Preparation steps of heat treatment process for forgings

Forging heat treatment process preparation is divided into two aspects. First, the processability evaluation: participate in the processability demonstration in the design, study the selection of materials, develop the process route, and determine the technical requirements. Second, the preparation of the heat treatment process program: according to the technical conditions, prepare the process program, design fixtures, determine the quality testing procedures and test verification and complete the process of countersigning and approval.

1. Collect information and research and analysis

(1) Study the feasibility and reasonableness of the technical requirements of heat treatment specified in the drawings to determine the technical requirements of heat treatment reasonably, which is a prerequisite for average heat treatment production, ensure product quality, reduce production costs, etc. For this purpose, the following factors should be considered.

• 1) According to the forgings use conditions, appropriate performance requirements, such as transmission shafts, are mainly subject to bending and torsional stress of the combined effect. Therefore, the quenching only requires quenching to the part radius of 1/2 or 1/3 can be.
• 2) Heat treatment requirements can only be set in the selected steel hardenability and hardenability within the allowable range; requiring large cross-sectional parts to obtain small-size specimens of performance indicators or mild steel without chemical heat treatment to achieve high hardness, etc., is not reasonable.
• 3) Heat treatment requirements should allow a certain amount of heat treatment deformation. As the forgings, heat treatment by phase change stress and thermal stress, heat treatment deformation is inevitable and should be based on the forgings selected steel and geometry, given a certain amount of deformation. These deformations can be corrected by subsequent machining or quenching before the processing size and other methods.
• 4) Economy. The proposed heat treatment technology requirements for forgings should consider the forgings’ manufacturing cost, service life, and other economic factors.

(2) Study the supply state of the billet or material according to the supply state of the billet or material, and determine whether to increase the preparatory heat treatment to meet the final heat treatment requirements and the precision of the billet size requirements.
(3) According to the forging manufacturing and processing route to determine the best location of the heat treatment process, mechanical parts are generally forged after the blank, cutting the heat treatment process to complete. Therefore, the heat treatment process and other process sequence arrangements are reasonable and will directly affect the forging processing and heat treatment quality.

• 1) Heat treatment and machinability of the relationship. Steel cutting processability and it’s chemical composition, metallurgical organization, and mechanical properties. Different steel compositions can be used through different heat treatment processes to obtain different organizations and properties, thereby improving the cutting properties of steel.
• In general, the hardness of the steel is in the range of 170-230HBW, and its cutting performance is good. Hardness is too high, difficult to process, and the tool is easy to wear; hardness is too low, cutting is easy to “sticky knife” so that the tool heat and wear, and the surface of the workpiece is not light. Therefore, preheating treatment should be arranged before the cutting process; generally speaking, low-carbon steel is normalized, while high-carbon steel and alloy steel hardness is too high after normalization and must be used to anneal.
• 2) Forgings processing process route on the impact of heat treatment. The parts processing process route arrangement is reasonable and will directly affect the heat treatment quality. For example, in quiet conditions, gears, long bushings, gaskets, and other parts allow the conditions first high-frequency sense bit quenching, then processing gears, long bore, keyway, or hole bushings in the gasket, which can reduce deformation, to ensure accuracy. For some precision parts, to minimize the impact of stress on dimensional stability caused by cutting into grinding, generally, the process route can be interspersed with arrangements for stress relief annealing or aging treatment.

2. Determine the heat treatment process program

• 1) Based on the technical requirements of forgings, the possible implementation of several heat treatment process options, the complexity of the process and the quality of the time box and other analysis and comparison, and then according to the size of the production batch and the existing equipment and the development trend of domestic and foreign heat treatment technology, a comprehensive technical and economic analysis, to determine the most economical, the complete process program.
• 2) The new material parts of the heat treatment program are generally divided into three steps: first, in the laboratory to determine the heat treatment process to test whether the test can achieve the mechanical properties of the flute index, as well as cold, hot processing process performance; second, the necessary bench test or installation test to assess the performance; finally, a small batch test and production test to assess the production conditions of various Process performance and quality of reliability. The forgings can be formally applied in production only when they meet the above test requirements.
• 3) Determine the process parameters according to the standards or relevant technical documents or verify the adjusted process parameters through process tests.
• 4) Combine the enterprise’s process, part characteristics, energy policy, and equipment conditions to select heat treatment equipment.
• 5) Design process tooling according to the requirements of the process program and arrange auxiliary processes (cleaning, cleaning, calibration, protection, etc.) according to the requirements of the part and the process implementation route.
• 6) determine the inspection method and equipment, and design special inspection tooling as required.

3. Develop heat treatment process protocols

By referring to the relevant heat treatment manuals and material standards or after the process test demonstration to develop heat treatment process procedures according to different process methods (quenching, carburizing or carbon ampoule coextrusion, induction quenching, etc.) to fill out the corresponding process card. The process card is a regulatory document that the operating workers must observe, and its basic contents are as follows.

• 1) Overview of forgings: the name and number of forgings, material grades, quality, contour size and heat treatment-related dimensions, process route, etc.
• 2) Heat treatment technical requirements. Heat treatment process card on the technical specifications than the heat treatment technical requirements proposed on the drawing more detailed, more specific, such as forgings after chemical heat treatment, but also cutting, heat treatment process card on the depth of the hardened layer should be added to the cutting amount.
• 3) Parts sketch. The process card is painted with parts sketch, easy to identify, check the parts, local heat treatment, hardness check parts, etc., and clear at a glance.
• 4) The way the furnace is and the amount of furnace loading.
• 5) Equipment and tooling name and number.
• 6) Process parameters, including holding time, cooling mode, cooling medium, etc., for chemical heat treatment, but also involves the carbon potential, nitrogen potential, and the flow of active media.
• 7) Quality inspection content, inspection method, and sampling rate.

4. Heat treatment process countersignature, approval

After the audit, the higher technical department will approve the prepared heat treatment process. It will come into effect and be implemented after the approval of the quality assurance department and the countersignature of other relevant departments.

Source: China Forgings Manufacturer – Yaang Pipe Industry (www.epowermetals.com)