–32 mm, and flat steel 80 mm × 10 mm. The original design specified blades made from 4CrW2Si steel, but the authors developed an alternative approach using 45 steel as the base material with hardfacing overlay on the cutting edges, eliminating the need for expensive purchased blades and solving supply chain issues.
Blade Design and Manufacturing Requirements
The GQ40-B cutting machine blade design presents specific challenges related to the cutting operation:
| Parameter | Specification | Engineering Significance |
|---|---|---|
| Blade material (original) | 4CrW2Si | High hardness, good wear resistance |
| Blade material (alternative) | 45 steel + hardfacing | Cost-effective, locally available |
| Round steel capacity | φ6–40 mm, σb ≤ 450 MPa | General construction steel |
| Deformed steel capacity | φ6–32 mm, σb ≤ 650 MPa | Reinforcing steel |
| Flat steel capacity | 80 × 10 mm | Structural applications |
| Blade edges per blade | 2 (reversible) | Extended service life |
| Blade geometry | As per Fig. 1 in paper | Critical for cutting performance |
The original design using 4CrW2Si steel provided adequate hardness and wear resistance for cutting operations, but the reliance on purchased blades created two problems: high cost and inconsistent quality. Some purchased blades failed to meet the drawing technical requirements, leading to premature blade failure and production downtime.
Surfacing Strategy for Blade Edge Hardening
The authors' approach of using 45 steel as the base material with hardfacing overlay on the cutting edges is a classic example of the bimetallic component design philosophy. The base material provides toughness and structural integrity, while the hardfacing overlay provides the wear resistance and hardness required for cutting operations.
The surfacing procedure would typically involve:
- Base material preparation: The 45 steel blade blanks are machined to the required geometry, with the cutting edges prepared for surfacing.
- Preheating: The blade is preheated to 200–300°C to reduce the cooling rate and prevent cracking in the base metal heat-affected zone.
- Hardfacing deposition: A hardfacing alloy, such as a high-carbon chromium alloy or a cobalt-based alloy, is deposited on the cutting edges using arc surfacing techniques. The choice of hardfacing alloy depends on the required hardness, wear resistance, and toughness.
- Post-weld heat treatment: The blade may be subjected to a stress relief treatment or a specific heat treatment to optimize the hardness profile and reduce residual stresses.
- Grinding and sharpening: The surfaced edges are ground to the required cutting geometry and sharpened to produce the final cutting edge.
Material Selection Considerations
The selection of the hardfacing alloy for cutting blade edges requires careful consideration of several factors:
| Hardfacing Type | Hardness (HRC) | Wear Resistance | Toughness | Suitability for Cutting |
|---|---|---|---|---|
| High-carbon chromium | 55–62 | Good | Moderate | Good for general cutting |
| Cobalt-based | 50–58 | Excellent | High | Excellent for heavy-duty cutting |
| Nickel-based | 40–50 | Moderate | High | Limited for cutting applications |
| Hardfacing with tungsten carbide | 60–68 | Excellent | Low | Good but may be brittle |
For the GQ40-B cutting machine application, where the blades must cut both mild steel and high-strength deformed steel, a high-carbon chromium hardfacing alloy would be a suitable choice. This type of alloy provides a good balance of hardness, wear resistance, and toughness, making it well-suited for the cutting operation.
Engineering Practice Implications
This paper illustrates a practical application of hardfacing technology in a simple but important manufacturing context. The steel bar cutting machine is a common piece of equipment in construction sites, steel fabrication shops, and metalworking facilities. The blade is a consumable component that requires regular replacement or resurfacing, making the cost of blade manufacturing a significant factor in the overall operating cost of the cutting operation.
The authors' approach of using locally available 45 steel as the base material and applying hardfacing overlay on the cutting edges offers several advantages:
- Cost reduction: The cost of 45 steel is significantly lower than 4CrW2Si steel, and the hardfacing material used is minimal.
- Supply chain independence: The use of locally available materials eliminates dependence on purchased blades from external suppliers.
- Quality control: In-house manufacturing allows for better quality control of the blade manufacturing process.
- Rapid replacement: The ability to manufacture and resurface blades in-house reduces downtime when blades need replacement.
Study Insights and Reflections
This paper, while addressing a seemingly simple application, demonstrates the fundamental principle that hardfacing technology can be used not only for repair and maintenance but also for the manufacturing of new components. The bimetallic approach of combining a tough base material with a wear-resistant overlay is one of the most versatile and cost-effective strategies in materials engineering. In my experience, many engineers overlook this approach in favor of using a single expensive material throughout the entire component, when a bimetallic design can often achieve equivalent or superior performance at significantly lower cost. The key to successful bimetallic component design lies in the proper selection of the interface material and the welding process to ensure a strong metallurgical bond between the base and overlay materials. This paper serves as a good example of practical engineering innovation that addresses real-world manufacturing challenges with simple but effective solutions.