Papers by Keyword: High-Carbon Steel

Abstract: The microstructure change by warm deformation in high-carbon steels with different initial ferrite (α) + cementite (θ) duplex microstructures has been examined. Three kinds of initial structures, i.e., pearlite, α+spheroidized θ and tempered martensite, were prepared using Fe-0.8C-2Mn and Fe-1.0C-1.4Cr alloys and compressed by 30-75% at 973K at a strain rate of 5x10-4 s-1. Equiaxed fine α grains, approximately 2μm in diameter and mostly bounded by high-angle boundaries, are formed with spheroidized θ by dynamic recrystallization during compression of the pearlite by 75%. When the (α+θ) duplex structure containing spheroidized θ was deformed, the original α grains become elongated and only subgrains are formed within them by dynamic recovery. For the tempered martensite, equiaxed α grains similar to those in the deformed pearlite were obtained after 50% compression. This indicates that the critical strain needed for the completion of dynamic recrystallization of α is smaller for the tempered martensite than for the other structures.

Abstract: The typical tool steels of the wood-cutting industry are the unalloyed and chromium and nickel containing, low-alloyed eutectoid steels. These materials, in tempered condition have a very high, 1200-1400 MPa tensile strength. One of the major failure forms of these tools is the fatigue fracture of the tool. The high pretension and the cyclic load, caused by the cutting and the bending of the tool, easily can cause high-cycle fatigue fracture, especially at the welded area and at the heat affected zone. Thus, one of the most critical part in the manufacturing process of the bandsaw blade is the welding. We have examined the fatigue properties of three types of joints: conventional and cold wire TIG welding, MIG welding, and resistance-butt welded joints. The structure at the weld and at the heat affected zone could highly affect the life-span of the tool. Therefore the welding parameters (preheat, post welding heat treatment (PWHT), shield gas, backing gas), affecting the microstructure of the weld, also have serious affects on the fatigue properties. The influence of welding parameters on the fatigue properties were examined by low-cycle fatigue test.

Abstract: A finite element model was developed to simulate the deformation, temperature and phase transformation behavior in high carbon steels. The heat capacity of each phase and the heat evolution due to phase transformation were obtained from the thermodynamic analysis of S45C, 50CrV4 and SK85 steels. Phase transformation kinetics of the steels were derived from continuous cooling experiments. An additivity technique was applied to a modified Johnson-Mehl-Avrami equation to analyze continuous cooling curve. To predict the strain due to TRansformation Induced Plasticity (TRIP), a variant selection model for diffusionless transformation and an accelerative creep model for diffusional transformation were adopted. In order to calculate the deformation behavior, the elastic strain, the volumetric strain due to thermal contraction and phase transformation, the plastic strain and the TRIP strain were taken into account. Using the finite element model developed in this study, the temperature-phase-deformation behavior of the high carbon steels was calculated.

Abstract: Bandsaw blades are one of the most commonly used tools of the wood cutting industry. Their base materials are mostly unalloyed or poorly Cr-alloyed tool steels. After the review of the bandsaw blade’s cyclic load characteristics, we present the typical failures, which can be, originate in it’s cracking. With the use of these information an overall systematization has been set up by the bandsaw blade cracking types and its root causes. The main place of the failure is the weld and the heat-affected zone’s area where the welding can failure or the lack of toughness can produce cracking. An other zone, where cracking may appear is the bandsaw blade’s tooth gullet because it raises the stress intensity factor. Special material testing methods have been made to investigate the tooth gullet’s notch sensitivity from the test results that a comparison of several bandsaw blade base material, are reviewed. With the use of the results a notch sensitivity rating system has been worked out, which can be used to rate different bandsaw blade base material’s notch sensitivity.