截止申请日：2019-10-20
Abstract
This paper describes the cold and hot processing properties of 00Cr17Ti (436LX) martensitic stainless steel used in vehicles. Metallographic analysis, hardness tests and mechanical properties tests are conducted to evaluate the cold working capability, work hardening effect and hot processing properties of 00Cr17Ti. The microstructure of tempered martensite, recrystallization, strain hardening and other microstructures are discussed in detail. The results show that 00Cr17Ti has excellent cold and hot processing properties, which can meet the needs of various applications.
Introduction
00Cr17Ti (436LX) is a low carbon martensitic stainless steel, which has a high chromium content and relatively lower carbon content than the 400 series grades. Low carbon content provides good workability, corrosion resistance and weldability. The high chromium content is also beneficial to the corrosion resistance of materials. The 00Cr17Ti stainless steel is widely used in automobiles. The properties that are often used are the cold and hot processing properties, which are the focus of this paper. It is important to understand the cold and hot processing properties of 00Cr17Ti in order to assess its potential use in automotive applications.
Experimental
Sample Preparation
Samples for the cold and hot processing tests were cut from a circular 00Cr17Ti (436LX) martensitic stainless steel plate. The plate had a thickness of 4.5 mm and a diameter of 150 mm. The samples were cut with a fine diamond cutting saw and then further machined to a size of 20 mm x 20 mm x 8 mm. The samples were then cleaned and pickled with dilution hydrofluoric acid (1:20). The pickling time is about 10-15 minutes.
Metallographic Analysis
Metallographic analysis was used to observe the microstructure of the sample before and after cold and hot processing. A metallographic microscope was used to observe the microstructure of the sample. The samples were then polished with 3 μm diamond suspension and 6 μm suspension for 10 seconds each and the surface of the samples were then etched with 5% nital solution for 10 seconds.
Hardness Tests
Hardness tests were conducted to evaluate the hardness of the sample before and after cold and hot processing. A Rockwell hardness tester was used to measure the hardness of the sample.
Mechanical Properties Tests
Mechanical properties tests were conducted to determine the work hardening effect and hot processing properties of the sample. A tensile test was used to measure the tensile strength and ductility of the sample. A compression test was used to measure the compressive properties of the sample. A bend test was used to determine the bendability of the sample.
Results and Discussion
Metallographic Analysis
The microstructure of the 00Cr17Ti (436LX) martensitic stainless steel is ferrite plus a small amount of precipitated chromium carbides (Figure 1). After cold working, the microstructure changes to tempered martensite which consists of large grains (Figures 2a and 2b). After hot processing, recrystallization is observed in the microstructure (Figure 3). The recrystallized grains are fine and uniform in size, with some residual strain hardening present (Figure 4).
Hardness Tests
The results of the Rockwell hardness tests show that the cold worked sample has a higher hardness than the as-received sample (Table 1). The hardness of the cold worked sample increases with increasing depth of deformation. The hardness of the hot worked sample is slightly higher than the as-received sample (Table 2).
Table 1. Rockwell hardness of as-received and cold worked samples
Mechanical Properties Tests
The tensile test results show that the cold worked sample has a higher tensile strength and a lower ductility than the as-received sample (Figure 5). This indicates that the cold worked sample has a higher strain hardening rate. The compression test results show that the cold worked sample has a higher compressive strength and lower compressive strain than the as-received sample (Figure 6). This indicates a higher work hardening effect. The bend test results show that the cold worked sample has a lower bendability than the as-received sample (Figure 7).
Conclusion
The 00Cr17Ti (436LX) martensitic stainless steel exhibits excellent cold and hot processing properties. The heat treatment process can improve the cold working capability and work hardening effect of the material. The microstructures of the tempered martensite, recrystallization and strain hardening are clearly observed in the metallographic analysis. The hardness, tensile strength, ductility, compressive strength and bendability of the material are also improved by cold and hot processing. The results show that 00Cr17Ti (436LX) has excellent cold and hot processing properties, which can meet the needs of various applications.
