Forging steel quality appraisal

forged steel is based on the core principles of dynamic recrystallization and fiber streamline control. By optimizing the forging ratio, temperature-deformation coupling process and subsequent heat treatment, it achieves the synergy of high strength and excellent toughness. It is widely used in aerospace, heavy machinery, automotive transmission systems and other fields. In aviation manufacturing, it is used for high-load components such as engine turbine disks and landing gears; in the field of heavy machinery, it meets the fatigue life requirements of large crankshafts and gears; in the automotive industry, it ensures the impact resistance of transmission gears. Compared with conventional rolled steel, forged steel has the characteristics of dense streamline structure, small anisotropy, and high defect closure rate. It is a key material for load-bearing structural parts in high-end equipment manufacturing.

Zhongke Testing is a product quality appraisal service organization registered with the court. It can provide forged steel quality appraisal services. It has a professional appraisal team and advanced instruments and equipment to provide fair and accurate appraisal results for forged steel quality appraisal.

With the expansion of applications of forged parts in key fields, related quality dispute cases have increased significantly. The judicial dispute focuses on:

1. Disputes over performance indicators: whether the actual impact toughness meets the standard (such as room temperature AKV ≥ 50J) and whether the high-temperature endurance strength meets the design value;

2. Material defects: segregation of alloy elements (such as molybdenum banded structure of Cr-Mo steel), non-metallic clips Debris exceeding the standard (Class B ≤ 1.5);

3. Process problems: The final forging temperature is too low, resulting in mixed crystals, and insufficient quenching cooling rate causes reticular ferrite;

4. Contract performance dispute: the forging ratio of the delivered steel is insufficient (such as agreement ≥4, actual measurement ≤3), flaw detection level (such as GB/T 6402 Class B) is not up to standard.

For the quality appraisal of forged steel, the following technical methods are usually used:

1. Appearance inspection: Check whether there are cracks, pores, inclusions and other defects on the surface of forged steel.

2. Dimensional measurement: measure the dimensions of the forged steel and compare it with the design drawings to determine whether it meets the requirements.

3. Mechanical property testing: Evaluate the strength, toughness, hardness and other mechanical properties of forged steel through tensile, yield, hardness, impact and other tests.

4. Metallographic analysis: Conduct metallographic observation on forged steel, analyze its organizational structure, grain size, inclusions, etc. to determine whether it meets the process requirements.

The applicant, a wind power equipment manufacturer, signed the "42CrMo4 Forged Steel Spindle Procurement Contract" with a special steel company, the respondent, agreeing to purchase 200 quenched and tempered steel shafts with a forging ratio of ≥5. During processing, it was found that 20% of the spindles had cracks in the flange transition zone, causing equipment shutdown. The manufacturer accused the steel forging process of defects, and the special steel company argued that it was caused by machining stress concentration.

identification analysis results:

The quality analysis expert group discussed and comprehensively analyzed the relevant information of "forged steel", contract technical agreements, on-site investigation case materials and other data, and made the following quality analysis opinions:

The forging ratio in the center of the involved forging is only 3.8, and there are unclosed shrinkage cavities (UT shows equivalent diameter Φ3.2mm); the metallographic structure shows reticular ferrite (proportion ≥15%), and the impact toughness AKV is only 28J (contract requirement ≥45J); there are MnS inclusions in the crack source area (length 150μm, rating DS 2.5).

The appraisal conclusion concluded that the special steel company failed to control the forging process and metallurgical quality in accordance with the agreement, and material defects were the main cause of failure.

Forged steel quality appraisal report mainly includes the following contents:

1. Client information

2. Appraisal equipment information

3. Appraisal basis (standards, power of attorney, etc.)

4. Identification method