Sylwia Wiewiórowska

The Influence of Strain Rate and Strain Intensity on Retained Austenite Content in Structure of Steel with TRIP Effect

TRIP (transformation induced plasticity) steels are low and medium-carbon steels containing soft ferritic groundmass responsible for low yield point and phases of hard particles such as martensite and/or bainite, which ensure high values of tensile strength. The most important content in structure of TRIP steel is occupied by a non-transformation retained austenite. The advantageous properties of these steels are obtained as a result of martensite transformation generated by plastic deformation process. The retained austenite induces increase of steel plasticity till the moment when by the impact of plastic deformation will undergo deformation in martensite, which results in the increase of steel mechanical properties. The speed of transformation of retained austenite in martensite is highly dependent on strain magnitude and strain rate magnitude. The paper presents the research of strain rate and intensity on retained austenite content ensuring TRIP effect in structure of low carbon steel (0.29%C). Finite element analysis for different strain rate and strain degree values in upsetting test was performed by means of software FORGE 3D. The practical analysis obtained from simulation results was realized by using metallurgical processes simulator Gleeble 3800.

Analysis of the Influence of Drawing Speed on the Amount of Retained Austenite in TRIP Steel Wires

The specific properties of TRIP steel can be obtained by the occurring the effect of additional plasticity during transformation of metastable retained austenite into martensite caused by plastic deformation process. Research carried out for highly alloyed austenitic steels with TRIP effect proved the influence of strain intensity, chemical composition and deformation temperature on efficiency marteniste transformation. In the work research concerned with the influence change of drawing speed on retained austenite amount in drawn wires structure was shown. In available literature there are no publications concerned with the influence of wire drawing process parameters on the structure evolution the medium carbon TRIP steel wires. Research shown in the work was realized with the assumption that the strain intensity is determined by scheme of single and total reductions, and the value of strain rate is a result of used in wire drawing process drawing speed.

The influence of drawing speed on fatigue strength TRIP steel wires

The paper assesses the effect of drawing speed on the fatigue strength and roughness of the surface of TRIP steel wires. The drawing process was accomplished on a testing machine and on a block drawing machine, while applying three drawing speeds: 0.02, 0.75 and 1.6 m/s. The performed tests showed a positive effect of drawing speed on the fatigue strength of wires. It was found that the better fatigue strength of wires drawn at the speed of 1.6 m/s compared to wires drawn at the speeds of 0.02 and 0.75 m/s was associated with a better surface condition of these wires.

The Mechanical Properties and Structure Evolution for High-Manganese TWIP Steel Wires

The increasing demand by the automotive industry has resulted in a search for materials of increasingly high mechanical properties and, at the same time, plastic deformability. These requirements are met by AHSS (Advanced High-Strength Steels) multiphase steels. The group of AHSS type steels may include: diphase (DP), TRIP-effect, hot formed (HF) martensitic, plastic formed heat treated (PFHT), and TWIP-effect steels.

Analysis of Rolling Process for Alloy on the Base of Silver BAg7

The variety of industrial use of brazing solders is associated in one way with plastic properties (more plastic materials are producing in the form of wires, sheets, bands, metal leafs, meshes etc, low plastic materials in the form: pig sows, bars, powders) and in another way with the kind of joining and use soldering or brazing method. Hard solders, which include analyzed solder BAg7, have a very wide range of melting points (from 400 to 2000°C) and are applied in those cases when very high values of strength are required for soldered joint. The research was carried out for the silver-based solder designated as Bag7 according to American Standard ANSI/AWSA 5.8-92. This solder has a typical application for the brazing process of food handling equipment requiring low melting values and for brazing aluminium alloys. In the literature, except for chemical composition and temperature of brazing, we cannot find the details concerned with the method of plastic working of BAg7. In the reported research work the metallographic analysis of rolling process was performed and optimal parameters of rolling process for the considered solder were determined.

Effect of the die approach zone shape on the transition of retained austenite and the mechanical properties of TRIP steel wires

Abstract One of the main factors influencing the transition of retained austenite into martensite in TRIP structure steels during drawing process is the strain intensity. In drawing processes, it occurs high strain inhomogeneity caused by the conical shape of the die approach section, as well as by the friction occurring between the tool and the material. The occurring redundant strain causes high inhomogeneity in the distribution of mechanical properties on the cross-section of wire being drawn. One of the directions aiming at enhancing the homogeneity of the drawn wire properties is to change the shape of the die working section. The paper presents the results of the investigation of the effect of the quantity of retained austenite in TRIP-type steel wires with a carbon content of 0.29 wt.-% C drawn using conical (conventional), concave and convex dies on the mechanical properties of drawn wires.

Examination of the Effect of Variation in Stress Magnitude on the Amount of Transformed Retained Austenite in the Structure of TRIP Steel Wires

A detailed analysis of the effect of variable stresses on the intensity of retained austenite transformation into martensite was carried out in the work. Tests were done for three bending stress (σmax) levels, lower than the value of the yield stress (R0.2) the material tested. Preliminary tests conducted for one bending stress value have shown that a certain amount of untransformed retained austenite remains in the material in spite of applying as many as 40 000 fatigue cycles. It is therefore necessary to determine whether and, if so, in what extent the magnitude of applied bending stress will increase or decrease that amount of retained austenite. It should be established whether, for different bending stress levels, the curves describing the variation in the volumetric fraction of retained austenite of the tested wire structure, will approximate asymptotically the same value, or the values will, after all, be different.The results of these studies have a practical dimension, since, e.g. a screw made of the TRIP steel, subjected to variable stresses in service, may undergo additional hardening to a varying extent, which will influence its mechanical properties, life and operation safety.The knowledge acquired from the studies will constitute a novelty in this scope of applications, and will be useful from the point of view of both the manufacturer and the user.

The Influence the Temperature of Drawing Process on the Transformation Retained Austenite into Martensite for TRIP Steel Wires

For the numerical analysis of TRIP steel wire drawing process, the Drawing 2d programme based of finite element method, has been used. The process was run following two variants, with small and large partial drafts for two drawing speeds: 1.11; 0.23 m/s. The investigations carried out allowed a relationship between temperature of drawing wires and the amount of retained austenite for wire surface and for wire axis.

Determination of Temperature Range Enabling the Plastic Deformation Process of CP302 Solder

The development of new technologies of metal joining processes including brazing methods requires improvement of solder properties. Copper-based brazing solders with phosphorus and tin additions belong to the group of silver-free brazing alloys with low ductility. The most common form of these solders are bars and wires so there is a need to determine the causes of technological problems concerned with plastic deformation of the solders. In the literature, except for the chemical composition and temperature of brazing, we can not find the details regarding the change of solder structure during heating processes. The preliminary tests carried out in the industry indicate high plasticity of solder in the narrow range of temperature. This encouraged the authors of the paper to perform dilatometric testing with the aim of establishing the precise temperatures of solder phase changes. The metallographic research with the use of scanning electron microscopy enabled the determination of phase composition of “freezing” structures and the evaluation of their flexibility to the plastic deformation.