P20 mold steel has a carbon content of 0.40%, which is considered a medium-low carbon level. The carbon content of cold-work wear-resistant steel SKD11 exceeds 1.0%, while the carbon content of rust-proof mirror steel S136 is 0.41%, which is similar to that of P20, but the performance alloy ratios may be completely different.

If the carbon content of P20 mold steel is lower, the steel texture will be softer; CNC machining, grinding, and drilling will be smoother; tool wear will be less, processing efficiency will be higher; it will be easy to get started, and there will be fewer problems such as tool breakage and edge chipping. High-carbon steel is hard but brittle and prone to cracking under stress, while P20 has a moderate carbon content and sufficient toughness. During mold trials, mold locking, and minor impacts, it is unlikely to crack or chip and has good stability. Its heat-treatment deformation is relatively small. P20 is pre-hardened steel, and it has been heat-treated before leaving the factory. Subsequent processing will not cause much deformation. It does not require secondary quenching and tempering, making it more suitable for making some plastic molds with fast delivery and conventional precision.

Generally speaking, due to the relatively low cost of anti-corrosion steel pipes, welding is the preferred method for their connection. Due to limitations such as construction period, construction conditions, and geographical environment, some projects will also adopt other connection methods, such as threaded connection, flange connection, socket connection, and grooved connection.

1. Flange connections generally have advantages such as speed, ease of construction, and simple tools, but they cannot meet the requirements of most projects in terms of safety and sealing. Generally, this type of connection is suitable for low-pressure pipelines, such as sludge discharge pipelines.

2. Grooved connection: also known as clamp connection technology.

The application of grooved pipe fittings technology has made the complex process of pipe connection simple, fast, and convenient. This represents a significant step forward in pipe connection technology.

Grooved connectors include two product categories: rigid joints, flexible joints, mechanical tees, and grooved flanges; bends, tees, crosses, reducers, blind flanges, spiral welded pipes, etc.

Grooved pipe fittings that serve to connect and seal mainly consist of three parts: sealing rings, clamps, and locking bolts. The rubber sealing ring located in the inner layer is placed on the outside of the connecting pipe and overlaps with the pre-roll groove. Then tighten the clamp to the outside of the rubber ring, and then secure it with two bolts. Because the rubber sealing ring and clamp adopt a special sealing structure design, the grooved connection has good sealing performance, and its sealing performance is improved accordingly as the fluid pressure in the pipeline increases.

Grooved connections facilitate pipe connection operations, improve construction safety, enhance system stability, facilitate maintenance, save time and labor, and offer good economic benefits. Although the individual price of clamps is higher when using clamp connections, the overall benefits of the entire pipeline installation are higher than those of flange connections.

3. As an advanced method of connecting anti-corrosion steel pipes, clamp-type pipe fittings can be installed either openly or concealed, i.e., steel joints or flexible joints. Therefore, it has broad application prospects. It is suitable for fire-fighting water supply systems, air conditioning hot and cold water systems, water supply systems, petrochemical pipeline systems, thermal power military pipeline systems, sewage treatment pipeline systems, etc.

Common testing items for steel:

1. Mechanical and technological performance testing: various hardness tests, tensile tests, compression tests, bending tests, flattening tests, impact tests, drop hammer tests, torsion tests, winding tests, bond strength, weld joint inspection, welding procedure qualification, etc.

2. Metallographic structure inspection: low magnification structure and defects, microstructure, grain size, hardenability, fracture surface inspection, carbides, graphite grading, sulfur markings, inclusions, decarburized layer, carburized layer, nitrided layer, corrosion test, taper hairline cracks, intergranular corrosion of stainless steel, etc.

3. Chemical composition analysis: the testing range covers most elements in the periodic table, up to about 70, including: carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, copper, molybdenum, vanadium, titanium, tungsten, cobalt, aluminum, niobium, zinc, cadmium, calcium, magnesium, boron, arsenic, antimony, tin, bismuth, lead.

4. Bending Test: Bending, Repeated Bending

5. Tensile Test: High Temperature, Room Temperature, Low Temperature Tensile Test

6. Hardness Test: Rockwell Hardness Test, Brinell Hardness Test, Vickers Hardness Test

7. Impact Test: Room Temperature Impact Test, Low Temperature Impact Test, High Temperature Impact Test

8. Compression Test: Compression Yield Point, Compressive Strength, Specified Non-proportional Compressive Stress, Specified Total Compressive Stress, Compression Modulus

9. Mechanical Property Tests for Welded Parts: Deformation, Fracture, Adhesion, Creep, Fatigue, etc.

10. Mechanical Property Tests for Fasteners: Tensile Test, Proof Load, Wedge Load Test, Torque Test, Hole Enlargement Test, Torque Coefficient, Anti-Slip Coefficient, etc.

11. Performance Tests: Tensile Load, Stress Relaxation Test, Zinc Plating Amount Test, Adhesion Test, Copper Immersion Test, etc.