Composite Steel Part Manufacturing via Segmented Carburizing
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Solution Overview
Problem
The existing manufacturing methods for composite steel parts with carburized and welded portions are costly and time-consuming due to the need for anti-carburizing processes, and they often result in inadequate wear resistance and weldability when high carbon content materials are used without carburization.
Innovation Solution
A manufacturing method that involves adding an extra portion to the welding expected area, heating it to austenitizing temperature in a carburizing atmosphere, cooling at a restricted rate, and then locally quenching with high-density energy to form a carburized quenched surface while maintaining bainite structure in the inner portion, allowing for the omission of anti-carburizing processes and improving weldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If anti-carburizing process is performed to protect welding portion during carburizing, then weldability is improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The steel part is segmented into two distinct zones: a welding expected portion with low carbon content (0.1-0.3% C) for good weldability, and a carburized portion with high carbon content (0.8-1.2% C) for wear resistance. This spatial segmentation of material properties eliminates the need for anti-carburizing processes while maintaining both weldability and surface hardness requirements
Solution Approach 2:
Different regions of the steel part are given different chemical compositions and microstructures tailored to their specific functional requirements. The welding portion maintains low carbon ferrite-pearlite structure for ductility and weldability, while the cylindrical portion develops high carbon martensite structure for hardness and wear resistance
2Productivity
If high carbon steel material is used to avoid carburizing treatment, then manufacturing steps are reduced, but surface hardness and wear resistance are insufficient
Solution Approach 1:
The steel part is prepared with a low carbon content base material before carburizing treatment, and the welding portion is pre-identified as a zone that should not be carburized. This preliminary setup enables selective carburizing of only the cylindrical portion, achieving high surface hardness where needed while maintaining manufacturing efficiency
Solution Approach 2:
Instead of carburizing the entire steel part or using high carbon material throughout, the invention applies carburizing treatment partially only to the cylindrical portion that requires wear resistance. The welding portion is deliberately excluded from carburizing, achieving the desired surface hardness improvement in the critical area without compromising overall manufacturability
3Reliability
If anti-carburizing agent is applied and then removed, then welding portion protection is achieved, but manufacturing time and labor cost increase
Solution Approach 1:
The steel part is segmented into two distinct zones: a welding expected portion with low carbon content (0.1-0.3% C) for good weldability, and a carburized portion with high carbon content (0.8-1.2% C) for wear resistance. This spatial segmentation of material properties eliminates the need for anti-carburizing processes while maintaining both weldability and surface hardness requirements
Solution Approach 2:
The invention extracts and removes the problematic anti-carburizing agent removal step from the manufacturing process entirely. By using low carbon steel material and controlling carburizing treatment to affect only the cylindrical portion, the welding portion remains inherently protected without requiring additional protective agents or removal operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves high surface hardness and wear resistance while maintaining dimensional accuracy and weldability, eliminating the need for anti-carburizing processes, thus reducing man-hours and energy consumption.
Implementation Method 1
a carburizing step in which the intermediate product is heated to an austenitizing temperature or more in a carburizing atmosphere to form the carburized layer on a surface of the intermediate product
Implementation Method 2
a cooling step, subsequent to the carburizing step, in which the intermediate product is cooled at a cooling rate less than a cooling rate at which martensitic transformation is caused
Implementation Method 3
a quenching step in which a desired portion of the cylindrical portion of the intermediate product is heated to an austenitizing range by high-density energy and thereafter cooled at a cooling rate equal to or more than the cooling rate at which martensitic transformation is caused
Data Source
AI summary
A manufacturing method for a composite steel part including preparing an intermediate product in which an extra portion, which has a thickness equal to or more than that of a carburized layer to be formed in a subsequent carburizing step, has been added to a welding expected portion, carburizing the intermediate product by heating to an austenitizing temperature or more in a carburizing atmosphere, then cooling the intermediate product at a cooling rate less than a rate at which martensitic transformation occurs and without completing structural transformation due to the cooling, quenching a portion of the intermediate product after heating to an austenitizing range by high-density energy and thereafter cooling to cause martensitic transformation to form a carburized quenched portion, removing an extra portion of the intermediate product; and then welding a second steel part to the welding expected portion.