Evaluation of Toughness of High Strength Low Alloy (HSLA) Steels as a Function of Carbon Content

The influence of carbon content on the microstructure and toughness of HSLA steel at room temperature was investigated based on experimental work and literature. It was revealed that increasing the carbon content in from 0.06 to 0.14 wt-% is detrimental to toughness, giving higher impact transition temperature. The deterioration of toughness was correlated to undesired changes in the microstructure, which showed an increase in pearlite volume fraction at the expense of ferrite. At high carbon content, cementite of pearlite was found to grow more rapidly to form continuous plates which act as preferred sites for crack nucleation and propagation. In addition, the lamellar spacing of the pearlite increased as a function of carbon content, which in turn gave worse toughness. The presence of high carbon content and carbide forming elements in the chemical composition was more detrimental to toughness due to the formation of thick carbides around the grain boundaries. These carbides act as a path for crack propagation, which makes it easy for cracks to cohere, leading to intergranular fracture. Keywords - HSLA steel, Carbon, Brittleness, Toughness, Impact Transition Temperature (ITT)

The influence of Widmanstätten ferrite, martensite and grain boundary carbides on the strength and impact behaviour of high Al (0.2%) and Nb containing hot rolled steels

The influence of Al and Nb on the strength and impact behaviour of hot rolled 0.06%C, 1.4%Mn steels has been determined after hot rolling to 15 and 30 mm thick plate. When 0.16%Al was added to the plain C-Mn steel, the impact behaviour significantly improved even though Widmanstätten ferrite (WF) was present. This improvement was due to refinement of the grain boundary carbides and removing the N from solution as AlN. The hot rolled steels all contained WF but when Nb was added more WF formed as well as MA giving poor impact behaviour. Reducing the hardenability from that shown in previous work by decreasing C from 0.1 to 0.06%, Nb from 0.03 to 0.02%, and cooling rate from 33 to 17 K/min had no effect in improving the impact performance of hot rolled Nb steels. To ensure optimum properties not only is it necessary to reduce the hardenability, but WF formation must be discouraged by having a high Ar3. This can only be presently achieved by refining the austenite grain size via control rolling the Nb containing steels; the benefit of adding Al can then, readily be seen. Suggestions are made as to how this might be achieved for hot rolling

Investigation of factors affecting the learning of final year advanced materials and manufacturing students

An investigation was recently conducted into the delivery of an Advanced Materials and Manufacturing Processes module which was presented to a sub-group of the final year engineering students at Dublin City University (DCU). Results from the class which has just completed their final year studies were examined in relation to the method of delivery. This cohort consisted of 25 students, 13 which studied for the Computer Aided Mechanical and Manufacturing Engineering (CAM) degree and 12 which studied for the Business and Manufacturing Engineering (BME) degree. This paper presents an examination of some of the factors affecting the overall results of these students. Factors evaluated include attendance of the student, as well as individual performance in continuous assessment and examination. Overall attendance at the lecture, the organised seminar series, and practical work were recorded. Results indicate a direct link between attendance and marks awarded. Students with higher attendance achieved better grades. Good continuous assessment performance did not automatically indicate good exam performance. Contrary evidence to this is discussed in relation to student learning styles where students may show better ability in exams with poorer ability in continuous assessment and vice versa

Affects of student attendance on performance in undergraduate materials and manufacturing modules

This paper investigates the class attendance of second year, third year and fourth year students and their overall performance at the school of Mechanical and Manufacturing Engineering in Dublin City University (DCU). An investigation was recently conducted into the delivery of different module which was presented to a group of second year, third year and fourth year engineering students at DCU. Attendance in the class was recorded and the continuous assessment results and the final overall performances were investigated with their attendance. Student performance on Strength of materials – part 1 (SM1), Strength of materials part - 2 (SM2), Mechanics of Materials and Machine (MMM) and Advanced Materials and Manufacturing Processes (AMMP) modules are presented in this paper. This paper presents an examination of some of the factors affecting the overall results of these students. Factors evaluated include attendance of the student, as well as individual performance in continuous assessment and examination. Overall attendance at the lecture, the organised seminar series, and practical work were recorded. Results indicate a direct link between attendance and marks awarded. Students with higher attendance achieved better grades

Employer and student perspectives on skills for engineers in the twenty first century and beyond

This research focused on skills identified among final year engineering students. It provided evidence of different levels of skills by students and identifies their greatest learning influences in these areas. The skills were self-assessed by students and covered seven areas designated by Engineers Ireland. Competency levels such as science, software, creativity, engineering practice, social and business, ethics, discipline specific were assessed. It also investigated the important role that work placements play in skills developed by students. Key skills sought by leading Engineering firms from graduates now and in the next five years were also researched in this paper. Employers were surveyed to determine and investigate skills needed from graduate engineers and how best to meet these challenges. The emphasis on work placements and its impact on skills’ development in engineering students such as business acumen and working effectively and efficiently in industry were highlighted

Designing pulse laser surface modification of H13 steel using response surface method

This paper presents a design of experiment (DOE) for laser surface modification process of AISI H13 tool steel in achieving the maximum hardness and minimum surface roughness at a range of modified layer depth. A Rofin DC-015 diffusion-cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). The response surface method with Box-Behnken design approach in Design Expert 7 software was used to design the H13 laser surface modification process. Metallographic study and image analysis were done to measure the modified layer depth. The modified surface roughness was measured using two-dimensional surface profilometer. The correlation of the three laser processing parameters and the modified surface properties was specified by plotting three-dimensional graph. The hardness properties were tested at 981 mN force. From metallographic study, the laser modified surface depth was between 37 8m and 150 8m. The average surface roughness recorded from the 2D profilometry was at a minimum value of 1.8 8m. The maximum hardness achieved was between 728 and 905 HV0.1.These findings are significant to modern development of hard coatings for wear resistant applications

Laser surface modification of Ti-6Al-4V for biomedical applications

Introduction. Ti-6Al-4V is used in biomedical engineering due to its excellent properties: high strength to weight ratio, low density, high corrosion resistance and good biocompatibility. However, the use of the alloy under severe friction conditions is restricted due to poor tribological properties such as high coefficient of friction and low hardness [1, 2]. Laser surface modification is known for its improved mechanical and tribological properties for biomedical titanium alloys. The treatment produces minimal contamination and increases osseointegration [3-5]. The present study evaluated the effects of high speed, laser processing parameters on surface roughness, hardness, chemical composition and biocompatibility. Materials and Methods A 1.5KW CO2 laser in continuous mode was irradiated on flat Ti-6Al-4V samples at three levels of irradiance 15.72, 20.43 and 26.72 KW/cm2 and three levels of residence time 1.08, 1.44 and 2.16 ms. Evaluation of the surface was carried out by scanning electron microscope (SEM) examination and mechanical profilometry in accordance to ISO 4287/4288. SEM analysis of the surface topography resulting from the various laser treatments was carried out. Energy Dispersive Spectroscopy (EDS) analysis was used to determine the chemical composition of the treated areas. The effect of surface topography on cellular attachment was investigated in vitro using MC3T3-E1 pre-osteoblast cells. Cell attachment was determined using the Hoechst DNA assay and cell morphology was examined using SEM analysis. Results and Discussion An increase in residence time resulted in improved depth of processing. An increase in irradiance did not always produce an increase in depth of processing; however higher irradiance levels were found to provide for a more uniform depth of processing which reached a maximum of 80 µm. Irradiation with the scanning beam produced a single phase microstructure, see Figure 1. This single phase occurred when various constituents in the alloy have dissolved with rapid solidification thwarting segregation of the various alloying elements into high and low concentration [6]. Improved homogenous chemical composition of the laser modified region was verified by the EDS analysis. Microhardness examination revealed an increase in hardness of up to 67% after laser treatment. A relationship between irradiance and roughness was observed, roughness decreasing with increase in irradiance

An overview of laser surface modification of die steels

In recent years, surface modification using advanced heat source like laser has been replacing the conventional methods to produce amorphous microstructure via rapid solidification. Due to the benefits of laser to enhance the tribological and mechanical properties of materials’ surface, several laser surface processing were developed including laser surface modification, namely laser alloying, transformation hardening, surface amorphization, shock hardening and glazing. In high temperature applications, the laser surface modification technique is beneficial to prolong the die life cycle, and also to improve the surface roughness of thermal barrier coatings (TBC). To produce the amorphous layer at a particular depth, laser parameter such as irradiance, frequency, and exposure time are controlled. Variations of parameter may result in modified microhardness properties of heat affected zone and transition zone. Nevertheless, works on laser glazing of bearings, railroad rails and TBC had proven the surface properties were enhanced through laser glazing to cope with excessive load, wear, fatigue, bending and friction demand

Development of a heat transfer and artificial neural networks teaching laboratory practical for biotechnology students

The paper describes a newly developed laboratory practical that teaches students how to develop an Artificial Neural Network model and its possible use in bio-processing. An emphasis is placed on giving students "hands on" experience with bio-processing equipment, namely bio-reactors and data acquisition systems in an attempt to help prepare them for work in bio-processing and chemical engineering industries